Enzyme Structure and Function

Question 1

Define an enzyme:

Answer 1

Highly specific biological catalysts.

Question 2

What is the purpose of an enzyme?

Answer 2

Increase the rate of a reaction without being changed at the end of the reaction.

Question 3

What defines the precise specificity?

Answer 3

The 3D structure of the enzyme.

Question 4

Give examples of proteases which undergo specificity.

Answer 4

Trypsin = cleaves after arginine or lysine residues. 
Thrombin = Cleaves between arginine and glycine only in particular sequences. 
Papain = Cleaves all peptide bonds irrespective of sequence.

Question 5

Name the two types of co - factors:

Answer 5

Coenzymes - organic molecules derived by vitamins

Metal Ions - Mg2+ and Zn2+ and Cu2+.

Question 6

What are co - enzymes?

Answer 6

Non - protein molecules which are required for enzyme // protein function.

Question 7

What is the protein part (excluding the cofactor) called?

Answer 7

Apoenzyme

Question 8

What is the protein - cofactor complex called?

Answer 8

Holoenzyme

Question 9

What determines whether the reaction will occur spontaneously or not?

Answer 9

The free energy change of the reaction. (delta g)

Question 10

In what state does (delta g) need to be in - in order for a reaction to occur?

Answer 10

(delta g) has to be in a negative state in order for a reaction to occur.

Question 11

What is required to reach the transition state?

Answer 11

Activation energy is required to reach the transition state.

Question 12

What factors affect enzyme activity?

Answer 12

1) Temperature
2) pH
3) Substrate / Enzyme Concentration

Question 13

What is the lock and key model?

Answer 13

Active site has rigid shape and therefore the substrates have a matching fit.

Question 14

What is the induced fit model?

Answer 14

Active site is flexible and therefore, the enzyme, active site and substrate adjust to maximise the fit.

Question 15

How do the enzymes lower the activation energy?

Answer 15

By stabilising the transition state.

Question 16

What are the interactions which stabilise the enzyme - substrate complex?

Answer 16

Electrostatic interactions
Hydrogen bonds
Van der Waals forces.

Question 17

What happens to enzymes once they go above a certain temperature?

Answer 17

The enzymes will denature (unfold) and then become inactive - thus meaning it’s irreversible.

Question 18

When does maximum activity occur?

Answer 18

When the enzyme is saturated.

Question 19

What are allosteric enzymes?

Answer 19

These are enzymes with more than one binding site. They had 2 conformations - one active and one inactive.
Binding of a regulatory molecule (known as a ligand) changes activity by stabilising one of the two conformations.

Question 20

What are activator ligands?

Answer 20

These bind at a regulatory binding site and thus stabilises the active conformation.
EG:
CTP - allosteric inhibitor
ATP - allosteric activator

Question 21

In terms of the concerted model and sequential model what effect does positive effectors have?

Answer 21

They stabilise the high affinity form of the sub - units.

Question 22

In terms of the concerted model and sequential model what effect does negative effectors have?

Answer 22

They stabilise the low affinity form of the sub - units.

Question 23

Explain the concerted model.

Answer 23

When substrate binds to the T form it causes all sub - units to convert to R form.
R form has higher affinity for substrate than T form and thus, enzyme activity increases rapidly after each enzyme molecule has bound one substrate molecule.

Question 24

Explain the sequential model.

Answer 24

When the substrate binds to T form it causes the sub - unit to which it binds to convert to R form.
Affinity increases once sub - unit has converted to R form and therefore, activity increases rapidly after protein has bound one substrate molecule.