regulation of protein function

Question 1

5 short term ways enzyme activity is regulated

Answer 1

1) substrate and product concentration
2) allosteric regulation
3) covalent modification
4) amplification
5) proteolytic cleavage

Question 2

2 long term ways enzyme activity is regulated

Answer 2

1) change in rate of protein synthesis

2) change in rate of protein degradation

Question 3

4 ways substrate and product concentration affect the rate

Answer 3

• If higher conc of substrate then there is a faster rate
• some coenzymes have limited avaliability (eg NADH) and therefore rate is limited by the lack of coenzymes
• end product inhibition. As conc of product increases it inhibits the enzyme more and rate will fall
• isoenzymes; enzymes that have the same role but different kinetic properties

Question 4

give an example of a pair of isoenzymes

Answer 4

hexokinase is an enzyme found in all cells and glucokinase is found in the liver. However, glucokinase has less affinity (seen by the much higher km) and therefore only becomes active when glucose concentrations are very high. Allows glucose to be taken up into liver cells and be converted to glycogen.

Question 5

What is allosteric regulation?

Answer 5

enzymes that have allosteric regulation are usually multisubunit. Activators may bind to the allosteric site and increase the number of enzymes in the R state or inhibitors may bind and increase the enzymes in the T state.

Question 6

Give an example of allosteric regulation

Answer 6

phosplhofructokianse is controlled by allosteric regulation. Activators include AMP and fructose 2, 6 bisphosphate. Inhibitors include ATP, citrate and H+.

Question 7

explain covalent modification

Answer 7

addition of a molecule which results in a change in conformation and a different enzyme function

Question 8

What is phosphorylation

Answer 8

protein kinases will transfer a pi group from ATP to and OH group to phophorylate it.
protein phosphotases will reverse effects of phosphorylation by hydrolytic removal of pi

Question 9

why is phosphorylation so effective?

Answer 9

adds negatively charged group (large conformational change possible)
phosphate group can make H bonds which interferes with other interactions
allows amplification

Question 10

explain amplification

Answer 10

1 hormone can lead to large response. The response increases by enzyme cascade. This means that each enzyme catalyses 1 substrate to produce multiple products

Question 11

explain proteolytic cleavage

Answer 11

part of protein is cut in order to activate it

Question 12

example of proteolytic cleavage

Answer 12

digestive enzymes are synthesised as zymogens and activated once in the stomach. For example chymotripsinogen is cleaved by trypsin (which is also activated by proteolytic cleavage and activates multiple enzyme in the stomach) to form chymotrypsin which is the active version.

Question 13

how is trypsin activity regulated

Answer 13

endogenous inhibitors bind irreversibly to trypsin and stop activity- when you are of these inhibitors you develop emphysema which leads to destruction of the alveolar walls.

Question 14

how is thrombin activated

Answer 14

the intrinsic pathway of factors and the extrinsic pathway of factors are activated and they result in the activation of factor 10. Factor 10 then converts prothrombin to thrombin and it becomes activated.

Question 15

how is prothrombin converted to thrombin

Answer 15

by proteolytic cleavage of the protease site on the gene. Cuts off Kringle sites which keep it inactivated

Question 16

describe the structure of the prothrombin gene.

Answer 16

has Kringle domains which keep it inactive and gla domains which tell the gene where to go. The gla domains have COOH groups (negative) on them which are attracted to ca2+ which are attracted to the site of breakage. This brings the clotting factors together and clotting cascade begins

Question 17

How is the blood clot formed

Answer 17

fibrinogen is coverted to fibrin subunits which have affinity for each other and stick together to form polymers. Factor 2 which is thrombin is what cleaves the negatively charged groups on fibrinogen which prevent the molecules from coming together. This converts fibrinogen to fibrin (factor 1) and they come together to form the clot.

Question 18

what is haemophilia?

Answer 18

deficiency in clotting factor 12. Unable to clot properly.

Question 19

how is clotting a self sustaining process

Answer 19

thrombin acts as feedback regulator for example after extrinsic pathway is regulated it activates certain factors in the intrinsic pathway to start that pathway.

Question 20

how is the clotting process stopped?

Answer 20

clotting factors are removed by liver, proteases digest different cofactors and antithrombin 3 acts as thrombin inhibitor

Question 21

how is the clot removed once the wound is healed

Answer 21

plasminogen is converted to plasmin by 2 enzymes called t-pa and streptokinase. Plasmin will then convert fibrin to fibrin fragments, breaking down the clot. These can be used in treatments such as warfarin to prevent blood clots