Biophysics Minimum Requirement Questions
0.0 / 5
- Created by: kpaul1234
- Created on: 14-06-22 17:00
Define kinetic energy in words and with a formula,
and give its unit!
and give its unit!
Kinetic energy is the amount of work an object with a mass of m moving at a speed of v can perform while its speed is reduced to zero:
Ekinetic=1/2mv^2
The unit of kinetic energy is joule.
Ekinetic=1/2mv^2
The unit of kinetic energy is joule.
1 of 275
Define electron volt (eV)!
Electron volt is a unit of energy. It is equivalent to the amount of kinetic energy gained by a single electron when accelerated through a voltage difference of 1 V.
2 of 275
Define what force is!
Force is a vector quantity characterizing the capability to cause acceleration.
3 of 275
Define acceleration in words and with a formula!
Acceleration is the rate of velocity change with time:
a=dv/dt
where a is acceleration, dv is the change in
velocity in time t.
a=dv/dt
where a is acceleration, dv is the change in
velocity in time t.
4 of 275
Define Newton’s 2nd law in words and with a
formula!
formula!
The acceleration of an object (a) is given by the ratio of the net (or resultant) force acting upon it (Fn) and the mass of the object (m):
a=Fa/m.
a=Fa/m.
5 of 275
Define centripetal acceleration in words and with a formula!
Centripetal acceleration (ac) is the rate of change in the direction of velocity with time:
ac=v^2/r=ω^2r.
ac=v^2/r=ω^2r.
6 of 275
Define angular velocity in words and with a formula!
Angular velocity (ω) is the ratio of the angle (∆ϕ, usually measured in radians) traversed to the amount of time (∆t) it takes to traverse the angle:
ω=∆ϕ/∆t.
ω=∆ϕ/∆t.
7 of 275
Define momentum in words and with a formula!
Momentum (p) is the product of the mass (m) and the velocity (v) of an object:
p=mv.
p=mv.
8 of 275
Define moment of inertia in words and with a
formula!
formula!
Moment of inertia (I) is characterized as the resistance of an object against angular acceleration, i.e. the change in angular velocity. It can be calculated by:
I=mr^2 , where m is the mass of the object, r is the
distance of the object from the axis.
I=mr^2 , where m is the mass of the object, r is the
distance of the object from the axis.
9 of 275
Define angular momentum!
Angular momentum is analogous to momentum, it
serves the same purpose in circular motion as
momentum does in linear motion. By definition, the product of the angular velocity and the moment of inertia of an object is its angular momentum.
serves the same purpose in circular motion as
momentum does in linear motion. By definition, the product of the angular velocity and the moment of inertia of an object is its angular momentum.
10 of 275
Define the potential energy of an object in a
homogenous gravitational field!
homogenous gravitational field!
The potential energy of an object with mass m at a height of h in a homogenous gravitational field characterized by a gravitational acceleration of g is given by the following equation:
Epot=mgh.
Epot=mgh.
11 of 275
Define the potential energy of a charged object in an electrostatic field!
The electrostatic potential energy of an object with charge Q at position A in an electrostatic field is:
Epot=QUA =where UA is the electric potential at point A.
Epot=QUA =where UA is the electric potential at point A.
12 of 275
Define work in words and with a formula!
Work is the amount of energy transferred by a force. It can be calculated according to the following formula:
W=Fs where W is work, F is force and s is the
displacement of the object in the direction of the force.
W=Fs where W is work, F is force and s is the
displacement of the object in the direction of the force.
13 of 275
Define buoyant force in words and with a formula.
Buoyant force is an upward force exerted by a fluid (or gas) on an object immersed in it. It's equal to the weight of the fluid (or gas) that the body displaces. Fb=ρfV'g, where ρf is the density of the fluid, V’ is the submerged volume, g is gravity.
14 of 275
Formulate the general form of the work-energy
theorem, and its special form for the electric and
homogenous gravitational fields!
theorem, and its special form for the electric and
homogenous gravitational fields!
General form:Ekinetic,B-Ekinetic,A=1/2m(v2B-v2A)=WAB,m is the mass, vB and vA are the speed of the object atpoint A and B, respectively, WAB is the work done on the
object between points A and B.
object between points A and B.
15 of 275
Define power in words and with a formula, and give its unit!
Power is the rate at which work is done, and it is
calculated according to the following formula:
P=W/t, where P is power, W is the amount of work perform in time t. The unit of power is watt (W=J/s).
calculated according to the following formula:
P=W/t, where P is power, W is the amount of work perform in time t. The unit of power is watt (W=J/s).
16 of 275
Define the term and unit of voltage!
The voltage between points A&B is the difference between the electric potentials of points A&B. The unit of voltage is volt (V). If the voltage between A&B is 1V (UB-UA=1V), the amount of work required to move a charge of 1 coulomb from A-B is 1 Joule.
17 of 275
Define electric current and derive its unit from other SI units!
Electric current is the amount of charge transported across a boundary per unit time. Its unit is ampere (A).
A=coulomb/second.
A=coulomb/second.
18 of 275
Define resistance and give its unit!
According to Ohm’s law resistance (R) of a piece of conducting material is the ratio of the voltage applied across the piece of material (U) and the current through the material (I):
R=U/I
The unit of resistance is ohm (Ω=V/A).
R=U/I
The unit of resistance is ohm (Ω=V/A).
19 of 275
Define what electric dipole is, and describe how to
calculate its electric dipole moment!
calculate its electric dipole moment!
An electric dipole is a separated pair of positive
charge (+q) and an equal amount of negative
charge (-q). The electric dipole moment (p) is defined by the following equation:
p=q⋅r, where r is the separation distance between the charges.
charge (+q) and an equal amount of negative
charge (-q). The electric dipole moment (p) is defined by the following equation:
p=q⋅r, where r is the separation distance between the charges.
20 of 275
Give the magnitude and direction of the electric
Lorentz force acting on a particle of charge, Q in an electric field, E. What is the consequence of the
force on the charged particle?
Lorentz force acting on a particle of charge, Q in an electric field, E. What is the consequence of the
force on the charged particle?
FL=EQ, where FL is the electric Lorentz force.
For positively charged particles the force is parallel, whereas for negatively charged particles it is antiparallel with the direction of the electric field. The particle will be accelerated linearly.
For positively charged particles the force is parallel, whereas for negatively charged particles it is antiparallel with the direction of the electric field. The particle will be accelerated linearly.
21 of 275
Give the magnitude of the magnetic Lorentz force
acting on a particle of charge, Q which moves at a
speed v in a magnetic field, B. What rule should be
applied to obtain the direction of the force? What is the consequence of this force on the charged
part
acting on a particle of charge, Q which moves at a
speed v in a magnetic field, B. What rule should be
applied to obtain the direction of the force? What is the consequence of this force on the charged
part
FL=QvBsinΘ,where FL is the magnetic Lorentz
force, θ is the angle enclosed by the velocity vector and the direction of the magnetic field.
Direction of the force can be determined by the right hand rule.
force, θ is the angle enclosed by the velocity vector and the direction of the magnetic field.
Direction of the force can be determined by the right hand rule.
22 of 275
Give the energy and momentum of a photon with
frequency f
frequency f
The energy of a photon with frequency f is hf, and its momentum is h f/c=h/λ , where h and c are
Planck’s constant and the speed of light in vacuum, respectively, and λ is the wavelength of the photon.
Planck’s constant and the speed of light in vacuum, respectively, and λ is the wavelength of the photon.
23 of 275
Align in ascending order the following components of the electromagnetic spectrum according to their energy: microwaves, gamma, ultraviolet, visible light, X-ray, infrared, radiowaves!
radiowaves < microwaves < infrared < visible light < ultraviolet < X-ray, gamma.
24 of 275
What is the definition of visible light?
The range of electromagnetic radiation observable by the human eye (approximately 400-750 nm).
25 of 275
Define the limiting frequency (fmax) of braking
radiation at an accelerating voltage of U.
radiation at an accelerating voltage of U.
fmax=eU/h
where h is Planck's constant and e is the charge of an electron.
where h is Planck's constant and e is the charge of an electron.
26 of 275
List the three most important mechanisms
responsible for the absorption of γ and X-rays!
responsible for the absorption of γ and X-rays!
- photoelectric effect
- Compton-effect
- pair-production
- Compton-effect
- pair-production
27 of 275
What is the major difference between the photoeffect and the Compton effect?
All of the energy of the X-ray (or gamma) photon is used to ionize the atom&set the electron in motion in photoelectric effect. Only part of the photon energy is used for these processes in Compton effect,&the photon having lower energy is scattered.
28 of 275
What is the minimal energy of a γ-photon needed for pair-production (not numerically)?
The energy equivalent to the rest mass of an electron&a positron:
E=(me+mp)c2, where me&mp are the rest masses of an electron&a positron, respectively, c is the speed of light in vacuum&E is the minimal energy of a γ-photon inducing pair production.
E=(me+mp)c2, where me&mp are the rest masses of an electron&a positron, respectively, c is the speed of light in vacuum&E is the minimal energy of a γ-photon inducing pair production.
29 of 275
Why is a heavy nucleus necessary for pairproduction?
The presence of a heavy nucleus is required by the law of conservation of momentum.
