AQA Unit 5 Revision Cards

Condensed Version of content, relevant to the current AQA Biol unit 5 Syllabus

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  • Created on: 28-05-10 06:39

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Unit 5 Revision Cards

Aim: Provide condensed revision cards, relevant to the AQA biology specification for unit 5, in 30 (front and back of a card= 1 card) cards or less.

Its not possible to insert diagrams so there is no way of including them, nevertheless they are important.

Note: not all of the content on some cards is shown, so selected and drag down, then copy and paste into a word document or something to see all the text


4 days later and sleep deprived they are finished. Once again i would like to state, that they may not be of use, but im glad i made them.

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Key of Abbreviations

Symp. NS- Sympathetic Nervous system, microorg.'s - microorganisms, GT - genetic/ gene therapy

Parasymp. NS- Parasympathetic Nervous system, PCR - polymerase chain reaction

MO- Medulla Oblongata, AMCB - actin-myosin cross bridge, GM - genetically modified

GP- Generator Potential, ER - Endoplasmic reticulum, RE - reduction endonucleases

NI- Nerve impulse, IoL - Islets of Langerhans, SC's - stem cells, GF - Genetic fingerprinting

S.A.N.- Sinoatrial Node, 2MM - secondary messenger model, RT - reverse transcriptase

PC- Pacinian Corpuscle, HGc - Heat Gain centre, HLc - Heat Loss centre

WBC - White Blood Cell, Hypothal. - Hypothalamus, Thermorec.'s - thermoreceptors

PD - Potential Difference, Comp. - complimentary, PGF's - plant growth factors

RP- Resting potential, AP- Action Potential, Ref.P - refractory period, tt. - test tube

VGC's - voltage-gated channels, peptide = amino acid (visa versa)

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Surival and Response (p1)

Organisms increase survival chances by responding to changes in their environment, therefore have greater chance of reproducing and passing on alleles to next gen. hence, selection pressure favours organisms with appropriate responses.

Sequnece of events from stimulus to response: stimulus -> receptor -> coordinator -> effector -> response

Taxis - simple response with direction determined by direction of stimulus. Positive taxis (movement towards stim.) and Negative taxis (movement away from stim.) e.g.

Kinesis - response in which organsims does not move towards or away from stimulus. More unpleasant the stimulus, more rapidly organism moves and changes direction. Response ment to bring organism back into favourable conditions.

Tropisms - growth movement of a part of a plant - response to directional stimulus. Plant grows towards stim. (+ve response) or away from (-ve response), examples:

  • plant shoots grow towards light (+ve phototropism)
  • plant roots grow away from light (-ve phototropism) and towards gravitity (+ve geotropism)
  • plant roots grow towards water (+ve hydrotropism)
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Survival and Response (p2)

Reflex - type of involuntary response to sensory stimulus

Reflex Arc - the pathway of neurones involved in a reflex

simple reflex arc: stimulus -> receptor -> sensory neur. -> int. neur. -> motor neur. -> effector -> response

Importance of reflex arcs:

  • Involuntary, hence, do not require decision making powers of brain. Hence, brain can carry out more complex responses and isn't overloaded.
  • Protect body from harmful stimuli - effective from birth and not learned
  • Fast - neurone pathway is short with few synapses (1 to 2)
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Receptors (p1)

Pascinian Corpuscles (PC) (occur in skin, fingers, soles of feet, external genitalia, joints, ligaments and tendons) respond to changes in mechanical pressure, its is:

  • Specific to a single type of stimulus
  • Produces a generator potential (GP) by acting as a transducer - transducer converts stimulus into form of information body can understand, nerve impulses. All receptors convert energy of stimulus into a nervous impulse known as a generator potential.

Process of generator potential (GP) creation:

pressure on PC -> corpuscle changes shape -> stretches membrane of neurone -> widens stretch -mediated Na ion channels -> allows Na ions into neurone -> changes potential of (depolarises) membrane -> produces GP

How Mechanical stimulus converted into NI:

Stimulus detected by pressure receptors/ mechanoreceptors -> stimulus deforms layers of connective tissue -> which press on sensory nerve ending -> causing deformation of stretch-mediated Na ion channels in neurone membrane cell membrane -> Na ion channels open and Na ions diffuse into the cell -> creating a GP -> if GP reaches threshold it triggers a NI/ action potential

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Receptors (p2)

Rod Cells: Rod-shaped, greater no. than cone cells, Distribution - more at the periphery of the retina, absent at the fovea, Give poor visual acuity and sensitive to low-intensity light

Cone Cells: Cone-shaped, fewer no. than rod cells, fewer at periphery of the retina, concentrated at the fovea, give good visual acuity and not sensitive to low-intensity light


  • Rods - sensitive to light (fire action potentials in dim light). As many rods join one neurone, so many weak GP's combine to reach the threshold and trigger action potential.
  • Cones - less sensitive than rods (only fire action potentials in bright light). One cone joins one neurone, so takes more light to reach the threshold and trigger action potential.

Visual Acuity (ability to tell apart points that are close together):

  • Rods - low visual acuity as many rods join the same neurone, hence light from two objects close together can't be told apart.
  • Cones - high visual acuity, as cones are close together and one cone joins one neurone. When light from 2 points hits 2 cones, 2 action potentials (one per cone) go to the brain - so 2 points close together can be distinguished as 2 separate points
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Control of Heart Rate (p2)

Chemoreceptors - found in carotid (brain servicing) arteries, sensetive to changes in pH and CO2 conc-n. Process of control 'Chemoreceptors' (CO2 conc-n):

  • Blood CO2 conc-n increases higher than normal, pH of blood is lowered
  • Chemoreceptors (carotid artery and aorta walls) detect change and increase Nerve impulses (NI's) frequency to MO
  • MO increases NI's frequency via Symp. NS to S.A.N. - increasing heart rate
  • Increased blood flow, leads to more CO2 being removed by lungs (via ventilation), hence level of CO2 returns to normal
  • pH of blood rises to normal and chemoreceptors (carotid artery and aorta walls) reduce frequency of NI's to MO
  • MO reduces frequency of NI's to sinoatrial node, decreasing heart rate to normal

Control by Pressure receptors (carotid artery and aorta walls)

  • Blood Pressure higher than normal - transmit NI's to MO. MO sends NI's to Parasymp. NS to S.A.N. of heart, decreasing rate at which heart beats.
  • Blood Pressure lower than normal - transmit NI's to MO. MO sends NI's to Symp. NS to S.A.N. of heart, increasing rate at which heart beats.
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Control of Heart Rate (p1)

Autonomic Nervous System (controls involuntary/ subconscious activities of internal muscles/ glands) has 2 divisions: Sympathetic Nervous System (Symp. NS) and Parasympathetic NS (Parasymp. NS), the actions of the systems oppose one another and are antagonistic.

Sympathetic NS - Stimulates effectors and speeds up an activity

Parasympathetic NS - Inhibits effectors and slows down any activity

Control of Heart - controlled by region of brain called medulla oblongata (MO), which has 2 centres:

  • Centre that Increases heart rate, linked to Sinoatrial node (S.A.N.) by Symp. NS
  • Centre that Decreases heart rate, linked to S.A.N. by Parasymp. NS

The centre stimulated depends upon: chemical and pressure changes in blood

Role of Chemoreceptors:

  • Detect changes in CO2 conc-n of the blood (via receptors in carotid artery and aorta walls)
  • Increase frequency of NI's toward Heart rate control centre (MO) when CO2 conc-n high (increase rate)
  • Reduce frequency of NI's toward Heart rate control centre (MO) when CO2 conc-n normal (reduce rate)
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Coordination Principles (p1)

2 Main forms of Coordination: Nervous System and Hormonal System

Nervous System - nerve cells (neurones) pass electrical impulses along their length and stimulate their target cells by secreting chemicals, neurotransmitters. Resulting in rapid communication (response) between specific organism parts, responses are rapid, short-lived and restricted to localised region of body. Effect is temporary and reveresible

Hormonal System - produce chemicals (hormones) transported in blood plasma to target cells, which they stimulate. Resulting in slower, less specific, more widespread and long-lasting communication (response) between organism parts. Effect may be permanent and irreversible

Chemical Mediators - chemicals released from mammalian cells and have effect of cells in immediate vicinity. Usually released by injured or infected cells. Secretion causes small arteries and arterioles to dilate -> rise in temp. and swelling of infected area - 'inflammatory response'. Examples:

  • Histamine (WBC's) - released following injury or in response to an allergen - causes dilation of small arteries and arterioles, increased capillary permeability, leading to localised swelling, redness and itching
  • Prostaglandins (Cell Mem.) - released following injury - caused dilation of small arteries and arterioles, increasing capillary permeability, affect BP and neurotransmitters also affecting pain transmission
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Coordination Principles (p2)

