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Isaak: Biochemistry MBS > Lecture 11: Enzyme Regulation > Flashcards

Lecture 11: Enzyme Regulation Flashcards

1
Q

Elevated enzyme levels in the blood can indicate what?

A

Tissue damage.

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2
Q

What enzyme is used to measure liver disease?

A

ALT, or alanine transferase.

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3
Q

What enzyme is used to measure lung damage?

A

α-1 antitrypsin

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4
Q

Zymogen

A

Inactive protein (or enzyme) precursors.

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5
Q

How are zymogens activated?

A

Proteolytic cleavage.

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6
Q

In the blood coagulation cascade, what zymogen is activated and what does it become?

A

Prothrombin —> thrombin.

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7
Q

True or false?

The two proteolytic cleavages of thrombin are reversible.

A

False.

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8
Q

What is the role of gamma carboxylation of glutamate residues on prothrombin?

A

This modification of prothrombin allows the binding of Ca 2+.

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9
Q

What is the role of Ca 2+ in the maturation of prothrombin to thrombin?

A

Ca 2+ binding to prothrombin allows it to expose its hydrophobic portion in order to associate with the cell membrane.

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10
Q

Why does prothrombin need to associate with the cell membrane in order to mature?

A

The protease that activates prothrombin to thrombin exists on the cell membrane.

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11
Q

What happens to prothrombin once it is cleaved by the membrane-bound protease?

A

It is release from the membrane so it can then exert its effects.

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12
Q

Once released from the membrane, how does thrombin exert its effects?

A

It exerts its effects through catalyzing the conversion of SOLUBLE fibrinogen into INSOLUBLE fibrin, which ultimately begins to clot.

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13
Q

(Fibrinogen/Fibrin) is insoluble.

A

Fibrin.

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14
Q

(Fibrinogen/Fibrin) is soluble.

A

Fibrinogen.

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15
Q

True or false?

Gamma carboxylation is a post-translation modification that regulates enzyme activity.

A

False.

It does not regulate enzyme activity, but is instead required for formation of the active enzyme for blood coagulation.

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16
Q

What is the co-factor required for gamma carboxylation of prothrombin?

A

Vitamin K.

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17
Q

Although zymogen activation is efficient, it is _______.

A

Irreversible.

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18
Q

How is thrombin inactivated?

A

Through the high-affinity binding of antithrombin.

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19
Q

Antithrombin

A

Binds to thrombin with very high affinity, serving to eliminate its ability to catalyze further blood clotting in the blood clotting cascade.

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20
Q

In what example tissue is the importance of enzyme activation demonstrated?

A

The lungs.

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21
Q

What type of enzyme is elastase?

A

A serine protease.

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22
Q

What protein does elastase degrade?

A

Elastase.

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23
Q

What is the etiology of emphysema?

A

The unregulated degradation of elastin by elastase in the lungs due to a dysfunctional a-1-antitrypsin, an inhibitor of elastase.

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24
Q

What cells release elastase and why?

A

Neutrophils release elastase in order to degrade foreign particles.

25
Q

In what patients would one expect to find a-1-antitrypsin mutations?

A

Homozygous individuals who carry two defective genes and heavy smokers.

26
Q

What is the treatment for a-1-antitrypsin deficiency?

A

Infusion of a-1-antitrypsin, though it is highly expensive.

27
Q

Where is a-1-antitrypsin normally secreted from?

A

The liver into the blood stream.

28
Q

What are two common mechanisms of enzyme regulation?

A

Phosphorylation and methylation.

29
Q

A phosphorylating enzyme.

A

Kinase.

30
Q

A dephosphorylating enzyme.

A

Phosphatase.

31
Q

What are the residues that kinases and phosphatases act upon?

A
  1. Serine
  2. Threonine
  3. Tyrosine
32
Q

Specifically, how do phosphorylation and dephosphorylation change the activity of an enzyme?

A

They change the charge of an amino acid, which, if near the active site, can change it’s activity dramatically.

33
Q

Half of commonly prescribed drugs are ______ ______.

A

Enzyme inhibitors.

34
Q

True or false?

Competitive inhibitors are irreversible.

A

False.

They are reversible and can be overcome by increasing [substrate].

35
Q

True or false?

Competitive inhibitors usually resemble the enzyme’s normal substrate.

A

True.

36
Q

Ki

A

k2 (E + I EI)

37
Q

The smaller the Ki, the greater the _______.

A

Effectiveness of the inhibitor.

38
Q

The less effective the inhibitor is, the ______ .

A

Greater the Ki.

39
Q

In regards to Michaelis-Menten enzyme kinetics, competitive inhibitors alter _____, but not _____.

A

Km, but not Vmax.

40
Q

True or false?

Non-competitive inhibitors usually resemble the enzyme’s normal substrate.

A

False.

They often do not bear any resemblance to the enzyme’s normal substrate.

41
Q

Where and when do non-competitive inhibitors bind?

A

They bind to a location other than the active site, irrespective of whether substrate is present or not.

42
Q

In regards to Michaelis-Menten enzyme kinetics, non-competitive inhibitors alter _____, but not _____.

A

Vmax, but not Km.

43
Q

True or false?

Non-competitive inhibition can be overcome by increasing [substrate].

A

False.

No matter how much substrate is added, the inhibition cannot be overcome. It is not about competition for the active site.

44
Q

What are the two types of non-competitive inhibitors?

A

Reversible and irreversible.

45
Q

What are two examples of irreversible non-competitive inhibitors?

A
  1. a-1-antitrypsin

2. antithrombin

46
Q

What is DIFP and what is its clinical significance?

A

Diisopropyl fluorophosphate.

This is a chemical poison (used as a component in mustard gas) that is an irreversible inhibitor of serine proteases.

In nerve cells, acetylcholinesterase is not degraded normally, resulting in interneuron communication disruption due to increased [acetylcholine].

47
Q

In regards to irreversible non-competitive inhibition, what does the half-life of its effect have to do with?

A

The time of re-synthesis of new proteins/enzymes.

48
Q

Many enzymes have [substrate] in the range of their _______, where they are most effective.

A

Km.

49
Q

What is product inhibition?

A

Where the product of the enzyme-catalyzed reaction inhibits that specific enzyme.

50
Q

What enzyme is an example of a product-inhibition?

A

Hexokinase. (Glucose + ATP —-> Glucose-6-phosphate

51
Q

Allosteric Enzyme

A

These enzymes change their activity from binding an effector, which may be another substrate molecule or a different effector molecule.

52
Q

Allosteric enzymes alternate between what two different conformations?

A

Relaxed and constrained.

53
Q

Binding of substrate to an allosteric enzyme increases the likelihood that it will enter its _____ conformation.

A

Relaxed.

54
Q

Allosteric enzymes can have multiple subunits that work together in a cooperative fashion.

On a velocity vs. [substrate] graph, what kind of shape would one of these enzymes assume?

A

Sigmoidal, as in that of hemoglobin.

55
Q

Positive Effector

A

Activator; promotes relaxed conformation.

56
Q

Negative Effector

A

Inhibitor; promotes constrained conformation.

57
Q

Why would allosteric enzymes be the enzyme to catalyze the first step of a reaction sequence?

A

They are easily regulated, especially by their own products, products later on in the reaction sequence, or substrates in related sequences.

58
Q

What is feedback inhibition?

A

When enzyme is inhibited by a substrate down the reaction sequence.

59
Q

What three things can normally be said about the first committed step in any given pathway?

A
  1. It is functionally irreversible.
  2. It is early in the pathway.
  3. It is committed solely to one pathway.

Isaak: Biochemistry MBS (11 decks)

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