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Biochem > Chapter 12 > Flashcards

Chapter 12 Flashcards

1
Q

a reaction of overall stoichiometry A –> P where A represents reactants and P represents products, may actually occur through a sequence …. (simple molecular processes)

A

elementary rxns

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2
Q

descriptions of each elementary reaction collectively constitute the … description of the overall rxn process

A

mechanistic

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3
Q

at constant temp, the rate of an elementary rxn is proportional to the frequency with which the reacting molecules. the proportionality constant is known as a … and is symbolized k

A

come together; rate constant

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4
Q

for the elementary rxn A –> P the instantaneous rate of appearance/disappearance of reactant, which is called the … of the rxn, is v = k[A]

A

velocity

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5
Q

the … of an elementary rxn corresponds to the … of the rxn, which is the number of molecules that must simultaneously collide to generate a product

A

reaction order; molecularity

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6
Q

a first order elementary rxn is a … rxn

A

unimolecular

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7
Q

… rxn is a second order rxn with an instaneous velocity v = k[A]^2

A

bimolecular

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8
Q

… rxns are unusual bc of the simultaneous collision of three molecules is a rare event

A

termolecular

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9
Q

the time for half of the reactant initially present to decompose, its … or …, t1/2, is a constant and hence independent of the initial concentration of the reactant

A

half-time; half-life

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10
Q

the half time for a second order rxn is expressed … and therefore, in contrast to a first order rxn, depends on the …

A

t1/2 = 1/k[A]0; initial reactant []

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11
Q

… rxn: when the concentration of one reactant relative to another in a bimolecular rxn is so large that the concentration of the other is not substantial

A

pseudo-first-order rxn

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12
Q

all enzymes can be analyzed such that their rxn rates as well as their overall efficiency can be …

A

quantified

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13
Q

E + S –> ES –> P + E
according to this model, when the substrate concentration becomes high enough to entirely convert the enzyme to the ES form, the second step of the rxn becomes the … and the overall reaction rate becomes insensitive to further increases in …

A

rate limiting; substrate []

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14
Q

the michaelis-menten equation describes the rate of the enzymatic rxn as a function of …

A

substrate []

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15
Q

(michaelis-menten assumptions) …–> menten and michaelist assumed that k-1&raquo_space; k2, so that the first step of the rxn reaches equilibrium

….: with the exception of the initial stage of the rxn [ES] remains approximately constant until the substrate is nearly exhausted. in other words, it maintains a … and can be treated as having a constant value

A

assumption of equilibrium assumption of steady state

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16
Q

a reaction that achieves a steady state is not … –> [S] and [P[ are rapidly changing throughout the interval that [ES] is essentially constant

A

at equilibrium

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17
Q

the michaelis constant, Km, is defined as:

A

(k-1 + k2)/k1

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18
Q

expression for the initial velocity of the rxn (velocity at t = 0)
v0 =

A

(Vmax * [S])/ (KM + [S])

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19
Q

the maximal velocity of a rxn, Vmax, occurs at high substrate concentrations, when the enzyme is …, that is, when it is entirely in the ES form

A

saturated

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20
Q

Vmax =

A

k2 * [E]T

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21
Q

KM is the substrate concentration at which the rxn velocity is …

A

half-maximal

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22
Q

if an enzyme has a small value of Km, it achieves maximal catalytic efficiency at … substrate concentrations

A

low

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23
Q

Since Ks is the dissociation constant of the Michaelis complex, as Ks decreases, the enzyme’s affinity for substrate …

A

increases

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24
Q

we can define the catalytic constant, kcat, of an enzyme as:
Kcat = …

A

Vmax/[E]t

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25
Q

kcat is known as the … of an enzyme because it is the number of reaction processes (turnovers) that each active site catalyzes per unit time.

A

turnover number

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26
Q

the quantity … is a measure of an enzyme’s catalytic efficiency

A

kcat/Km

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27
Q

there is an upper limit to the value of kcat/Km; it can be no greater than …; that is the decomposition of ES to E + P can occur no more frequently than E and S come together to form ES. The most efficient enzymes have kcat/Km values near the … of 10^8 to 10^9 M^-1*s^-1

A

k1; diffusion-controlled limit

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28
Q

a better method for determining the values of Vmax and Km uses the reciprocal of the Michaelis-Menten equation –> … or … plot

A

Lineweaver-Burk; double-reciprocal plot

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29
Q

slope of Lineweaver burk is …, the 1/v0 intercept is …, and the extrapolated 1/[S] intercept is ..

