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Bcem 341 > Lecture 12/13: Enzyme kinectics/Allosteric enzymes > Flashcards

Lecture 12/13: Enzyme kinectics/Allosteric enzymes Flashcards

1
Q

a first order reaction

A

there is only a single reactant
A → B.

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2
Q

rate of first order reaction

A

A → B

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3
Q

Units for first-order rate constants, K are …

A

s^-1

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4
Q

second order reaction

A

there are two reactants
A + B → products

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5
Q

rate of second order reaction

A

v = k[A][B]

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6
Q

Units for second-order rate constant (K)

A

M^-1s^-1

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7
Q

What determines the rate of a
reaction?

A

The height of the energy barrier, ∆Go‡, determines the rate of the reaction.

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8
Q

pseudo first order

A

a second-order or bimolecular reaction that is made to behave like a first-order reaction

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9
Q

Zero order

A

Does not depend on concentration of reactants

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10
Q

Initial velocity V0

A

Moles of products formed per second at very early time points

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11
Q

The simplest enzyme mechanism involves the equation:

A
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12
Q

Michalis Menten Kinectics assumptions (2)

A
  1. ignore E+P going back to ES (ignore K-2)
  2. Concentration of enzyme substrate complex is constant
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13
Q

Km formula with rate constants

A
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14
Q

The Michaelis-Menten Model assumes Steady state kinectics. This means

A
  • Measurements of V0 while [ES] is relatively stable
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15
Q

Vmax is directly dependent on

A

enzyme concentration

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16
Q

Michaelis-Menten, what happens when [S]«Km

A

When [s]«Km, velocity is directly porportional to [s]

17
Q

Michaelis-Menten, what happens when [S]»Km

A

Rate is zero order, independent of [s]

18
Q

Michaelis-Menten, what happens when [S]=Km

A

Km is equal to the [s] at which the reaction rate is half its maximal value

19
Q

Talk about Km value (3)

depends+what it is+ cellular concentration

A
  • Depends on the substrate, PH, temperature, ionic strength
  • Km is the concentration of substrate at which half of the enzyme molecules are bound to substrate
  • The cellular concentration of a particular substrate is often close to the Km value
20
Q

Why is it beneficial for the cellular concentration of a particular substrate to be close to the Km value?

A
  • significant catalysis, sensitive to flunctuations in [s]
  • If enzyme always operate at vmax (saturated) we will have signifigant velocity but any slight changes in [s] wil not change vmax
21
Q

slope, x-inyersept and y interscept in lineweaver plot what is that

A
22
Q

Turnover (2)

What it is+ condition of

A
  • The number of substrate molecules that the enzyme can turn into products per unit time when fully saturated with substrate
  • condition of max velocity
23
Q

1/ Kcat

A

Time to convert 1 molecule of substrate into product

24
Q

Km and Vmax values are always

A

positive

25
Q

Formula for Vo not in formula sheet

Use two formula to reaarange from sheet

A
26
Q

Vo depends on (3)

A
  • [s]
  • [E]T
  • Kcat/Km
27
Q

Kcat/Km (3)

called+measure of+ takes into account

A
  • rate constant for ES formation
  • Called the specificity constant
  • Measure of catalytic efficiency because it takes into account rate of catalysis (Kcat) and nature of interaction between E and S / binding affinity between the enzyme and substrate (Km)
28
Q

Note that Kcat/Km is always

A

less than K1

29
Q

What happens if the rate of product being formed (Kcat) is much greater than the dissociation of ES (k-1)? (2)

A
  • Kcat/Km approaches K1 value
  • K1, the rate of formation of the enzyme-substrate complex is the rate limiting step (diffusion: how quickly the enzyme encounters substrate)
30
Q

Catalytic perfection

A

y.yy x 10^ 8 or y.yy x 10^9

31
Q

How does PH influence enzymatic activity?

A

It influences ionization state of important residues in the active site.

32
Q

allosteric enzymes

A
  • more than 1 subunit
  • has quaternary structure
  • more than 1 active site
33
Q

curve for allosteric enzyme

A

allosteric enzymes display sigmodal kinectics

34
Q

concerted model

A

enzyme subunits are connected in such a way that a conformational change in one subunit is necessarily conferred to all other subunits. Thus, all subunits must exist in the same conformation

35
Q

sequential state

A

Bcem 341 (32 decks)

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