Enzyme Kinetics

Question 1

What is enzyme kinetics ?

Answer 1

The study of the rates of enzyme catalysed reactions

Question 2

What is measured in enzyme kinetics ?

Answer 2

The reaction rate is measured and the effects of varying the conditions of the reactions investigated

Question 3

What does studying enzyme kinetics reveal ?

Answer 3

1. The catalytic mechanism of an enzyme
2. The enzymes role in metabolism
3. How the enzyme activity is controlled
4. How a drug or poison might inhibit the enzyme

Question 4

What type of relationship is there between the rate of an enzyme catalysed reaction and the concentration of substrate at a fixed concentration of enzyme ?

Answer 4

Hyperbolic relationship

Question 5

At low substrate concentrations what happens to the rate of reaction with increasing substrate concentration ?

Answer 5

Steep increase

Question 6

What is the rate at which product can be formed limited by ?

Answer 6

The concentration of the substrate available

Question 7

What is the initial rate of the enzyme-catalysed reaction to the concentration of substrate ?

Answer 7

Directly proportional

Question 8

What is a first order reaction ?

Answer 8

The steep increase at the beginning of the curve

Question 9

What happens to the enzyme as the concentration of the substrate increases ?

Answer 9

The enzyme becomes saturated with substrate

Question 10

What happens as soon as the catalytic site is empty ?

Answer 10

More substrate is available to bind and undergo reaction

Question 11

What happens at the high concentrations of substrate while the substrate continues to increase ?

Answer 11

Decreased enzyme response

Question 12

When is the maximum velocity achieved ?

Answer 12

At substrate saturation

Question 13

What is a zero order reaction ?

Answer 13

Proceeds at a constant rate

Question 14

At maximum velocity, what does the rate of formation of the product depend on ?

Answer 14

The activity of the enzyme itself. Adding more substrate will not affect the rate of reaction to any significant effect

Question 15

What is the hyperbolic relationship between substrate concentration and initial velocity also known as ?

Answer 15

Michaelis Menten equation

Question 16

What is the michaelis constant ?

Answer 16

Km

Question 17

What does the michaelis constant equal ?

Answer 17

The substrate concentration resulting in half the Vmax

Question 18

What is the michaelis constant express as ?

Answer 18

In terms of substrate concentration in moles per litre

Question 19

What is the michaelis constant independent of ?

Answer 19

Enzyme concentration

Question 20

What does the Km value for mammalian enzymes usually fall between ?

Answer 20

10 micromolar to 1 minimolar

Question 21

What is the dissociation constant of the enzyme substrate constant ?

Answer 21

Ks

Question 22

What is the affinity constant of the enzyme for the substrate ?

Answer 22

1/Ks

Question 23

What does Km provide a measure of ?

Answer 23

The affinity of an enzyme for the substrate

Question 24

What does a large Km indicate ?

Answer 24

A low affinity for substrate

Question 25

What does a low Km indicate ?

Answer 25

A high affinity for substrate

Question 26

What are enzyme inhibitors ?

Answer 26

Molecules that interact in some way with the enzyme to prevent it from working in its normal manner

Question 27

What are enzyme inhibitors normally ?

Answer 27

Poisons and drugs

Question 28

What is a competitive inhibitor ?

Answer 28

Competes with the substrate for binding at the enzyme active site - prevents substrate binding.

Question 29

What does the competitive inhibitor have in its structure ?

Answer 29

A chemical structure similar to the substrate

Question 30

How is an enzyme inhibitor complex formed ?

Answer 30

A competitive inhibitor reacts reversibly with the enzyme

Question 31

What is the inhibitor constant ?

Answer 31

Ki

Question 32

What is Ki defined as ?

Answer 32

The dissociation constant of the enzyme inhibitor complex

Question 33

What does the competitive inhibitor do to the Km value of the enzyme for substrate ?

Answer 33

Increases the Km- Requires a higher substrate concentration to achieve Vmax

Question 34

What is uncompetitive inhibition ?

Answer 34

When an inhibitor binds to the enzyme substrate complex and renders the enzyme catalytically inactive

Question 35

What do plots of 1/initial velocity against 1/substrate concentration measured at different concentrations of an uncompetitive inhibitor give ?

Answer 35

A series of parallel lines

Question 36

What is non-competitive inhibition ?

Answer 36

Occurs when the inhibitor binds at a site different from the active site

Question 37

How does binding at a site other than the active site effect enzymes ?

Answer 37

Reduces the enzymes ability to convert substrates into products in the active site

Question 38

What happens when noncompetitive inhibitors are added into a reaction ?

Answer 38

The Vmax reduces as the enzyme can no longer function as well as it could in the absence of the inhibitor

Question 39

Does the km for a noncompetitive inhibitor change during this reaction ?

Answer 39

No - stays the same

Question 40

Why does the Km not change in noncompetitive inhibition ?

Answer 40

The enzyme can still bind the substrate but just isnt catalyzing the reaction well