MCBG - Regulation Of Protein Function

Question 1

What are the effects of short term regulation of enzyme activity?

Answer 1

Change in substrate and product concentration, change in enzyme conformation

Question 2

What are some effects of long term regulation of enzymes?

Answer 2

Change in rate of protein synthesis/degradation

Question 3

What are isoenzymes?

Answer 3

Different forms of the same enzyme which have different kinetic properties.

Question 4

What is product inhibition?

Answer 4

This occurs when accumulation of the product of a reaction inhibits the forward reaction.

Question 5

What is the shape of the curve in a graph of reaction rate against substrate concentration for an allosteric enzyme?

Answer 5

Sigmoid

Question 6

What are the two states that allosteric enzymes can exist in?

Answer 6

T state (low affinity) and R state (high affinity).

Question 7

What do allosteric activators do in terms of T and R states?

Answer 7

They increase the proportion of enzyme in the R state.

Question 8

What do allosteric inhibitors do in terms of T and R states?

Answer 8

They increase the proportion of enzyme in the T state.

Question 9

Are ATP, citrate and H+ inhibitors or activators of phophofructokinase?

Answer 9

Inhibitors. AMP and fructose-2,6-bisphosphate are activators.

Question 10

What do protein kinases do?

Answer 10

Transfer phosphate from ATP to the -OH group of ser, thr and tyr. This is “covalent modification”.

Question 11

What do protein phosphatases do?

Answer 11

Reverse effects of kinases by catalysing hydrolytic removal of phosphoryl groups from proteins.

Question 12

Give some reasons why a molecule might be phosphorylated.

Answer 12

• adds two negative charges
• phosphoryl groups can make H-bonds (useful)
• rate of phosphorylation (or dephosphorylation) can be adjusted
• allow for application affects
• link energy status of cell to metabolism through ATP

Question 13

What is specific proteolytic cleavage?

Answer 13

A means of activating enzymes in biological systems, eg digestive enzymes are synthesised as zymogens.

Question 14

What does pancreatic trypsin inhibitor do?

Answer 14

Binds to trypsin and stops it from activating other enzymes.

Question 15

Which disorder is characterised by deficiency of alpha 1 antitrypsin and destruction of alveolar walls by elastase?

Answer 15

Emphysema

Question 16

What are the two pathways of blood clotting?

Answer 16

Intrinsic and extrinsic. They both lead to factor 10 activation.

Question 17

Briefly outline the blood clotting cascade.

Answer 17

Intrinsic/extrinsic pathways lead to factor X activation. This leads to thrombin activation, which leads to formation of a fibrin clot.

Question 18

What is the benefit of blood clotting being a “cascade”?

Answer 18

It allows formation of a clot from activation of very small amounts of initial factor.

Question 19

Is Ca2+ involved in the intrinsic pathway?

Answer 19

Yes.

Question 20

Why does prothrombin contain two “Kringle” domains?

Answer 20

To ensure that it stays inactive.

Question 21

What is the role of gamma-carboxyglutamate residues?

Answer 21

Post-translational modification of some factors in liver, addition of COOH groups to glutamate residues, allows interaction with sites of damage and brings together clotting factors.

Question 22

How does prothrombin bind calcium ions?

Answer 22

Via gla residues

Question 23

Roughly outline formation of a fibrin clot.

Answer 23

• Thrombin cleaves fibrinopeptides A and B from central globular domain
• globular domains at C-terminals of b and g chains interact with exposed N-termini of cleaved b and a chains to form clot

Question 24

How is the clotting process stopped?

Answer 24

Prothrombin is diluted and removed by liver, factors are digested by proteases, specific inhibitors

Question 25

Give a disease where the clotting process is inhibited.

Answer 25

Haemophilia

Question 26

Define “zymogen”.

Answer 26

Inactive substance which is converted into an enzyme when activated by another enzyme