Session 11-Regulation of protein function Flashcards Preview

Semester 1-MCBG > Session 11-Regulation of protein function > Flashcards

Flashcards in Session 11-Regulation of protein function Deck (39):
1

What are isoenzymes?

Different forms of the same enzyme that have different kinetic properties

2

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

TRUE

3

Give an example of product inhibition

Glucose-6-phosphate inhibits hexokinase activity

4

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

Sigmoidal, rather than rectangular hyperbola seen for simple enzymes

5

Complete the sentence:

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

Easier

6

What do allosteric activators do?

Increase the proportion of enzyme in the R state

7

What do allosteric inhibitors do?

Increase the proportion of enzyme in the T state

8

True or false: phosphofructokinase is not allosterically regulated

FALSE - it is and it sets the pace of glycolysis

9

What are the allosteric activators for phosphofructokinase? (2)

AMP
Fructose-2,6-bisphosphate

10

What are the allosteric inhibitors for phosphofructokinase? (3)

ATP
Citrate
H+

11

What do protein kinases do?

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

12

What do protein phosphatases do?

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

13

Why is protein phosphorylation so effective? (5)

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

14

Complete the sentence:

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

Increases geometrically

15

What does amplification of signals by kinase cascades allow?

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

16

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

The signals that stimulate glycogen breakdown also inhibit glycogen synthesis

17

Which enzyme catalyses glycogen breakdown?

Phosphorylase a

18

Which enzyme catalyses glycogen synthesis?

Glycogen synthase

19

How are many enzymes activated?

Specific proteolytic cleavage

20

How are digestive enzymes synthesised by specific proteolysis?

They are synthesised as zymogens in the stomach and pancreas

21

What are zymogens?

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

22

How is blood clotting mediated?

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

23

How is apoptosis mediated?

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

24

What do endogenous inhibitors do?

Regulate protease activity

25

What binds to trypsin and stops its activity?

Pancreatic trypsin inhibitor

26

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

Alpha1-antitrypsin

27

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

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

28

What are the two types of short term protein regulation?

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

29

What are the two types of long term protein regulation?

1. Change in rate of protein synthesis
2. Change in rate of protein degradation

30

What is an example of enzyme induction/repression?

Alcoholics make more alcohol dehydrogenase

31

Which enzyme catalyses the formation of a fibrin clot?

Thrombin

32

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

Once it starts, it is self-sustaining

33

What are Gla domains?

Gamma-carboxyglutamate residues which are very negatively charged

34

What do Kringle domains do?

Keep prothrombin in the inactive form

35

How does Ca2+ play a role in blood clotting?

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

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.

Amide
Lysine
Glutamine
Transglutamine
Protransglutaminase

37

What is classic haemophilia a defect in?

Factor VIII

38

What are two ways to stop the clotting process?

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

39

How is the clotting process regulated? (1)

Specific inhibitors - antithrombin III (AT3)