Chapter 7- Kinetics

Question 1

What is the Michaelis-Menten equation & Km

Answer 1

It describes the variation of enzyme activity as a function of substrate concentration= half active sites filled
**V0= Vmax [S]/[S] + Km
Where, Km= (k-1 + k2) /k1 –> it is a compilation of rate constants called the Michaelis constant, is unique to each enzyme and is independent of enzyme concentration. Km describes the properties of the ES interaction and thus will vary for enzymes that can use different substrates

Question 2

What is Vmax

Answer 2

Vmax is directly dependent on enzyme concentration

Vmax, like perfection, is approached but never obtained.

Question 3

Lineweaver-Burk equation (aka double reciprocal plot)

Answer 3

The and Michaelis Menton equation can be transformed into: (for plotting)

(1/V0) = (Km/Vmax) • (1/S) + (1/Vmax)

Produced a straight line with a y-intercept–Rarely used, sensitive to errors.

Question 4

Turnover number

Answer 4

The number of substrate molecules that an enzyme can convert into product per unit time when the enzyme is fully saturated with substrate

-it is = to the rate constant k2 (kcat).
-if the total number of active site [E]T are known,
Vmax= k2[E]T

Question 5

Substrate concentration

Answer 5

Under physiological conditions, the amount of substrate present is usually between 10% and 50% Km.

Thus, the [S]/Km ratio is typically between 0.01 and 1.0

Question 6

Allosteric enzymes

Answer 6

Are like traffic lights, stop signs on road–they regulate.

Allosteric enzymes always catalyze the committed step of metabolic pathways

Do not conform to Michaelis Menten kinetics: they have enhanced responsiveness near km which allows for more sensitive control of reaction velocity (“Sigmoidal”)

Question 7

Feedback inhibition

Answer 7

In the example A - B - C -D - E -F, A to B is the committee step. B must convert to F. In order to not create too much F, F is able to bind reversely to the enzyme between A and B to inhibit the reaction.

F would not bind to the active site, but a regulatory site on the allosteric enzyme.

Question 8

Concerted model (MWC model)

Answer 8

Two states:
R- relaxed, active conformation which catalyze a reactions
T- Tense, significantly less active

In the absence of substrate, R & T are in equilibrium with T being the more stable/common state

The binding of substrate disrupts the T R equilibrium in favor of R (“cooperatively”)-accounts for the sharp increase of v0 on the curve

Question 9

Regulator molecules for R/T

Answer 9

Positive effector binds to R at the regulatory site and stabilizes making R more likely

Negative effector binds to T and stabilizes it; increasing the concentration of T and making R less likely to bind