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Z OLD Molecules, Genes and Disease > Regulation of Protein Activity > Flashcards

Regulation of Protein Activity Flashcards

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1
Q

Why is important that we are able to control a proteins activities?

A

Proteins need to be functional at specific times for specific reasons

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2
Q

What are the short term methods of protein regulation?

A

NAME?

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3
Q

How can a change in protein conformation be induced?

A
  • Allosteric inhibition
  • Covalent regulation
  • Proteolytic cleavage
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4
Q

What are the long term methods of protein regulation?

A
  • Change in rate of protein synthesis

- Change in rate of protein degradation

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5
Q

How does substrate concentration affect the rate of enzyme activity?

A

Substrate availability affect the rate of enzyme activity

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6
Q

What are isoenzymes?

A

Different forms of the same enzyme- they catalyse the same reaction

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7
Q

How do isoenzymes differ from one another?

A

NAME?

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8
Q

What is the advantage of isoenzymes?

A

Allow for greater control

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9
Q

How can coenzymes regulate enzyme activity?

A

Some have limited availability

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10
Q

What is product inhibition?

A

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

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11
Q

How does product inhibition work?

A

The product molecule acts as a competitive inhibitor

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12
Q

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

A

Sigmoid

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13
Q

How does the relationship between rate and substrate concentration for allosteric enzymes differ form normal?

A

Usually is a rectangular hyperbola for simple enzymes

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14
Q

What is allosteric inhibition a method of?

A

Controlling enzymes depending on their structure

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15
Q

How can multi subunit enzymes regulate?

A

They can vary the efficiency in which they bind to their substrate

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16
Q

How can multi subunit enzymes exist?

A

In 2 conformations, the T state (low state) and the R state (high affinity)

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17
Q

What does substrate binding to one subunit of a multi sub unit enzyme result in?

A

Subsequent binding to other sub units is easier

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18
Q

What can allosteric regulation add?

A

Small molecules

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19
Q

What effect does the addition of small molecules in allosteric regulation have?

A

Affects enzyme activity

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20
Q

What do allosteric activators do?

A

Increase the proportion of enzyme in the R state

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21
Q

Where do allosteric activators bind?

A

Somewhere over than the active site

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22
Q

How do allosteric activators work?

A

They tend to change the conformation of one sub-unit, stabilising the high affinity state

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23
Q

What do allosteric inhibitors do?

A

Increase the proportion of enzyme in the T state

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24
Q

Give an example of an enzyme that is allosterically regulated

A

Phosphofructokinase

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25
Q

What does phosphofructokinase set the pace of?

A

Glycolysis

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26
Q

When do allosteric activators tend to control things?

A

In low energy

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27
Q

What activates phosphofructokinase?

A

AMP, fructose-2,6-bisphosphate

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28
Q

What inhibits phosphofructokinase?

A

ATP, citrate, H +

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29
Q

When does modification of proteins occur?

A

Post translation

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30
Q

Are post translational modifications of proteins transient or permanent?

A

Can be either

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31
Q

How are proteins covalently modified?

A

Phosphorylation

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32
Q

What phosphorylates proteins?

A

Protein kinases

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33
Q

What do protein kinases do?

A

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

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34
Q

What reverse the effects of protein kinases?

A

Protein phosphatases

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35
Q

What do protein phosphatases do?

A

Catalyse hydrolytic removal of phosphoryl groups from proteins

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36
Q

How can signals be amplified?

A

By protein cascades

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37
Q

What is being amplified in protein cascades?

A

Signals by kinase cascades

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38
Q

What do protein cascades allow for?

A

Amplification of signals by several orders of magnitude in a few milliseconds

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39
Q

Give an example of where reciprocal control of pathways is used?

A

Glycogen breakdown and synthesis

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40
Q

Where is specific proteolytic cleavage common?

A

Activating enzymes in biological systems

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41
Q

What happens in specific proteolytic cleavage?

A

Specific proteases cut proteins in a specific place

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42
Q

What is the effect of specific proteolytic cleavage?

A

The enzyme goes from completely off to completely on instantly

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43
Q

What type of molecule is specific proteolytic cleavage needed for?

