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ESA1 - Medical Cell Biology and Genetics > Regulation of Protein Function > Flashcards

Regulation of Protein Function Flashcards

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1
Q

How are enzymes regulated in the short term?

A

Substrate/product concentration and change in enzyme conformation (allosteric regulation, covalent modification, proteolytic cleavage)

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2
Q

How are enzymes regulated in the long term?

A

Change in rates of protein synthesis and degradation

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3
Q

What will substrate availability have an effect on?

A

Rate of enzyme activity

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4
Q

What are isoenzymes?

A

Different forms of the same enzyme that have different kinetic properies (catalyse same reaction)

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5
Q

What is product inhibition?

A

Accumulation of the product of a reaction inhibits the forward reaction

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6
Q

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

A

Sigmoid

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7
Q

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

A

Rectangular hyperbola

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8
Q

What are allosteric enzymes?

A

Enzymes that change their conformation upon binding of an effector

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9
Q

What are the two states that multi-subunit enzymes can exist in?

A

T state - low affinity

R state - high affinity

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10
Q

What is the effect on subsequent binding of a substrite binding to one subunit of an enzyme?

A

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

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11
Q

What do allosteric activators do?

A

Increase the proportion of enzyme in the R state (increase affinity)

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12
Q

What do allosteric inhibitors do?

A

Increase the proportion of enzyme in the T state (decrease affinity)

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13
Q

What does a shift to the left of the graph show in terms of affinity?

A

Shift to left = higher affinity = increased proportion of enzyme in R state

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14
Q

Do activators shift the graph to the left or right?

A

Left

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15
Q

What enzyme sets the pace for glycolysis?

A

Phosphofructokinase - it is allosterically regulated

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16
Q

What are some allosteric activators of phosphofructokinase?

A

AMP, fructose-2,6-bisphosphate

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17
Q

What are some allosteric inhibitors of phosphofructokinase?

A

ATP, citrate, H+

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18
Q

What can protein kinases do to serine, threonine and tyrosine?

A

Transfer the terminal phosphate from ATP to the OH group of these amino acids

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19
Q

What do protein phosphatases do?

A

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

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20
Q

Why is protein phosphorylation so effective?

A

Adds 2 negative charges, phosphoryl group can make H bonds, rate of phosphorylation/dephosphorylation can be adjusted, links energy status of the cell to metabolism through ATP, allow for amplification effects

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21
Q

What can the two negative charges added to proteins via phosphorylation do?

A

Cause conformational change

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22
Q

What is the difference between a phosphoryl group and a phosphate?

A 
Phosphate = PO4(^3-)
Phosphoryl = PO3 (^2-)
23
Q

What is a zymogen?

A

An inactive substance which is converted into an enzyme when activated by another enzyme (precursor to enzymes)

24
Q

How is apoptosis mediated?

A

Proteolytic enzymes (caspases) which are synthesised in inactive (procaspase) form - only activated when there is a covalent breakage of peptide bond

25
Q

What is the ‘master regulator’ of the activation of enteropeptidases?

A

Trypsin

26
Q

a1-antitrypsin inhibits a range of proteases. What is a disease that involves the deficiency of a1-antitrypsin?

A

Emphysema - destruction of alveolar walls by elastase

27
Q

What do both the intrinstic and extrinsic pathways of the blood clotting cascade lead to?

A

Factor X activation, which leads to thrombin activation and the formation of fibrin clot

28
Q

What is factor X?

A

Endopeptidase that contains Gla residues. Also known as the Stuart-Prower factor.

29
Q

What is the activated form of factor X?

A

Factor Xa, activated by hydrolysis

30
Q

How does factor X act?

A

Cleaves prothrombin in two places which yields the active thrombin

31
Q

What does thrombin do?

A

Converts fibrinogen into fibrin

32
Q

What plays a role in the activation of the intrinsic pathway?

A

Membrane damage

33
Q

In the intrinsic pathway, what are targeted to membrane by Gla domains?

A

Factor IX and X

34
Q

What helps keep prothrombin in the inactive form?

A

The two kringle domains

35
Q

In which domain of prothrombin is the protease function (thrombin part) contained?

A

C-terminal

36
Q

What targets prothombin to appropriate sites for its activation?

A

Gla domains

37
Q

What is Gla?

A

g-carboxyglutamate

gamma

38
Q

What is the role of Gla residues?

A

Post translational modification of factors I, VII, IX, X in the liver, addition of COOH groups to glutamate residues which form Gla and allows interaction with sites of damage and brings together clotting factors

39
Q

What does prothrombin bind to?

A

Calcium ions via Gla residues

40
Q

How are clots localised to the site of damage?

A

Only prothrombin next to the site of damage will be activated

41
Q

What is the structure of fibrinogen?

A

340 kDa protein
2 sets of tripeptides joined at N termini by disulphide bonds
3 globular domains linked by rods

42
Q

What prevents aggregation of fibrinogen?

A

N terminal regions of alpha and beta chains are highly negatively charged

43
Q

How is a fibrin clot formed?

A

Thrombin cleaves fibrinopeptides from the central globular domain of fibrinogen. Globular domains at the C terminal ends of the b and g chains interact with exposed sequences at the N termini of the cleaved b and a chains to form a fibrin clot

44
Q

What is the newly formed clot stabilised by?

A

Formation of amide bonds between side chains of lysine and glutamate residues

45
Q

What is the cross linking reaction in formation of blood clots catalysed by?

A

Transglutaminase

46
Q

What is classic haemophilia a defect in?

A

Factor VIII

47
Q

What is factor VIII and what is it increased by?

A

It is not a protease but stimulates the activity of factor IX which is. It is increased by limited proteolysis by thrombin and factor Xa. This positive feedback amplifies the clotting signal and accelerates clot formation

48
Q

How is the clotting process stopped?

A

Localisation of prothrombin - dilution of clotting factos by blood flow and removal by liver.

Digestion by proteases

49
Q

What is protein C?

A

Degrades factors Va and VIIIa. Activated by thrombin binding to thrombmodulin.

50
Q

What can defects in protein C cause?

A

Thrombotic disease

51
Q

How can the clotting process be regulated?

A

Specific inhibitors - antithrombin III

52
Q

What are some key control points in blood clotting?

A

Inactive zymogens present at low concentration, proteolytic activation, clusetering of clotting factors and site of damage, feedback activation by thrombin ensures clotting continuation, clot breakdown by proteolytic activation

53
Q

How can clot formation be reversed?

A

Proteolytic cleavage of fibrin by the enzyme plasmin

ESA1 - Medical Cell Biology and Genetics (18 decks)

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