Plant growth factors (PGF's) - plants respond to (abiotic/ non-living factors): light, gravity and water. Plants respond to external stimuli by means of 'plant hormones' or plant growth factors (PGF); PGF is more descriptive than plant hormone, as PGF's:

  • Exert influence by affecting growth
  • Made by cells located throughout plant, rather than particular organs
  • Some affect the tissues that release them rather than acting on target organ

PGF's produced in small quanitities - they have their effects close to the tissues that produces them, an example is Indole Acetic Acid (IAA), which controls tropisms as follows:

  • Cells in tip of shoot produce IAA - transported down shoot
  • IAA initially transported all sides as it moves down shoot
  • Light causes movement of IAA from light side of shoot to dark side of shoot
  • Greater conc-n of IAA builds on shaded side of shoot and causes cells to elongate
  • Elongation of cells via greater IAA conc-n, means cells on shaded side of shoot elongate more
  • Shaded side of shoot grows faster, causing shoot to bend towards light

IAA controls bending of roots in direction of gravity - high conc-n of IAA: inc. growth in stem cells, but decreases growth in root cells

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Nerve Impulse (p1)

Nerve Impulse - self-propagating wave of electrical disturbance, which travels along surface of axon membrane. A temporary reversal of electical potential difference (charges) across the axon membrane. Reversal between 2 states: Resting potential (RP) and Action potential (AP). Movement of Na^+ ions and K^+ ions, across axon membrane controlled by:

  • phospholipid bilayer of axon membrane
  • intrinsic proteins or ion channels (some containing gates) spanning phospholipid bilayer; different gates for Na ions and K ions.
  • Active transport via Sodium-Potassium (Na-K) pumps

Inside of axon is negatively charged (relative to outside) - its Resting potential. RP usually 65mV, between 50-90mV - the axon is said to be polarised (diff. charges insided and out).

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Nerve Impulse [Resting Potential] (p2)

RP established by:

  • Na ions actively transported out of axon and K ions actively transported into axon.
  • active transport of Na ions > that of K ions, ratio 3 Na ions out: 1 K ions in
  • outward movement of Na (from axon) > inward movement of K (into axon), hence, more Na ions in tissue fluid surrounding axon and more K ions inside axon (cytoplasm), creating chemical gradient
  • Na ions then diffuse back into axon, while K ions diffuse back out of axon
  • Most Na ion gates closed, most K ion gates open
  • Hence - Membrane more permeable to K ions, which diffuse out of axon faster than Na ions diffuse in - increasing potential difference [between: greater negative inside of axon and greater positive outside of axon]

Basic Explanation of How movement of ions establishes RP:

  • Active transport of Na ions out of axon by Na-K pump faster than active transport of K ions into axon
  • K ions diffuse out of axon, but few Na ions diffuse into the axon because
  • the sodium ion 'gates' are closed
  • Overall there are more positive ions outside axon than inside
  • therefore outside of axon is positive relative to the inside
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Nerve Impulse [Action Potential] (p3)

A Stimulus recieved by nerve ending causes temporary reversal of charges on the axon membrane - an action potential . Resulting in a change in charges from -65mV (inside membrane) to +40mV. Now, the membrane is said to be depolarised.

Depolarisation occurs because channels (gates) in the axon membrane change shape, hence, opening or closing - depending on voltage across the membrane - voltage-gated channels (VGC's).

Sequence of Events: (Stim., Dep., Rep., Hyp. and RP)

  • At RP K VGC's open but Na VGC's are closed
  • Stimulus - excites neurone cell membrane, opening Na ion VGC's -> membrane more permeable to Na ions, so Na ions diffuse into neurone along electrochemical gradient - inside of neurone less negative
  • Depolarisation - if PD reaches threshold (-55mV), more Na ion VGC's open - more Na ions diffuse into neurone
  • Repolarisation - at PD (+30mV) Na VGC's close and K VGC's open -> membrane more permeable to K ions, so K ions diffuse out of neurone down electrochemical gradient - bringing membrane back to RP
  • Hyperpolarisation - K VGC's close slowly, so slight overshoot - too many K ions diffuse out of Neurone.
  • Resting Potential (RP) - ion channels reset. Na-K pump returns membrane to RP and maintains it until next stimulated
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Nerve Impulse [Action Potential] (p4)

Movement of the Action potential:

  • At RP, surface of axon membrane is polarised. Due to higher conc-n of Na (+ve charged) ions outside axon and lower conc-n of K (lower +ve charge) ions inside the membrane.
  • Stimulus causes influx of Na ions, reversing charge on the axon (action potential) and the membrane is depolarised
  • Localised electrical circuits established by influx of Na ions cause opening of Na VGC's - further along axon. The influx of Na ions into this region causes depolarisation. Behind new region of depolarisation: Na VGC's close and K VGC's open.
  • K ions begin to leave axon along electorchemical gradient
  • AP (depolarisation) propagated (carried on) further along the neurone. Outward movement of K ions continues until axon membrane behind AP has been Repolarised.
  • Repolarisation of neurone allows Na ions to be actively transported out, returning neurone to RP, ready for new stimulus
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Nerve Impulse (p5)

Factors affecting the speed of Action Potentials (AP's):

  • Mylein sheath - causes saltatory conduction as charges jump from one node of ranvier to another - moving faster
  • Diameter of Axon - greater diameter faster speed of conductance - less leakage of ions from large axon
  • Temperature - greater temp. greater kinetic energy, greater rate of particle movement, faster rate of diffusion of ions, faster NI movement

Refractory Period (Ref.P)- Time period in which movement of Na ions is prevented as Na VGC's are closed. During this time its impossible for further AP's to be generated. Important in order to:

  • Ensure AP is propagated in one direction only - as AP cannot be propagated in Ref.P
  • Produces discreet impulses - New AP cannot be formed immediately after first one
  • Limits no. of AP's - AP's seperated from one another limiting no. of AP's passing down axon at given time

All or nothing principle - there is a particular level of stimulus that triggers an AP:

  • Any level above threshold - stimulus will trigger an AP regardless of size of stimulus (all).
  • Below this threshold, no AP is triggered (nothing)
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Synaptic Transmission (p1)

Synapses - transmit NI's from one neurone to another, acting as a junction, allowing: single impulses to be transmitted to a number of different neurones and combines a number of NI's at a synapse. Facts about synapses:

  • chemical (neurotransmitter) made only in presynaptic neurone
  • neurotransmitter stored in synaptic vesicles released into synapse when AP reaches synaptic knob
  • neurotransmitter diffuses across synapse to receptor molecules on postynaptic neurone
  • neurotransmitter binds with receptor molecules and sets up new AP in postsynaptic neurone

Features of Synapses:

  • Unidirectionality - synapses can only pass impulses in one direction, from pre- to post- synaptic neurone. Hence, synapses act like valves
  • Summation - build-up of neurotransmitter in synapse to trigger new AP, by 2 methods: Spatial Summation - many presynaptic neurones together release enough neurotransmitter to exceed threshold value of presynaptic neurone. Temporal Summation - one presynaptic neurone releases neurotransmitter many times over short period, if total amount of neurotransmitter exceeds threshold of presynaptic neurone, new AP is triggered.
  • Inhibition - Cl^- ion channels open in synapse & Cl ions diffuse in, Hyperpolarising postsynaptic membrane- preventing new AP's forming
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Synaptic Transmission (p2)

How drugs affect synaptic transmission:

  • have same shape as neurotransmitter, hence, mimick action at receptor
  • block receptors on postsynaptic neurone (drugs called antagonists)
  • inhibit enzyme that breaks down neurotransmitters (enzyme: acteylcholinerase)
  • stimulate the release of neurotransmitter from postsynaptic neurone
  • inhibit release of neurotransmitters from postsynaptic neurone

Basic events in transmission of a NI from one neurone to another:

AP at presynaptic membrane stimulates Ca VGC's to open -> Ca ions diffuse into neurone -> causeing synaptic vesicles, containing acetylcholine to fuse with presynaptic membrane -> the vesicles release acetylcholine into synaptic cleft -> acteylcholine diffuses across synaptic cleft -> and binds to cholinergenic receptors on postsynaptic membrane -> causing Na ion channels in postsynaptic membrane to open -> influx of Na ions triggers new AP to be generated at the postsynaptic membrane

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Muscle Contraction [Sliding Filaments] (p1)

Role of Myosin and Actin (myofibril contraction):

  • Myosin filaments have hinged globular heads - can move back and forth
  • Each mysosin head has binding site for actin and one for ATP
  • Actin filaments have binding sites for mysoin heads, called actin-myosin binding sites
  • Tropomyosin and troponin are found between actin filaments. Proteins are attached to each other and help myosin filaments move fast

Tropomyosin blocks binding sites in resting muscle - hence actin-myosin binding sites blocked and held in place by troponin. Myofilaments can't slide past each other as myosin heads cant bind to actin-myosin binding site on actin filament.