30 of 275
What is annihilation?
The process in which an electron and a positron (or in general a particle-antiparticle pair) collide with each other and the total mass-energy of this particle system is converted to the energy of two gamma photons, is called annihilation.
31 of 275
Define interference
Interference is the superposition of waves that results in the generation of a new wave pattern.
32 of 275
What is constructive and destructive interference?
Interference is constructive when the amplitude of the resultant wave is greater than the amplitudes of the individual waves, and it is destructive when the amplitude of the resultant wave is less than that of the individual waves.
33 of 275
What is the requirement for maximally constructive and maximally destructive interference if two propagating waves with identical wavelength interfere with each other?
Maximally constructive interference takes place, if the path difference (∆s) between the waves is an integer multiple of the wavelength (λ):
∆s=lλ , where l=0,1,2,3….
Maximally destructive interference is generated, if ∆s=(l+1/2)λ.
∆s=lλ , where l=0,1,2,3….
Maximally destructive interference is generated, if ∆s=(l+1/2)λ.
34 of 275
Give the condition for constructive interference for an electromagnetic wave with wavelength λ
diffracted on a crystal with a grating constant of c!
(angle of incidence is 90o)
diffracted on a crystal with a grating constant of c!
(angle of incidence is 90o)
c cosα=lλ , where l=0,1,2,3,...n, α=angle of diffraction.
35 of 275
What is the definition of transverse and longitudinal waves?
In a transverse wave the displacement of oscillating particles is perpendicular to the direction of propagation of the wave. In a longitudinal wave the displacement is parallel to the direction of propagation.
36 of 275
What is monochromatic light?
Light is monochromatic if its spectrum consists of a single wavelength only.
37 of 275
. What kind of special characteristics does laser light have?
- monochromatic
- coherence in time and distance
- small divergence
- high light density.
- coherence in time and distance
- small divergence
- high light density.
38 of 275
List the types of interactions laser light can have
with tissues.
with tissues.
- photothermal (laserthermy, coagulation,
vaporization, carbonization)
- fluorescence, photochemical reactions
- photodissociation
- multiphoton ionization
vaporization, carbonization)
- fluorescence, photochemical reactions
- photodissociation
- multiphoton ionization
39 of 275
When is electromagnetic radiation coherent?
If it consists of photons capable of forming observable interference fringes.
40 of 275
What basic phenomena is the generation of laser
emission based on?
emission based on?
- population inversion is needed for light amplification to occur, and it is only possible in systems with 3 or more energy levels.
- stimulated emission is needed to give rise to coherent monochromatic light.
- stimulated emission is needed to give rise to coherent monochromatic light.
41 of 275
. What is the approximate coherence length of a laser and that of a classical light source?
10^10 cm and a couple of cm, respectively.
42 of 275
Align in ascending order the following transitions
according to their energy difference: vibrational,
rotational and electronic!
according to their energy difference: vibrational,
rotational and electronic!
rotational < vibrational < electronic.
43 of 275
Write the Lambert-Beer law and interpret the
variables in the formula!
variables in the formula!
lg J0/J=εcL=A or J=J0 10^-cεL
J-intensity of light after passing through a material with thickness L, Jo-incident intensity of light, A–absorbance, ε-molar extinction coefficient, c-conc, L-optical path length.
J-intensity of light after passing through a material with thickness L, Jo-incident intensity of light, A–absorbance, ε-molar extinction coefficient, c-conc, L-optical path length.
44 of 275
What does the molar extinction coefficient depend on?
It depends on the type of the absorbing material, the wavelength of the light, temperature, the type of the solvent and the environment.
45 of 275
How many fold does the intensity of light decreases if the absorbance (optical density, extinction) of a solution is 1?
It decreases 10-fold.
46 of 275
What is the definition of the molar extinction
coefficient?
coefficient?
It is the absorbance (optical density) of a solution with a concentration of 1M and an optical path length of 1 cm.
47 of 275
At what wavelength are the characteristic absorption maxima of proteins and nucleic acids?
proteins 280 nm, nucleic acids 260 nm.
48 of 275
Which amino acids have reasonably high
absorption?
absorption?
Tyr, Trp, Phe.
49 of 275
What is the definition of a singlet and a triplet state?
In a singlet and a triplet state the number of unpaired electrons is zero and two, respectively. In a singlet and a triplet state, the value of the resultant spin multiplicity is 1 and 3, respectively.
50 of 275
What are the possible ways of relaxation of an
excited electron in a molecule? (List at least 5 of
them!)
excited electron in a molecule? (List at least 5 of
them!)
- vibrational relaxation
- internal conversion
- intersystem crossing
- fluorescence
- phosphorescence
- delayed fluorescence
- energy transfer to another molecule.
- internal conversion
- intersystem crossing
- fluorescence
- phosphorescence
- delayed fluorescence
- energy transfer to another molecule.
51 of 275
What is the definition of fluorescence lifetime?
The time during which the number of excited molecules decreases to 1/e-times (37 %) of its initial value.
52 of 275
What is a., scintillation, b., chemiluminescence, c.,photoluminescence?
Processes where photon emission is elicited by
a., ionizing radiation
b., chemical reaction
c., excitation by photons.
a., ionizing radiation
b., chemical reaction
c., excitation by photons.
53 of 275
How can fluorescence quantum efficiency (yield) be defined?
(One definition is sufficient.)
(One definition is sufficient.)
The fraction of excited molecules emitting a fluorescent photon, OR the number of fluorescence photons divided
by the number of absorbed photons, OR the rate
constant of fluorescence divided by the rate constants of all possible de-excitation processes.
by the number of absorbed photons, OR the rate
constant of fluorescence divided by the rate constants of all possible de-excitation processes.
54 of 275
Why is the fluorescence quantum yield always
smaller than one?
smaller than one?
Because relaxation from the excited state can be
accomplished not only by fluorescence emission.
accomplished not only by fluorescence emission.
55 of 275
What is the lifetime range of fluorescence?
τ = 10-9 – 10-7s.
56 of 275
What is the lifetime range of phosphorescence?
τ = 10-6 – 10 s.
57 of 275
Why is phosphorescence lifetime longer than
fluorescence lifetime?
fluorescence lifetime?
Because phosphorescence is the result of spin forbidden transitions.
58 of 275
Why is Förster type resonance energy transfer a
sensitive method for distance measurements?
sensitive method for distance measurements?
Because its probability is proportional to the inverse sixth power of the separation between the donor and the acceptor.
59 of 275
. What can Förster-type resonance energy transfer be used for in biology?
For measuring inter- and intramolecular distances.
60 of 275
List at least five parameters which can be
determined using fluorescent measurements!
determined using fluorescent measurements!
- DNA, RNA, protein and lipid content of a cell, or the quantity of any kind of material that we tagged with a fluorescent label.
- permeability of the cell membrane.
- intracellular enzyme activities.
- membrane potential.
- intracellular calcium level.
- permeability of the cell membrane.
- intracellular enzyme activities.
- membrane potential.
- intracellular calcium level.
61 of 275
Define the index of refraction!
The index of refraction (n) gives the speed of light (c) in a given material according to the following equation:
c=c0/n, where c0 is the speed of light in vacuum.
c=c0/n, where c0 is the speed of light in vacuum.
62 of 275
Write Snell’s law of refraction!
A light beam is refracted when it travels from a material with a refractive index of n1 into a material with one of n2 (n2≠n1). Refraction is described by the equation:
sinα/sinβ=c1/c2=n2/n1, where α&β are the angles of incidence & refraction.
sinα/sinβ=c1/c2=n2/n1, where α&β are the angles of incidence & refraction.
63 of 275
. What is the shortest resolvable distance in a light
microscope?
microscope?
approximately 200 nm
64 of 275
How can the resolving power of a microscope be
increased?
increased?
-by decreasing the wavelength of light.
-by increasing the index of refraction of the material between the objective and the object.
-by increasing the half angle of the objective.
-by increasing the index of refraction of the material between the objective and the object.
-by increasing the half angle of the objective.
65 of 275
What is numerical aperture?
It is the product of the index of refraction of the material between the object and the objective (n), and the sine of the half angle of the objective (sinα): n sinα.
66 of 275
Give the formula for the resolving power (f) of a
conventional light microscope!
conventional light microscope!
f=1/d=2nsinα/λ, where: n = refractive index of the
medium between the coverslip and the objective, α= half angle of the objective, λ = wavelength of light, d = the minimum distance between two points at which they are resolvable.
medium between the coverslip and the objective, α= half angle of the objective, λ = wavelength of light, d = the minimum distance between two points at which they are resolvable.
67 of 275
What is the function of the dichroic mirror in a
fluorescence microscope?
fluorescence microscope?
It reflects the excitation light, and is transparent for the emitted photons, therefore it separates the excitation and emission light paths.
68 of 275
What is the function of the excitation filter in a
fluorescence microscope?
fluorescence microscope?
It is transparent only in the wavelength range in which the fluorescent dye can be excited, therefore it allows only those photons to reach the sample which can excite the fluorescent molecule.
69 of 275
What is the function of the emission filter in a
fluorescence microscope?
fluorescence microscope?
