Biology AQA AS Unit 1 Revision Notes

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Waqas Mahmood
Biology Revision Notes
Biochemical Tests:
Proteins add biurettes reagent to the sample. If protein is present, clear colour change from
blue to purple.
Reducing Sugars ­ add Benedict's reagent to the sample. Heat in Bunsen or water bath. If
reducing sugars are present, clear colour changes from blue > orange red precipitate.
Lipids ­ dissolve sample in ethanol. Slowly pour the solution into the water slowly. If lipids
are present a white emulation forms on the surface.
Starch ­ add iodine solution to the sample. If starch is present clear colour change from
orange red to blue black.
Non reducing sugars ­ do the reducing sugars test. Add Benedict's to the sample & heat.
You get a negative result. Take a fresh sample and add heat with dilute acid. Bring to the
boil. This hydrolyses it! Then, neutralise it with an alkali and test with pH paper. Add
Benedict's and heat again. If non reducing sugars are present, clear colour change from blue
to an orange red precipitate.
Enzymes
Enzymes are protein molecules that act as biological catalysts. An enzyme catalyses a
specific reaction. They have an active site... Substrate ENZYME Products. Maltose is
broken down by the enzyme maltase to glucose and glucose. The reactions enzymes
catalyse can be anabolic or catabolic Anabolic meaning
building, catabolic meaning breaking down. They do not die.
They are simply denatured. They are affected by temperature,
pH and concentration of enzyme and/or substrate. They can be affected by inhibitors. NON
COMPETETIVE ARE THINGS THAT STICK IN THE SIDE. COMPETETIVE FIT IN
ACTIVE SITE AND ARE COMPLIMETRY IN SHAPE
The structure of an enzyme
Enzyme molecules tend to be 100's of amino acid long. They are
named `globular proteins'. They are arranged with charged `R'
groups pointing outwards so they dissolve in water. They have a
complex tertiary structure. One region of this is where the substrate
fits. This is called the active site.
The active site is complimentary in shape to the substrate plus it is
similar in charge too.
How do they work?
Reactions need energy to proceed. To start the reaction,
you need to add some energy at the start of the reaction, to
`kick start' it. But remember, don't say that! This is named
the activation energy. When an enzyme is catalysing a
specific reaction, it lowers this activation energy, therefore
speeding it up, or increasing the rate of reaction.
Theories of enzyme action
1 1

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The lock and key model:
This theory suggests that the substrate is able to fit into the active site like a key fits into a
lock. It states that the active site is complimentary in shape to the substrate. The substrate
then fits into the active site and binds forming an ENZYME SUBSTRATE COMPLEX.…read more

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1. competitive inhibitors
2. noncompetitive inhibitors
A competitive inhibitor molecule is similar in shape to the substrate therefore it can fit into the
active site of the enzyme, temporarily blocking it.
A non competitive enzyme inhibitor is different in shape to the substrate and binds to another
site, other then the active site. When it binds to the enzyme, the tertiary structure is changed.…read more

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Fibrosis: It is non communicable. This disease increases fibrous tissue that grows in the
lungs. This means the diffusion distances are increases so the rate of diffusion is decreased.
Lung tissue is also then less elastic, difficulty breathing out.
Risk Factors: significant exposure to dust.
Lung Cancer: is non communicable. A cancer that starts in the lung tissue. Sells divide out of
control and form a tumour.…read more

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membrane. There you have it! Water potential is represented by a very weird sign and the
units are kPa.
B i
o lo g y: Th e
H uman
Immu n e Sy ste m
P a th og en s
A
P at
h ogen:
a di
sease causin g mi croor gan i
sm.…read more

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Mucus Lining
many
epi
thel
ia
layer
s pr
oduce
mucus
w hi
ch
the
pat
hogens
st
ick
to.
Ci
lia t
ransp ort i
t
ba ck
up t
h e
tr
ach ea
by a `
beati
ng'
movement
and
t
hen swall
o wed
into t
h e st
o mach.…read more

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Cell
Mediat
ed Respon se:
ma cr
o phages
ingest
the pat
h ogens
that
have ant
igens
on
t
heir
surf
ace.
Th e
ma cr
op hages
then pr
oce ss
the ant
igen molecul
es and
displ
ay
t
hem on
thei
r
surface.
I
t
b ecomes an
an t
igen
p r
es e nt
ing
ce l
l
.…read more

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3. Dead
Pat
hogens
Vacci
nati
on l
eads t
o a
person
becoming immu ne.
I
f
a
high
enough pr
oport
ion
of
the
popul
ati
on ar
e vacci
nated
you get
her
d
immu ni
ty.
The % of
peopl
e t
hat
aren'
t
vacc
inat
ed i
s not
hi
gh enough
for
disease t
o spr
ead.…read more

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