Role of ATP (myofibril contraction)

  • provides energy for muscle contraction
  • energy from ATP moves myosin head - pulling actin along in rowing action
  • provides energy to break actin-myosin cross bridge
  • provides energy for active transport of Ca ions back to sarcoplasmic reticulum
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Muscle Contraction [Sliding Filaments] (p2)

The cycle of actinomyosin bridge formation (cycle continues aslong as Ca ions are present and bound to troponin):

  • AP from motor neurone stimulates muscle cell, depolarising sarcolemma, depolarisation spreads down tubules to sarcoplasmic reticulum
  • causing reticulum to release Ca ions into sarcoplasm
  • Ca ions bind to troponin, changing its shape - pulling tropomyosin out of actin-myosin binding site on actin filament
  • exposing binding site - allowing myosidn head to bind
  • actin-myosin cross bridge (AMCB) formed when myosin head binds to actin filament
  • Ca ions activate enzyme ATPase - providing energy for muscle contraction
  • ATP energy moves myosin head - pulling actin filament along (rowing action)
  • ATP provides energy to break AMCB, so myosin head detaches from actin filament after its moved
  • myosin head reattaches to different binding site further along acting filament - new AMCB formed as cycle repeats

Muscle Relaxation: Nervous stimulation stops -> CA ions actively transported back into ER using ATP energy; reabsorption of Ca ions allows tropomyosin to block actin filament again -> myosin heads aren't able to bind to actin filaments and contraction ceases.

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Muscles as Effectors (p1)

Role of ATP and phosphocreatine in providing energy:

  • Hydrolysis of ATP provides energy for movement of myosin heads and reabsorption of Ca ions into ER by active transport
  • Phosphocreatine - stored in muscle and acts as a reserve supply of phosphate, able to immediately combine with ADP to regenerate ATP. Store replenished using phosphate from ATP when muscle relaxed.

2 types of muscle fibres: slow twitch and fast twitch

  • slow twitch: found in calf muscles, muscle fibres that contract slowly, used for posture, good for endurance, can work for a long time without fatigue, energy released slowly through aerobic respiration and reddish in colour - rich in myoglobin
  • fast twitch: found in eyes or muscles (biceps) of upper arms, muscle fibres that contract quickly, used for fast movement, good for short bursts of power and speed, fatigue very quickly, energy released quickly via anaerobic respiration using glycogen and white in colour - not much myoglobin
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Homeostasis [Principles] (p1)

Homeostasis - physiological control systems that maintain a constant internal environment in an organism; importance of homeostasis (regulation of blood temp. and glucose conc-n, maintained by negative-feedback mechanisms):

  • organisms able to maintain constant internal environment have - wider geographical range, greater chance of finding food & shelter, hence, increasing survival & reproductive chances.

importance of maintaining constant temp. and pH:

  • Enzymes controlling metabolic pathways - sensitive to temp. & pH changes
  • Enzymes function within narrow temp. & pH ranges
  • Fluctuations from optimum temps. & pH's mean enzymes won't function properly
  • Extreme variations may denature enzymes
  • Constant temp. & pH ensure reactions occur at predictable and constant rate

Importance of constant blood glucose conc-n:

  • changes to water pot. of blood or tissue fluid may cause cells to shrink and expand (possibly bursting point), due to osmosis
  • hence, ensures constant water pot.
  • ensures reliable source of glucose for cell respiration
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Homeostasis [Temp. Control] (p2)

  • Ecotothermic reptiles (outside heat) - derive heat from environment; methods: exposing to sun, taking shelter, gaining ground warmth, generating metabolic heat and colour variation
  • Endothermic mammals (Inside heat) - derive heat from metabolic activity; methods: keep body temp. constant and maintain compromise between high body temp. (enzymes work faster) and energy to maintain high body temp.

Mechanisms of heat - production, conservation and loss:

  • Heat production: shivering, increased metabolic rate (hormones i.e. adrenaline) and behavioral mechanisms
  • Heat conservation: reduced sweating, raising of hair and vasoconstriction (skin surface arterioles constrict, lessening blood flow through capillaries and reducing heat loss)
  • Heat loss: increased sweating, lowering hair and vasodilation (skin surface arterioles dilate, increasing blood flow through capillaries and increasing heat loss)

Body temp control: skin thermoreceptors (temp. receptors) send NI's via Autonomic NS to Hypothalamus

  • Hypothalamus contains a thermoregulatory centre made of Heat Gain centre (HGc) (activated by fall in blood temp) and Heat Loss centre (HLc) (activated by rise in blood temp); also monitors temp. of blood passing through it
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Homeostasis (p3)

Factors influencing blood glucose conc-n, sources of blood glucose:

  • Diet - breakdown of carbohydrates
  • Breakdown of glycogen (glycogen-o-lysis) - glycogen converted to glucose
  • Gluco-neo-genesis - production of new glucose from sources other than carbohydrates

Role of Liver: Only liver cells have receptors that bind to glucagon, hence they respond by: increasing rate of gluconeogenesis (peptides & glycerol to glucose) and activating enzyme catalysing glycongenolysis (glycogen to glucose)

Adrenaline: increases blood glucose conc-n, secreted by adrenal glands (when excited or stressed), works via 2MM by: activating enzyme hydrolysing glucose in liver and inactivating enzyme synthesising (making) glycogen from glucose.

second messenger model (2MM):

  • hormone (1st messenger) binds to specific receptors on cell-surface membrane of target cells to form hormone-receptor complex
  • hormone-receptor complex activates enzyme inside cell, resulting in production of chemical (2nd messenger)
  • 2nd messenger causes series of chemical changes producing required response
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Homeostasis [Glucose conc-n control 1/2] (p4)

Pancreas - made up largely of cells producing digestive enzymes. Also contains Hormone-producing cells Islets of Langerhans (IoL), which have 2 types: Alpha (a) cells - larger & produce glucagon and Beta (b) Cells - smaller & produce Insulin. [Hormones: produced by glands and secreted directly into blood stream (endocrine gland), carried in blood plasma to target cells and effective in very small quantities]

Insulin and B panc. Cells - Detect rise in blood glucose conc-n, respond by secreting Insulin into blood plasma. (almost all body cells have glycoprotein receptors on their cells surfaces to bind with insulin, except RBC's); effects of insulin:

  • alters tertiary structure of glucose transport channels - increasing permeability of cell membrane to glucose
  • activates enzymes that convert glucose to glycogen (glycogenesis) and fats
  • increases number of carrier molecules in cell-surface membrane and cell respiration rate

Lowering blood glucose conc-n by:

  • increasing cell glucose absorption rate
  • increasing cell respiratory rate
  • increasing glycogenesis rate (glucose to glycogen)
  • increasing conversion of glucose to fat
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Homeostasis [Glucose conc-n control 2/2] (p5)

Glucagon and A panc. Cells - Detect fall in blood glucose conc-n, respond by secreting glucagon into blood plasma. (only liver cells have receptors that bind to glucagon, hence only liver cells respond); effects of glucagon:

  • activate enzyme catalysing glycogenolysis (glycogen to glucose)
  • increase rate of gluconeogenesis (peptides and glycerol to glucose)

overall effect: increase blood glucose conc-n, returning conc-n of blood glucose to normal and raised blood glucose conc-n causes a cells to reduce glucagon secretion.

Diabetes: metabolic disorder caused by inability to control blood glucose level due to lack of insulin or loss of responsiveness to insulin. Has 2 forms: Type 1 and Type 2

  • Type 1 (Insulin Dependant) - develops quickly - body not producing insulin (possible auto-immune response - immune system attacks B panc. cells in IoL). Control: injection of insulin matched to glucose intake.
  • Type 2 (Insulin Independant) - develops slowly - body cell glycoproteins lose responsiveness to insulin or pancreas supplies inadequate amount of insulin. Control: regulating carb. intake & matching it to excercise. Supplemented by injections or insulin production-stimulating drugs (other drugs reduce body glucose absorption rate)
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Negative Feedback Mechanisms (p1)

Negative Feedback - feedback causes restoration of systems to their original level; causing corrective measures to be turned off - restoring system to normal level; 2 examples blood temp. and glucose conc-n

Blood Temp:

  • Rise - thermoreceptors (thermorec.'s) in Hypothalamus (Hypothal.) send NI's to HLc, hypothal. sends NI's to skin (effector), vasodilation, sweating and loweing of hairs reduce body temp., cooler blood from skin passes through hypothal., thermorec.'s detect blood temp. at norm. set point, thermorec.'s stop sending NI's to HLc;
  • Fall - thermorec.'s in hypothal. sends NI's to HGc, hypothal. sends NI's to skin (effector), vasonconstriction, reduced sweating and hair raising increase body temp., warmer blood from skin passes through hypothal., thermorec.'s detect blood temp. at norm. set point, thermorec.'s stop sending NI's to HGc.

