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MCBG > Session 11: Regulation of Protein Function > Flashcards

Session 11: Regulation of Protein Function Flashcards

1
Q

What are the four short-term ways by which enzyme activity can be regulated?

A

Substrate and product concentration
Allosteric regulation
Covalent modification
Proteolytic cleavage

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2
Q

What are the two long-term ways by which enzyme activity can be regulated?

A

Change in the rate of protein synthesis

Change in the rate of protein degradation

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3
Q

Which is the easiest way to control the activity of an enzyme?

A

Changing substrate and product concentration

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4
Q

What are isoenzymes?

A

Different forms of the same enzyme that have different kinetic properties

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5
Q

What is product inhibition?

A

When accumulation of the product of a reaction inhibits the forward reaction

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6
Q

Give an example of product inhibition

A

Glucose-6-phosphate inhibiting hexokinase activity

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7
Q

Allosteric enzymes have what feature in regard to their subunits?

A

They are multiple subunits

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8
Q

What kind of curve do allosteric enzymes show in a relationship between rate and substrate concentration?

A

Sigmoidal curve

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9
Q

Allosteric enzymes can exist in two forms, what are they? How does this form relate to their affinity?

A

T state “Tense” - low affinity

R state “Relaxed” - high affinity

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10
Q

Allosteric activators increase the proportion of enzyme in what state?

A

R “relaxed” state

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11
Q

Allosteric inhibitors increase the proportion of enzyme in what state?

A

T “tense” state

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12
Q

Which enzyme responsible for setting the pace of glycolysis is allosterically activated?

A

Phosphofructokinase (PFK)

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13
Q

What are the two allosteric activators of PFK?

A

AMP

Fructose-2,6,-bisphosphate

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14
Q

What are the three allosteric inhibitors of PFK?

A

ATP
Citrate
Hydrogen ions

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15
Q

What is allostery?

A

Regulation of a protein by the binding of an allosteric molecule at a size other than they enzymes active site

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16
Q

How do allosteric effectors work?

A

They bind to an allosteric site and change the conformation of the protein which changes to shape of the active site and therefore inhibits or enhances the substance

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17
Q

Give three examples of a covalent modification of proteins

A

Phosphorylation
Acetylation
Sulfation
Ubiquitination

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18
Q

Which of the methods of covalent modification of proteins is most important in terms of regulation?

A

Phosphorylation

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19
Q

How does phosphorylation work?

A

Protein kinases can transfer phosphate from ATP to the -OH (hydroxyl) group of Serine, Theronine and Tyrosine residues to produce a phosphorylated protein

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20
Q

What group of molecules are able to reverse the affects of kinases? How do they do this?

A

Phosphatases

By catalysing the hydrolytic removal of the phosphoryl group from proteins

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21
Q

Phosphate is transferred onto what structural aspect of proteins?

A

-OH (hydroxyl group)

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22
Q

Why is protein phosphorylation so effective? (5things)

A

Hydrogen bonds can be made by the phosphoryl group
Amplification of the signal
Rate of phosphorylation/dephosphorylation can be adjusted
ATP linked to the energy status of the cell
Negative charges added (2)- changes the conformation

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23
Q

Using an example, explain what is meant by reciprocal regulation?

A

In glycolysis, breakdown of glycogen is induced by the same signals that inhibit the synthesis of glycogen

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24
Q

Why are enzyme cascades important?

A

They allow amplification of initial signal by several orders of magnitude within a few milliseconds

25
Q

What is a kinase?

A

An enzyme that add phosphates to proteins

26
Q

What is a phosphatase?

A

An enzyme that removes phosphates from proteins

27
Q

Why does phosphorylation have an effect?

A

Changes the conformation of the protein which leads to the recruitment and interaction of the protein with different molecules and changes its activity

28
Q

What is a zymogen?

A

An inactive enzyme precursor

29
Q

Which processes in the body use zymogens?

A 
Digestion 
Blood clotting 
Development 
Synthesis of protein hormones 
Apoptosis
30
Q

Give some examples of zymogens used in digestion? What are they activated to form?

