Enzyme Kinetics

Question 1

What is K1 in terms of enzyme kinetics?

Answer 1

K1 is the rate of the forward reaction to form the ES complex

Question 2

What is K -1 in terms of enzyme Kinetics?

Answer 2

K-1 is the rate of the backward reaction from the ES complex to E + S

Question 3

What is the general equation used to show how enzymes catalyse reactions?

Answer 3

E + S -> ES -> E + P

Question 4

What is the Michaelis constant (Km) ?

Answer 4

It describes the rate at which the enzyme substrate (ES) complex is formed

Question 5

What is the Michaelis Constant equation (Km) ?

Answer 5

Km = (K-1 + K2) / K1

Question 6

What is K2 in terms of enzyme Kinetics?

Answer 6

K2 is the rate of the second forward reaction, from Es to form the E + P

Question 7

If an enzyme follows the Michaelis-Menten Kinetics, by what two values can it be described?

Answer 7

V max - The maximal rate of reaction at unlimited substrate level

Km

Question 8

What is Vmax in terms of Michaelis Menten Kinetics?

Answer 8

The Maximal rate of reaction at unlimited substrate level

Question 9

How do you determine the velocity at which a reaction occurs?

Answer 9

The Progress of a reaction is record for a substrate

Product Vs Time graph

After some time equilibrium is reach - No more net change of substrate and product

Tangents/Gradients of the curve at specific points is the velocity

Plot a graph of Velocity vs Substrate

At infinite substrate concentration the reaction rate approaches Vmax

Question 10

What is the Michaelis Constant (KM) equivalent to?

Answer 10

Km = the substrate concentration were it is half V max

Question 11

What is the concentration of Km?

Answer 11

(M) molar

Question 12

What does a low Km mean?

Answer 12

A low Km means that an enzyme only needs a little substrate to work at half maximal velocity

Question 13

What does a high Km mean?

Answer 13

A high Km means that an enzyme needs a lot of substrate to work at half maximal velocity

Question 14

How can the Michaelis Menten equation be graphically defined?

Answer 14

A Michaelis Menten equation can be rearranged to form a Lineweaver Burk Pot (straight line graph)

This is a lot easier to read the V max

Question 15

How do you find the V max on a Lineweaker - Burk Plot?

Answer 15

Where the straight line crosses the Y axis is 1/Vmax

Question 16

How do you find the Km on a Lineweaker - Burk Plot?

Answer 16

Where the straight line corsses the X axis is -1/Km

Question 17

Is the Km the same for Isoforms?

Answer 17

No

Question 18

What is a reversible inhibitor?

Answer 18

A substance that binds to an enzyme to inhibit it, but which can be released

Question 19

What are the two types of Reversible inhibitors?

Answer 19

• Competitive: Binds to the active catalytic site and blocks access to it by substrate
• Non-competitive: Binds to a site other than the active site and changes its conformation

Question 20

What is an Irreversible Inhibitor?

Answer 20

A substance that causes inhibition that cannot be reversed

Question 21

What happens to the Km if a competitive inhibitor is present

Answer 21

The Km will increase - It requires more substrate to reach half of Vmax

Question 22

What happens to Vmax if a competitive inhibitor is present?

Answer 22

Vmax will remain the same

Question 23

What happens to the Vmax if a non-competitive inhibitor is present?

Answer 23

The V max will decrease

The 1/Vmax will look like it has increased, only as it is a reciprocal

Question 24

What are the mechanisms of enzyme control?

Answer 24

Allosteric Control
Regulation of trascription
Reversible Covalent Bond Modication 
Irreversible Covalent Bond modification 
Degradation

Question 25

What is a common inhibiting rate limiting step?

Answer 25

Allosteric Control

Enzyme requires a high Km, this means there will be a rate limiting step - as concentration levels need to build

Question 26

Do Allosteric Enzymes follow Michaelis Menten Kinetics?

Answer 26

No.

Question 27

What is an allosteric enzyme?

Answer 27

Allosteric enzymes are enzymes that change their conformational ensemble upon binding of an effector,

Question 28

What type of Reaction(V) vs Substrate graph does a Allosteric enzyme form?

Answer 28

A sigmoidal curve

ALLOSTERIC ENZYMES DO NO CONFORM TO KM

Question 29

What does a sigmoidal curve on a Reaction(V) vs Substrate graph indicate?

Answer 29

Indicates co-operative behaviour

Question 30

What are Allosteric ezymes governed by?

Answer 30

Allosteric activators

Allosteric Inhibitors

Question 31

What does a Allosteric inhibitor do to the sigmoidal curve on a Reaction(V) vs Substrate graph?

Answer 31

It causes a right shift - Causes the Vmax to lower and is less step

Question 32

What does a Allosteric Activator do to the sigmoidal curve on a Reaction(V) vs Substrate graph?

Answer 32

It causes a left shift - Causes Vmax to increase and has a steeper gradient

Question 33

What does co-operativity in terms of allosterism mean?

Answer 33

The influence of a binding ligand to a receptor that has an effect on the binding of another ligand to bind to a receptor

Question 34

What are the two ways an enzyme can bind a substrate?

Answer 34

R (relaxed) - Binds substrate tightly [This is the active form]

T (Tight) - Binds substrate less tightly. [This is the inactive forms}

Question 35

What affect does a substrate have when it binds to allosteric enzyme ?

Answer 35

Changes the enzyme from the Tight form to the relaxed form

This causes other subunits to change