Enzyme kinetics

Question 1

Velocity versus substrate concentration

Answer 1

Initial reaction velocity only depends on the RDS which is K2, so as substrate concentration increases so does velocity.

Question 2

Equation for velocity

Answer 2

v + d[P]/dt = K2*[ES]

Question 3

Michaelis Menten equation

Answer 3

Hyperbolic
v = (Vmax*[S])/(Km+[S])

Question 4

Michaelis constant

Answer 4

Km = (K-1+K2)/K1
describes the enzyme’s affinity for a substrate.

Question 5

Equation for Vmax

Answer 5

Vmax = K2*[E]total

Question 6

Kcat

Answer 6

The catalytic rate constant (turnover number) when the enzyme is saturated with S. Determines how quickly the enzyme acts in mechanistic terms.

Question 7

Enzyme efficiency

Answer 7

is measured by Kcat/Km

Question 8

Kcat/Km also indicates the preferred ______ of an enzyme.

Answer 8

Substrate

Question 9

Lineweaver-Burk plot

Answer 9

Takes the reciprocal of the Michaelis-Menten data where slope = Km/Vmax, and y-int = 1/Vmax.

Question 10

If a mutation to an enzyme decreases Kcat but does not affect Km, what does this reflect of the mutated amino acid?

Answer 10

The mutated amino must be important in the catalytic mechanism of the enzyme.

Question 11

Irreversible enzyme inhibitors

Answer 11

Irreversible bind covalently to the enzyme active site so that it cannot perform catalysis. Decrease in a max due to decrease in available enzymes, but no change to Km.

Question 12

Reversible enzyme inhibition

Answer 12

Inhibitors bind non-covalently and usually resemble the transition state. Distinguished by enzyme kinetics.

Question 13

Classes of reversible enzyme inhibitors

Answer 13

Competitive
Non-competitive
Uncompetitive
Mixed

Question 14

Competitive inhibitors

Answer 14

Bind to the active site such that a substrate-enzyme complex cannot form. Increases Km, but does not change Vmax.

Question 15

Non-competitive inhibitors

Answer 15

Bind to the allosteric site to decrease the mechanistic efficiency of the enzyme. Decreases the Vmax and Kcat.

Question 16

Mixed inhibitors

Answer 16

Bind to a more distant site that modifies both Vmax (decreases), and Km (increases).

Question 17

Exceptions to the Michaelis-Menten kinetics

Answer 17

It is only valid for the simple 2-step enzymes reactions, many others involve several substrates, products, and multiple steps. Km is a complicated function of many rate constants.

Question 18

Allosteric enzymes

Answer 18

Have multiple subunits that bind to substrates in a cooperative fashion that can either be positive or negative.

Question 19

Regulation by substrate availability

Answer 19

Effector - substrate
Result - change velocity
Time - immediate

Question 20

Regulation by product inhibition

Answer 20

Effector - product
Result - change Vmax/Km
Time - immediate

Question 21

Regulation by allosteric control

Answer 21

Effector - end product
Result - change Vmax/Km
Time - immediate

Question 22

Regulation by covalent modification

Answer 22

Effector - another enzyme
Result - change in Vmax/Km
Time - immediate to minutes

Question 23

Regulation by localisation

Answer 23

Effector - another enzyme
Result - change in cellular location
Time - immediate to minutes

Question 24

Regulation by enzyme synthesis/degradation

Answer 24

Effector - hormone/metabolite
Result - change in enzyme level
Time - hours to days

Question 25

Regulation often involves an ____ and/or ________ sep in the metabolic pathway

Answer 25

early; commited