Enzyme Kinetics 3

Question 1

What is the Active Site ?

Answer 1

The active site is the region that binds the substrates (& cofactors if any)

Question 2

What does the active site contain ?

Answer 2

It contains the residues that directly participate in the making & breaking of bonds (these residues are called catalytic groups)

Question 3

What does the interaction of the enzyme and substrate at the active site promote ?

Answer 3

It promotes the formation of the transition state

Question 4

The active site is the region that most directly lowers ?

Answer 4

ΔG‡ of the reaction - resulting in rate enhancement of the reaction

Question 5

The active site is a ?

Answer 5

A 3-dimensional cleft formed by groups that come from different parts of the amino acid sequence

Question 6

The active site takes up ?

Answer 6

A relatively small part of the total volume of an enzyme. Why are enzymes so big? Scaffolding, regulatory sites, interaction sites for other proteins, & channels

Question 7

Active sites are ?

Answer 7

Clefts or crevices -

exclude H2O

Question 8

Substrates are bound to ?

Answer 8

Enzymes by multiple weak attractions (electrostatic interactions, hydrogen bonds, Van der Waals forces, & hydrophobic interactions can be Involved)

Question 9

The specificity of binding depends on ?

Answer 9

The precisely defined arrangement of atoms at the active site

Question 10

The specificity of an enzyme is due ? This is a result of ?

Answer 10

To the precise interaction of substrate with the enzyme. The intricate three-dimensional structure of the enzyme protein

Question 11

DIPF (nerve gas) reacts ?

Answer 11

With Ser in acetylcholinesterase

Question 12

Alanine non-competitively inhibits ?

Answer 12

Pyruvate kinase

Question 13

Alanine is one product of a series of enzyme-catalyzed reactions, the first step of which is catalyzed by Alanine is one product of a series of enzyme-catalyzed reactions, the first step of which is catalyzed by ?

Answer 13

Phosphenol kinase

Question 14

Apoenzyme + cofactor =

Answer 14

Holoenzyme

Question 15

Cofactors often derived from?

Answer 15

Vitamins

Question 16

When tightly bound to enzyme, cofactor =

Answer 16

Prosthetic group

Question 17

4-hydroxyproline required in?

Answer 17

Collagen (connective tissue in vertebrates)

Question 18

Scurvy from ?

Answer 18

Ascorbate deficiency

Question 19

Enzyme has tightly bound Fe2+ ion, which reacts with O2 to form ?

Answer 19

Oxidised iron complex, which inactivates enzyme

Question 20

Ascorbate rescues enzyme by ?

Answer 20

Reducing the ferric ion

Question 21

What is Cooperativity ?

Answer 21

Enzyme can bind two substrate molecules at different binding sites. Binding at one site affects the affinity for the other.

Question 22

Usually, the binding of the first S changes the rate at ?

Answer 22

Which the second S binds.

Question 23

If the binding rate of the second S is increased, it’s ?

Answer 23

Positive cooperativity

Question 24

If the binding rate of the second S is decreased, it’s?

Answer 24

Negative cooperativity

Question 25

Give details about Allostery?

Answer 25

• Modulation of protein activity(enzymeorcarrier protein) by an EFFECTOR molecule.
• REGULATORY SITE is separate from the active site
• Enzyme exists in two states-tense and relaxed. Binding of the effector influences further binding of substrate

Question 26

Alanine is an allosteric inhibitor of ?

Answer 26

Pyruvate kinase

Question 27

What are the steps for extraction of energy from food ?

Answer 27

Stage 1 = Depolymerisation
Stage 2 = Glycolysis
Stage 3 = TCA cycle and oxidative and phosphorylation

Question 28

What is Hexokinase ?

Answer 28

A highly regulated enzyme

Question 29

What does Hexokinase catalyse ?

Answer 29

First step of glycolysis

Question 30

How does Hexokinase work? Also, allosterically inhibited ?

Answer 30

Works by induced fit: a conformational change in the enzyme occurs upon binding to its substrate.
It’s inhibited by product

Question 31

Hexokinase and glucokinase conduct the same reaction, but ?

Answer 31

Have different properties

Question 32

Hexokinase is found in and is what ?

Answer 32

In the brain and in skeletal muscle, and is a regulatory enzyme (i.e. it is inhibited by high concentrations of its product).

Question 33

Hexokinase also has a higher affinity for ?

Answer 33

For glucose, with a Km value of 5 X 10-5 M

Question 34

Glucokinase is found in and absent from ?

Answer 34

Glucokinase is found in the liver, and is absent in brain and muscle

Question 35

What is Glucokinase and has a lower affinity for ?

Answer 35

It is non-regulatory, and has a lower affinity for

glucose (Km = 2 X 10-2 M)

Question 36

At normal blood glucose, hexokinase is operating at ?

Answer 36

Near Vmax, ensuring that the brain gets an ample supply of glucose

Question 37

Glucokinase is operating far below its ?

Answer 37

Vmax under these conditions

Question 38

If blood glucose rises significantly, hexokinase can? what does this result in ?

Answer 38

Speed up slightly, but glucokinase speeds up dramatically. Therefore: excess blood glucose is taken up by the liver, and converted to glycogen and fat.

Question 39

If blood glucose falls below normal, hexokinase is ?

Answer 39

Still operating near Vmax, while glucokinase is essentially inactive. In this way, a constant supply of glucose is ensured for the brain at all times.