enzymes

Question 1

describe the induced-fit model of enzyme action and how an enzyme acts as a catalyst. (3)

Answer 1

1. substrate binds to active site/enzyme
   OR
   enzyme-substrate complex forms;
2. active site changes shape (slightly) so it is complementary to substrate;
3. reduces activation energy;

Question 2

suggest and explain a procedure the scientists could have used to stop each reaction. (2)

Answer 2

1. boil
   OR
   add (strong) acid alkali;
2. denatures the enzyme/ATP synthase;
   OR
3. put in ice/fridge/freezer;
4. lower kinetic energy so no enzyme-substrate complexes form;

Question 3

a competitive inhibitor decreases the rate of an enzyme-controlled reaction.
explain how. (3)

Answer 3

1. inhibitor similar shape to substrate;
2. fits/binds to active site;
3. prevents/reduces enzyme-substrate complex forming;

Question 4

explain how the active site of an enzyme causes a high rate of reaction. (3)

Answer 4

1. lowers activation energy;
2. induced fit causes active site (of enzyme) to change shape;
3. enzyme-substrate complex causes bonds to form/break;

Question 5

describe how a non-competitive inhibitor can reduce the rate of an enzyme-controlled reaction. (3)

Answer 5

1. attaches to the enzyme at a site other than the active site;
2. changes shape of the active site;
   OR
   changes tertiary structure of enzyme
3. so active site and substrate no longer complementary so less/no substrate can fit/bind;

Question 6

formation of an enzyme-substrate complex increases the rate of reaction.
explain how. (2)

Answer 6

1. reduces activation energy;
2. due to bending bonds
   OR
   without enzyme, very few substrates have sufficient energy for reaction;

Question 7

suggest two variables the biochemist controlled when investigating the effect of temperature on the rate of breakdown of a protein by protease. (1)

Answer 7

1. enzyme concentration;
2. pH;

Question 8

explain how
i) raising the temperature to 35°C affects carbohydrase activity
ii) decreasing the pH affects carbohydrase activity (7)

Answer 8

i)
1. increase in temperature increases kinetic energy;
2. increases collisions between enzyme/active site/ substrate;
3. increase rate of breakdown of starch/carbohydrase activity;

ii)
4. decreasing the pH increases the H+ ions;
5. h.bonds broken which denatures enzyme
OR
changes tertiary structure;
6. changes shape of active site/ e-s complex no longer form;
7. decreases rate of breakdown of starch/carbohydrase activity;

Question 9

gout is a disease caused by the build-up of uric acid crystals in joints. uric acid is produced from xanthine in a reaction catalysed by the enzyme xanthine oxidase.
allopurinol is a drug used to treat gout. the diagram shows the structures of xanthine and allopurinol.

use this information to suggest how allopurinol can be used to treat gout. (3)

Answer 9

1. allopurinol is a similar shape to xanthine;
2. allopurinol enters the active site // competitive inhibitor;
3. less xanthine binds, fewer e-s complexes formed, fewer uric acid crystals formed;