It is transparent only in the wavelength range in which the fluorescent dye emits photons, therefore only the photons emitted by the fluorescent dye will reach the detector.
70 of 275
List at least three of the imaging aberrations in
optical systems!
optical systems!
-chromatic aberration
-spherical aberration
-astigmatism
-coma
-curvature of the field of the image
-barrel-shaped and cushion-shaped distortion of
the image.
-spherical aberration
-astigmatism
-coma
-curvature of the field of the image
-barrel-shaped and cushion-shaped distortion of
the image.
71 of 275
Give the equation for the relationship between the
image distance (i), object distance (o) and the focal
distance (f)!
image distance (i), object distance (o) and the focal
distance (f)!
1/i+1/o=1/f.
72 of 275
Give the definition and SI unit of diopter!
D (diopter)=1/f, is the refractive power of the lens, where f is the focal length of a given lens.
SI unit: 1/m.
SI unit: 1/m.
73 of 275
What were those two discoveries that made
construction of an electron microscope possible?
construction of an electron microscope possible?
-an electron can be regarded as a wave, and its
wavelength is only a fraction of the wavelength of visible light.
-an electron beam can be focused with a magnetic field.
wavelength is only a fraction of the wavelength of visible light.
-an electron beam can be focused with a magnetic field.
74 of 275
List at least three signals that can be detected during an electron microscopic measurement!
-back-scattered electrons
-secondary electrons
-characteristic X-rays
-Auger electrons
-absorbed electrons
-cathode luminescence
-transmitted electrons.
-secondary electrons
-characteristic X-rays
-Auger electrons
-absorbed electrons
-cathode luminescence
-transmitted electrons.
75 of 275
What are the two types of electron microscopes?
transmission electron microscope (TEM)
scanning electron microscope (SEM)
scanning electron microscope (SEM)
76 of 275
What is the principle of transmission electron
microscopy?
microscopy?
A thin, typically 100 nm thick, sample is illuminated with an electron beam. The sample scatters a fraction of the electrons. Using magnetic lenses an image is formed from the electrons going across the sample.
77 of 275
What is the principle of scanning electron
microscopy?
microscopy?
The sample is scanned by a thin electron beam.
Secondary electrons induced by the electron beam are detected on a pixel-by-pixel basis.
Secondary electrons induced by the electron beam are detected on a pixel-by-pixel basis.
78 of 275
Give the definition of isotopes!
Isotopes are the variants of a chemical element with a given atomic number whose mass numbers are different.
79 of 275
List the isotopes of hydrogen with their mass
number and the constituents of their nuclei!
number and the constituents of their nuclei!
Hydrogen | Mass Number:1 | Composition: 1 proton
Deuterium | Mass Number:2 | Composition: 1 proton+1 neutron
Tritium | Mass Number:3 | Composition: 1 proton+2 neutrons.
Deuterium | Mass Number:2 | Composition: 1 proton+1 neutron
Tritium | Mass Number:3 | Composition: 1 proton+2 neutrons.
80 of 275
What is the mass defect of nuclei?
The mass defect equals the difference between the mass of a nucleus and the total mass of its constituents:
∆m = (Z mproton + [A-Z] mneutron) - matom, where ∆m is the mass defect.
∆m = (Z mproton + [A-Z] mneutron) - matom, where ∆m is the mass defect.
81 of 275
What is the relationship between the total binding
energy (∆E) and the mass defect (∆m) of a given
nucleus?
energy (∆E) and the mass defect (∆m) of a given
nucleus?
∆E=∆m⋅c2, according to Einstein's mass-energy
equivalence principle (c is the speed of light in vacuum).
equivalence principle (c is the speed of light in vacuum).
82 of 275
Describe how the binding energy per nucleon
changes as a function of mass number.
changes as a function of mass number.
Binding energy per nucleon has a maximum at nuclei with mass numbers 55-60 (i.e. Fe).
83 of 275
What are the properties of nuclear force (their range, strength and direction)?
Nuclear forces have limited range, their effect is
negligible at a distance of more than a single nucleon and they are independent of charge. They are very powerful attractive forces whose magnitude exceeds that of electrostatic forces.
negligible at a distance of more than a single nucleon and they are independent of charge. They are very powerful attractive forces whose magnitude exceeds that of electrostatic forces.
84 of 275
On what kind of energy level does a nucleon reside in a nucleus compared to the energy of a free particle?
A bound nucleon has negative potential energy
compared to a free particle.
compared to a free particle.
85 of 275
List the types of radioactive radiation and
characterize the particles constituting them!
characterize the particles constituting them!
Alpha radiation consists of helium nuclei. Negative beta radiation (β-) is composed of electrons, whereas positive beta radiation (β+) consists of positrons. Gamma radiation is an electromagnetic radiation consisting of high energy photons.
86 of 275
What is the direction of changes in the atomic
number and the mass number of nuclei during alpha decay, both types of β decay, electron capture and gamma decay?
number and the mass number of nuclei during alpha decay, both types of β decay, electron capture and gamma decay?
α decay | change in mass number:-4 | change in atomic number:-2
β(-)decay | change in mass number:0 | change in atomic number:+1
β(+)decay&electron capture | change in mass number:0 | change in atomic number:-1
γ decay | change in mass & atomic number:0
β(-)decay | change in mass number:0 | change in atomic number:+1
β(+)decay&electron capture | change in mass number:0 | change in atomic number:-1
γ decay | change in mass & atomic number:0
87 of 275
. Why is the spectrum of beta decay continuous?
Besides an electron (or a positron) an antineutrino (or a neutrino) is also emitted, and the energy released during the decay is shared randomly between the two particles.
88 of 275
What is electron capture and what does it produce?
Some nuclei are capable of capturing an electron
residing on the K shell decreasing their atomic number by one. The vacancy generated this way on the K shell is filled by an electron from a higher shell which generates characteristic X-ray&/or an Auger el
residing on the K shell decreasing their atomic number by one. The vacancy generated this way on the K shell is filled by an electron from a higher shell which generates characteristic X-ray&/or an Auger el
89 of 275
Give the equation describing the number of
undecayed nuclei as a function of time (i.e. the law
of radioactive decay).
undecayed nuclei as a function of time (i.e. the law
of radioactive decay).
N=N0e^(−λt)
N0: number of radioactive nuclei at t=0,
N: number of undecayed radioactive nuclei at the time of investigation,
λ: decay constant,
t: time.
N0: number of radioactive nuclei at t=0,
N: number of undecayed radioactive nuclei at the time of investigation,
λ: decay constant,
t: time.
90 of 275
What is the physical meaning of the radioactive
decay constant?
decay constant?
Radioactive decay constant is equal to the inverse first power of the mean lifetime of a radioactive nucleus.
91 of 275
. What is the relationship between the radioactive
decay constant (λ) and the half life (T)?
decay constant (λ) and the half life (T)?
T=ln 2/λ
ln 2: the natural logarithm of 2.
ln 2: the natural logarithm of 2.
92 of 275
Define biological half life.
Biological half life is the time period during which half of the initial quantity of the radioactive isotope leaves the living system undecayed due to metabolism, secretion or excretion.
93 of 275
Define effective half life.
Effective half life gives the time during which the initial activity of a given type of radioactive nucleus decreases to half of its original value either by physical decay or metabolism.
94 of 275
Describe the relationship between the effective (Teff), the physical (Tphys) and the biological (Tbiol) half lives!
1/Teff=1/Tphys+1/Tbiol
95 of 275
Describe the relationship between the physical
(λphys), the biological (λbiol) and the effective (λeff) decay constants!
(λphys), the biological (λbiol) and the effective (λeff) decay constants!
λeff = λphys + λbiol
96 of 275
Write the formula describing the attenuation of
gamma or X-ray radiation in an absorbing material.
gamma or X-ray radiation in an absorbing material.
J=J0e^(−µx)
where J0 denotes the incident intensity and J is the transmitted intensity after passing through an absorber of thickness x. µ is the absorption/attenuation coefficient.
where J0 denotes the incident intensity and J is the transmitted intensity after passing through an absorber of thickness x. µ is the absorption/attenuation coefficient.
97 of 275
What is the definition of the attenuation coefficient of a material for gamma or X-ray and what is its SI unit?
The attenuation coefficient is the reciprocal of the
distance at which the intensity of the radiation decreases to 1/e-times (≈37%) of the initial value. [µ]=1/m.
distance at which the intensity of the radiation decreases to 1/e-times (≈37%) of the initial value. [µ]=1/m.
98 of 275
How does the intensity of α-radiation change as a
function of the distance from the radiation source?
function of the distance from the radiation source?
It is constant in the beginning then suddenly decreases to zero.
99 of 275
Why are alpha and beta(-) radiations called directly
ionizing radiations?
ionizing radiations?
Due to their charge, ionization is caused by the direct electrostatic interaction with atomic electrons. Their energy decreases in a series of ionizations along their path.
100 of 275
Why do we call gamma radiation and X-rays
indirectly ionizing radiation?
indirectly ionizing radiation?
Primary (direct) interactions between the photons and atomic electrons account for only 5% of ionizations. The majority (95%) of ionizations are caused by high-energy electrons emitted during the primary interactions.