A

Km/Vmax; 1/Vmax; -1/Km

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30
Q

the steady state kinetic analysis of a rxn cannot unambiguously establish its

A

mechanism

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31
Q

If kinetic data are not compatible with a given mechanism, then that mechanism must be …

A

rejected

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32
Q

Reactions in which all substrates must combine with the enzyme before a reaction can occur and products be released are known as …

A

sequential reactions

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33
Q

sequential reactions can be subclassified into those with a compulsory order of substrate addition to the enzyme, which are said to have an … mechanism, and those with no preference for the order of substrate addition, which are described as having a … mechanism

A

ordered; random

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34
Q

Group-transfer reactions in which one or more products are released before all substrates have been added are known as …

A

Ping Pong reactions.

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35
Q

note that in ping pong rxns, the substrates A and B do not … one another on the … of the enzyme

A

encounter; surface

36
Q

substances that reduce an enzyme’s activity by combining with it in a way that influences the binding of substrate and/or its turnover number are …

A

inhibitors

37
Q

irreversible enzyme inhibitors, or …, bind to the enzyme so tightly that they permanently block the enzyme’s activity

A

inactivators

38
Q

reversible enzyme inhibitors diminish an enzyme’s activity by interacting .. with it

A

reversibly

39
Q

a substance that competes directly with a normal substrate for an enzyme’s substrate-binding site is known as a …

A

competitive inhibitor

40
Q

competitive inhibitors usually resemble the … so that it specifically binds to the active site but differs from the substrate so that it cannot react as the substrate does.

A

substrate

41
Q

…: in this phenomenon, a product of the rxn, which necessarily is able to bind to the enzyme’s active site, may accumulate and compete with substrate for binding to the enzyme in subsequent catalytic cycles. this is one way in which the cell controls the activities of its enzymes

A

product inhibition

42
Q

…: Ki, the dissociation constant for enzyme-inhibitor binding)

A

inhibition constant

43
Q

… are particularly effective inhibitors.

A

transition state analogs

44
Q

several of the drugs used to block …, an essential enzyme for production of the human immunodeficiency virus, are compounds that were designed to mimic the enzyme’s transition state and bind to the enzyme with high affinity

A

HIV protease

45
Q

a competitive inhibitor reduces the concentration of … available for substrate binding

A

free enzyme

46
Q

michaelis-menten for when an inhibitor is present:

v0 =

A

(Vmax[S])/(aKm + [S])

47
Q

a in michaelis-menten is:

A

a = 1 + [I]/Ki

48
Q

… = a*Km, which is the apparent Km, that is, the Km value that would be measured in the absence of the knowledge that inhibitor is present

A

app

Km

49
Q

a is the factor by which … in order to overcome the effect of the presence of inhibitor

A

[S] must be increased

50
Q

as [S] approaches infinity, v0 approaches … for any concentration of inhibitor. the inhibitor does not affect the enzyme’s turnover number

A

Vmax

51
Q

competitive inhibition is the principle behind the use of … to treat methanol poisoning

A

ethanol

52
Q

in …, the inhibitor bind directly to the enzyme substrate complex but not to the free enzyme

A

uncompetitive inhibition

53
Q

the binding of uncompetitive inhibitor, which need not resemble substrate, presumably …, thereby rendering the enzyme catalytically inactive

A

distorts the active site

54
Q

uncompetitive inhibition requires that the inhibitor affect the … function of the enzyme but not its …

A

catalytic; substrate binding

55
Q

uncompetitive inhibition is significant only for … enzymes

A

multisubstrate

56
Q

…: many reversible inhibitors interact with the enzyme in a way that affects substrate binding as well as catalytic activity

A

mixed inhibition/noncompetitive inhibition

57
Q

a mixed inhibitor binds to enzyme sites that participate in both .. and ..

A

substrate binding; catalysis

58
Q

as in uncompetitive inhibition, the apparent values of … and … are modulated by the presence of inhibitor

A

Km and Vmax

59
Q

if the enzyme and enzyme substrate complex bind the inhibitor with equal affinity, then Km apparent is unchanged from the Km for the rxn in the absence of inhibitor. in this case, only Vmax is affected, a phenomenon that is named …

A

pure noncompetitive inhibition

60
Q

the kinetics of an enzyme inactivator (an irreversible inhibitor) resembles that of a … bc the inactivator reduces the concentration of functional enzyme at all substrate concentrations

A

pure noncompetitive inhibitor

61
Q

Double-reciprocal plots for mixed inhibition consist of lines that have the slope …, a 1/νo intercept of …, and a 1/[S] intercept of… (Fig. 12-10).

