lecture 19 Flashcards

1
Q

in normal situations does the Km change?

A

no, only the Vmax can be increased by adding more enzyme concentration.

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2
Q

What does a low Km mean?

A

This reflects a high affinity of the enzyme for the substrate

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3
Q

What does a high Km mean?

A

This means that their is a low affinity of the enzyme for the substrate

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4
Q

What are the two kinds of reversible inhibition?

A

competitive and non-competitive

bind non-covalently

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5
Q

What is a competitive inhibitor?

A

is a structural analog of the substrate that competes
with the substrate for the binding to the active site of
the enzyme.

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6
Q

Example of a competitive inhibitor?

A

statin drug that competitively inhibits HMG CoA reductase which is the regulated enzyme of cholesterol synthesis.

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7
Q

how does a competitive inhibitor impact the M-M graph?

A

It increases the Km, but does not impact the Vmax

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8
Q

How does a non-competitive inhibitor impact the M-M graph

A

Does not change the Km but decreases the Vmax

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9
Q

How is the lineweaver-burk different from the M-M graph?

A
  1. It is a straight line…. instead of a hyperbolic curve
  2. dont need as many data points (less money)
  3. Vmax is mathematically obtained, instead of estimated
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10
Q

Why are some inhibitors irreversible?

A

The drug or poison will bind covalently to the enzyme

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11
Q

how to reverse irreversible inhibitors

A

The enzyme must be degraded and a new enzyme must be made

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12
Q

What leads to irreversible inhibition?

A
  1. modification of the active site
  2. blocking the sulfhydryl-group enzyme
  3. interfere with metal cofactor
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13
Q

Explain DFP (di-isopropyl flourophosphate)

A

it is an irreversible inhibitor of acetylcholinesterase

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14
Q

What symptoms does DFP poisoning have?

A

It leads to an accumulation of acetylcholine thus:

  1. blurred vision
  2. bronchoconstriction
  3. seizures
  4. respiratory arrest and death
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15
Q

How does DFP inhibit acetylcholinesterase?

A

The poison blocks a specific serine that forms normally a covalent bond with the acetyl group during catalysis.

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16
Q

What kind of inhibitor is aspirin?

A

irreversible inhibitor

17
Q

What does aspirin inhibit?

A

COX-1 and COX-2

cyclooxygenase enzyme

18
Q

What is aspirin used for?

A

300-500 mg pain relief

81 mg for reduced blood clotting

19
Q

How is COX involved in blood clotting?

A

Thromboxane and prostacycin are involved in blood clotting

Throm- more blood clotting

prosta- less blood clotting

20
Q

What does a low dose of aspirin do exactly?

A

It inhibits the COX genes in both epithelial cells and platelets

platelets cannot synthesize new COX, thus less thromboxane is made

21
Q

What are suicide inhibitor drugs?

A

the enzyme itself changes the structure of the drug resulting in an irreversible inhibitor

22
Q

What is an example of a suicide inhibitor drug?

A

Allopurinol

23
Q

What does allopurinol do?

A

Xanthine oxidase uses the drug allopurinol instead of hypoxanthine as substrate and forms the irreversible inhibitor drug alloxanthine.

Alloxanthine (oxypurinol) binds irreversibly to the active site of xanthine oxidase and reduces the formation of uric acid

24
Q

What does allopurinol treat?

A

Gout