Blood Conc-n:

  • Decrease - A-cells in IoL produce glucagon increasing glycogenolysis and gluconeogenesis, increasing blood glucose conc-n to norm., blood with norm glucose level circulates back to panc. - stoppin glucagon production;
  • Increase - B-cells in IoL produce insulin, insulin increases cellular glucose uptake and glycogenesis, reducing blood glucose conc-n, blood with norm glucose level circulates back to panc. - stoppin insulin production.
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Negative Feedback Mechanisms (p2)

Positive Feedback - cause system to deviate from original level, occurs mostly n breakdown of control systems. Example: [Neurone] stimulus causes influx of Na ions, increasing neurone permeability to Na ions, more Na ions enter (increasing permability further), causing rapid build up of an AP allowing rapid response to stimulus.

  • Typhoid fever - causes break down of temp. regulation, causing rise in body temp. - leading to hyperthermia. Opposite can occur (fall in body temp. - leading to hypothermia)

Hormonal Control of Oestrous Cycle:

  • 4 Hormones: Folicle-stimulating hormone (FSH), Luteinising Hormone (LH), Progesterone and Oestrogen
  • Pituitary Gland produces: FSH - stimulates folicle development in ovary, stimulates oestrogen production and LH - causes ovulation, stimulates ovary to produce progesterone from corpus luteum
  • Ovaries (also glands) produce: Oestrogen (inhibits FSH) - stimulates LH secretion (via pituitary gland), rebuilds uterus lining after mensturation and Progesterone (inhibits LH) - maintains uterus lining to recieve fertilised egg
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Control of Mammalian Oestrus Cycle (p1)

Mammalian Oestrous Cycle:

  • Day 1-5: uterus lining shed along with blood
  • Pituitary gland releases FSH into blood, stimulating folicles in ovary to mature
  • Growing folicles secrete oestrogen into blood. Oestrogen conc-n rises, building up uterus lining & inhibits release of FSH from pituitary gland (= negative feedback)
  • Day 10: Oestrogen level increases until reacheing critical point where it stimulates pituitary gland to release FSH & LH (= Positive Feedback)
  • Day 14: Surge in LH causes folicle in ovary to release its egg (ovulation)
  • After ovulation - LH stimulates folicle to develop into corpus luteum - secretes progesterone
  • Progesterone maintains uterus lining and inhibits FSH & LH release from pituitary gland (= negative feedback)
  • Egg not fertilised - corpus luteum degenerates and stops producing progesterone
  • Less progesterone: FSH no longer inhibited -> lining of uterus no-longer maintained -> breaks down (menstruation)
  • FSH release resumes & cycle repeats
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Genetic Code (p1)

Genetic Code - Base triplets in mRNA which code for specific amino acid; codon is a sequence of 3 nucleotide bases on mRNA that code for each amino acid in a protein (anticodon complimentary bases to bases in codon, located on tRNA - opposite codon). Genetic code is:

  • Degenerate - more than one codon (sequence of base triplets) can code for a particular amino acid
  • Non-overlapping - each base in sequence read once
  • Universal - same codon codes for same amino acids in all organisms (exceptions)
  • few amino acids have only a single codon

Structure of mRNA (messenger RNA) and tRNA (transfer RNA):

  • mRNA - contains codon, single polynucleotide chain, smaller than DNA & larger than tRNA, single-helix molecule, pentose sugar ribose, bases: A,G,C and U, manufactured in nucleus - found throughout cell, quantity varies from cell to cell with level of metabolic activity and is chemically unstable - easily broken down
  • tRNA - contains anticodon, single polynucleotide chain, smaller than DNA & mRNA, clover-shaped molecule, pentose sugar ribose, bases: A,G,C and U, manufactured in nuclues - found throughout cell, quantity varies from cell to cell with level of metabolic activity and chemically more stable than mRNA - less than DNA

DNA (deoxyribonucleic) - double polynucleotide strand, larger than mRNA & tRNA, pentose sugar deoxyribose, bases: A,G,C and T, mostly found in nucleus, quantity constant for all cells of a speices (expt. gametes) and is chemically stable

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Polypeptide Synthesis (p1)

Polypeptide synthesis - process by which polypeptides are made; Summary of Complete process of Polypeptide Synthesis:

  • DNA provides instructions in form of long sequence of Nucleotide bases
  • Transcription - complimentary section of part of sequence made in for of molecule called pre-mRNA
  • Splicing - pre-mRNA modified to mRNA via removal of non-functional DNA base sequences (introns)
  • Translation - mRNA used as template to which complimentary tRNA molecule attaches, the amino acids carried by the tRNA can link to form a polypeptide chain (ribosomes join them)

Transcription: [production of mRNA from DNA]

  • DNA helicase acts on specific region of DNA to break H-bonds between bases causing 2 strands to separate - exposing nucleotide bases in that region
  • RNA polymerase moves along template strand, causing bases on strand to join with individual complimentary nucleotides from pool present in nucleus
  • RNA polymerase adds nucleotides joins nucleotides, forming pre-mRNA until it reaches nonsense/ stop codon on DNA
  • DNA strands rejoin behind RNA Polymerase; when RNA polymerase reaches stop codon - it detaches and producing pre-mRNA

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Polypeptide Synthesis (p2)

Splicing: removes non functional introns from pre-mRNA, occurs in eukaryotic cells - intervening non-functional introns removed and exons joined together; Exons- DNA sections coding for proteins and Introns- DNA sections that don't code for proteins; splicing details:

  • Once introns removed, exons rejoined in diff. combinations, hence, single section of DNA (gene) can code for up to 12 different amino acids - depending on exon order
  • Mutations can affect splicing of pre-mRNA
  • Introns left on mRNA - lead to production of non-functional polypeptides or no polypeptides

Role of RNA polymerase (transcription), tRNA and Ribosomes (translation):

  • RNA polymerase - causes bases on template strand to join with individual comp. nucleotides in nucleoplasm, joins together comp. nucleotides to form pre-mRNA and stops joining nucleotides when it reaches stop codon on template strand
  • tRNA - attaches peptide at one end with anticodon on other, transfered to ribosome on mRNA molecule, anticodon on tRNA pairs with comp. codon sequence on mRNA, anticodon on tRNA pairs with comp. codon seq. on mRNA. Further tRNA molecules with peptides attached line mRNA in sequence determined by mRNA bases- ensuring correct sequence of peptides in polypeptide
  • Ribosomes - controls formation of one polypeptide, attaches to mRNA by small subunit, larger subunit can hold 2 mRNA codons: one [codon] held in P (peptidyl) and other in A (aminoacyl) site - each codon attracts anticodon (comp. base triplet), ribosome moves along mRNA from 5' to 3' end; completion of translation is signalled by nonsense or stop codons on mRNA
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Polypeptide Synthesis [Translation] (p3)

Translation: [production of polypeptides from sequence of codons carried by mRNA]

  • ribosome attaches to starting codon on mRNA
  • tRNA (carrying peptide) with complimentary anticodon sequence moves along ribosome & pairs with mRNA sequence
  • a tRNA with complementary anticodon pairs with next codon on mRNA
  • ribosomes move along mRNA - bringing together 2 tRNA molecules at a time (each tRNA corresponding to mRNA sequence)
  • 2 amino acids on tRNA joined by peptide link via means of enzyme and ATP
  • ribosome moves to 3rd codon in mRNA sequence, linkin the amino acids on the 2nd & 3rd molecules
  • as this happens, first tRNA released from its amino acid - free to collect another peptide from amino acid pool in cell
  • process continues, up to 15 peptides linked per second, until complete polypeptide chain built
  • up to 50 ribosomes can pass immediately behind first - identical polypeptides can be assembled simultaneously
  • synthesis of polypeptide contunues until ribosome reaches stop codon - at which point ribosome, mRNA and last tRNA molecule all separate - polypeptide chain is complete.

Factors affecting protein formed: polypeptide coiled & folded (secondary struct.), secondary struct. folding (tertiary struct.) and how different polypeptide chains & non-protein groups linked (quat. struct.)

