Kinetics of enzyme reactions

Question 1

what is kinetics

Answer 1

study of the rate at which compounds react

Question 2

the rate of an enzymatic reaction is affected by what 5 things

Answer 2

enzyme, substrate, effectors, temperature, pH

Question 3

What is the unit for the rate of change in concentration

Answer 3

Moles/L Sec-1

Question 4

Write out the Rate equation and explain what each thing

Answer 4

picture

Question 5

Describe the relationship between the reactant and time for first order reactions

Answer 5

The amount of reactant decays exponentially

Question 6

The slope for first order reactions for graph ln vs time is what?
How can you tell when a reaction is first order?

Answer 6

-k

Rate depends on the first power of the concentration

Question 7

What is the equilibrium constant

Answer 7

Ratio of forward and reverse rate constants

Question 8

Most biochemical reactions are what order

Answer 8

second order

Question 9

what is the unit for second order reactions

Answer 9

(Mol/L)-1 s-1

Question 10

Rate equations for second order

Answer 10

V= K2[A]^2 
V= K2[A][B]

Question 11

What allows enzymes to find their substrates

Answer 11

Thermal motion

Question 12

How is initial velocity determined?

Answer 12

Bymeasuringproductformationasafunctionoftime velocity of reaction),andthendetermining thevelocitysoonafterthereactionhasstarted

Question 13

What apparatus is used to measure initial velocity

Answer 13

Stopped flow apparatus

Question 14

what is the michaelis menten equation?

Answer 14

V0= Vmax[S]/Km+[S]

Question 15

What did Michaelis and Menten speculate about the enzyme, substrate and rate determining step? And show this in simple form

Answer 15

Substrate forms to an enzyme to make a complex in a fast and reversible step.
This complex then breaks down in a slower step to yield the free enzyme and product so is the rate limiting step.
E+S ES-> E + P

Question 16

Assumptions made in deriving the M&M equation about k-2

Answer 16

k-2 = 0, so reverse reaction between P and E is negligible

Question 17

why is the overall rate proportional to the concentration of Enzyme Substrate

Answer 17

The slower second reaction limits the overall rate

Question 18

When [S] is small most of enzyme is in what form and so the rate is proportional to what?

Answer 18

Is in uncombined form and the rate is proportional to [S] (pseudo first order)

Question 19

The maximum initial rate is observed when? (assumptions made in deriving MM equation)

Answer 19

when all the E is in the ES complex at high [S] i.e.

E is saturated (zero order)

Question 20

when there is excess substrate the reaction quickly achieves what state

Answer 20

Steady state in which enzyme substrate remains approximately constant over time

Question 21

How else V0 can be written

Answer 21

= v = Kcat [Etot][S]/ Km + [S]

Question 22

What is Kcat the same as

Answer 22

K2

Question 23

What is Kcat

Answer 23

turnover number

The number of substrate molecules one enzyme molecule can convert per second

Question 24

Km is what

Answer 24

Michaelis constant

Approx measure of substrates affinity for an enzyme and the substrate conc which gives half maximal velocity (Vmax)

Question 25

At high [S], velocity doesnt depend on what (Saturation Kinetics)

Answer 25

[S]

Question 26

When Vo = 0.5Vmax, what is [S]

Answer 26

Km, Km is the substrate concentration that yields .5Vmax

Question 27

The ideal rate is the M&M equation but deviations from this equation is due to what 4 things

Answer 27

- Limitation of measurements - Substrate inhibition - Substrate prep contains inhibitors - Enzyme prep contains inhibitors

Question 28

What is Km in terms of velocity

Answer 28

Conc of substrate giving half-maximal velocity

Question 29

What is defined as the dissociation constant Kd of the ES complex or affinity of the enzyme for its substrate

Answer 29

When k2 is rate limiting k2

Question 30

What is Km in terms of K-1, k2 and K1

Answer 30

(K-1+K2)/K1

Question 31

Turnover number Kcat has units of sec-1, describe what is shows

Answer 31

Number of substrate molecules turned over per enzyme molecule per second

Question 32

k1 (first order) has what unit and what does a large k1 mean?

Answer 32

K1 is the rate constant unit s-1 | Large K1 means a fast reaction

Question 33

``` Define Vmax Km V0 and which two contribute to measuring enzyme perfomance? ```

Answer 33

Vmax is maximumm velocity Km is the substrate concentration at which V0 is equal to one half of Vmax V0 is the initial velocity Vmax and Km measure enzyme performance

Question 34

How is Catalytic/Enzyme efficiency calculated? And what value must the result be in for it to be efficient?

Answer 34

Kcat/ Km Determined by the frequency with which S and E collide 108‐109M‐1s‐1 (The diffusion-controlled limit)