101 of 275
Compare the path of alpha- and beta(-) particles
passing through an absorbing material.
passing through an absorbing material.
The path of the alpha particle is straight, whereas that of the beta(-) particle is zigzagged.
102 of 275
What kind of radioactive radiations can be detected by a GM-counter?
α-, β- and γ-particles can be detected.
103 of 275
What is the basic principle of operation of a
photomultiplier tube?
photomultiplier tube?
Electrons liberated from a light sensitive cathode by photons are accelerated in an electric field&collide into other dynodes whose potentials are increased in succession along the length of the tube. The no of electrons increases at each dynode.
104 of 275
What is the basic operation principle of ionization
detectors?
detectors?
Electrons and positive ions produced by the ionization process are separated by the electric field of the detector. The charged particles are attracted towards the appropriate electrodes and generate electric impulses.
105 of 275
What is the principle of detection of radioactive
radiation by a scintillation detector?
radiation by a scintillation detector?
In certain organic and inorganic substances the energy of radioactive particles is converted to luminous energy, i.e. they generate visible light flashes.
106 of 275
List the radioactive radiations in order of increasing penetrability!
α<β<γ
107 of 275
What is the biological effect of radioactive radiation based on?
Excitation and ionization of atoms and/or molecules of living systems.
108 of 275
What kind of particles are able to produce a
biological effect in radiation biology?
biological effect in radiation biology?
Particles giving their energy partially or totally to the biological object are able to produce a biological effect.
109 of 275
What is a hit in radiation biology?
If one or more ionizations are produced in the
radiosensitive volume of a biological object.
radiosensitive volume of a biological object.
110 of 275
How can a dose-response curve be constructed?
The applied radiation dose is plotted on the horizontal axis and the ratio of the surviving organisms (N) and the total number of organisms before irradiation (N0) is plotted on the vertical axis.
111 of 275
What is the probability of generating exactly ‘n’ hits when applying a dose of D in volume V?
Pn= (VD)^n /n! e^-VD
112 of 275
How does the number of ionizations depend on the dose of the radiation?
The number of ionizations is linearly proportional to the dose.
113 of 275
Write the equation describing the dose-response
curve when one hit is necessary for inactivation?
curve when one hit is necessary for inactivation?
N/N0=e^-VD
where N is the number of surviving organisms, No is the total number of organisms, D is the dose and V is the radiosensitive volume.
where N is the number of surviving organisms, No is the total number of organisms, D is the dose and V is the radiosensitive volume.
114 of 275
What is D37?
D37 denotes the dose at which 37 % of the irradiated objects survive. If one ionization causes inactivation, D37 corresponds to one hit in a radiosensitive volume (VD=1,
that is D=1/V).
that is D=1/V).
115 of 275
What is the principle of the indirect action of
radiation?
radiation?
In aqueous solutions a particle of an ionizing radiation most probably causes ionization of the solvent (H2O) because H2O molecules outnumber solute molecules.
Radicals generated by this process are
responsible for damaging solute molecules. This way the
Radicals generated by this process are
responsible for damaging solute molecules. This way the
116 of 275
What kind of products are capable of damaging
biological objects arise during irradiation of
aqueous solutions?
biological objects arise during irradiation of
aqueous solutions?
hydrated e–, H•, OH•, H2O2
117 of 275
What is the definition of absorbed dose?
Absorbed dose, Da, is defined for any ionizing radiation as the ratio of radiation energy converted into ionization energy and the mass taking up the ionization energy.
Unit: Gray (Gy), 1 Gy= 1J/kg.
Unit: Gray (Gy), 1 Gy= 1J/kg.
118 of 275
. Define the unit of equivalent dose!
Its unit is 1 Sievert (Sv). 1 Sv is the dose of any ionizing radiation which produces the same effect on human beings as 1 Gy absorbed dose of conventional X-ray. Conventional X-ray consists of 250 keV photons.
119 of 275
Define effective dose. Why is it necessary to
introduce effective dose when examining radiation
damage in biological organisms?
introduce effective dose when examining radiation
damage in biological organisms?
Effective dose is the weighted sum of the equivalent doses in all specified tissues and organs of the human body/other biological organism.
It's used coz the extent of radiation damage is influenced by the radiation sensitivity of the irradiated tissues.
It's used coz the extent of radiation damage is influenced by the radiation sensitivity of the irradiated tissues.
120 of 275
List the physical factors influencing radiation
sensitivity!
sensitivity!
The quality of radiation (it influences radiation sensitivity through ionization density and penetrability), time factor, temperature, the effect of oxygen, substances protecting from radiation.
121 of 275
What is the smallest dose which can produce a
biological effect?
biological effect?
Theoretically even a single quantum is enough to
produce a point mutation, since any photon that is able to produce ionization is capable of breaking a chemical bond.
produce a point mutation, since any photon that is able to produce ionization is capable of breaking a chemical bond.
122 of 275
. How can radioactive radiation cause a double strand break in DNA?
A double strand break of DNA can be caused by a single ionization event or as a result of simultaneous single strand breaks on the opposite strands of DNA helix which are produced by ionizations originating from separate events.
123 of 275
Write the equation describing cell survival according to the linear-quadratic model.
S(D)=N/N0=e^-(αD+βD^2)
Where S(D) is the survival fraction as a function of dose D, α&β are tissue&radiation dependent constants. Parameters α&β are proportional to the probability of "one-step"&“two-step” DNA double strand breaks, respectively.
Where S(D) is the survival fraction as a function of dose D, α&β are tissue&radiation dependent constants. Parameters α&β are proportional to the probability of "one-step"&“two-step” DNA double strand breaks, respectively.
124 of 275
. In which part of the cell cycle are cells the most and the least sensitive to radioactive radiation?
Generally, the majority of cells are considered to be the most radiosensitive during mitosis and most resistant in late S phase.
125 of 275
How does radiosensitivity changes as a function of
the level of oxygenation?
the level of oxygenation?
The well-oxygenated cells have greater radiosensitivity than hypoxic cells, because in the presence of oxygen there is higher chance to produce radicals.
126 of 275
How and why does fractionation of radioactive
radiation influence the radiation sensitivity of cells?
radiation influence the radiation sensitivity of cells?
Fractionation decreases the radiation sensitivity of cells, because radiation-induced damage can be partly repaired between exposures to the radiation.
127 of 275
Give the frequency range of sound waves audible by a normal human ear!
Lower limit: 16-20 Hz
Upper limit: 16000-20000 Hz.
Upper limit: 16000-20000 Hz.
128 of 275
What is ultrasound?
Sounds whose frequency is between 20000 Hz and 10^10Hz.
129 of 275
Give the definition and unit of sound intensity!
The energy carried by the sound wave perpendicularly through unit cross-sectional area per unit time. Its unit is Watt/m2.
130 of 275
Define in words the compressibility of a medium.
Compressibility is given by the relative volume decrease of the medium caused by a unit increase of pressure.
131 of 275
Define acoustic impedance of a medium and provide a formula showing how it depends on other properties of the medium.
Acoustic impedance is a material constant, which can be defined as the resistance of the medium against bringing its particles into motion. Acoustic impedance (Z) depends on the density (ρ)&the compressibility (κ) of the medium:
Z=√p/κ
Z=√p/κ
132 of 275
What does the propagation speed of sound depend on?
Propagation speed of sound is determined by the
acoustic impedance and the density of the medium according to the equation below:
c=Z/ρ, where Z: acoustic impedance, ρ: density.
acoustic impedance and the density of the medium according to the equation below:
c=Z/ρ, where Z: acoustic impedance, ρ: density.
133 of 275
List the most widespread effects suitable for the
generation of ultrasound!
generation of ultrasound!
- inverse piezoelectric effect
- electrostriction effect
- magnetostriction effect
- electrostriction effect
- magnetostriction effect
134 of 275
Describe the relationship between the amplitude of the ultrasound-induced pressure fluctuation (ΔPmax) and the intensity of ultrasound (J)!
∆pmax=√2ZJ, where Z is acoustic impedance.
135 of 275
What is cavitation?
Attractive forces between fluid particles may be
overcome by the alternating pressure changes induced by ultrasound and microscopic cavities containing no fluid particles may be generated.
overcome by the alternating pressure changes induced by ultrasound and microscopic cavities containing no fluid particles may be generated.
136 of 275
How does the intensity of ultrasound change while it passes through a certain medium?
J=J0e^-µx
where J0 is the intensity of the ultrasound entering the medium, µ is the absorption coefficient and x is the thickness of the medium.
where J0 is the intensity of the ultrasound entering the medium, µ is the absorption coefficient and x is the thickness of the medium.
137 of 275
What does the reflexivity (extent of reflection on the interface of two media) of ultrasound depend on?
Extent of reflection is determined by the accoustic
impedances of the two media. The greater the difference in their acoustic impedances, the larger the reflected fraction of ultrasound is.
impedances of the two media. The greater the difference in their acoustic impedances, the larger the reflected fraction of ultrasound is.
138 of 275
What is the basis of imaging with ultrasound?
A part of a u.s beam is reflected at the interfaces of different tissues w/ different acoustic impedance, so the boundaries of different tissues can be mapped using the intensity &the delay of the echo compared to the impulse leaving the transducer.