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Gene Mutation (p1)

Gene mutations: spontaneous, might arise during DNA replication; may delete or substitute bases; rate of mutation increased by mutagenic agents; mutation rate 1 per 100 000 genes per generation

Gene mutations could be result of Base Substitution: (nucleotide replaced by another with a different base)

  • Nonsense mutation - base change codes for 1 of 3 stop codons; production of polypeptide stopped prematurely, final protein would be different and (possibly) won't perform normal function
  • Mis-sense mutation - base changes codes for different amino acid; diff. polypeptide by 1 peptide (significance depends on role of single peptide) - if important in forming bonds in tertiary struct. replacement peptide may not form bonds, protein shape may change and not function properly
  • Silent mutation - substituted base codes for same amino acid as before; due to degenerate genetic code nature - most peptides have more than one codon; no change in polypeptide produced, so mutation has no effect

or Base Deletion: (when nucleotide is lost from normal DNA sequence)

  • usually, peptide sequence of polypeptide is completely diff. - bases read in 3's, one deleted nucleotide creates 'frame-shift' - reading frame of 3 letters of code shifted to left by one. Hence, Gene read wrong, peptide and polypeptide produced have diff. function;
  • Deleted base at start of sequence could alter every base sequence, as opposed to deletion at sequence end (little effect)
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Gene Mutation (p2)

Basic mutation rate increased by outside factors 'Mutagenic agents' including: high energy radiation (can disrupt DNA) and chemicals that alter DNA struct. & interfere with transcription. Benefits: produce genetic diversity for natural selection and speciaiton. Negatives: mutations in gametes can disrupt normal cellular activities (cell division). Cell Division controlled by 2 genes: Proto-oncogenes (stimulate cell div.) and Tumor suppressor genes (inhibit cell div.)

Role of Proto-oncogenes:

  • Growth factors attach to receptor protein on cell-surface and via relay protein (in cytoplasm) switching on genes for DNA replication
  • mutation of proto-oncogenes to oncogenes can affect cell division by: permanent activation of receptor protein on cell-surface membrane and oncogene coding for growth factor then produced in excessive amounts; cells divide to rapidly and tumor or cancer, develops

Role of Tumor Suppressor genes:

  • maintain normal rates of cell div. and prevent formation of tumors
  • mutated tumor suppressor gene is inactiveated, stops inhibiting cell div. (which increases) - most mutant cells (have diff. struct. and funct. to normal cells) die - cells that survive can clone and form tumors
  • Harmful tumor (malignant); Harmless tumor (benign)
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Gene Mutation (p3)

Mutagenic Agents (mutagens) cause damage by:

  • certain chemicals removing nucleotide bases
  • other chemicals adding groups to nucleotides
  • Ionising radiation - x rays produce free radicals that alter DNA shape
  • UV radiation - affects thymine in DNA. Thymine forms bonds with nucleotides on either side of it
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Control of Gene Expression [Stem Cells] (p1)

Totipotent cells - cells with ability to mature into any type of cell in an organism; cells like a fertilised egg can develop into any body cell, cells later differentiate and become specialised for a particular function - as during process of specialisation only some genes are expressed, hence, only part of DNA of cell translated into proteins and cell only makes proteins required to carry out specialised function. Ways gene prevented from expression:

  • preventing transcription and preventing mRNA production
  • breaking down mRNA before genetic code can be translated

Specialisation of cells irreversible in most animal cells, matured and specialised cells can no longer develop into other cells. Few adult stem cells (totipotent cells) exist in mature animals.

Stem cells (SC's) - undifferentiated dividing cells that occur in adult animal tissues and need constant replacement. found in inner lining of small intestine, skin and bone marrow. Under certain conditions SC's can develop into any other type of cell & used to treat variety of disorders (blood diseases and sickle cell anaemia). Embryonic stem cells - stem cells that occur in embryonic stage of development

Mature plants have many totipotent cells - under right conditions many plant cells can develop into any other cell, e.g. via growing cells outside of a living organism (in Vitro development) and cells from most plant species can be used to clone new plants; PGF features: wide range of effects on plant, effects on particular tissue dependent on concentration of growth factor, same concentration affects diff. tissues in diff. ways and one growth factor can modify another by its presence

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Control of Gene Expression (p2)

General principles of preventing expression of a gene by preventing transcription:

  • transcriptional factors (move from cytoplasm to nucleus) - molecules that stimulate transcription
  • transcriptional factor have site that binds to specific region of DNA in nucleus
  • this binding stimulates region of DNA to start transcription
  • mRNA produced and genetic code it carries is translated into a polypeptide
  • when gene not being expressed, site on transcriptional factor that binds to DNA is blocked by inhibitor molecule
  • Inhibitor molecule prevents transcriptional factor binding to DNA - preventing transcription and polypeptide synthesis

Process of Oestrogen binding to transcriptional factor, switching on a gene & releasing inhibitor:

  • Oestrogen diffuses through phospholipid cell-surface membrane
  • Inside cytoplasm, Oestrogen combines with site receptor on transcriptional factor (with comp. shape)
  • combining with site Oestogen changes shape of receptor molecule - which releases inhibitor from DNA binding site on transcriptional factor
  • transcriptional factor can now enter nucleus through pores and combine with DNA
  • combination of transcriptional factor with DNA stimulates transcription of gene making up DNA portion
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Control of Gene Expression (p3)

Small Interfering RNA (siRNA) - short, double strand of RNA that interferes with the expression of a specific gene; Effect of siRNA on gene expression - gene expression prevented by break down of mRNA before its genetic code and can be translated; process is as follows:

  • Enzyme cuts double stranded RNA into smaller sections siRNA
  • 1 of 2 siRNA strands combines with an enzyme
  • siRNA guides enzyme to mRNA by pairing with complementary bases on mRNA
  • enzyme (in position) cuts mRNA into smaller sections
  • mRNA can't be translated in polypeptide, hence, gene was blocked (not expressed)

Uses of siRNA: used to identify role of genes in biological pathways and used to block disease causing genes and prevent disease.

Cancer 2 hit Hypothesis; tumors can develop as a result of:

  • Takes mutation of both alleles (required to mutate proto-oncogenes and tumor suppressor genes) to inactivate tumor suppressor genes (2-Hits)
  • as natural mutation rates are slow, it takes considerable time for both alleles to mutate, hence, increased risk of cancer as one gets older

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Control of Gene Expression [Cancer control] (p4)

  • Cancer - caused by Acquired Mutations: Prevention - protective clothing, sunscreen and vaccination; Diagnosis - usually after symptoms appear, high risk individuals can be screened for cancer general pop. not privy to (earlier diagnosis -> increases recovery chances) & if specific mutation known more sensitive tests can be developed (earlier and more accurate diagnosis -> improving recovery chances); Treatment - different for different mutiations, agressiveness of treatment can differ depending on mutaiton (fast-growing cancer- treated with higher doses of radiotherapy or removing large areas of tumor and surrounding tissue), if specific gene known - gene therapy may be able to treat it
  • Cancer - caused by Hereditary Mutations: Prevention - people with family history should avoid gaining extra acquired mutations by avoiding mutagenic agents, if mutation causes high risk of cancer preventative surgery may be carried out (removing organ cancer likely to affect) before cancer develops; Diagnosis - screening or increased earlier screening, for family history & those with hereditary mutation can lead to early detection (increasing survival chances); Treatment - different for different mutations, aggressiveness of treatment can differ depending on mutation (fast-growing cancer- treated with higher doses of radiotherapy or removing large areas of tumor and surrounding tissue), if specific gene known - gene therapy may be able to treat it
  • Genetic disorders caused by Hereditary Mutations: Diagnosis - DNA analysis of person with family history of genetic disorder, tested and diagnosed - treatment can begin earlier, knowing if they have or carry disorder - allows determination of likelihood of children having disorder; Treatment - gene therapy, diff. treatment for diff. mutations; Prevention - carriers or sufferers of genetic disorders can undergo preimplantation genetic diagnosis during IVF to prevent offspring having disease (embryos with mutation implanted in womb)

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Human Embryonic Stem cells and Disease treatment (

stem cell research allowed in UK under license & specified conditions (use as a means of increasing knowledge about embryo development and serious disease)

Debate: should embryos (14> days old) have same respect as fetus or adult person?