A

αKM/Vmax; α′/Vmax; −α′/αKM

62
Q

The lines for increasing values of [I] (representing increasing saturation of E and ES with I) intersect to the left of the … axis. For pure noncompetitive inhibition, the lines intersect on the 1/[S] axis at …. As with uncompetitive inhibition, substrate binding does not reverse the effects of mixed inhibition.

A

1/νo; −1/KM

63
Q

two ways control of catalytic activities may occur:
control of enzyme …: the amount of a given enzyme in a cell depends on both its … and its… each of these rates is directly controlled by the cell and is subject to dramatic changes over time spans of minutes (in bacteria) to hours (in higher organisms).

A

availability; rate of synthesis; rate of degradation;

64
Q

two ways control of catalytic activities may occur:
control of enzyme …; can be inhibited/modulated
an enzyme’s substrate-binding affinity may vary with the binding of small molecules, called … these mechanisms can cause large changes in enzymatic activity

A

activity; allosteric effectors

65
Q

the activities of many enzymes are controlled by …, usually phosphorylation and dephosphorylation of specific Ser, Thr, or Tyr residues

A

covalent modification

66
Q

aspartate transcarbamoylase from E. coli catalyzes the formation of … from … and ..

A

N-carbamoyl aspartate; carbamoyl phosphate; aspartate

67
Q

…: inhibits an earlier step in its own biosynthesis

A

feedback inhibitor

68
Q

for ATcase, the regulatory subunits allosterically reduce the activity of the … in in the intact enzyme

A

catalytic subunits

69
Q

for ATCase, the binding of substrate to one catalytic subunit increases the … and … of the other five catalytic subunits and accounts for the enzyme’s cooperative substrate binding

A

substrate-binding affinity; catalytic activity

70
Q

the activity of ATCase is increased by … and decreased by …, which alter the conformation of the catalytic sites by stabilizing the R and the T states of the enzyme, respectively

A

ATP; CTP

71
Q

the enzymatic activity of glycogen phosphorylase is controlled by its ../… as well as by the influence of …

A

phosphorylation; dephosphorylation; allosteric effectors

72
Q

phosphorylation/dephosphorylation modification/demodification processes are catalyzed by enzymes known as … and …

A

protein kinases; protein phosphatases

73
Q

glycogen phosphorylase catalyzes the … (bond cleavage by the substitution of a phosphate group) of glycogen to yield glucose-1-phosphate (G1P)

A

phosphorolysis

74
Q

mammals express three … (catalytically and structurally similar but genetically distinct enzymes from the same organism; also called …) of glycogen phosphorylase, those from muscle, brain and liver

A

isozymes; isoforms

75
Q

glycogen phosphorylase has two conformational states, the enzymatically active … state and the enzymatically inactive .. state.
the inactive state is so bc of the fact that it has a malformed active site and a surface loop that blocks substrate access to its binding site

A

R; T

76
Q

the phosphorylation of … promotes phosphorylase’s T –> R conformational change

A

Ser 14

77
Q

… and … (to which the G1P product of the glycogen phosphorylase rxn is converted preferentially bind to the T state of phophorylase b and inactivate the enzyme whereas …preferentially binds to the r state of phosphorylase b and activates it

A

ATP; glucose-6-phosphate (G6P); AMP

78
Q

the Ser 14 phosphate group of glycogen phosphorylase functions as a sort of internal … that shifts the enzymes T R equilibrium in favor of the …state

A

allosteric effector; R

79
Q

the enzymes that catalyze the phosphorylation and dephosphorylation of glycogen phosphorylase are … and …

A

phosphorylase kinase; phosphoprotein phosphatase

80
Q

a drug candidate that exhibits a desired effect is called a …
a good one binds to its target protein with a dissociation constant of less than 1 micromolar

A

lead compound

81
Q

a lead compound is used as a point of … to design more efficacious compounds

A

departure

82
Q

besides causing the desired response in its isolated target protein, a useful drug must be delivered in sufficiently … to this protein where it resides in the human body

A

high concentration

83
Q

the most effective drugs are usually a compromise; they are neither too … nor too ..

A

lipophilic; hydrophilic

84
Q

differences in rxns to drugs arise from … among individuals as well as differences in their …, other drugs they are taking, age, sex, and environmental factors

A

genetic differences; disease states

85
Q

drug-drug interactions are often mediated by …

A

cytochromes P450

86
Q

an … can be developed for use as a drug through structure-based and/or combinatorial methods. it must then be tested for safety and efficacy in clinical trials

A

enzyme inhibitor

Biochem (23 decks)

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