139 of 275
List the most important types of applications of
radioactive isotopes in medical diagnosis!
radioactive isotopes in medical diagnosis!
− in vitro laboratory tests
− determination of the volume of body compartments
− two- or three-dimensional imaging of the distribution of radioactive isotopes in the body
− determination of the volume of body compartments
− two- or three-dimensional imaging of the distribution of radioactive isotopes in the body
140 of 275
What is the principle of direct radioimmunoassay
(RIA)?
(RIA)?
An RIA is a very sensitive in vitro assay technique used to measure nano- or picomolar concentrations of substances. An antibody specific for the investigated substance is bound to a solid carrier (capture antibody).
141 of 275
What is the principle of particle acceleration in
linear and cyclic accelerators?
linear and cyclic accelerators?
Both in linear&cyclic accelerators charged particles gain K.E moving through an electric field. In linear accelerators particles are subjected to electric fields generated by a series of electrodes w/ alternating polarities arranged along a linear beamlin
142 of 275
What is the operation principle of a γ-camera?
A substance labeled w/ a radioactive isotope is injected into the body (radiopharmacon). The emitted γ photon passes through a collimator&collides into a scintillation detector. The distribution of the radiation source can be mapped by the counts of PMTs.
143 of 275
What is the principle of SPECT?
Images are taken from different directions by a γ-camera. The three-dimensional distribution of the radiation source is calculated from these images.
144 of 275
What kind of isotopes can be used in PET?
Only nuclei with positive β-decay can be used.
145 of 275
What is the principle of determination of the location of a radioactive isotope in PET?
A positron is generated in a positive βdecay. It
collides with an electron in a distance shorter than 1 mm from its generation&the 2 particles are annihillated. 2 γ photons generated in the reaction leave the place of annihilation in opposite directions.
collides with an electron in a distance shorter than 1 mm from its generation&the 2 particles are annihillated. 2 γ photons generated in the reaction leave the place of annihilation in opposite directions.
146 of 275
What is the principle of computer tomography?
X-ray images are taken of the human body from different directions. The X-ray absorption capacity of volume units (voxels) of the body can be calculated from these images.
147 of 275
In which respect does a CT image provide more
information than a conventional X-ray image?
information than a conventional X-ray image?
A conventional X-ray image contains only the two
dimensional projection of the distribution of the X-ray absorbing material, while a CT image also reveals the third dimension (depth) of the object.
dimensional projection of the distribution of the X-ray absorbing material, while a CT image also reveals the third dimension (depth) of the object.
148 of 275
Which nuclei are able to give an NMR signal?
Whose resultant nuclear spin is different from zero; i.e. those nuclei which contain odd number of protons and/or odd number of neutrons.
149 of 275
List at least three nuclei which can be used in
biological applications of nuclear magnetic
resonance!
biological applications of nuclear magnetic
resonance!
1H, 13C, 15N, 23Na, 31P
150 of 275
What happens to the elementary magnetic moments in an external magnetic field?
The interaction of magnetic moments with the external magnetic field causes their alignment as well as their precession about the magnetic field.
151 of 275
What are the possible states of the magnetic
moment of a 1H nucleus in an external magnetic
field?
moment of a 1H nucleus in an external magnetic
field?
The nuclear spin of 1H is ½, therefore its magnetic
moment has 2 possible alignments: it can be aligned either w/ (parallel alignment-lower energy level or ground state) or against (antiparallel alignment-higher energy level or excited state).
moment has 2 possible alignments: it can be aligned either w/ (parallel alignment-lower energy level or ground state) or against (antiparallel alignment-higher energy level or excited state).
152 of 275
What is the condition for resonance absorption in
NMR?
NMR?
E2-E1=hf=gNµNB=γNBhh
E2-E1: the energy diff between the excited&ground states of the nuclear spin
B: magnetic field
h: Planck's constant
f: frequency of the applied EM radiation
gN: nuclear g-factor; γN: gyromagnetic ratio
μN: nuclear magneton.
E2-E1: the energy diff between the excited&ground states of the nuclear spin
B: magnetic field
h: Planck's constant
f: frequency of the applied EM radiation
gN: nuclear g-factor; γN: gyromagnetic ratio
μN: nuclear magneton.
153 of 275
Define the gyromagnetic ratio of a nucleus!
It is the ratio of the magnetic moment (MN) to the intrinsic angular momentum (spin; LN) of the given nucleus:
γN=MN/LN=(μNgN)/h
gN is the nuclear g-factor, μN is the nuclear magneton&h=h/2π (h is the Planck constant).
γN=MN/LN=(μNgN)/h
gN is the nuclear g-factor, μN is the nuclear magneton&h=h/2π (h is the Planck constant).
154 of 275
What region of the electromagnetic spectrum can be used to excite nuclear spins placed in a magnetic field?
Radiowaves ( ∼10^8 Hz): NMR
155 of 275
What is the nuclear magneton?
It is a physical constant and the natural unit for
expressing magnetic dipole moments of heavy particles (e.g. nucleons, atomic nuclei).
μN=eh/2mp
e: elementary charge, mp: mass of the proton
h= h/(2π) (h is Planck's constant).
expressing magnetic dipole moments of heavy particles (e.g. nucleons, atomic nuclei).
μN=eh/2mp
e: elementary charge, mp: mass of the proton
h= h/(2π) (h is Planck's constant).
156 of 275
What factors influence the resonance frequency in
NMR?
NMR?
Quality of the absorbing nucleus, its chemical
environment and the strength of the external magnetic field.
environment and the strength of the external magnetic field.
157 of 275
How can the relative concentration of absorbing
nuclei be determined from an NMR spectrum?
nuclei be determined from an NMR spectrum?
From the area under the absorption lines corresponding to different nuclei.
158 of 275
What is chemical shift in NMR?
The local magnetic field experienced by a given nucleus is altered by the chemical environment resulting in a change in its original resonance frequency.
159 of 275
What is the macroscopic consequence of the
alignment of nuclear magnetic moments by the
external magnetic field?
alignment of nuclear magnetic moments by the
external magnetic field?
A macroscopic magnetization (equilibrium or longitudinal magnetization) is formed in the direction of the external magnetic field.
160 of 275
What provides the signal in pulse NMR techniques?
The precession of transverse magnetization generated by a short, intense radiofrequency pulse. Precession takes place at the resonance frequency of the nucleus in the given
magnetic field.
magnetic field.
161 of 275
What is spin-spin and spin-lattice relaxation?
Spin–spin relaxation is the mechanism responsible for the decay of transverse magnetization generated by the radiofrequency pulse. Spin–lattice relaxation is responsible for the recovery of the original longitudinal magnetization vector.
162 of 275
What kind of parameters does an MRI image reveal?
About the density of 1H nuclei in a volume unit (voxel) and about their spin-spin and spin-lattice relaxation rates.
163 of 275
How is the signal localized in MRI?
Linear magnetic field gradients are applied in different directions. Since the resonance frequency is linearly proportional to the magnetic field experienced by the nucleus, location of the signal can be encoded on the basis of frequency.
164 of 275
What is in vivo magnetic resonance spectroscopy
(in vivo MRS)?
(in vivo MRS)?
It is a non-invasive, analytical technique that can be used to study metabolic processes in the volume of interest of a living organism on the basis of characteristic NMR
spectra of the respective metabolites.
spectra of the respective metabolites.
165 of 275
What is the definition of chemical potential?
Chemical potential of a substance is the Gibbs free
energy of 1 mole of the given substance, i.e. the
chemical pot of a substance gives by how much the G.F.E of a thermodynamic system increases when one mole of the given substance is added to the system.
energy of 1 mole of the given substance, i.e. the
chemical pot of a substance gives by how much the G.F.E of a thermodynamic system increases when one mole of the given substance is added to the system.
166 of 275
Define the frictional force (Ff) acting on a molecule with velocity v in an aqueous environment
Ff=-fv, where f is the form factor.
167 of 275
What is the relationship between the absolute
temperature (T) and the average kinetic energy of a molecule (Ekin) in a system containing monatomic gas in thermal equilibrium?
temperature (T) and the average kinetic energy of a molecule (Ekin) in a system containing monatomic gas in thermal equilibrium?
Ekin=3/2kT, where k is the Boltzmann constant.
168 of 275
What is diffusion?
Net flow of material propelled by Brownian motion due to a gradient of the chemical potential.
169 of 275
What is the physical meaning of the diffusion
constant?
constant?
The diffusion constant (D) is the amount of material transported through unit surface area in unit time at a unit concentration gradient. It characterizes the mobility of molecules.
170 of 275
What is the unit of diffusion constant?
[D] = m2/s
171 of 275
Give the average squared displacement of a particle with diffusion constant D!
∆x^2 =2Dt
where t is time, and 2 ∆x is the average squared
displacement.
where t is time, and 2 ∆x is the average squared
displacement.
172 of 275
Write Fick's first law and interpret the constants and physical quantities!
Iv=-DA(∆c/∆x)
Iv is the quantity of material transported through the surface A per unit time by a concentration gradient Δc/Δx, D is the diffusion constant.
Iv is the quantity of material transported through the surface A per unit time by a concentration gradient Δc/Δx, D is the diffusion constant.