  • Case For: Wrong to allow humans suffering where it can be prevented, embryo's produced for other uses can still be used for research purposes, embryo at early stage of development bears no resemblance to a human and laws prohibiting cloning in UK are sufficient to provide protection
  • Case Against: Wrong to use humans or embryo's just for research, embryo's used like this undermine respect for human life, further move towards cloning (illegal in UK) and information gained could be used for deviant purposes

Stem cells (adult) can be obtained from bone marrow of consenting human adult, this method:

  • raise no real ethical issues
  • more restricted medical applications than embryonic stem cells (presently)
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Gene Cloning and Transfer (p1)

Fragments of DNA can be produced by: Conversion of mRNA to cDNA (using RT), Cutting DNA at specific palindromic recognition sequences (using RE) and Using the polymerase chain reaction (PCR) to form multiple copies of DNA fragments

Process of making protein via DNA technology: Isolation - of DNA fragments with gene for desired protein, Insertion - DNA fragment into Vector (carrier), Transformation - Transfer of DNA into host cell, Identification - of host cells that have taken up gene using gene markers, Growth/ Cloning - of population of host cells. 2 enzymes used to isolate and identify genes from DNA:

  • Reverse transcriptase (RT) - catalyses prodction of DNA from RNA; process of isolating gene: cells readily producing protein selected, relevent mRNA is extracted from cells, RT used to make DNA from RNA - DNA produced known as complimentary DNA (cDNA) - made of nucleotides complimentary to mRNA, to make other DNA strand DNA polymerase builds up comp. nucleotides on cDNA template; double stranded gene is required
  • Restriction endonucleases (RE) - enzymes that cut up DNA; many types of RE cut DNA double-strand at diff. specific 'recognition sequence' of bases, RE can cut between 2 opposite base pairs leaving straight edge (blunt edges). Other RE's cut DNA in staggered fashion, leaving uneven cut in which each DNA strand is exposed unpaired bases or 'sticky ends';

Palindromic sequence - anti-parallel arrangement of bases.'6 bp palindromic sequence' - six anti-parallel base pairs (6 base pairs that read the same in opposite directions)

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Gene Cloning and Transfer [In Vitro] (p2)

In Vitro Cloning - using PCR to form multiple copies of DNA fragments;

Advantages: Extremely rapid (can produce 100bn copies in a few hours) - useful where minute amount of DNA present Doesn't require living cells - only base sequence of DNA needing amplification required

PCR requires the following: DNA fragments - to be copied, DNA polymerase (thermostable) - enzyme that joins nucleotides together, DNA Primers - short nucleotide sequence with bases comp. to those at one end of each 2 DNA fragments and Thermocycler - computer controlled machine, which varies temp. precisely of time period. PCR reaction and temp. cycle process:

  • Separation of DNA strands - DNA frag.'s, primers & DNA polymerase placed in vessel in thermocycler. Temp. increased to 95oC, causing 2 DNA frag. strands to separate
  • Annealing (addition) of Primers - mixture cooled to 55oC, annealing primers to comp. bases at DNA frag. end; Primers provide starting sequence for DNA polymerase (only attach nucleotides to end of existing chain) to copy DNA and Primers prevent 2 separate strands rejoining
  • DNA Synthesis - temp. increased to 72oC (optimum temp. for DNA polymerase to work), DNA polymerase begins (adding comp. nucleotides along each separated DNA strand) at primers on both stands - adding nucleotides in sequence until end of chain

Both strands copied simultaneously - producing 2 copies of original fragment: once 2 DNA strands completed process is repeated, over 1 mil copies can be made in only 25 temp. cycles and 1 temp. cycle takes 2 mins

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Gene Cloning and Transfer [In Vivo 1/3] (p3)

In Vivo Cloning - Transferring DNA fragments to a host cell using a vector

advantages - useful for introducing a gene into another organism, involves no contamination risk, very accurate, cuts out specific gene and produces transformed bacteria that can be used to produce large amounts of gene products

Importance of 'sticky ends' - sequence of DNA cut by RE (recognition sites); if same RE used to cut DNA - all fragments produced will have ends complimentary to one another, hence, single-stranded end of any one fragment can be stuck to single-strand of any other fragment & once comp. nases of 2 'sticky ends' have paired up, DNA ligase used to join sugar-phosphate backbone of 2 sections of DNA together; If same RE used, DNA from one organism can be combined with DNA of any another.

(stage1) Insertion of DNA fragments into a vector (a carrier, like plasmid carrying DNA into a cell or to organism that carries a parasite to its host); process of DNA frag. Insertion:

  • RE used is same one that cut out DNA fragment
  • DNA fragments then mixed with openend up plasmid - may incorporate the fragment
  • where incorporated- join is made permanent by DNA ligase
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Gene Cloning and Transfer [In Vivo 2/3] (p4)

(stage 2) Introduction of DNA into host cells:

transformation - process of incorporation of DNA fragment into plasmid and its reintroduction into bacterial cells; Involves:

  • mixing plasmids and bacterial cells with medium containing Ca ions,
  • Ca ions and temp. change -> increase permeability of bacteria ->allowing plasmids to pass through cell membrane into cytoplasm
  • Not all bacterial cells will posses DNA fragments as: only few bacterial cells take up the plasmid and some plasmids will close up without incorporating the DNA frag.

Identification - using bacterial mechanism for resisting antibiotics (produces enzyme that breaks down antibiotic before it can destroy bacterium). some plasmids carry resistance gene for more than one antibiotic - one example is the R-plasmid, carries gene resistance for: ampiclin and tretracycline. Process for Ampicilin:

  • All bacterial cells grown on medium containing antibiotic ampicilin
  • bacterial cells that have taken up plasmids will have acquired ampicilin resistance gene
  • these bacterial cells are able to break down ampicilin and survive
  • bacterial cells that haven't taken up plasmid are not resistant to ampicilin and die

effective method of showing bacterial cells which have taken up plasmids; but, some cells will have taken up plasmid but closed up without incorporating gene and will have survived - must id and eliminate these cells

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Gene Cloning and Transfer [In Vivo 3/3] (p5)

(stage 3) Gene Makers - involve using seperate gene on plasmid. second gene easily identifiable as: may be resistant to antibiotic, contain flourescent protein easily see or produce enzyme whose action is identifiable

Antibiotic-resistance gene markers - to identify cells uptaking plasmid with new gene replica plating technique is used. Process uses antibiotic-resistance gene in plasmid - gene cut to incorporate required gene (as gene cut - no longer produces enzyme that breaks tetracycline (bacteria that have taken up gene, not resistant to tetracycline) and bacteria identified by growing them on culture containing tetracycline; process is as follows:

  • Bacterial cells that survived first antibiotic (ampicilin)- have taken up a plasmid and are cultured by spreading thinly on nutrient agar plates
  • each seperate cell on growth plate will grow into genetically identical colony, sample of each colony transfered onto 2nd replica plate in exact same position as on original plate
  • 2nd plate contains second antibiotic (tetracycline), against which antibiotic-resistance gene will be useless if new gene was taken up
  • colonies killed by antibiotic must be ones that have taken up required gene
  • colonies in exact same positions on original plate are ones that posses required gene. these colonies are made up of GM bacteria and have been transformed

Floursescent gene markers - green flourescent protein (GFP) - gene to be cloned is transplanted into centre of GFP gene, bacterial cell that takes up plasmid with gene to be cloned will not produce GFP. As bacterial cells with desired gene are not killed, no need for replica plating; result obtained by viewing sample under microscope and retaining bacterial cells which don't flouresce.

Enzyme gene markers - gene that produces lactase (turns particular colourless substrate blue), required gene transplanted into gene making lactase, if plasmid with required gene is present in bacterial cell, colonies grown will not produce lactase and hence no colour change occurs. Where gene hasn't transformed bacteria, colonies will turn substrate blue

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Gene Cloning and Transfer [rDNA 1/2] (p6)

GM Microorganisms - 3 substances produced using GM microorg.'s:

  • Antibiotics - produced naturally by bacteria; GM has produced bacteria that increase quantity of antibiotics produced and rate at which they're made
  • Hormones - Genetic engineering method (for hormone production) avoids killing animals and need to modify insulin before its injected into humans; other hormones produced: human growth hormone, cortisone and sex hormones - testosterone and oestrogen
  • Enzymes - GM (bacteria) manufactured enzymes used in food industry. Including amylases to break down starch to produce beer, lipases to improve flavour of cheeses and proteases to tenderise meat

GM Plants, examples: Genetically modified tomatoes - gene insterted comp. to base sequence producing enzyme that causes tomatoe softness. mRNA transcibed from inserted gene comp. to mRNA of original - the 2 strands combine to form double-strand, preventing mRNA of original gene being trnaslated - softening enzyme not produced. Herbicide resistant crop - when herbicide sptayed on crops, weeds competing are killed, as crops are resistant to herbicide and unaffected. Disease resistant crops - gene added allowing plant to make toxin which kills insects (that eat plant), but harmless to other animals (including humans)

GM Animals, examples: transfer of gene from animal with natural resistance to disease into diff. animal - 2nd animal made resistant; addition of fast growing hormones - animals grow larger and at faster rate; Producing rare and expensive proteins for use in human medicine - via domesticated animals e.g. gene for required proteins inserted alongside gene coding for proteins in milk, hence protein produced in milk. [see anti-thrombin section on next card]

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Gene Cloning and Transfer [rDNA 2/2] (p7)

Use of recombinant DNA tech.: increasing yield of plant& animal crops, improving food nutrient content, introducing resisitance to disease and pests, making crop plants tolerant to herbicides, developing tolerance to environmental conditions, making vaccines and producing medicines for treating disease.

