Week 4 - Enzymes

Question 1

Describe globular protein structure

Answer 1

Polypeptide chain folds into compact ball-like structure

Question 2

Describe fibrous protein structure

Answer 2

Individual protein molecule spanning a large distance, with quite a simple elongated 3D structure

Question 3

Describe enzymes

Answer 3

Globular proteins which acts as biological catalysts to speed up metabolic reactions, without being used in the process

Question 4

5 enzyme functions

Answer 4

Metabolism, Movement, Digestion, Cell signalling, Gene expression

Question 5

Why can a single amino acid hugely change how an enzyme functions

Answer 5

Enzymes are highly specific, a single amino acid can change the protein shape, changing active site and no longer being able to catalyse a reaction

Question 6

Name the two theories of enzyme binding

Answer 6

Lock and key, induced fit model

Question 7

How is an enzyme so specific

Answer 7

Complimentary shape of substrate, charge and hydrophilic/hydrophobic interactions

Question 8

What is an allosteric site

Answer 8

A distinct area away from active site which can induce a conformational change to the enzyme when something binds to it

Question 9

Describe a cofactor

Answer 9

Any factor essentially needed for enzyme activity/protein function (inorganic)

Question 10

Describe a coenzyme

Answer 10

A cofactor which is directly involved in catalysed reaction (organic)

Question 11

Describe a prosthetic group

Answer 11

A covalently associated non-protein constituent needed for a specific function

Question 12

Describe an apoenzyme

Answer 12

The protein segment of the enzyme

Question 13

Describe a holoenzyme

Answer 13

The whole enzyme with any cofactors

Question 14

Typically, how are enzymes classified

Answer 14

Name of substrate + ase ending

Question 15

How do enzymes affect a reaction

Answer 15

Enzymes only affect rate of reaction, by reducing activation energy needed for reaction to occur

Question 16

Name the four main catalytic mechanisms

Answer 16

Metal ion catalysis, catalysis by approximation, covalent catalysis, acid base catalysis

Question 17

How do enzymes reduce activation energy

Answer 17

Binding to reactant and holding them in a way which the bond breaking or making process takes place much more easily and readily

Question 18

How do we work out enzyme velocity

Answer 18

Amount of substrate converted to product per unit of time

Question 19

Why do we take velocity at the start of a reaction

Answer 19

Fastest rate, highest S concentration, least amount of P and least amount of inhibition

Question 20

Describe the relationship between [S] and enzyme velocity

Answer 20

Proportional increase between [S] and velocity, until there is more substrate than active sites readily available, where velocity will remain constant

Question 21

Describe the relationship between [E] and enzyme velocity

Answer 21

Same as [S] except once active sites are higher than amount of [S] velocity remains constant

Question 22

What is Michaelis constant

Answer 22

A measure of enzyme affinity for substrate, a high constant indicates weak binding, a low constant indicates strong binding

Question 23

How do we get Michaelis constant

Answer 23

Half the Vmax and then concentration of substrate at that point on the graph

Question 24

Explain how temperature affects an enzyme

Answer 24

Enzymes have a temperature range, with an optimum which they can work at.
Rise in T will increase rate until optimum surpassed, which will denature protein structure

Question 25

Explain how pH affects enzymes

Answer 25

Small deviations in optimum pH result in decreased activity yet large deviations cause denaturation

Question 26

Describe enzyme inhibition

Answer 26

Where certain products inhibit earlier pathway steps of an enzyme

Question 27

Name 3 types of reversible inhibition

Answer 27

Competitive, Non-competitive and uncompetitive

Question 28

Describe competitive inhibition

Answer 28

Competitive inhibitors have affinity for active site, competing for access with the substrate, reducing rate of activity

Question 29

How can competitive inhibitors be overcome

Answer 29

Increasing [S]

Question 30

How does competitive inhibition affect Vmax and Km

Answer 30

Vmax stays the same but Km increases , reducing affinity

Question 31

Describe non competitive inhibition

Answer 31

Inhibitor binds to allosteric site to change active site so the substrate cannot bind

Question 32

How does non competitive inhibition affect Vmax and Km

Answer 32

Vmax reduced and Km stays the same

Question 33

Describe uncompetitive inhibition

Answer 33

Inhibitor binds to the enzyme substrate complex and inhibits catalysis