A

Digestive enzymes

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44
Q

What are digestive enzymes synthesised as?

A

Zymogens

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45
Q

What are zymogens?

A

Inactive precursors

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46
Q

Where are digestive enzyme zymogens synthesised?

A

Stomach and pancreas

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47
Q

Why do digestive enzymes need to be synthesised as zymogens?

A

Don’t want enzymes active in wrong location

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48
Q

Other than digestive enzymes, what else is synthesised as zymogens?

A

Some protein hormones, e.g. insulin

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49
Q

What is blood clotting mediated by?

A

Cascade of proteolytic activations

50
Q

What does the mediation of blood clotting ensure?

A

A rapid and amplified response

51
Q

What are many developmental processes controlled by?

A

Activation of zymogens

52
Q

How do zymogens control developmental processes?

A

They contribute to tissue remodelling

53
Q

What is apoptosis?

A

Programmed cell death

54
Q

Is is apoptosis mediated by?

A

Caspases

55
Q

What are caspases?

A

Proteolytic enzymes

56
Q

How are caspases synthesised?

A

In their inactive form- procaspases

57
Q

Give an example of a molecule that is proteolytically activated

A

Chymotrypsinogen

58
Q

How is chymotrypsionogen activated?

A

Cleaved, some amino acids removed, and then rejoined by disulphide bonds

59
Q

Where is a cascade effect often found?

A

In the digestive system

60
Q

Give an example of the cascade effect in the digestive system

A

Pancreatic proteases- starts at enteropeptidase → trypsin → different molecules, all with different specificites

61
Q

What regulates protease activity?

A

Endogenous inhibitors

62
Q

Give an example of an endogenous inhibitor?

A

Pancreatic trypsin inhibitor, which stops the activity to trypsin

63
Q

Give an example of a disease caused by failure of pancreatic trypsin inhibitors?

A

Emphysema

64
Q

What causes emphysema?

A

α 1 -antitrypsin deficiency

65
Q

What does theα 1 -antitrypsin deficiency cause?

A

Destruction of the alveolar walls by elastase

66
Q

How can a change in rate of protein synthesis be induced?

A

Enzyme induction/repression

67
Q

How can a change in rate of protein degradation be induced?

A

Ubiquitin-proteasome pathway

68
Q

What is required for the blood clotting cascade?

A

A range of inactive zymogens

69
Q

What does the intrinsic pathway for blood clotting do?

A

Damaged endothelial lining of blood cells promotes factor XII binding

70
Q

What does the extrinsic pathway for blood clotting do?

A

Trauma releases tissue factor III

71
Q

What is the common end point of blood clottings intrinsic and extrinsic pathway?

A

Factor X activation

72
Q

What does Factor X activation lead to?

A

Thrombin activation

73
Q

What does thrombin activation lead to?

A

Formation of a fibrin clot

74
Q

What does the blood clotting cascade allow?

A

The formation of a clot from activation of a very small amount of initial factor

75
Q

Why is important that a clot can be formed from a very small amount of factor?

A

Because there is a very low concentration of clotting factors in the blood

76
Q

What are proenzymes?

A

Proteins of blood coagulation that don’t do anything until we need to clot

77
Q

What kind of enzymes are used in blood coagulation?

A

Lots of peptidases

78
Q

What do the peptidases in blood coagulation do?

A

Break peptide bonds in specific places in target proteins

79
Q

What is activated in the extrinsic pathway?

A

Factor VII

80
Q

What causes the activation of factor VII?

A

Membrane damage

81
Q

How does membrane damage lead to the activation of factor VII?

A

It exposes the extracellular domain of tissue factor III, which leads to the autocatalytic activation of factor VII

82
Q

What is the purpose of the intrinsic pathway?

A

It keeps blood clotting going

83
Q

What plays a role in intrinsic pathway activation?

A

Membrane damage

84
Q

What happens in the intrinsic pathway?

A

Factor XI and X are targeted to the membrane by Gla domains

85
Q

What ion plays a role in the intrinsic pathway

A

Calcium

86
Q

What is the intrinsic pathway needed for?

