1.	(a)	the site (on the surface of an enzyme) to which substrate(s) bind / the site (on the
enzyme) where it catalyzes a chemical reaction;	1
 
(b)	bring substrates close together in active site / in correct orientation;
forms enzyme-substrate complex / substrate(s) bind to active site;
lowers the activation energy for the reaction;
weakens bonds in the substrate;	2 max
 
(c)	enzymes have an optimal pH;
lower activity above and below optimum pH / graph showing this;
too acidic / basic pH can denature enzyme;
change shape of active site / tertiary structure altered;
substrate cannot bind to active site / enzyme-substrate complex cannot form;
hydrogen / ionic bonds in the enzyme / active site are broken / altered;	3 max
 
(d)	energy storage / source of energy / respiration substrate;
(heat) insulation;
protection (of internal organs);
water proofing / cuticle;
buoyancy;
(structural) component of cell membranes;
electrical insulation by myelin sheath;
(steroid) hormones;
glycolipids acting as receptors;	2 max
Three correct [2], one or two correct [1].
	Use one tick to mark the first one or two correct answers. Use a second tick to mark the third correct answer. Mark the first three answers only.
[8]

2.	(a)	peptide bonds / peptidic bonds;	1
(b)	alpha-helix / alpha helices;	1
(c)	ionic / polar / hydrogen / hydrophobic / van der Waals’ / 
disulfide; (not covalent)	1
 
(d)	linking together of polypeptides to form a single protein;
using the same bonding as for tertiary structure;
linking of a non-polypeptide structure / prosthetic group;
named example of quaternary structure 
eg hemoglobin (has four polypeptides);	2 max
[5]

3.	(a)	Any two from the following.
fibrous: eg fibrin, collagen (do not accept “tendon”);
globular: eg hemoglobin, fibrinogen, amylase (do not accept “enzyme”);	2
 
(b)	a new reaction pathway is created;
activation energy is reduced;
the equilibrium for the reaction is achieved more quickly / 
the reaction is faster;	2 max
 
(c)	ATP inhibits phosphofructokinase at (allosteric) site away from the active site;
inhibition alters the enzyme’s conformation / structure;
the active site does not accept the substrate molecule;
when respiration increases ATP levels phosphofructokinase is inhibited;
respiration slows down;
phosphofructokinase is the first enzyme in the respiration pathway so 
there is no build up of metabolic intermediates;
as ATP is used up by the cell the inhibition of phosphofructokinase is reduced;
respiration speeds up again;
this is an example of negative feedback;	4 max
[8]

4.	(a)	(i)	III	1
(ii)	IV	1
(iii)	I	1
 
(b)	II and III have the most similarities;
both have ring shaped molecules;
both have one oxygen atom in the ring;
both have the same relative amounts of C, H and O;
both have only –OH and –H linked to the carbon atoms;
both are monosaccharides / sugars / reducing sugars;
I and IV both have a carboxyl / COOH / acid group;
I and IV both are linear;	3 max
[6]

5.	(a)	held together by hydrogen bonds;
between CO and NH groups;
(α-helix for) structure of fibrous proteins / keratin;
one of four levels of structure;
provides stability of structure;
a-helix;
b-sheet;	3 max
 
(b)	malonate / Prontosil	1

(c)	competitive similar to substrate and non-competitive not;
competitive attaches to the active site, non-competitive does 
not bind to the active site;
non-competitive changes enzyme shape, competitive does not;
competitive change reversible;	2 max
[6]

6.	(a)	margarine / sunflower seeds / vegetable oil / peanuts / nuts,
etc. (no animal products)	1
(b)	energy storage / energy supply;
hormone production;
cushioning / protection;
insulation;
(constituent of) membranes;
cell respiration;
myelin sheath;	2 max
 
(c)	saturated fatty acids cause high cholesterol;
atherosclerosis / narrowing of (lumen of) arteries;
CHD / formation of clots / heart attack / heart failure / thrombosis / stroke;
hypertension / high blood pressure;
obesity / overweight;
which is linked to diabetes;
although there are also genetic factors / some countries eat a lot of fats 
and have low CHD;	4 max
[7]

7.	

[1]

8.	condensation;
involves the removal of water to join monosaccharides together / equation to show this;
catalysed by enzymes;
consists of many monosaccharides linked (glycosidic) to make polysaccharide;
[2]

9.	as substrate concentration increases enzyme activity increases;
at high substrate concentration enzyme reaches maximum activity;
active sites saturated;
labelled sketch-graph showing above relationship;
[3]

10.	(a)	compounds containing carbon (found in living organisms)	1
 
(b)	carbon, hydrogen and oxygen	1
 
(c)	(i)	proteins / named protein / DNA / RNA / 
chlorophyll / amino acid / 
other compound containing nitrogen	1
 
(ii)	DNA / RNA / nucleotides / ATP / phospholipids / 
GP (glycerate 3 phosphate) / 
other compound containing phosphorus	1
[4]