Enzymes 2.5, 8.1

Question 1

How do enzymes lower the activation energy of a reaction ?

Answer 1

• substrate binds to the enzymes active site
• due to the binding the bonds in the substrate molecule are stressed and become less stable
• binding lowers overall energy level of transition state
• activation energy of the reaction is therefore reduced

Question 2

Inhibitor

Answer 2

a molecule that binds to an enzyme and slows or stops the enzymes function

Question 3

Competitive and non-competitive inhibitors

Answer 3

competitive inhibitor - inhibitor fits the active site and prevents substrate from entering

non-competitive inhibitor - inhibitor fits on allosteric site causing a conformational change in the active site

Question 4

competitive inhibition

Answer 4

Even with the competitive inhibitor the same max. rate of reaction will be achieved if more substrate is added.

EXAMPLE - Antabuse Drug for alcohol addiction

e.g Antabuse (competitive inhibitor) competes with aldehyde oxidase and prevents the acetaldehyde from being converted.

Question 5

non - competitive inhibitors

Answer 5

1. Bind to allosteric site on enzyme
2. as concentration increases, rate of reaction decreases
3. fewer functional sites available for reaction
4. max rate reduced - even if substrate increased
5. e.g ACE inhibitors are medications that inhibit Angiotensin-converting enzymes. prevent increased blood pressure

Question 6

Endproduct inhibition / Feedback inhibition

Answer 6

ESSENTIAL AMINO ACID ISOLEUCINE

1. Bacteria synthesize isoleucine from threonine in a series of five enzyme catalysed reaction
2. concentration of isoleucine increases, some bind to the allosteric site of threonine deaminase
3. isoleucine acts a non-competive inhibitor
4. pathway turned of regulating isoleucine production

Question 7

Compare competitive and non competitive inhibition of enzymes

Answer 7

Competitive

1. same shape as substrate
2. binds to active site
3. no change active site
4. increase in substrate concentration reduces inhibition

Non- Competitive

1. chemically different, different shape
2. binds at allosteric site
3. inhibition changes shape of active site
4. increase substrate no effect on the inhibition

BOTH:

1. reduce enzyme activity
2. both bind to enzyme
3. both prevent substrate from binding to active site

EXAMPLE COMPETITIVE
1. succinate dehydrogenase inhibited by malonate
EXAMPLE NON - COMPETITIVE
1. pyruvate kinase inhibited by alanine

Question 8

What is an Enzyme ?

Answer 8

1. globular protein that works as a catalyst
2. speeds up chemical reactions
3. remain unchanged
4. effective in small amounts
5. shape and chemical properties of the active site and substrate match

Question 9

Collision

Answer 9

coming together of substrate and enzyme active site due to continuous molecular motion in liquid

Question 10

Metabolic pathways

Answer 10

cycles or chains of enzmye catalysed reactions-
chemical change from one molecule to another in a sequence of small steps
e.g krebs cycle and glycolysis