Session 11 (Regulation Of Protein Function)

Question 1

How can enzyme activity be regulated in the long term?

Answer 1

Change rate of protein synthesis/degradation

Question 2

How can enzyme activity be regulated short term? (2)

Answer 2

Alter product/substrate concentrations

Change enzyme conformation

Question 3

What are the ways in which you can change enzyme conformation? (3)

Answer 3

Allosteric regulation
Covalent modification
Proteolytic cleavage

Question 4

What are allosteric enzymes?

Answer 4

Enzymes that can be conformationally changed by the binding of activators and inhibitors thus affect the rate of reaction

Question 5

What shape curve is produced when dealing with allosteric enzymes?

Answer 5

Sigmoidal-binding makes subsequent binding to other subunits easier

Question 6

What are the 2 states an allosteric enzyme can be found in?

Answer 6

T= low affinity
R= high affinity

Question 7

How can the proportion of allosteric enzyme in a particular state be increased?

Answer 7

R=allostatic activators (stabilise this state)

T=allostatic inhibitors (stabilises this state)

Question 8

Give an example of an allosteric enzyme

Answer 8

PFK (used in glycolysis)

Question 9

Name some activators that work on PFK (an allosteric enzyme) (2)
Explain why these are activators

Answer 9

AMP (sign of no energy therefore glycolysis needs to happen)

Fructose-2,6-bisphosphate (is a substrate of glycolysis)

Question 10

Name some inhibitors of PKF (allosteric enzyme) (3)

Explain why they are inhibitors

Answer 10

ATP (energy in full supply, process can stop)
Citrate (intermediate of glycolysis, increased conc signals enough glycolysis has occurred so reaction can stop)
H+ (inhibits by product inhibition- similar to the work of citrate in inhibiting glycolysis)

Question 11

Give two examples of covalent modification

Answer 11

Phosphorylation

Acetylation

Question 12

What is phosphorylation?

Answer 12

Adding a PO4 group to an amino acid residue

Question 13

What 2 enzymes are involved in phosphorylation? How?

Answer 13

Protein kinase (adds PO4)
Protein phosphatase (removes it)

From OH of ser/thr/tyr

Question 14

What is covalent modification?

Answer 14

Using enzymes to modify the structure of an enzyme thereby altering it activity levels

Question 15

Why is protein phosphorylation good? (3)

Answer 15

Adds 2 negative charges, PO4 makes H bonds (stronger IMF), rate can be changed,
allows for amplification effects

Question 16

Why are cascades important?

Answer 16

They allow for amplification, initial signal increased

Question 17

What is an isoenzyme?

Answer 17

Different forms of the same enzymes that have different kinetic properties

Question 18

What is Proteolytic cleavage?

Answer 18

Process in which peptides bonds are broken

Question 19

What is a zymogen?

Answer 19

An inactive substance that can be converted into an enzyme when activated by another enzyme

Question 20

What do cascade mechanisms allow?

Answer 20

Allow the amplification of regulatory signals

Question 21

What are the 2 pathways for the blood clotting cascade? What do they have in common?

Answer 21

Intrinsic and extrinsic

Both involve enzymes activated by proteolytic cleavage

Question 22

What factor is involved in the intrinsic pathway?

Answer 22

Factor 12 (after damage to endothelial lining)

Question 23

What 2 factors are involved in the extrinsic pathway?

Answer 23

Factor 3 which activated factor 7 by autocatalysis (after tissue damage)

Question 24

What is the common endpoint of both pathways?

Answer 24

Factor 10

Question 25

What does factor 10 lead to?

Answer 25

Thrombin activation= fibrin clot formation

Question 26

How is a clot formed?

Answer 26

COO- (gla residues) binds to Ca2+
Prothrombin activated to form thrombin
Thrombin Proteolytically cleaves fibrinogen
Fibrin mesh formed

(See notes for diagram)

Question 27

How is the clotting cascade amplified?

Answer 27

By thrombin- involved in positive feedback mechanism

Question 28

How can the clotting process be stopped? (3)

Answer 28

Diluting clotting factors (blood flow and liver)
Removing factors by protein C (digestion by proteases)
Specific inhibitors

Question 29

What is the process of breaking down a clot called?

Answer 29

Fibrinolysis

Question 30

What happens during fibrinolysis?

Answer 30

Plasminogen activated

=plasmin (enzyme that performs proteolytic cleavage of fibrin forming fibrin fragments)