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Biochemistry I/II > Lecture 3: Regulation and Inhibition of Enzymes > Flashcards

Lecture 3: Regulation and Inhibition of Enzymes Flashcards

1
Q

___ bind substrate(s), increase rate of reaction, and are NOT consumed during reaction

A

Enzymes

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2
Q

____: Special pocket formed by protein folding that contains amino acids that participate in substrate binding and catalysis, which chemically facilitates a reaction

A

Active Site

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3
Q

_____forms upon binding of substrate to the enzyme and leads to conformation change

A

Enzyme-substrate (ES) complex

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4
Q

The ___ changes shape slightly as substrate binds

A

Enzyme

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5
Q

Kcat (_____) = molecules substrate converted to
product(s) per molecule enzyme per second

A

Turnover number

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6
Q

True or False: Enzymes have
catalytic efficiency and specificity

A

True

(enzymes usually interact with one or very few substrates and catalyze only
one type of reaction = specificity)

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7
Q

_____:non-protein molecules that enhance
enzyme activity

A

Co-factor/Co-enzyme

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8
Q

Zinc or iron is an example of a ____while small organic molecule derived from vitamins (NAD+) are examples of ____

A

cofactor; coenzyme

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9
Q

___: an active enzyme associated with its non-protein
component

____: inactive enzyme without its non-protein component

A

Holoenzyme

Apoenzyme

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10
Q

Enzymes provide a more energetically favorable path from reactants to
products by lowering the ______ barrier

A

activation energy

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11
Q

True or False; Each reaction has an activation energy barrier separating the substrates (reactants) and the products

A

True

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12
Q

____: energy difference
between reactants and transition state

A

Free energy of activation

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13
Q

_____: high-energy intermediate formed
prior to product formation

A

Transition state (T*)

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14
Q

Enzymes ↓ free energy of activation required to reach ___

A

Transition state (T*)

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15
Q

True or False: Free energy of overall reaction (ΔG) is unchanged when enzyme acts on a reaction

A

True

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16
Q

True or False: There is a difference in the free energy of the overall reaction (energy of reactants - energy of products) between the catalyzed and uncatalyzed reaction

A

False - there is NO difference in the free energy

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17
Q

A ____ ⇆ T* (high-energy intermediate) ⇆ B (product)

A

A (substrate)

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18
Q

A reaction occurs if molecules contain enough ___ to overcome the energy
barrier to achieve T*

A

energy

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19
Q

Reaction _____ is determined by # of molecules that have sufficient
energy to overcome the barrier

A

rate or velocity

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20
Q

True or False: If free energy of activation is low: less molecules have enough energy to reach T* and reaction proceeds more slowly

A

False - If free energy of activation is low: MORE molecules have enough energy to reach T* and reaction proceeds more quickly

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21
Q

Why do enzymatic reactions have a more rapid reaction rate?

A

1) Enzyme provide an alternate reaction pathway
2) lower free energy of activation
3) more molecules possess enough energy to overcome barrier

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22
Q

An enzyme’s ____ is a complex molecular machine that facilitates
conversion of substrate into product

A

active site

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23
Q

Substrate binds and initiates conversion into ___

A

Substrate binds and initiates conversion into T*

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24
Q
A
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25
Q

What do amino acid residues at the active site do?

A
  1. Donate or accept protons
  2. Hydrogen bonding to promote T state formation
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26
Q

True or False: Enzymes are usually least responsive to changes in [S]

A

False - Enzymes are usually most responsive to changes in [S]

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27
Q

_____: # of substrate molecules converted to product per unit of time when enzyme levels are constant

A

Rate or velocity (V) of enzymatic reactions

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28
Q

What three factors influence enzymatic reaction velocity?

A
  • substrate concentration [S]
  • Temperature
  • pH
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29
Q

With constant [E], reaction rate increases with ↑[S] until reaching ___

A

Vmax (max velocity)

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30
Q

High [S] eventually leads to ____ of all binding sites on enzymes, which causes
______ to level off

A

saturation; reaction rate

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31
Q

True or False: Once Vmax is reached, reaction rate increases with addition
of more substrate

A

Once Vmax is reached, reaction rate does NOT increase with addition
of more substrate

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32
Q

True or False: Increasing temperature generally increases the rate of a reaction

A

True

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33
Q

What happens to enzymes at extremely high or low pH?

A

Enzyme denatured
and no longer functional

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34
Q

An abnormal pH affects functionality of amino acids located in the active site and lowers what variable?

A

Vmax

35
Q
A

Michaelis-Menten kinetics

36
Q

Enzymes following Michaelis-Menten Kinetics show a ____ curve. Allosteric enzymes show a ___ curve

A

hyperbolic; sigmoid

37
Q

___: describes how reaction velocity varies with [S]

A

Michaelis-Menten Kinetics

38
Q

True or False: Enzyme (E) reversible combines with substrate (S) to form an enzyme-
substrate (ES) complex, which yields a product.

Free energy is generated.

A
39
Q

What assumption does MM-Kinetics make?

A

1) [S]&raquo_space; [E]
2) rate of ES formation = rate of ES breakdown

40
Q

MM Equation?

