Session 11-Regulation of protein function

Question 1

What are isoenzymes?

Answer 1

Different forms of the same enzyme that have different kinetic properties

Question 2

True or false: accumulation of the product of a reaction inhibits the forward reaction

Answer 2

TRUE

Question 3

Give an example of product inhibition

Answer 3

Glucose-6-phosphate inhibits hexokinase activity

Question 4

What relationship do allosteric enzymes show between rate and substrate concentration?

Answer 4

Sigmoidal, rather than rectangular hyperbola seen for simple enzymes

Question 5

Complete the sentence:

Substrate binding to one subunit makes subsequent binding to other subunits progressively ______

Answer 5

Easier

Question 6

What do allosteric activators do?

Answer 6

Increase the proportion of enzyme in the R state

Question 7

What do allosteric inhibitors do?

Answer 7

Increase the proportion of enzyme in the T state

Question 8

True or false: phosphofructokinase is not allosterically regulated

Answer 8

FALSE - it is and it sets the pace of glycolysis

Question 9

What are the allosteric activators for phosphofructokinase? (2)

Answer 9

AMP

Fructose-2,6-bisphosphate

Question 10

What are the allosteric inhibitors for phosphofructokinase? (3)

Answer 10

ATP
Citrate
H+

Question 11

What do protein kinases do?

Answer 11

Transfer the terminal phosphate from ATP to the -OH group of Ser, Thr and Tyr

Question 12

What do protein phosphatases do?

Answer 12

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

Question 13

Why is protein phosphorylation so effective? (5)

Answer 13

1. Adds two negative charges
2. A phosphoryl group can make H-bonds
3. Rate of phosphorylation/dephosphorylation can be adjusted
4. Links energy status of the cell to metabolism through ATP
5. Allow for amplification effects

Question 14

Complete the sentence:

When enzymes activate enzymes, the number of affected molecules _________ _____________ in an enzyme cascade

Answer 14

Increases geometrically

Question 15

What does amplification of signals by kinase cascades allow?

Answer 15

Amplification of the initial signal by several orders of magnitude within a few milliseconds

Question 16

What does it mean by “glycogen breakdown and synthesis are reciprocally regulated”?

Answer 16

The signals that stimulate glycogen breakdown also inhibit glycogen synthesis

Question 17

Which enzyme catalyses glycogen breakdown?

Answer 17

Phosphorylase a

Question 18

Which enzyme catalyses glycogen synthesis?

Answer 18

Glycogen synthase

Question 19

How are many enzymes activated?

Answer 19

Specific proteolytic cleavage

Question 20

How are digestive enzymes synthesised by specific proteolysis?

Answer 20

They are synthesised as zymogens in the stomach and pancreas

Question 21

What are zymogens?

Answer 21

Inactive precursors - converted into an enzyme when activated by another enzyme

Question 22

How is blood clotting mediated?

Answer 22

By a cascade of proteolytic activations that ensures a rapid and amplified response

Question 23

How is apoptosis mediated?

Answer 23

By proteolytic enzymes, caspases, which are synthesised in an inactive form (procaspase)

Question 24

What do endogenous inhibitors do?

Answer 24

Regulate protease activity

Question 25

What binds to trypsin and stops its activity?

Answer 25

Pancreatic trypsin inhibitor

Question 26

What is an example of a protein that inhibits a range of proteases?

Answer 26

Alpha1-antitrypsin

Question 27

What are people with emphysema deficient in and what does this cause?

Answer 27

Alpha1-antitrypsin which leads to the destruction of alveolar walls by elastase

Question 28

What are the two types of short term protein regulation?

Answer 28

1. Substrate and product concentration

2. Change in enzyme conformation (allosteric regulation, covalent modification and proteolytic cleavage)

Question 29

What are the two types of long term protein regulation?

Answer 29

1. Change in rate of protein synthesis

2. Change in rate of protein degradation

Question 30

What is an example of enzyme induction/repression?

Answer 30

Alcoholics make more alcohol dehydrogenase

Question 31

Which enzyme catalyses the formation of a fibrin clot?

Answer 31

Thrombin

Question 32

Why is the intrinsic pathway more important than the extrinsic pathway of blood clot formation?

Answer 32

Once it starts, it is self-sustaining

Question 33

What are Gla domains?

Answer 33

Gamma-carboxyglutamate residues which are very negatively charged

Question 34

What do Kringle domains do?

Answer 34

Keep prothrombin in the inactive form

Question 35

How does Ca2+ play a role in blood clotting?

Answer 35

Interacts with damaged membranes and acts as a cross-bridge with Gla domains to allow for a quicker reaction

Question 36

Complete the sentences:

The newly formed clot is stabilised by the formation of _____ bonds between the side chains of ______ and _________ residues in different monomers. This cross-linking reaction is catalysed by _________________ which is activated from _________________ by thrombin.

Answer 36

Amide
Lysine 
Glutamine 
Transglutamine 
Protransglutaminase

Question 37

What is classic haemophilia a defect in?

Answer 37

Factor VIII

Question 38

What are two ways to stop the clotting process?

Answer 38

1. Localisation of (pro)thrombin - dilution of clotting factors by blood flow and removal by liver
2. Digestion by proteases

Question 39

How is the clotting process regulated? (1)

Answer 39

Specific inhibitors - antithrombin III (AT3)