A

Pepsinogen is activated to give pepsin

Trypsinogen is activated to give trypsin

31
Q

Pancreatic proteases such as elastase have a wide range of specificities, their activation is controlled by what?

A

Trypsin

32
Q

How are pancreatic proteases turned-off once activated by trypsin?

A

Pancreatic trypsin inhibitor: alpha1-antitrypsin binds to trypsin and stops its activity

33
Q

A deficiency in alpha1-antitrypsin can cause what disease? What causes this?

A

Emphysema

The proteases are not controlled, alveolar walls are destroyed by elastase

34
Q

What causes the long-term regulation of proteins by changing the rate of protein synthesis?

A

Enzyme induction or repression

35
Q

What causes the long-term regulation of proteins by changing in rate of protein degradation?

A

Ubiquitin-proteasome pathway

36
Q

The protease function (thrombin part) is contained in the C- terminal or the N-terminal domain of prothrombin?

A

C-terminal

37
Q

What is the importance of the clotting cascade?

A

It allows the formation of a vital clot from the activation of small amounts of initial factor through amplification

38
Q

The extrinsic pathway of the clotting cascade is caused by what?

A

Damage to the membrane which exposes extracellular domain of tissue (factor III)

39
Q

The intrinsic pathway of the clotting cascade is caused by what?

A

Membrane damage that leads to factor IX and X being targeted to the membrane at damage site by Gla domains which are attracted to positively charged calcium ions

40
Q

Where do post-translational modification of clotting factors II, IV, IX and X occur?

A

In the liver

41
Q

How is carboxyglutamate (Gla) formed?

A

The addition of COOH to glutamate residues

42
Q

The carboxylation of glutamate to form Gla residues in the liver is dependent on what?

A

Vitamin K

43
Q

What is the name of the domains that help to keep prothrombin in the inactive form?

A

Kringle domains

44
Q

The Gla domain is responsible for what?

A

The targeting of clotting factors to sites of damage

45
Q

Why is the calcium-binding region of prothrombin so important?

A

It means that only prothrombin next to the site of damage will be activated and clots will be localised to only this site

46
Q

Describe the important structural features of fibrinogen

A

It has 3 globular domains linked by rod-like alpha helices

2 sets of tripeptides (alpha,beta,gamma) are joined by N-terminal disulphide bonds

47
Q

What feature of fibrinogen prevents the aggregation of the molecules?

A

The N-terminal regions of alpha and beta chains are highly negative so they cannot come together

48
Q

How does thrombin cause the activation of fibrinogen into fibrin?

A

Cleaves off the fibrinopeptides at the N-terminal regions, they can then interact with the globular domains to for a fibrin mesh or clot

49
Q

The initial clot that is formed prior to cross-linking is known as what? What do we call this following formation of cross-links?

A

“Soft-clot” initially

Then forms a “hard-clot”

50
Q

Classic haemophilia is cause by a defect in what?

A

Clotting factor VIII

51
Q

Clotting factor VIII is an example of a what?

A

Allosteric activator

52
Q

What does factor VIII do?

A

Stimulates he activity of factor IXa (A serine protease)

53
Q

The intrinsic pathway is maintained by what, meaning that it doesn’t need to extrinsic pathway to maintain the clotting process?

A

Positive feedback to members of the upstream pathway

54
Q

What three methods are needed to regulate the clotting process?

A

Localisation of (pro)thrombin
Digestion of proteases
Specific inhibitors

55
Q

Which molecule is responsible for breaking up clotting factors in order to inactivate them?

A

Protein C

56
Q

What are some examples of regulators of clotting?

A 
Antithrombin III (AT3)
Plasminogen
57
Q

Plasminogen is activated by what to produce its activate form plasmin?

A

Tissue plasminogen activator (t-PA)

Streptokinase

58
Q

Plasmin does what?

A

Breaks up fibrin clot into fibrin fragments

MCBG (9 decks)

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