A
41
Q
A
42
Q

Km =

A

[S] at ½ Vmax

43
Q

Km demonstrates the affinity of enzyme for _____

A

substrate

44
Q

Small Km means ___ affinity of enzyme for substrate and ___ [S] needed to reach Vmax

A

high; low

45
Q

Large Km means ___ affinity of enzyme for substrate and __ [S] needed to reach Vmax

A

low; high

46
Q
A
47
Q
A
48
Q

For Lineweaver burk plot:

A
49
Q

If an inhibitor is covalently bound to enzyme, preventing it from interacting with S and resulting in “loss” of enzyme activity (i.e., lead poisoning), it is likely to be what type of inhibitor?

A

Irreversible Inhibitor

50
Q

True or False: Reversible inhibitors use non-covalent binding with enzyme, which allows for recovery of enzyme

A

True

51
Q

What are the two types of reversible inhibitors?

A

-Competitive
-Noncompetitive

52
Q

Why are competitive inhibitors called “competitive”

A

They bind to SAME site as substrate – in that way, then, they compete with S to bind enzyme’s active site

53
Q
A
54
Q

How does a competitive inhibitor affect…
-Km apparent?
-Vmax?

A

Vmax = unchanged
Km apparent = increased

55
Q

True or False: Statin drugs (like: Pravastin) are examples of non-competitive inhibitors?

A

False - Statin drugs (like: Pravastin) are examples of competitive inhibitors

56
Q

Statin drugs inhibit rate-limiting step in ______
(HMG CoA => Mevalonic Acid)

A

cholesterol biosynthesis

57
Q

Statin drugs compete with substrate HMG-CoA for
binding to _____

A

HMG CoA-reductase

58
Q

What type of inhibitor bind to different sites than the substrate and prevents an enzymatic reaction from occurring?

A

Non-competitive inhibitor

59
Q

How is it possible that non-competitive inhibitors can bind to either: a free enzyme or the ES complex?

A

The inhibitor binds to a different place than the substrate

60
Q
A
61
Q

How do non-competitive inhibitors affect….
-Km?
-Apparent Vmax?

A

Km = unchanged
Apparent Vmax = decreased

62
Q

True or False: For non-competitive inhibitors, large quantities of substrate CAN overcome
inhibition

A

False - for non-competitive inhibitors, even large quantities of substrate cannot overcome inhibition

63
Q
A
64
Q

What type of inhibitors are Penicillin and Amoxicillin?

Mechanism of action?

A

Irreversible Inhibitors

Inhibition of bacterial cell wall synthesis

65
Q

What type of inhibitors are ACE inhibitors (captopril, enalapril, and lisinopril)?

A

Reversible Competitive Inhibitors

66
Q

NSAIDs are all ____inhibitors. However: acetylsalicylic acid (aspirin) is ____while ibuprofen is _____

A

competitive
irreversible
reversible

67
Q

True or False: Increase [S] increases reaction rate/velocity

A

True

68
Q

Other mechanisms (3) involved in regulating enzyme activity?

A

1) Allosteric regulation
2) Covalent modification
3) Induction/repression of enzyme synthesis

69
Q

True or False: Allosteric enzymes usually contain only one subunit and catalyze the last step in a pathway

A

False - allosteric enzymes
often contain multiple subunits and frequently catalyze the committed, rate-limiting step in a pathway

70
Q

True or False: Allosteric enzymes do not follow M-M kinetics

A

True (makes a sigmoidal curve)

71
Q

What type of molecules regulate allosteric enzymes?

A

Effector molecules

72
Q

_____: bind noncovalently at a site other than active site

A

Effector molecules

73
Q

What type of effector reduces or inhibits enzyme activity?

What type of effector stimulates or increases enzyme activity?

A

Negative effector
Positive effector

74
Q

What can effectors modify?

A

1) Vmax
2) Affinity of enzyme for S (K0.5)
3) or both

75
Q

Homotropic effector are usually ___ effectors

A

Positive

76
Q

Binding of substrate at allosteric site enhances activity at substrate-
binding site. This is known as ____

A

cooperativity

77
Q

For a homotropic effector, what type of curve is visible? Why?

A

Sigmoidal curve

1) higher [S] initially
needed for reaction to proceed
2) substrate must bind at two different sites

78
Q

True or False: In homotropic effectors, substrate = effector

A

True

79
Q

True or False: In a heterotropic effector, substrate does not equal effector

A

True

80
Q

____: downstream product in pathway
serves as effector for an enzyme required in an upstream reaction

A

Feedback Inhibition

81
Q

An example of covalent modifications is: phosphorylation of specific ___, ___, or ____ residues:

A

Ser, Thr or Tyr

82
Q

True or False: Phosphorylation only inhibits its target

A

False - phosphorylation may activate or inhibit its target enzyme

83
Q

What are two ways to induce/repress enzyme synthesis?

A

1) Change rate of synthesis or degradation of enzyme
2) Slow mode of regulation (hours to days)

84
Q

True or False: Allosteric and covalent modifications are slower

A

False - they are more rapid!(seconds to minutes)

Biochemistry I/II (23 decks)

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