173 of 275
How does the diffusion constant (D) depend on
temperature (T) and the radius (r) of a spherical
molecule?
temperature (T) and the radius (r) of a spherical
molecule?
D∼T/r
174 of 275
Write down the equation describing the relationship between the diffusion constant (D) and the form factor (f)!
D=kT/f
where k is the Boltzmann constant and T is the absolute temperature.
where k is the Boltzmann constant and T is the absolute temperature.
175 of 275
Which parameters tend toward spatial equilibrium
during a diffusion process?
during a diffusion process?
The chemical potentials of the components.
176 of 275
Write down van't Hoff's law!
Π = posmosis = cRT, where Π = posmosis - osmotic pressure, R is the universal gas constant, T is absolute temperature, c is the molar concentration of the material in solution.
177 of 275
What is osmosis?
Flow of the solvent to a concentrated solution from the more dilute one, if the two compartments are separated by a semipermeable membrane. This material flow decreases the concentration gradient between the two
solutions.
solutions.
178 of 275
What is the osmotic pressure?
It is the pressure, which is able to prevent the solvent flow from the pure solvent to the solution through the semipermeable membrane.
179 of 275
What is the permeability constant?
The permeability constant is the amount of material transported through the membrane per unit surface in unit time due to unit concentration difference.
180 of 275
Give the equation describing the flux of material
transported across a membrane due to
concentration difference between two
compartments separated by the membrane!
transported across a membrane due to
concentration difference between two
compartments separated by the membrane!
Jm=-p⋅∆c
Jm – is the flux of the material, which is the amount of material transported through a unit membrane area in a
unit time Unit: mol/(m2s)
p–membrane permeability constant, (m/s)
∆c – conc diff between the
concs on the 2 sides of the membrane.
Jm – is the flux of the material, which is the amount of material transported through a unit membrane area in a
unit time Unit: mol/(m2s)
p–membrane permeability constant, (m/s)
∆c – conc diff between the
concs on the 2 sides of the membrane.
181 of 275
What does it mean that phospholipids are
amphipathic molecules?
amphipathic molecules?
They consist of hydrophobic and hydrophilic parts.
182 of 275
What are the possible forms of motion of a lipid
molecule in a membrane?
molecule in a membrane?
-lateral diffusion
-rotational diffusion
-transmembrane flip-flop
-flexible motion of fatty acid side chains.
-rotational diffusion
-transmembrane flip-flop
-flexible motion of fatty acid side chains.
183 of 275
What are the possible phase states of biological
membranes?
membranes?
-gel phase
-liquid crystal/ fluid phase
-liquid crystal/ fluid phase
184 of 275
What changes in the properties of the fatty acid side chains increase the transition temperature of a membrane?
-increase in the saturation of fatty acid carbon-carbon bonds
-increase in the length of the fatty acid side chains.
-increase in the length of the fatty acid side chains.
185 of 275
How does cholesterol change the fluidity of lipid
membranes?
membranes?
Below the phase transition temperature it usually
increases, above the phase transition temperature it decreases.
increases, above the phase transition temperature it decreases.
186 of 275
What is the magnitude of the lateral diffusion
constant of lipids and proteins in biological
membranes?
constant of lipids and proteins in biological
membranes?
lipids: 10^-8 - 10^-9 cm2/s
proteins: 10^-9 - 10^-12 cm2/s.
proteins: 10^-9 - 10^-12 cm2/s.
187 of 275
Which methods can be used to measure the lateral
diffusion of proteins in biological membranes?
diffusion of proteins in biological membranes?
- Fluorescence Recovery After Photobleaching (FRAP)
- Single Particle Tracking (SPT)
- Fluorescence Correlation Spectroscopy (FCS)
- Single Particle Tracking (SPT)
- Fluorescence Correlation Spectroscopy (FCS)
188 of 275
For what kind of molecules is the permeability of
biological membranes the highest?
biological membranes the highest?
For small, uncharged, apolar molecules, e.g. O2, N2.
189 of 275
How can membrane proteins be classified based on their function?
- transport and channel proteins
- receptor and signal transducing proteins
- enzymes
- structural membrane proteins.
- receptor and signal transducing proteins
- enzymes
- structural membrane proteins.
190 of 275
. What are the extra- and intracellular concentrations of Na+, K+ and Ca2+ ions?
Na+ | extracell: 140mM | intracell: 10-20mM |
K+ | extracell: 5mM | intracell: 140-150mM |
Ca2+ | extracell: 1-2mM | intracell: 10^-4mM |
K+ | extracell: 5mM | intracell: 140-150mM |
Ca2+ | extracell: 1-2mM | intracell: 10^-4mM |
191 of 275
What is passive transport?
Transport processes driven by the electrochemical
potential gradient which do not need active metabolism are called passive transport.
potential gradient which do not need active metabolism are called passive transport.
192 of 275
What is active transport?
Transport processes that results in material flow against the electrochemical potential gradient at the expense of energy utilization are called active transport.
193 of 275
What is primary active transport?
The transporter pumps ions/molecules across the
membrane against their electrochemical gradient using energy from ATP hydrolysis.
membrane against their electrochemical gradient using energy from ATP hydrolysis.
194 of 275
What is secondary active transport?
Secondary active transport moves ions/molecules
across the membrane against their gradient using
energy stored in the gradient of another ion, created by a primary active transport mechanism.
across the membrane against their gradient using
energy stored in the gradient of another ion, created by a primary active transport mechanism.
195 of 275
What is simple diffusion across biological
membranes?
membranes?
The passive transport of small and lipid-soluble
molecules across the membrane.
molecules across the membrane.
196 of 275
What is facilitated diffusion?
The passive transport of membrane impermeant
ions/molecules across the membrane aided by transport proteins (ion channels or carriers) molecules.
ions/molecules across the membrane aided by transport proteins (ion channels or carriers) molecules.
197 of 275
What are the properties of facilitated or carriermediated diffusion?
-transporter proteins specifically bind the transported molecules
-the transport can be selectively inhibited
-the flux of transport can be saturated over a given
concentration of the transported material.
-the transport can be selectively inhibited
-the flux of transport can be saturated over a given
concentration of the transported material.
198 of 275
What kind of ion channels do you know based on
their mode of activation?
their mode of activation?
-ligand gated ion channels
-voltage gated ion channels
-second messenger gated ion channels
-mechanical deformation (stretch) activated ion
channels.
-voltage gated ion channels
-second messenger gated ion channels
-mechanical deformation (stretch) activated ion
channels.
199 of 275
What is the function of ionophores?
They promote the selective transport of ions through lipid membranes.
200 of 275
How can ionophores be grouped according to the
mechanism of ion transport?
mechanism of ion transport?
- carrier ionophores
- channel forming ionophores
- channel forming ionophores
201 of 275
List the factors contributing to the maintenance of
resting membrane potential!
resting membrane potential!
- diffusion potential
- Donnan potential
- active transport by ion pumps.
- Donnan potential
- active transport by ion pumps.
202 of 275
Write the Nernst equation!
Uo,x=Ex=-RT/zxF ln [x]i/[x]o
where U0,x (or Ex) is the equilibrium pot of the given ion,
R is the universal gas const
T is the absolute temp
zx is the charge of the given ion
F is the Faraday const
[x]e and [x]i are the e.c&i.c conc
of the given ion.
where U0,x (or Ex) is the equilibrium pot of the given ion,
R is the universal gas const
T is the absolute temp
zx is the charge of the given ion
F is the Faraday const
[x]e and [x]i are the e.c&i.c conc
of the given ion.
203 of 275
What is the equilibrium potential of an ion?
The membrane potential where the net flux of the given ion is zero, i.e. the system is in thermodynamic equilibrium for the given ion.
204 of 275
Are the ions on the two sides of the membrane of a living cell in thermodynamic equilibrium? Why?
No. There is no thermodynamic equilibrium because the net passive flux of a given ion is not zero at the resting membrane potential.
205 of 275
Describe the relationship between net fluxes of
major permeating ions at the resting membrane
potential!
major permeating ions at the resting membrane
potential!
JNa+JK+JCl=0, where Jx is the flux of ion x.
206 of 275
Give the definition and unit of flux!
Flux (J) is the amount of transported items across unit cross section area per unit time. Unit: mol/(m2s)
207 of 275
Give the Goldmann-Hodgkin-Katz equation!
Um=Em=-RT/F ln (PNa[Na+]i+PK[K+]i+PCl[Cl-]o+...) / (PNa[Na+]o+PK[K+]o+PCl[Cl-]i+...)
Um (Em) is the resting m.p (diffusion pot);
R the universal gas const;
T the absolute temp;
F the Faraday const;
[x]o&[x]i are the e.c&i.c conc of ion x.
Um (Em) is the resting m.p (diffusion pot);
R the universal gas const;
T the absolute temp;
F the Faraday const;
[x]o&[x]i are the e.c&i.c conc of ion x.
208 of 275
Give the definition and unit of conductivity!
G (conductivity)=1/R (where R is the resistance)
Unit: 1/Ω =siemens (S).
Unit: 1/Ω =siemens (S).
209 of 275
Give the current carried by ion x through the cell
membrane if the membrane potential is Em!
membrane if the membrane potential is Em!
