Enzymes

Question 1

What is a cofactor?

Answer 1

Non-protein component of enzymes that are needed for activity

Question 2

What is a coenzyme?

Answer 2

A complex organic molecule usually formed from vitamins

Question 3

What is a prosthetic group?

Answer 3

Cofactor covalently bound (or very tightly associated) to an enzyme

Question 4

What is an apoenzyme?

Answer 4

Protein component of an enzyme containing a prosthetic group

Question 5

What is a holoenzyme?

Answer 5

The whole enzyme

Question 6

How to enzymes catalyse reactions?

Answer 6

They increase the rate of spontaneous reactions, lower activation energy and accelerates movement towards equilibrium

Question 7

What do spontaneous reactions contain?

Answer 7

An energy barrier

Question 8

What happens as [S] increases?

Answer 8

The initial velocity increases up to Vmax

Question 9

What is the shape of the initial rate in a [S] vs Vo graph when the [enzyme] is much lower than [substrate]?

Answer 9

Hyperbolic

Question 10

What is Vo?

Answer 10

The initial reaction velocity that is the steady state of a reaction

Question 11

What is Vmax?

Answer 11

The maximum reaction velocity, when all the active sites are saturated by substrate

Question 12

What is Km?

Answer 12

Michaelis constant

Question 13

What is the function of Km?

Answer 13

Measures an enzymes affinity for its substrate

Question 14

What is the affinity when Km is low?

Answer 14

High

Question 15

What is the affinity when Km is high

Answer 15

Low

Question 16

What does the Michaelis-Menton (M-M) equation tell us?

Answer 16

Km= 1/2Vmax= (k-1 + k2)/k1

Question 17

What does k1 determine?

Answer 17

The overall rate

Question 18

What is k2?

Answer 18

It is slower than k1 and is reversible

Question 19

What is the M-M equation useful for?

Answer 19

Measuring Vo and Vmax

Question 20

What are the 3 types of enzyme inhibitors?

Answer 20

Competitive, non-competitive and uncompetitive

Question 21

What is a competitive inhibitor?

Answer 21

An inhibitor that binds non-covalnetly to the active site. Their affect is overcome by high substrate concentrations and they mimic the substrate. They do not affect Vmax

Question 22

Can Vmax still be achieved in competitive inhibition?

Answer 22

Yes as it is overcome by high substrate concentrations

Question 23

What affect does competitive inhibition have on Km?

Answer 23

It increases Km, decreasing affinity for the substrate

Question 24

What is a non-competitive inhibitor?

Answer 24

It is an inhibitor that binds non-covalnety to the allosteric site. They are not overcome by high substrate concentrations

Question 25

What affect does non-competitive inhibition have on Km?

Answer 25

It is unchanged as substrates can still bind to the active site

Question 26

What affect does non-competitive inhibition have on Vmax?

Answer 26

Vmax decreases as the inhibitor can't be displaced

Question 27

What is an uncompetitive inhibitor?

Answer 27

An inhibitor that binds to the complex formed by the enzyme and substrate

Question 28

What affect does uncompetitive inhibition have on Km?

Answer 28

It decreases

Question 29

What affect does uncompetitive inhibition have on Vmax?

Answer 29

It decreases

Question 30

What is an enzyme assay?

Answer 30

A method of measuring enzyme activity for clinical diagnosis

Question 31

What regulates enzyme activity?

Answer 31

Allosteric effectors

Question 32

What are allosteric effectors?

Answer 32

They can be inhibitors or activators that enable changes in the ICE and ECE which changes the flow of metabolic pathways

Question 33

What are allosterically-regulated enzymes?

Answer 33

Multimeric proteins in which a conformational change in one of the polypeptides affects the whole the protein

Question 34

What is a multimeric protein?

Answer 34

Many polypeptides held together

Question 35

What is the shape of the initial reaction rate against [S] graph fro allosterically-regulated enzymes?

Answer 35

Sigmoidal

Question 36

What is an example of a reaction that would produce a sigmoidal curve?

Answer 36

When oxygen binds to haemoglobin

Question 37

What is reversible covalent modification?

Answer 37

Modification in amino acid side chains which affects enzyme activity