Enzyme Kinetic parameters

Question 1

Substrate concentration effect on rate of reaction explained

Answer 1

Increase in concentration increases the rate of reaction. Increases the number of successful collisions.

Question 2

Saturation effect explained

Answer 2

At a constant enzyme concentration the reaction rate increases with increasing substrate concentration until it reaches a limiting maximum value.

Maximum ES complex formed so rate of formation of product can no longer be increased even with an increase in substrate.

Evidence for ES complex formation

Question 3

What may the ES complexes go through in a catalytic cycle?

Answer 3

reaction intermediates.

Question 4

Enzyme concentration effect on rate of reaction

Answer 4

For an unlimited substrate concentration, an increase in enzyme concentration increases the rate of reaction.

Question 5

Rate equation definition

Answer 5

Gives experimentally observed dependence of rate on the concentration or reactants.

Question 6

General scheme for one substrate one product reaction

Answer 6

E+S ⇌ ES –> E + P

Question 7

What is the rate represented by for each arrow?

Answer 7

Top arrow- K1
Bottom arrow K-1
final arrow K2

Question 8

Equilibrium Assumption

Answer 8

Formation of ES complex from E and S is at equilibrium. Therefore the value of K2 is considered to be much smaller in magnitude compared to K1 and K-1

Question 9

Steady State definition

Answer 9

State variables are constant in spite of ongoing processes that strive to change them.

Entire system must contain flow through a system.

Question 10

Steady State Assumption

Answer 10

Not always true that K2 is negligible, concentration of ES is unchanged because its formation and disappearance rates are equal.

Question 11

Michaelis- Menten equation

Answer 11

v= Vmax[S]

Km + [S]

Question 12

What is Vmax?

Answer 12

The maximum rate of reaction, when the enzyme is fully saturated with substrate.

Question 13

What is Km?

Answer 13

The concentration of substrate at which 1/2 Vmax.

Question 14

Units for Vmax

Answer 14

Micromole product formed per minute per mg

Question 15

Unit for Km

Answer 15

concentration - micro mole

Question 16

When is Vmax constant?

Answer 16

amount of enzyme catalyst [Et] is fixed

Question 17

What should [S] in a reaction?

Answer 17

Around the Michaelis Menten constant Km, so if there are changes in enzyme the substrates can accommodate it. If a lot more, they are under-utilised; if not enough may not be able to control changes.

Question 18

Turnover number definition

Answer 18

The number of catalytic cycles the enzyme can undergo in a unit of time when the enzyme is fully saturated with substrate. The number of substrate molecule each enzyme site converts to product per unit time.

Question 19

Kcat definition

Answer 19

A fundamental property of the enzyme, the turnover number.

Question 20

Specificity constant definition

Answer 20

The ratio of Kcat/kM- describes the relative velocities of two substrates competing for a single enzyme. Expresses the ability of an enzyme to discrimination favour of any one substate over another.

The higher the specificity constant the higher the affinity for the substrate

Question 21

KI definition

Answer 21

The inhibitor complex, showing how potent an inhibitor is. The concentration required to produce half maximum inhibition.

Question 22

Irreversible inhibitor definition

Answer 22

Permanent inactivation of an enzyme, often as a result of covalent modifications of the enzyme protein. Net result reduces Vmax, while the KM of the remaining active enzyme is unaltered.

Question 23

Example of irreversible inhibitor

Answer 23

Suicide substrates- Unreactive molecules recognised as substrates by the enzyme however during catalytic turnover the target enzymes convert them into a reactive entity. Such as penicillin .

Question 24

Lineweaver Burk Plot derivation

Answer 24

V= Vmax[S] / Km + [S]. find inverse

1/V = Km + [S] / Vmax[S]

1/V = 1/[S] ( Km/Vmax) + 1/Vmax

Question 25

lineweaver Burk plot axis and intersection meanings

Answer 25

Y axis= 1/V
X axis = 1/[S]
Gradient= Km/Vmax
x intersection = -1/Km
Y intersection = 1/Vmax

Question 26

How can Lineweaver Burk plot distinguish between inhibitors?

Answer 26

Competitive inhibitors have the same y intercept as uninhibited enzymes, as the maximum rate is still the same

Noncompetitive inhibitors produce plots with the sam x intercept as inhibited enzymes.

Question 27

Uncompetitive inhibition definition

Answer 27

Inhibitor reacts exclusively with ES complex, not free enzyme.