Use of recombinant DNA to produce organisms that benefit humans:

  • Benefits - use of microorganisms (microorg.'s) to produce range of substances, use microorg.'s to control pollution, GM plants can be transformed to produce specific substance in particular plant organ, GM crops engineered to have economic advantages, GM crops help prevent disease, GM animals able to produce drugs cheaply, Gene therapy (GT) used to cure genetic disorders and Genetic fingerprinting used in forensic science
  • Risks - cant predict effect of releasing GM organisms into environment, recombinant gene may pass from one organism to another, DNA manipulation has effect on cells metabolic pathway, GM bacteria may resist gene markers, all genes mutate, long-term consequences of new gene introduction, economic consequences of plants & animals grown in new regions, cost of genetic engineering (justified?) and genetic fingerprinting (reliable forensic tool?)

Effect of rDNA on Animals: Anti-thrombin, process of production in goats milk: mature egg removed and fertilised, normal gene for anti-thrombin production from human added alongside genes coding for milk, genetically transformed egg implanted into female goat, resulting goats cross bred to give heard anti-thrombin containing milk and anti-thrombin extracted from milk - purified and given to humans

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Gene Therapy (p1)

Cystic Fibrosis - most common genetic disorder in causican population of europe and north america (1 in 20k have disease), caused by mutant recessive allele where AAA bases are missing (deletion mutation), mutation causes single peptide to be left out of cystic fibrosis trans-membrane-conductance-regulator (CFTR) gene - disabling protein from transporting Cl ions across epithelial membrane - mucus layer builds up (no water diffuses out and carries it away). CFTR is Cl ion protein channel.

Symptoms: mucus congestion in lungs, breathing difficulties, accumulation of thick mucus in pancreatic ducts and accumulation of mucus in sperm ducts

Treatment of Cystic Fibrosis using gene therapy:

  • Gene replacement - defective gene replaced with a health gene
  • Gene supplementation - one or more copies of health gene added alongside defective allele

2 additional GT techniques based on type of cell being treated:

  • Germ-line GT - replacing or supplementing defective gene in a fertilised egg
  • Somatic-cell GT - targeting affected tissue only (i.e. lungs not sperm or egg, hence, not passed onto future generations) by introducing additional gene; repeated treatment needed as lung cells continually die and are replaced. Long-term aim: target undifferentiated SC's that give rise to mature tissues (treatment then affective for life of individual)
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Gene Therapy (p2)

Delivering cloned CFTR Genes; aim of somatic-cell GT to introduce cloned normal genes into lung epithelial cells:

Using harmless viruses (Adenoviruses) - Adenoviruses made harmless by interfering with replication gene and grown in epithelial cells in lab alongside plasmids with normal CFTR gene, CFTR gene incorporated into adenovirus DNA and Adenovirus isolated from epithelial cells then purified, Adenoviruses with CFTR introduced into patients nostril and inject DNA into lung epithelial cells

Wrapping gene in lipid molecule - Genes wrapped in lipid molecules can easily pass through a phospholipid cell-surface membrane;

  • process of delivering CFTR to target cells: CFTR genes isolated and inserted into bacterial plasmid vector, plasma vector reintroduced to bacterial host cell and gene markers detect which bacteria have succesfully picked up CFTR containing plasmids, Bacteria then cloned to produce multiple copies of plasmids with CFTR gene, Plasmids extracted from bacteria and wrapped in lipid molecules - liposome, liposomes containing CFTR sprayed into patients nostrils & drawn into lungs (inhalation) and liposomes pass across phospholipid cell-surface membrane into lung epithelial cells.

Methods not always effective because: adenoviruses may cause infections, patients may develop immunity to adenoviruses, liposome aerosol may not be fine enough to pass through bronchioles of lungs and very few CFTR genes are expressed

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Gene Therapy (p3)

Severe combined immunodificiency (SCID) treatment using gene therapy: people with disorder don't show cell mediated immunity and can't produce antibodies - arises when person inherits defect gene for enzyme ADA (enzyme destroys toxins that otherwise kill WBC's); Attempts at treatment disorder with gene therapy:

  • normal ADA gene isolated using RE from healthy human and ADA gene inserted into retrovirus
  • retrovirus growing with host cells in lab to increase number and copies of ADA gene
  • retroviruses mixed with patients T cells (WBC's), retroviruses inject copy of normal ADA into T cells
  • T cells then reintroduced into patients blood to provide genetic code needed to make ADA

Treatment effectiveness limited as T cells have 6-12 months lifespan & treatment has to be repeated at intervals; recent treatments - transform bone marrow SC's (bone marrow SC's divide to produce T cells)

Effectiveness of Gene Therapy, limited success to somatic-cell GT, because: effect is short lived (S cells aren't passed to daughter cells - re-treatment necessary), Can induce immune response (gene and vector can induce response, hence often rejected - antibodies often remain to initiate greater response), Using viral vectors to deliver gene presents problem (viruses can lead to toxic, inflammatory immune response), Genes not always expressed (small proportion of introduced genes usually expressed) and Not effective in treating conditions that arise from more than one gene

Risks and Benefits of Gene therapy: who decides what is normal and what a disability is? Do disabilities need to be cured or prevented? are disabilities part of genetic variety that makes up all species? Is money for gene therapy better spent elsewhere? what might the long-term consequences of introducing inheritable genes into population be?

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Medical Diagnosis (p1)

DNA Probes: short, single-stranded section of DNA, with label attached making it easily identifiable; used to Identify gene by: probe being comp. to bases on portion of DNA sequence desiring to find, DNA tested for - separated into 2 strands, One separated strand with comp. bases to probe - mixed with and binds to probe, probe binding site identified by radioactive exposure or fluorescence probe emits. Two types: Radioactively labelled probe (nucleotides have isotope - identified via photographic plate - when exposed to radioactivity) and Fluorescently labelled probe (fluoresces under certain conditions).

DNA Sequencing - sanger method used to sequence exact order of nucleotides in a section of DNA, using modified nucleotides (terminators) that can attach to next base in sequence when being joined together (4 diff. terminators i.e. A,T,G and C); process of sequencing:

  • First stage - set up 4 test tubes containing: many single-stranded DNA frag.'s to be sequenced, mixture of nucleotides, small quantity of 1 of 4 terminator nucleotides (tt.1 A term., tt.2 T term e.t.c), primer starts DNA synthesis process and DNA polymerase catalyses DNA synthesis. Binding of nucleotides to template is random process (equal prob. of norm. or term. nucleotide addition), DNA frag.'s in the diff. tt.'s will have varying lenghts.
  • Second stage (Gel Electrophoresis) - process: DNA (-ve charge) frag.'s placed on agar gel in petri dish & voltage applied, resistance of gel means larger frag.'s move more slowly, over fixed time period smaller frag.'s move further (experience less resistance), hence - DNA frag.'s separated, sheet of photographic film placed over agar plate for several hours and radioactivity (labelled probe) from each gel frag. exposes film showing where frag.'s situated on gel. Only DNA frag.'s up to 500 bases long can be sequenced in this way. [DNA moves from cathode to anode]
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Medical Diagnosis (p2)

Restriction mapping - involves cutting DNA with series of diff. RE, frag.'s produced are then separated by gel electrophoresis/ Distance between recognition sites can be determined by patterns on frag.'s:

  • Diff. RE's used to cut labelled DNA into frag.'s and DNA frag.'s separated by gel electrophoresis
  • Size of frag.'s produced determines relative locations of cut sites
  • restriction map of original DNA made- diagram of DNA plasmid showing different cut sites and where recognition sites of RE's used are found

Automation of DNA sequencing and Restriction mapping:

  • 4 terminator nucleotides labelled with fluorescent dye and each type makes up different colour: adenine (green), thymine (red), cytosine (blue) and guanine (yellow)
  • DNA synthesis takes place in a single test tube and PCR cycles used to speed up process
  • Electrophoresis carried out in a single narrow capillary gel
  • Results scanned by lasers and interpreted by computer software, give DNA sequence in fraction of time taken by conventional methods.

further automation includes use of PCR to produce DNA frag.'s required in these techniques and methods continually updated as further innovations in field of DNA tech. and computer software develop

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Medical Diagnosis (p3)

Genetic Counseling: special form of social work, advice and info. given enabling people to make personal decisions about themselves and offspring. Closely linked to GS, screening results provide genetic counsellor basis for informed discussion. Important aspect is - resarch into family history of inherited disaese and to advise parents on likelihood of it arising in their children. A Counsellor can: inform people of effects of disease and its emotional, physiological, medical, social and economic consequences; can also make them aware of any further medical tests that might give more accurate predictions of whether children will have the condition. Summary of genetic screening (GS):

  • Nucleotide order on mutated gene determined by DNA sequencing. Genetic libraries store DNA sequences of many genes responsible for common genetic disease
  • DNA frag. with comp. bases to mutated gene is produced and DNA probes formed by labeling frag.
  • Multiple DNA probe copies formed via PCR & added to single-stranded DNA frag. from person being screened
  • DNA frag. from donor with mutated gene has nucleotide sequence comp. to probe - which binds to comp. bases on donor DNA
  • these DNA frag.'s now labeled with probe and can be distinguished by X-ray film
  • if comp. frag.'s are present, DNA probe will be taken up and X-ray film exposed; if no comp. frag.'s present DNA probe will not be taken up and X-ray film not exposed

Implications of genetic screening: who decides who should be screened? who has access to results? what are the responsibilities of someone who caries a gene for inherited disease? Does mankind have a responsibility to maintain genetic diversity? who decides what is a defect or disease?

