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MCAT > Enzymes > Flashcards

Enzymes Flashcards

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MCAT flashcards
1
Q

What is enzyme specificity?

A

A given enzyme will only catalyze a single reaction or class of reactions with these substrates

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2
Q

Oxidoreductases

A

Enzymes that catalyze oxidation-reduction reactions - transfer of electrons between biological molecules

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3
Q

What cofactor do many oxidoreductases have?

A

One that acts as an electron carrier - NAD+ or NADP+

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4
Q

Reductant

A

Electron donor

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5
Q

Oxidant

A

Electron acceptor

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6
Q

What class of enzymes does a dehydrogenase fall within?

A

Oxidoreductase

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7
Q

What class of enzymes does a reductase fall within?

A

Oxidoreductase

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8
Q

Transferases

A

Enzymes that catalyze the movement of a functional group from one molecule to another

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9
Q

What class of enzymes does a kinase fall within?

A

Transferase

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10
Q

What do kinases do?

A

Catalyze the transfer of a phosphate group (usually from ATP) to another molecule

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11
Q

Hydrolases

A

Enzymes that catalyze the breaking of a compound into two molecules using the addition of water

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12
Q

What class of enzymes does a nuclease fall within?

A

Hydrolase

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13
Q

What class of enzymes does a phosphatase fall within?

A

Hydrolase

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14
Q

Lysases

A

Enzymes that catalyze the cleavage of a single molecule into two products WITHOUT the use of water as a substrate

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15
Q

What is a lysase often called when catalyzing its reverse reaction?

A

Synthase

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16
Q

Isomerase

A

Enzyme that catalyzes the rearrangement of bonds within a molecule

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17
Q

Ligases

A

Enzyme that catalyzes addition or synthesis reactions, generally between large, similar molecules, often requiring ATP

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18
Q

What class of enzymes would catalyze the synthesis of small molecules?

A

Lysase

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19
Q

What class of enzymes would catalyze the synthesis of large molecules?

A

Ligase

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20
Q

What type of molecules are cofactors typically?

A

Inorganic or metal ions

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21
Q

How does the body obtain cofactors?

A

Diet

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22
Q

What type of molecules are coenzymes typically?

A

Small organic groups

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23
Q

How does the body obtain coenzymes?

A

Vitamins

24
Q

Prosthetic groups

A

Cofactors or coenzymes that are tightly bound to an enzyme and are necessary for enzyme function

25
Q

Apoenzymes

A

Enzyme without its cofactor

26
Q

Holoenzymes

A

Enzyme with its cofactor

27
Q

Enzyme saturation

A

No active sites are left and reaction cannot go any faster

28
Q

How can Vmax be increased?

A

Adding more enzyme

29
Q

Describe Michaelis-Menten Plot

A

x axis has substrate concentration
y axis has reaction velocity
Km is the substrate concentration at half of Vmax
Slope increases and then reaches Vmax

30
Q

Michaelis-Menten Equation

A

v=(Vmax[S])/(Km+[S])

31
Q

When comparing two enzymes, does a higher Km suggest a higher or lower enzyme affinity?

A

Lower - requires more substrate to reach half-saturated

32
Q

Describe Lineweaver-Burk Polot

A 
Double reciprocal of Michaelis-Menten Plot
x axis is 1/[S]
y axis is 1/v
x-intercept is 1/Km
y-intercept is 1/Vmax
33
Q

How does enzyme cooperativity affect the Michaelis-Menten Plot?

A

Becomes sigmoidal - Substrate binding encourages change in shape from tense to relax, further improving enzyme affinity for substrate

34
Q

Hill’s coefficient

A

Numerical quantification of cooperativity

35
Q

Hill coefficient >1

A

Positive cooperation - binding of substrate improves enzyme affinity for more substrate

36
Q

Hill coefficient <1

A

Negative cooperation - binding of substrate decreases enzyme affinity for more substrate

37
Q

Hill coefficient =1

A

Enzyme does not exhibit cooperative binding

38
Q

What are the four types of reversible enzyme inhibition?

A

Competitive
Non-competitive
Mixed
Uncompetitive

39
Q

What occurs to the enzyme in competitive inhibition?

A

Inhibitor binds to the active site

40
Q

How is competitive inhibition overcome?

A

Add more substrate

41
Q

Does competitive inhibition change Vmax and why?

A

No - if enough substrate is added it will still run at maximum velocity

42
Q

Does competitive inhibition change Km and why?

A

Yes - more substrate will be needed to reach half of Vmax

43
Q

What occurs to the enzyme in noncompetitive inhibition?

A

Inhibitor binds to an allosteric site and induces a change in enzyme conformation (can bind either enzyme or enzyme-substrate complex with same affinity)

44
Q

Does noncompetitive inhibition change Vmax and why?

A

Yes - lowers it because there is less enzyme available to react

45
Q

Does noncompetitive inhibition change Km and why?

A

No - the noncompetitive inhibitor does not change the affinity for substrate and adding more will not change the reaction

46
Q

Allosteric site of an enzyme

A

Non-catalytic site that binds regulators

47
Q

What occurs to the enzyme in mixed inhibition?

A

Inhibitor can bind either the enzyme or enzyme-substrate complex with different affinities

48
Q

Does mixed inhibition change Vmax and why?

A

Yes - lowers it because there is less enzyme available to react

49
Q

Does mixed inhibition change Km and why?

A

Yes - it raises Km if it preferentially binds to the enzyme and it lowers Km if it preferentially binds to the enzyme-substrate complex

50
Q

What is similar and different about noncompetitive and mixed inhibitors?

A

Both can bind to both the enzyme alone and the enzyme-substrate complex. Noncompetitive have the same affinity for both while mixed have different affinities

51
Q

What occurs to the enzyme in uncompetitive inhibition?

A

Inhibitor binds to allosteric site only to enzyme-substrate complex and locks the substrate into the enzyme

52
Q

Does uncompetitive inhibition change Vmax and why?

A

Yes - lowers it because reaction cannot reach full speed

53
Q

Does uncompetitive inhibition change Km and why?

A

Yes - lowers it because technically increases enzyme affinity by keeping substrate locked into enzyme

54
Q

When is irreversible inhibition most applicable?

A

Drugs / medications - irreversibly bind to enzymes that modulate pain or inflammatory pathways, for example

55
Q

Allosteric enzymes

A

Have multiple binding sites and alternate between an active and inactive form

56
Q

What are examples of covalent enzyme modifications?

A

Phosphorylation, glycosylation

57
Q

Zymogens

A

Inactive forms of very dangerous enzymes such as apoptotic or strong digestive enzymes that contain an active and regulatory domain - the regulatory domain must be altered to expose the active site

MCAT (31 decks)

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