Effects Of Competitive And Noncompetitive Inhibition Of Enzymes

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Chapter 2
Answers to examination-style questions
Answers

Marks Examiner’s tips

1 (a)  and structure (of A) is complementary to
A
that of the active site;

1

You must be able to explain how enzymes act.

(b) dea that non-competitive inhibitor (C) i binds at a site that is not the active site;  binding causes a change in the shape of the active site;  substrate is no longer able to bind to the active site;

3

Make sure that you know the different effects of competitive and noncompetitive inhibition of enzymes.

1

Peptide bonds hold amino acids together.
Do not confuse them with disulfide bridges, hydrogen or ionic forces which maintain the secondary, tertiary and quaternary structure of a protein.

(ii) idea that amino acid chain folds/

tertiary structure;  named bond holding tertiary structure,
e.g. ionic/disulfide/hydrogen;

2

Do not confuse peptide bonds with disulfide bridges, hydrogen or ionic forces which maintain the secondary, tertiary and quaternary structure of a protein. 2 (a) (i)  ubstances/molecules have more s (kinetic) energy/moving faster (reject vibrate);  increased collisions/enzyme substrate complexes formed;

2

Explain changes in rate of reaction in terms of collisions between substrate and enzyme and activation energy. Any factor that increases collisions or lowers the activation energy of the enzyme reaction or reduces the energy needed for the reaction will speed up the reaction.

(ii) causes denaturation/tertiary structure/

shape change; hydrogen/ionic bonds break; shape of active site changed;  substrate no longer binds/not complementary to active site;

3

(b)  ll substrate changed into product/reaction a is complete; same amount of product formed; same initial substrate concentration;

2

3 (a) 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;

3

(c) (i) peptide;

AQA Biology AS Level © Nelson Thornes Ltd 2008



Chapter 2
Answers to examination-style questions
Answers

(b) (i) 48, 56–58, 51–54 (all correct);

Marks Examiner’s tips
1

(ii) description –
6 max  increase up to 48/optimum (allow ECF from (i));  decrease above 48/optimum (allow
ECF from (i)); explanation of increase – increased KE/move faster;  therefore more collisions/more enzyme–substrate complexes formed with active site; explanation of decrease –  denaturation/3D structure changed/ tertiary structure changed;  detail, e.g. breaking of hydrogen/sulfur bonds (reject peptide bonds); shape of active site changed; substrate no longer fits;

Plan out your answer to make sure you cover every part of the question. Write your answer in full sentences.
ECF means error carried