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Biochemistry > Regulation of enzyme activity > Flashcards

Regulation of enzyme activity Flashcards

1
Q

5 says of regulating enzymatic activity

A

Allosteric control
Multiple forms of enzymes
Reversible covalent modification
Proteolytic activation
Controlling the amount of enzyme present

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2
Q

Example of reversible covalent modification

A

Phosphorylation

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3
Q

What does allosteric regulation do?

A

Modulates activity of key enzymes through reversible binding ina different site than active site

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4
Q

Is allosteric regulation fast or slow working?

A

Fast

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5
Q

What are allosteric effectors typically?

A

Small chemicals either positive or negative

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6
Q

Example of allosteric enzyme

A

Aspartate transcarbamoylase (ATCase)

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7
Q

What does Aspartate transcarbamoylase (ATCase) catalyse?

A

First reaction of pyrimidine synythessi

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8
Q

What is the committed step?

A

The step which is determines what reactive pathway you’ll take, after that step (typically the first step) there can be no more control

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9
Q

What is feedback inhibition

A

When the last product inhibits the first step so the reaction can’t happen again
Like negative feedback

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10
Q

Is cytidine a pyrimidine or purine?

A

Pyrimidine

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11
Q

What kind of kinetics does ATCase display?

A

Sigmoidal kinetics

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12
Q

How many subunits does native ATCase consist of?

A

12:
6 regulatory (3 dimers)
6 catalytic (2 trimers)

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13
Q

What is an analog?

A

Something that is structurally and chemically similar

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14
Q

What does PALA do?

A

Freeze it in the R state (suicide inhibitor)

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15
Q

Is ATP a positive or negative regulator?

A

Postive (favours R-state)

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16
Q

Is ATP a positive or negative regulator?

A

Negative (favours T-state)

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17
Q

Is ATP purine or pyrimidine?

A

Purine

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18
Q

How do ATP block CTP ?

A

Because there has to be equal amounts of purine and pyrimidine so the excess amount of CTP will not act because of the limiting number of ATP

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19
Q

What can the concerted model be described as?

A

All or nothing

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20
Q

Where does CTP bind?

A

Regulatory site

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21
Q

What kind of cooperatively does haemoglobin use?

A

Sequential cooperatively

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22
Q

Which amino acids are most commonly phosphorylated?

A

Tyrine
Serine
Threonine

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23
Q

What can ATP serve as a donor of?

A

Phosphate

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24
Q

What does kinases need to phosphorylate and gives it high specificity?

A

Consensus sequences which serves as a marker for which amino acid to phosphorylate

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25
Q

Are the consensus sequences the same for all kinases?

A

No they are very different

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26
Q

6 reasons for phosphorylation being highly effective

A

Free energy
Adds 2 negative charges to protein
Can form 3 or more hydrogen bonds
Is fast
Often evoke highly amplified effects
ATP is cellular energy currency

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27
Q

What does training do to the phosphorylation of many proteins?

A

Increases it

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28
Q

Types of proteolysis (a common way of activating enzymes)

A

Digestive enzymes
Blood clotting
Apoptosis
Hormones
Collagen

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29
Q

What does elastase cleave?

A

Proteins in bacteria, therefor important in lungs to protect them from infection

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30
Q

2 fast reacting enzyme regulation mehtods

A

Allosteric control
Reversible covalent modification

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31
Q

What does allosterism describe?

A

The change in the affinity for binding of a ligand or substrate that is caused by the binding of another ligand away from the active site

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32
Q

What happens to enzymatic catalysis if the allosteric effector is negative?

A

The enzymatic catalysis is reduced

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33
Q

What inhibits aspartate transcarbomylase?

A

The end product of the pathway
Feedback inhibition

34
Q

What does the fact that ATCase display sigmoidal kinetics indicate??

A

Cooperativity

35
Q

What kind of regulator is ATP?

36
Q

What kind of regulator is CTP?

37
Q

Which state does ATP favour?

38
Q

Which state does CTP favour?

39
Q

What are allosteric interactions in ATCase mediated by?

A

Large changes in quaternary structure

40
Q

What is the allosteric coefficient?

A

The ratio of enzyme in the T state to that in the R state

41
Q

Which mechanism of allosteric enzymes does ATCase adhere to? Concerted or sequential?

42
Q

What is L?

A

The equilibrium constant for the T-toR equilibrium

43
Q

What alters the value of L?

A

Allosteric effectors (heterotrophic effectors)

44
Q

What effect does ATP have on Km?

45
Q

What effect does ATP have on affinity?

A

Highers it

46
Q

What effect does CTP have on affinity?

47
Q

What effect does CTP have on Km?

A

Highers it

48
Q

Which is faster, the concerted model or the sequential?

49
Q

3 most common target residues for phosphorylation

A

Tyrosine
Serine
Threonine

50
Q

What controls the extent of protein phosphorylation?

A

Kinases and phosphatases

51
Q

How does protein kinases modify proteins?

A

By attaching a phosphate to a serene, throning or tyrosine

52
Q

What do protein phosphates do?

A

They remove phosphates added by kinases

53
Q

What does phosphorylation in glycogen phosphorylase cause?

A

A conformation change

54
Q

What activates protein kinase A?

A

Protein kinase A

55
Q

How does protein kinase A activate cyclic AMP?

A

It alters the quaternary structure

56
Q

What causes protein kinase A to dissociates from the catalytic subunits?

A

cAMP binding to PKA’s regulatory (R) subunits

57
Q

What is Cushing’s syndrome?

A

A collection of diseases

58
Q

What does Cushing’s syndrom result from?

A

Excess secretion of cortisol by adrenal cortex

59
Q

What does unregulated excretion of cortisol cause?

A

Suppression of the immune system
Inhibition of bone growth

60
Q

What is zymogen?

A

The inactive precursor that is cleaved to form an active protease enzyme

61
Q

What is proprotein or proenzyme?

A

Precursors that are cleaved to form other proteins

62
Q

What are the 3 chains in chymotryosing linked together by?

A

Covalently linked by disulphide bridges

63
Q

How much of the pancreas is acing cells?

64
Q

Which cells in the pancreas produce hormones?

A

Endocrine cell

65
Q

What does acing cells do?

A

Store and secrete digestive enzymes

66
Q

Which digestive enzymes are secreted by the pancreas?

A

Amylase
Protease
Lipase
HCO3-

67
Q

What are many digestive enzymes stored as?

A

Inactive zymogens or proenzymes in secretory vesicles in the pancreas

68
Q

When are zymogens secreted?

A

Following a meal

69
Q

Where are zymogens secreted?

A

Pancreatic juice

70
Q

Where ar zymogens activated?

A

In the gastrointestinal tract

71
Q

What converts trypsinogen to active trypsin?

A

Enteropeptidase

72
Q

What does trypsin activate?

A

All the pancreatic zymogens

73
Q

What does pancreatic trypsin inhibitor protect against?

A

Premature activation of trypsin in the pancreas

74
Q

How does trypsin inhibitor work?

A

It binds so tightly to the active site that it cannot progress to the transition state

75
Q

What are neutrophil elastase secreted by?

A

Neutrophils

76
Q

When are neutrophil elastase secreted?

A

During inflammation

77
Q

What is elastase?

A

A serine protease

78
Q

What produces elastase?

79
Q

What can lack of enzyme inhibitors lead to?

A

Damage of connective tissue and more enzyme specific places (like pancreas or alveolar wall)

80
Q

What is methionine 358 essentail for binding?

Biochemistry (28 decks)

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