Biol Mol

Question 1

Explain what is meant by a polymer.

Answer 1

(Molecule) made up of many identical/similar molecules/monomers/
subunits;

Question 2

Describe the structure of an amino acid molecule and explain how amino acids link together.

Answer 2

1 Amino acid based on carbon with four groups attached;
2 Amino/ NH2 and carboxyl / COOH;
3 R-group/ side chain + hydrogen;
4 R-group differs from one amino acid to another;
5 Amino acids joined by condensation;
6 Bond formed between NH2 and COOH;
7 Involves removal of molecule of water;
8 H from NH2 and OH from COOH;

Question 3

Explain how proteins are suited for their roles as receptor molecules.

Answer 3

Many different sorts of proteins;
Different primary structures/sequences of amino acids;
Tertiary structure;
Shape; allowing formation of receptor/binding site/site into which
substance/substrate fits;

Question 4

Explain how the structure of fibrous proteins is related to their functions.

Answer 4

Long chains of aa;
Folding of chain into a coil / folds / helix / pleated sheet;
Association of several polypeptide chains together;
Formation of fibres / sheets explained; 2
H bonds / Disulphide bonding (In context);
Fibres provide strength (and flexibility);
Sheets provide flexibility;
Example e.g. keratin in hair, collagen in bone; (MUST be in context)
Insoluble because external R-groups are non-polar;

Question 5

Describe how you would use a biochemical test to show that a solution contained protein.

Answer 5

Biuret / alkali + copper sulphate;

Lilac/purple/mauve/violet;

Question 6

Triglyceride and phospholipid;

Answer 6

Phospholipid has (one) phosphate / Phosphoric acid;	
replacing fatty acid;

Question 7

Saturated and unsaturated.

Answer 7

Saturated – all valencies of C filled / saturated with hydrogen / all (C–C)
single bonds / no double bonds;
fatty acid 1 is saturated/fatty acids 2 and 3 are unsaturated;

Question 8

Describe a chemical test you could carry out to show that a piece of coconut contains lipids.(3)

Answer 8

(Crush in) ethanol / alcohol;
Add (to) water (Order of adding is critical for this point);
Emulsion / white colour

Question 9

Describe how you could use Benedict’s reagent to test a urine sample for the presence of glucose.

Answer 9

Add (Benedict’s) reagent (to urine sample) and heat / heat the mixture;
red/ brown/ orange/ green/ yellow;

Question 10

Describe a further biochemical test to find out if a substance is a non-reducing sugar.

Answer 10

Heat with acid, then neutralise / hydrolyse using enzyme;

(heat) with Benedict’s (solution);

Question 11

Many reactions take place in living cells at temperatures far lower than those required for the same reactions in a laboratory. Explain how enzymes enable this to happen.

Answer 11

lowers activation energy;
relevant mechanism e. g. brings molecules close together / reaction in smaller
steps / change in charge distribution / proton donation or acceptance / induced
fit ensuring substrates brought in correct sequence;
including relevant reference to active site;

Question 12

Explain how a substrate is broken down by the enzyme.

Answer 12

Substrate enters active site;
Complimentary shapes / Lock and Key;
(Binding) to form enzyme-substrate complex;
Lowering of activation energy;
Conformational / shape change;
Breaking of bonds in substrate;
Products no longer fit active site and so are released;

Question 13

Describe how the condensation reaction can be catalysed by an enzyme.

Answer 13

enzyme has an active site;
with a complementary shape to the substrate molecules;
enzyme-substrate complex formed;
lowering the (activation) energy for the reaction;
glycosidic bond formed/bringing together hydroxyl groups/water
molecule removed;
products leave the active site;
enzyme unchanged;

Question 14

Explain how a change in pH affects enzymes activity

Answer 14

(decrease in pH) increases H+ ions/protons;
5 attach/attracted to amino acids;
6 hydrogen/ionic bonds disrupted/broken;
7 denatures enzyme / changes tertiary structure;
8 changes shape/charge of active site;
9 active site/enzyme unable to combine/fit with starch/enzyme-substrate
complex no longer able to form decreases rate of breakdown of starch/rate of reaction/carbohydrase activity

Question 15

Describe and explain how an increase in temperature affects the rate of an enzyme controlled reaction.

Answer 15

Temperature
Rate of reaction increases;
Increasing temperature increases rate of movement of molecules/
kinetic energy;
Collide more often/substrate enters active site more often/more
enzyme-substrate complexes formed;
Up to optimum;
Rate of reaction decreases;
High temperatures cause denaturation/loss of tertiary structure/3D structure;
By breaking specified bonds (not peptide bond);
Active site altered/substrate cannot bind/fit/

Question 16

Explain how inhibitors affect the rate of enzyme-controlled reactions.

Answer 16

1 Statement about two types, competitive and non-competitive;
Note. Award points 2 –5 only in context of competitive and
non-competitive inhibition
Competitive
2 Similarity of shape of inhibitor and substrate;
3 Inhibitor can enter/bind with active site (of enzyme);
Non-competitive
4 Affect/bind to enzyme other than at active site;
5 Distorts shape of active site;
Inhibitors
6 Prevent entry of/binding of substrate to active site;
7 Therefore fewer/no enzyme-substrate complexes formed;

Question 17

Use your knowledge of protein structure to explain why enzymes are specific and may be affected by non-competitive inhibitors.

Answer 17

1 each enzyme/protein has specific primary structure / amino acid sequence;
2 folds in a particular way/ has particular tertiary structure;
3 active site with unique structure;
4 shape of active site complementary to/ will only fit that of substrate;
maximum of three marks for inhibition, points 5 – 8
5 inhibitor fits at site on the enzyme other than active site;
6 determined by shape;
7 distorts active site;
8 so substrate will no longer fit / form enzyme-substrate complex;