Ix=Gx(Em-Ex)
where Ix is the current;
Gx is the conductivity of the membrane for ion x (G=1/R);
Em is the actual membrane potential;
Ex is the equilibrium potential of ion x.
where Ix is the current;
Gx is the conductivity of the membrane for ion x (G=1/R);
Em is the actual membrane potential;
Ex is the equilibrium potential of ion x.
210 of 275
Define the action potential and interpret the ionic
basis of its generation.
basis of its generation.
The a.p is a characteristic, time-dependent change in the m.p as a result of time&m.p-dependent changes in the ion permeabilities of the membrane. In the depolarization phase the Na+ permeability is dominant, the subsequent repolarization is the result of
211 of 275
. How do the concentrations of Na+ and K+ in the intraand extracellular spaces change during a single action potential?
Due to the short duration of opening of Na+ and K+ channels the concentrations of Na+ and K+ change negligibly during a single action potential.
212 of 275
What causes the abrupt membrane potential
changes during an action potential in a neuron?
changes during an action potential in a neuron?
Changes in the permeabilities for Na+ and K+ and the consequent miniature inward Na+ and outward K+ currents, without significant changes in the concentration gradients, lead to the abrupt membrane potential changes in a neuronal action potential.
213 of 275
What is the role of the Na+/K+ ATPase in the
membrane potential changes during a single action potential? Why?
membrane potential changes during a single action potential? Why?
The Na+/K+ ATPase doesn't have any role in the
m.p changes in a single a.p, because: it's too slow to transport enough ions in a couple of ms to change ion conc significantly or carry significant net charge.
m.p changes in a single a.p, because: it's too slow to transport enough ions in a couple of ms to change ion conc significantly or carry significant net charge.
214 of 275
What is the principle of voltage-clamp?
The membrane potential is held at a controlled value independently of ion currents through the membrane.
215 of 275
List the methods that can be used for measuring the membrane potential of living cells!
-optical methods with membrane potential sensitive dyes;
-electrophysiological methods (microelectrode, currentclamp).
-electrophysiological methods (microelectrode, currentclamp).
216 of 275
What kind of currents can be measured by patchclamp?
-single channel currents (eg. cell-attached configuration)
-ion currents flowing through the entire membrane of the cell (whole-cell configuration).
-ion currents flowing through the entire membrane of the cell (whole-cell configuration).
217 of 275
What are the most important features of ion
channels?
channels?
-selective permeability: the channel is permeable only to certain ion species;
-gating: appropriate trigger/signal/event causes a
conformational change in the channel protein resulting in the transition among different states (closed, open, inactivated).
-gating: appropriate trigger/signal/event causes a
conformational change in the channel protein resulting in the transition among different states (closed, open, inactivated).
218 of 275
What is the range of the voltages corresponding to
the R waves of an ECG?
the R waves of an ECG?
millivolts
219 of 275
Give the Einthoven-Waller rule and interpret the
variables in the formula!
variables in the formula!
R1 + R3 = R2, where R1, R2 and R3 are the projections of the integral vector on the sides of the Einthoven triangle.
220 of 275
What is the meaning of an ECG curve in the case of unipolar and bipolar leads?
Unipolar: It is the potential difference between an
exploring and a reference electrode.
Bipolar: It is the potential difference between two
exploring electrodes.
exploring and a reference electrode.
Bipolar: It is the potential difference between two
exploring electrodes.
221 of 275
Which physical characteristics of the eye lens are
changed during accommodation?
changed during accommodation?
The shape (radius of curvature) and the refractive index of the lens. In the case of humans the former is the dominant.
222 of 275
What is the resolution of an eye?
The smallest visual angle at which the images of two points can be distinguished.
223 of 275
What is the physical and biological limit of the
resolution of an eye?
resolution of an eye?
Physical: The separation between the 2 points to be distinguished shouldn't be less than the wavelength of the illuminating light.
Biological: Images of the 2 points to be distinguished have to be on different photoreceptors.
Biological: Images of the 2 points to be distinguished have to be on different photoreceptors.
224 of 275
What does it mean that photons are only triggers for photoreceptors?
The energy of photons is used by the receptors for
inducing chemical (signal transducing) processes.
inducing chemical (signal transducing) processes.
225 of 275
Which receptor cells of the retina are responsible for color vision and vision under dim conditions!
color vision: cones; vision under dim conditions: rods.
226 of 275
What is the principle of Young-Helmholtz theory?
The physiological basis of color vision is the existence of three different color sensitive receptors (the cones) with different photopigments which are able to make a distinction between red, green and blue colors.
227 of 275
What is ERG?
Electroretinogram: it records the potential changes of the retina as a whole during stimulation with light.
228 of 275
What is the threshold intensity of hearing? Specify
its value!
its value!
Threshold intensity of hearing is the minimal intensity of the 1000 Hz sinusoidal sound audible by a normal human ear. Its value is about 10-12 Watt/m2.
229 of 275
How does the intensity of sensation (loudness)
changes as a function of the intensity of the
stimulus?
changes as a function of the intensity of the
stimulus?
Sensation is proportional to the logarithm of the relative intensity of the stimulus.
230 of 275
What is the advantage of the phon scale compared
to the bel (decibel) scale?
to the bel (decibel) scale?
When using the phon scale, intensities of both the reference&actual sound intensities are converted to intensities of the corresponding 1000 Hz sound, both inducing the same sensation of loudness. ∴, the threshold of hearing is 0 phon for every frequency.
231 of 275
Give the Weber-Fechner law!
sensation=const⋅lg (actual stimulus intensity) / (reference stimulus intensity)
232 of 275
A sound with intensity J and frequency of 2000 Hz is produced by a sound generator. What is the
loudness according to the phon scale?
loudness according to the phon scale?
Hphon=10⋅lg J1000/J0 (phon)
where Hphon is the loudness in phons;
J1000 is the intensity of the sound w/ a frequency of 1000 Hz causing the same sensation of loudness as the sound w/ a frequency of 2000 Hz w/ intensity J; J0 is the threshold intensity
where Hphon is the loudness in phons;
J1000 is the intensity of the sound w/ a frequency of 1000 Hz causing the same sensation of loudness as the sound w/ a frequency of 2000 Hz w/ intensity J; J0 is the threshold intensity
233 of 275
What kind of relationship is represented by the
isophonic curves?
isophonic curves?
The sound intensities producing the same sensation of loudness are plotted against the sound frequency.
234 of 275
Give the threshold values of hearing according to
the phon scale for sounds whose frequencies are
1000 Hz and 2000 Hz, respectively!
the phon scale for sounds whose frequencies are
1000 Hz and 2000 Hz, respectively!
0 phon, the threshold of hearing is the same (0 phon) for any frequency.
235 of 275
What is the basis of the sone scale?
Sensation can be more precisely described by the power of the relative stimulus intensity w/ a fractional exponent.
Hsone=1/16⋅(J/J0)^0.3
where Hsone is the loudness in sone, and J&J0 are the stimulus intensity&the reference stimulus intensity.
Hsone=1/16⋅(J/J0)^0.3
where Hsone is the loudness in sone, and J&J0 are the stimulus intensity&the reference stimulus intensity.
236 of 275
What is the mechanism of hearing by air conduction (also called ossicular conduction)?
The vibration reaches the inner ear through the auditory meatuses and the system of the tympanic membrane and auditory ossicles.
237 of 275
What are the physical principles giving rise to an
increased pressure on the foot plate of the stapes
compared to the pressure of the original sound?
increased pressure on the foot plate of the stapes
compared to the pressure of the original sound?
1. the cross-sectional area of the ear drum is much larger than that of the stapes foot plate;
2. lever-like functioning of auditory ossicles.
2. lever-like functioning of auditory ossicles.
238 of 275
What does it mean that the biceps is at a mechanical disadvantage when lifting a weight?
The junction point of the biceps is much closer to the elbow joint than the line of action of the lifted object’s weight. Since the moment arm for the biceps is shorter than that of the load, it must exert a greater force than the weight of the load.
239 of 275
What is the structural elementary unit of contraction in striated muscle and what filaments make it up?
The elementary unit of contraction is the sarcomere, which is made up of actin and myosin filaments.
240 of 275
What does it mean that bones are mechanically
anisotropic?
anisotropic?
It means that the resistance of bones to mechanical stress depends on the direction of the force.
241 of 275
List the types of joints based on the movements they allow with one example for each.
I. Uniaxial joints: hinge joint: knee, fingers, jaws
pivot joint: head on neck, elbow (ulna&radius).
II. Biaxial joints ellipsoidal joint: wrist
saddle joint: Carpometacarpal joint of the thumb.
III. Triaxial joints (multiaxial) ball&socket: shouler&hip.
pivot joint: head on neck, elbow (ulna&radius).
II. Biaxial joints ellipsoidal joint: wrist
saddle joint: Carpometacarpal joint of the thumb.
III. Triaxial joints (multiaxial) ball&socket: shouler&hip.
242 of 275
What mechanical advantage does a hollow (tubular) bone have compared to solid bone?
Resistance to bending is proportional to the 4th power of the outer diameter. A hollow bone of given mass can have much larger diameter than a solid rod-like bone and therefore can resist bending better.