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Medical Diagnosis (p4)

Sickle Cell Anaemia - result of gene mutation in gene producing haemoglobin; gene that has 2 co-dominant alleles HbA (normal) and HbS (sickle); malarial paraside [plasmodium] unable to exist in sickled red blood cells;

3 possible genotypes of these 2 alleles, their phenotypes and selection pressures:

Homozygous for Haemoglobin S (HbS HbS): individuals suffer from sickle cell anaemia; rarely live long enough to pass on genes to next gen.; this form of aneamia is so severe it outweighs advantage of being resistant to one form of malaria, hence, this individual is always selected against (more likely to die).

Homozygous for Haemoglobin A (HbA HbA): individuals will lead normal lives; susceptible to malaria in areas of world where disease is endemic (prevalent) and they are therefore selected against (more likely to die) only in these regions.

Heterozygous for Haemoglobin (HbA HbS): individuals have sickle cell traits - only affected when blood O2 conc-n is low (excercising muscles), sufferers may become tired more easily; generally condition is symptomless. Also have malaria resistance - outweighs disadvantage of tiredness in some areas of world where malaria occurs. Heterozygous individuals therefore selected against (more likely to die) in areas without malaria, but selected for (more likely to survive) in areas where malaria is common.

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Genetic Fingerprinting (p1)

Genetic fingerprinting (GF) - technique relies upon fact that genome of an organism contains core (repetitive) sequences of introns (non coding bases of DNA); core sequence number and length varies in every individual (except identical twins). GF takes place in 5 main stages [process]:

  • Extraction - DNA extracted from sample (blood, hair root or *****)
  • Digestion - RE's cut DNA into frag.'s (cut close but not within groups of core sequences)
  • Separation - Frag.'s separated using gel electrophoresis, then, DNA frag.'s transfered from Gel to nylon membrane via Southern Blotting process
  • Hybridisation - radioactive DNA probes added to label the fragments (attach to specific fragments)
  • Development - Membrane with radioactive DNA frag.'s placed on X-ray film; development of X-ray film reveals dark bands where radioactive DNA probes have attached

Southern Blotting Process - thin nylon membrane laid over gel, membrane covered with many sheets of absorbent paper (draws up liquid containing DNA by capillary action, transfering DNA frag.'s to nylon membrane in same position that occured on gel and DNA frag.'s fixed to membrane using UV light

Interpreting Result - if there is a match between 2 DNA samples, pattern of bars of each fingerprint visually checked, then passed through automated scanning machine - calculating lengths of DNA frag.'s from bands (obtain data by measuring distances travelled by frag.'s during elctrophoresis by standard, known lengths of DNA) and odds calculated of someone having identical fingerprint - closer the match, greater prob. the 2 DNA sets are from same person.

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Genetic Fingerprinting (p2)

Uses of DNA Fingerprinting - Used in forensic science to indicate whether individual connected to a crime (from blood or ***** at scene), resolve paternity cases (individuals inherit DNA from parents, half father & half mother - hence, each band on DNA GF should have corresponding band in parents' DNA GF) and useful in determining genetic variability within population (more closely related 2 individuals closer their resemblance of their GF). Other uses of genetic fingerprinting (GF):

  • Forensic science - GF can: using small quantity from crime scene establish whether person was present at crime scene; however, close at match between suspects DNA and DNA at crime-scene doesn't mean suspect commited crime as, DNA may: have been left on innocent occasion, belong to close relative or contaminated after crime (other suspects DNA or chemicals affecting RE); probability of DNA being someone else's has to be calculated (calculation based on assumption - DNA produces bonding patterns randomly distributed in community).
  • Medical diagnosis - GF can: help diagnose diseases [like Huntingtons Disease: 3-nucleotide segment at one chromosome end continually repeated, fewer than 30 rep's - unlikely to get disease; 38 + rep's - certain to get disease; 50 + rep's - disease occurrence earlier than norm. DNA from person with Huntingtons allele can be cut by ER & DNA GF preparied and matched with various of Huntingtons allele's allowing determination of probability and timing of symptom development] and identify nature of microbial infection by comparing fingerprints found in patients with known pathogens
  • Plant and Animal breeding - GF can: prevent undesireable interbreeding in breeding programmes, identify plants or animals with desireable gene allele (individuals with desired gene can be selected for breeding - increasing probability offspring will have encoded characteristic) and determine paternity in animals and establish pedigree (family tree) of an individual
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Wow! Thank you! As for pictures, could you not put them in a word document and upload and link that? If you wanted to of course, I could probably do that myself mind you!

Thanks again! You've made revision for my lazy self very easy!

seetal rupra

These are like identical to the notes i made but so much neater and a bit more condensed. Very helpful, thank you!

becky harvey



wooooooooow! THANK YOU :)


That was very helpful thanks


Cheers for this, but you really need to work on your spelling. I converted this to a .MOBI file so I could put it on my Amazon Kindle and it had a tonne of spelling errors.

Noura Ali

Wow best revision cards seen here!!!! Thanks so much ur a star!!!


These are excellent, thank you! =]


Abs brilliant amazin rev tool!

Chris Williams

i love you


these notes are really good, i found it hard to make notes on unit 5 and these have helped so much thank you

Samar Mandour

you are sooo amazing, thank you <33333 x


great, but the mp3 is just awful..


thanks, these are brilliant!!


Thank you! But I didn't know we were allowed to abbreviate in the exam.


Very helpful thankyou!!!!!! Will use these 4 my biology exam.


Give This Man A Medal!


Always wanted to make a complete revision set but never had the determination to finish them!

Fantastic work!

KathrynSalvatore :)

Thankyou very much, these are fab :)


really really really really GOOD!!!! thanks!!!!!!!!!!1


ur a life saver !!!!!! 


Really good. Thank you. Found it a little difficult to flow with all the different acronyms.

Charlotte Heggie

Thank you so much, they have helped me loads! I've been ill over the last few of my exams, so when it came down to revision I really haven't been able to do much, but these revision cards have made me able to revise the whole topic over 4 days! 

Once again, thank you so much!


Holly Wakelin

these are pretty much copied out of the AQA textbook by Glenn and Susan Toole, but it's nice to have the notes condensed into neat chunks, instead of spread out over 100 pages. Thanks!


Thank you to the person who made these, they are amazing - just what i needed!!


Perfect! Thank you


Thank you soooo much. Exam tomorrow and these cards help a ton =D


wooooooooow! freaked out bout how much i need to learn but thnx a lot :)


Thank you !:)



vicky marsland

awesome, thank you! you dont know where there are any like this for all of the other previous units do you? 


Thabk you sooooo much!!!!

Matthew Mills

Steffi wrote:

There is a printable pdf version?

Matthew Mills

natasha wrote:

Very helpful thankyou!!!!!! Will use these 4 my biology exam.

Really?!? I thought they were for my maths exam....


these notes are soo helpful!!! thankyou x


These are great, cheers! Forgot how long this unit is though, ugh!


Hey by the way it's 3Na ions out : 2 K ions in when establishing resting potential. Other than that..yes very efficient notes indeed :)


Veru helpful! Thank you!

joey williams

siiiiiick mate! got me an A* in my mock


cheers man


I accidentally rated this 1 but it's actually a five thanks **

Aziza Mohamed

Thank you soo much for this resource, incredibly helpful. :D 

Aziza Mohamed

Thank you soo much for this resource, incredibly helpful. :D 


hey, how do i scroll down as some of the cards have information bellow but i can t read it


great notes! Thanks for uploading 

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