A

For sustained thrombin activation

87
Q

What part of prothrombin has the protease function?

A

The thrombin part

88
Q

Where is the thrombin part of prothrombin?

A

Contained in the C terminal domain

89
Q

What helps keep the prothrombin in its inactive form?

A

2 kringle domains

90
Q

What targets prothrombin to the appropriate sites for its activation?

A

Gla domains (carbyoxyglutamate domains)

91
Q

How is thrombin activated?

A
  • Proteolytic cleavage at Arg274 to release fragment containing first 3 domains
  • Cleavage after Arg323 releases fully active thrombin
92
Q

What does active thrombin consist of?

A

2 chains, linked by a disulphide bond

93
Q

What is the role of Gla residues in blood clotting?

A
  • Post translational modification of factors II, VII, IX and X in liver
  • Addition of COOH groups to glutamate residues to form carboxyglutamate
  • Allows interaction with sites of damage and brings together clotting factors
94
Q

What odes capillary damage attract?

A

Calcium

95
Q

What is the function of calcium in blood clotting?

A

NAME?

96
Q

Describe the structure of fibrinogen

A
  • 3 peptide chains wound around each other
  • 2 sets of tripeptides, α, ß andγ, joined at N-termini by disulphide bonds
  • 3 globular domains linked by rods
97
Q

What is the charge of N terminal regions of α and ß chains?

A

Highly negative

98
Q

What is the advantage of the negative charge on the N terminal regions of fibrinogen?

A

Prevents aggregation of fibrinogen

99
Q

How is a fibrin clot formed?

A
  • Thrombin cleaves fibrinopeptides at cleavage site from central globular domain of fibrinogen
  • Globular domains at the C-terminal ends of ß and γ chains interact with exposed sequences at N-termini of the cleaved ß and α chains to form fibrin mesh/clot
  • Newly formed clot stabilised by formation of amide bonds between the side chains of lysin and glutamine residues in different monomers
100
Q

What is the cross linking reaction of fibrinopeptides catalysed by?

A

Transglutaminase

101
Q

How is transglutaminase activated?

A

From protransglutaminase, by thrombin

102
Q

What is haemophilia?

A

A defect in factor VIII

103
Q

What does factor VIII do?

A

Stimulates activity of IXa

104
Q

What is factor IXa?

A

A serum protease

105
Q

What is the importance of factor VIII?

A

Activity of factor VIII markedly increased by limited proteolysis by thrombin and factor Xa- positive feedback amplifies the clotting signal, accelerating clot formation

106
Q

What is the treatment for haemophilia?

A

With recombinant factor VIII

107
Q

What mechanisms are involved in stopping the clotting process?

A
  • Localisation of (pro)thrombin
  • Digestion by proteases
  • Specific inhibitors
108
Q

How is (pro)thrombin localised?

A

Dilution of clotting factors by blood flow, and removal by the liver

109
Q

Give an example of something that stops clotting by digestion?

A

Protein C

110
Q

What does protein C do?

A

Degrades factors Va and VIIIa

111
Q

How is protein C activated?

A

By thrombin binding to endothelial receptor, thrombomodulin

112
Q

What can defects in protein C cause?

A

Thrombotic disase

113
Q

Give an example of a specific inhibitor for the clotting process?

A

Antithrombin III (AT3)

114
Q

What does AT3 do?

A

Binds extremely tightly to thrombin and factor V, whcih stops the activity

115
Q

What is the advantage of AT3 stopping activity?

A

Means can be degraded more efficiently

116
Q

What enhances AT3?

A

Heparin binding

117
Q

Does AT3-heparin act on thrombomodulin-bound thrombin?

A

No

118
Q

How does fibrinolysis occur?

A

NAME?

119
Q

Why is plasminogen secreted in the inactive form?

A

Because we don’t want it to be activated at the wrong time

120
Q

How can fibrinolysis be a point of control?

A

Can control rate of conversion of plasminogen into plasmin, and hence breakdown of fibrin

121
Q

What increases the rate of conversion of plasminogen into plasmin?

A
  • †-PA

- Streptokinase

Z OLD Molecules, Genes and Disease (14 decks)

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