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Biochem 1 (WPH) > Enzymes 2 - kinetics Spencer > Flashcards

Enzymes 2 - kinetics Spencer Flashcards

1
Q

chemical kinetics is the study of…

A

rates of chemical reactions

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2
Q

enzyme kinetics is the study of…

A

rates of enzyme catalyzed reactions

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3
Q

A -> P
what is the rate v
what is the order
what are the units of the rate constant

A

v = ∆P / dt = -∆A / dt = k[A]
1st order rxn
k = s^-1

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4
Q

what are the units of reaction rate, or velocity v

A

M/s

moles per second

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5
Q

A + B -> P
what is the rate v
what is the order
what are the units of the rate constant

A 
v = ∆P/dt = -∆A/dt = -∆B/dt = k[A][B]
2nd order (1st in A, 1st in B)
k = M^-1 s^-1
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6
Q 
A = P
what is the rate v
what is the order
what are the units of the rate constant
equilibrium constant
A

v = ∆P / dt = -∆A / dt = k1[A] - k2[P]
1st order rxn
k = s^-1
Keq = k1/k2 = [P]/[A]

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7
Q

what is the equilibrium constant for a reversible reaction

A

Keq = [products]/[reactants]

= kforward/kreverse

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8
Q

for 1-substrate enzyme kinetics, what do the following graphs look like
[P] vs t
v0 vs [S]

A
  • [P] vs t is hyperbolic, with slope (v0) initially linear, and greater [P] plateaus with greater [S]initial
  • v0 vs [S] is hyperbolic
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9
Q

what is the general reaction equation for michelis-menten kinetics

A

k1 k3
E + S ES -> E + P
k2

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10
Q

what is the michelis constant

A

Km = (k2+k3)/k1

when [S] = Km, v0 = .5Vm

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11
Q

michelis menten equation

A

v0 = Vm [S] / Km + [S]

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12
Q

what are 5 assumptions of michelis-menten kinetics

A
  • t = 0 (initial velocities only)
  • k4 = 0 at t ~ 0 (no back reaction from P)
  • negligible S depletion [S]&raquo_space; [E]
  • ES complex formed
  • [ES] is at steady state
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13
Q

[S]&raquo_space; Km, v0 =

A

v0 = Vm = k3[E]t
all active sites saturated
zero order… v0 independent of S

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14
Q

[S] = Km, v0 =

A

v0 = 1/2 Vm

50% active sites filled

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15
Q

[S] &laquo_space;Km, v0 =

A

v0 = VmS / Km = k3EtS / Km

v0 is proportional to [S]

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16
Q

Vm =

A

k3[E]t
all active sites saturated
zero order… v0 independent of S

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17
Q

what are the units of a first order rate constant

A

s^-1

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18
Q

what are the units of a second order rate constant

A

M^-1 s^-1

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19
Q

michelis-menten Kd =

A

k2/k1 = [reactants]/[products] = [E][S]/[ES]

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20
Q

Km = Kd when…

A

k2&raquo_space; k3

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21
Q

how can you increase Vm?

A

increase [E]t

Vm = k3Et

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22
Q

mechelis-menten kcat =

A

k3

catalytic ability of the enzyme

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23
Q

michelis-menten turnover number =

A

kcat = k3

catalytic ability of the enzyme

24
Q

the catalytic ability of a michelis-menten enzyme =

A

kcat = k3 = turnover number

25
Q

catalytic efficiency =

A

kcat / Km

~ how well enzyme reacts with substrate

26
Q

Km is a measure of…

A

the strength of the ES interaction

27
Q

what is the catalytic efficiency of a “perfect enzyme” ?

A

10^8 to 10^9

limited only by rate of diffusion

28
Q

what does the v0 vs [S] plot look like for a michelis-menten enzyme?

A

hyperbolic

29
Q

how can you linearize the michelis-menten equaiton?

A

take the inverse

1/v0 = Km/Vm x 1/[S] + 1/Vm

30
Q

lineweaver-burke equation

A

1/v0 = Km/Vm x 1/[S] + 1/Vm

31
Q

y-axis on lineweaver-burke plot =

A

1/v0

32
Q

x-axis on lineweaver-burke plot =

A

1/[S]

33
Q

slope on lineweaver-burke plot =

A

Km/Vm

34
Q

y-intercept on lineweaver-burke plot =

A

1/Vm

35
Q

x-intercept on lineweaver-burke plot =

A

-1/Km

36
Q

reactions with same lineweaver-burke slope…

A

have same Km/Vm (same catalytic efficiency)

37
Q

how can you tell catalytic efficiency from a lineweaver-burke plot?

A

smaller slope = greater catalytic efficiency

slope = Km/Vm ~ the inverse of kcat / Vm

38
Q

reactions with same lineweaver-burke x-intercept

A

same Km

39
Q

reactions with same lineweaver-burke y-intercept

A

same Vm

40
Q

advantage of lineweaver-burke plot

A

can easily compare Vm, Km, and Km/Vm

41
Q

lineweaver-burke plot does not work well for…

A

low or high [S]

distorts errors

42
Q

if 2 enzymes have same catalytic efficiency kcat/Km, do you pick the one with higher kcat or lower Km?

A

the one with higher kcat (don’t know why, spencer just says)

43
Q

2 mechanisms of bi-substrate reactions

A

sequential

ping-pong

44
Q

2 types of sequential bi-substrate reactions

A

ordered sequential

random sequential

45
Q

how does a sequential bi-substrate reaction work?

A

all substrates are bound before any products are released

46
Q

how does an ordered sequential bi-substrate reaction work?

A

E always binds substrate A, then B, then transformation occurs (EAB -> EPQ), then release of P, then Q, left with E

47
Q

how many rate constants are involved in a sequential bi-substrate reaciton?

A

10 (5 forward, 5 back)

k1 through 5 and k-1 through -5

48
Q

howehow does a random sequential bi-substrate reaction work?

A

E can bind A or B first and release P or Q first, order does not matter

49
Q

how does a ping-pong bi-substrate reaction work?

A

E + A = EA = FP = F + P

F + B = FB = EQ = E + Q

50
Q

which bi-substrate reaction mechanism is characterized by a substituded enzyme intermediate, sequential or ping-pong mechanism?

A 
ping-pong
E +A = EA = FP = F + P
F + B = FB = EQ = E + Q
vs
E+A = EA+B = EAB = EPQ = EQ+P = E+Q
51
Q

what is the catalytic efficiency of a “perfect enzyme” ?

A

k1
because
Km perfect = kcat/k1 (no k2)
so k1 = kcat/Km = catalytic efficiency

52
Q

what are the units of Km?

A

M

53
Q

in kinetics, what is the difference between K and k?

A

K units are M = [products] / [reactants]

k units are s^-1 or M^-1 s^-1 etc = rate

54
Q

what are the units of kcat?

A

s^-1

55
Q

what are the units of Ki?

A

M

56
Q

what are the units of k1?

A

M^-1 s^-1

Biochem 1 (WPH) (15 decks)

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