243 of 275
Name the anatomical reference planes of the human body
Coronal or frontal plane, transverse plane and sagittal plane.
244 of 275
At what contraction speed does striated muscle
produce the greatest power?
produce the greatest power?
At about one third of the maximum contraction speed.
245 of 275
What are pennate muscles?
Muscles, in which the fibers attach obliquely (in a
slanting position) to the tendon.
slanting position) to the tendon.
246 of 275
Write the continuity equation for fluid flow!
A1v1=A2v2, where A1 and A2 are the cross sectional areas of the tube, v1 and v2 are the average velocity of the fluid at cross sections A1 and A2, respectively.
247 of 275
Describe in words the meaning of the continuity
equation!
equation!
In the case of incompressible fluids the volumetric flow rate is uniform along the entire tube.
248 of 275
Describe in words the law of Bernoulli!
The sum of the statical, dynamic and gravitational
(hydrostatic) pressures is constant along a streamline.
(hydrostatic) pressures is constant along a streamline.
249 of 275
Describe in words the Hagen-Poiseuille law!
The volumetric flow rate in a tube is directly proportional to the pressure gradient (Δp/Δl) and the fourth power of the radius of the tube, whereas it is inversely proportional to the viscosity of the fluid.
250 of 275
Give the formula for the Hagen-Poiseuille law!
Iv=-(π/8η)R^4 Δp/Δl
where Iv is the volumetric flow rate, R is the radius of the tube, η is the viscosity of the fluid and Δp/Δl is the pressure gradient.
where Iv is the volumetric flow rate, R is the radius of the tube, η is the viscosity of the fluid and Δp/Δl is the pressure gradient.
251 of 275
What does the critical velocity of flow depend on in a tube! Give the formula!
Vcrit=Re(η/ρR)
where η and ρ are the viscosity and the density of the fluid, respectively. R is the radius of the tube, Re is the Reynolds number.
where η and ρ are the viscosity and the density of the fluid, respectively. R is the radius of the tube, Re is the Reynolds number.
252 of 275
Define laminar and turbulent flow!
Laminar flow: at low flow velocities liquids flow in
parallel layers (w/out mixing); it can be characterized by parallel velocity vectors. Turbulent flow: exceeding the critical velocity fluids display erratic flow&mixing.
parallel layers (w/out mixing); it can be characterized by parallel velocity vectors. Turbulent flow: exceeding the critical velocity fluids display erratic flow&mixing.
253 of 275
What is lung compliance and what is its normal
value?
value?
Lung compliance (C) is the extent to which the lungs will expand (∆V) for each unit increase in transpulmonary pressure (∆P), C=∆V/∆P=200 ml/cmH2O.
254 of 275
Which factors determine predominantly lung
compliance?
compliance?
Lung compliance is manly determined by tissue elastic recoil and surface tension.
255 of 275
Define surface tension!
Surface tension is the work required to a unit increase in the surface area of a liquid. γ=W/∆A, where γ is the surface tension ∆A is the change in the surface area, W is the work (energy) required. Its unit is J/m2.
256 of 275
Define Laplace law for alveoli and interpret the
variables!
variables!
p=2γ/r, p is the press generated due to surface tension, γ is the surface tension, r is the radius of the alveolus. The smaller the alveolus, the greater the alveolar press cozed by the surface tension. This press can be decreased by decreasing
the surfac
the surfac
257 of 275
What type of mechanical levers are the ribs
considering the respiration process?
considering the respiration process?
The ribs are Class 2 levers considering the breathing process. At one end of the lever is considered as the fulcrum. Lifting forces, generated by the intercostal muscles, act at the other end of the levers. The load occurs around the middle of the levers
258 of 275
List the major signals being detected in a flow
cytometer! Give the information provided by them.
cytometer! Give the information provided by them.
Forward angle light scatter: size, index of refraction;
Side scatter: intracellular structure/complexity;
Fluorescence signal(s): the size/value of the cellular parameter for which the fluorescence probe was used for(e.g. protein expression, DNA content).
Side scatter: intracellular structure/complexity;
Fluorescence signal(s): the size/value of the cellular parameter for which the fluorescence probe was used for(e.g. protein expression, DNA content).
259 of 275
How can a flow cytometric histogram be
constructed?
constructed?
Signal intensity (or the value of the respective cellular parameter) is plotted on the horizontal axis, whereas the vertical axis shows the number of cells possessing the given signal intensity.
260 of 275
What is the dot plot and how can it be constructed?
Dot plot is a type of 2-parameter data visualization, where the 2 parameters are plotted in a correlated fashion. Each cell is represented by a dot in the coordinate system w/ coordinate values corresponding to the parameters plotted on the X-&Y-axes.
261 of 275
What does gating mean in flow cytometry?
Gating is the restriction of flow cytometric acquisition and/or data analysis to a subset of cells having desired parameters. The cell population of interest can be defined on the basis of either one or two-dimensional plots.
262 of 275
How does flow cytometric cell sorting take place?
The fluid stream containing the cells is illuminated&the fluorescence/scatter signal is detected. The charged droplets pass through an electric field, where they are deflected&∴can be
collected in separate test tubes.
collected in separate test tubes.
263 of 275
List the advantages of flow cytometry and flow
cytometric cell sorting (FACS)!
cytometric cell sorting (FACS)!
- info can be obtained for a given sample on a cellby-cell basis;
- multiple signals can be detected simultaneously for a given cell;
- numerous cells can be studied w/in a short time;
- homogeneity or heterogeneity of a cell population can be revealed;
-
- multiple signals can be detected simultaneously for a given cell;
- numerous cells can be studied w/in a short time;
- homogeneity or heterogeneity of a cell population can be revealed;
-
264 of 275
What is the operating principle of a confocal laser
scanning microscope?
scanning microscope?
A pinhole with a small diameter blocks the way of light beams originating from out of focal planes. This way the image of the object will be sharp. The whole process is extended to the whole plane by scanning.
265 of 275
What is the principle of atomic force microscopy?
A silicium tip hovers ∼5 nm above the surface because it can't get any closer due to electrical repulsion&the weak spring constant of the suspension. In this way the tip is able to scan the surface of the object&detect the height differences at each point
266 of 275
What is the resolution limit of atomic force
microscopy?
microscopy?
Angström (0.1 nm)
267 of 275
Explain the aim and principle of mass spectrometry
The aim of mass spectrometry is to determine the
charge-to-mass ratio of particles. The ionized form of the investigated substance should be introduced to the gaseous phase&then accelerated in an electric field.
& the charge-to-mass ratio is determined.
charge-to-mass ratio of particles. The ionized form of the investigated substance should be introduced to the gaseous phase&then accelerated in an electric field.
& the charge-to-mass ratio is determined.
268 of 275
List forces and their directions acting on a molecule sedimenting in a centrifuge tube!
Centrifugal force pointing away from the axis of rotation, and both frictional force and buoyant force pointing towards the axis of rotation.
269 of 275
Define the sedimentation constant and give its unit!
The sedimentation constant is the sedimentation velocity of a molecule achieved at unit acceleration, that is the sedimentation velocity divided by the centripetal acceleration.
Unit: 1 Svedberg (S)=10-13 sec.
Unit: 1 Svedberg (S)=10-13 sec.
270 of 275
How can the density of an unknown macromolecule be determined by sedimentation experiments?
Macromolecules centrifuged in a density gradient (e.g. cesium chloride) stop sedimenting in the layer whose density is identical to their own.
271 of 275
How does the sedimentation equilibrium depend on the form factor in the case of sedimentation
equilibrium method and why?
equilibrium method and why?
It is independent because after reaching the equilibrium molecules stop moving.
272 of 275
What is electrophoretic mobility?
Electrophoretic mobility is the velocity generated by unit electric field strength.
273 of 275
List the factors influencing the electrophoretic
mobility of a macromolecule!
mobility of a macromolecule!
- molecular mass
- net charge,
- pH of the medium
- form factor.
- net charge,
- pH of the medium
- form factor.
274 of 275
What is the principle of isoelectric focusing?
During electrophoresis in a pH gradient each compound migrates towards the location, where the pH is equal to its isoelectric point. At this point the net charge of a molecule becomes zero, and the molecule stops migrating.
275 of 275
Other cards in this set
Card 2
Front
Define electron volt (eV)!
Back
Electron volt is a unit of energy. It is equivalent to the amount of kinetic energy gained by a single electron when accelerated through a voltage difference of 1 V.
Card 3
Front
Define what force is!
Back
Card 4
Front
Define acceleration in words and with a formula!
Back
Card 5
Front
Define Newton’s 2nd law in words and with a
formula!
formula!
Back
Related discussions on The Student Room
- Examination queries »
- University requirements »
- Advice for University »
- Natural science advice?? »
- Uni courses »
- I can't decide between two degree options. »
- biology at the university of York!! important »
- some questions about cognitive science (BSC/MA) programme »
- Biomedical engineering »
- Ucas questions »
Similar Physics resources:
1.0 / 5 based on 1 rating
0.0 / 5
0.0 / 5
0.0 / 5
0.0 / 5
0.0 / 5
5.0 / 5 based on 1 rating
Teacher recommended
Comments
No comments have yet been made