Lecture 12/13: Enzyme kinectics/Allosteric enzymes

Question 1

a first order reaction

Answer 1

there is only a single reactant
A → B.

Question 2

rate of first order reaction

Answer 2

A → B

Question 3

Units for first-order rate constants, K are …

Answer 3

s^-1

Question 4

second order reaction

Answer 4

there are two reactants
A + B → products

Question 5

rate of second order reaction

Answer 5

v = k[A][B]

Question 6

Units for second-order rate constant (K)

Answer 6

M^-1s^-1

Question 7

What determines the rate of a
reaction?

Answer 7

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

Question 8

pseudo first order

Answer 8

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

Question 9

Zero order

Answer 9

Does not depend on concentration of reactants

Question 10

Initial velocity V0

Answer 10

Moles of products formed per second at very early time points

Question 11

The simplest enzyme mechanism involves the equation:

Answer 11

Question 12

Michalis Menten Kinectics assumptions (2)

Answer 12

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

Question 13

Km formula with rate constants

Answer 13

Question 14

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

Answer 14

• Measurements of V0 while [ES] is relatively stable

Question 15

Vmax is directly dependent on

Answer 15

enzyme concentration

Question 16

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

Answer 16

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

Question 17

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

Answer 17

Rate is zero order, independent of [s]

Question 18

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

Answer 18

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

Question 19

Talk about Km value (3)

depends+what it is+ cellular concentration

Answer 19

• 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

Question 20

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

Answer 20

• 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

Question 21

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

Answer 21

Question 22

Turnover (2)

What it is+ condition of

Answer 22

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

Question 23

1/ Kcat

Answer 23

Time to convert 1 molecule of substrate into product

Question 24

Km and Vmax values are always

Answer 24

positive

Question 25

Formula for Vo not in formula sheet | Use two formula to reaarange from sheet

Answer 25

Question 26

Vo depends on (3)

Answer 26

- [s] - [E]T - Kcat/Km

Question 27

Kcat/Km (3) | called+measure of+ takes into account

Answer 27

- 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)

Question 28

Note that Kcat/Km is always

Answer 28

less than K1

Question 29

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

Answer 29

- 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)

Question 30

Catalytic perfection

Answer 30

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

Question 31

How does PH influence enzymatic activity?

Answer 31

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

Question 32

allosteric enzymes

Answer 32

- more than 1 subunit - has quaternary structure - more than 1 active site

Question 33

curve for allosteric enzyme

Answer 33

allosteric enzymes display sigmodal kinectics

Question 34

concerted model

Answer 34

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

Question 35

sequential state

Answer 35