Enzyme Kinetics

Question 1

When is a cofactor/coenzyme called a prosthetic group?

Answer 1

When it is tightly or covertly bound to an enzyme

Question 2

Name three ways that rearrangement of covalent bonds in specific active sites increase the rate of reaction.

Answer 2

1. General acid-base catalysis (aa side chain of enzyme donate/accept H+ to stabilize transition state)
2. Covalent catalysis (transient covalent bond is formed b/w E and S)
3. Metal ion catalysis (bound metals help position S or drive ox-red runs)

Question 3

Almost one-third of all enzyme utilize which type of chemistry catalysis?

Answer 3

Metal Ion Catalysis

Question 4

What does the ratio of kcat/Km tell us about an enzyme?

Answer 4

The larger the ratio, the mor efficient the enzyme.

“Catalytic perfection” is around 10^8 /m/s

Question 5

What are the differences between competitive, uncompetititve, and mixed inhibitors?

Answer 5

Competitive: bind E only, compete at active site, increase Km

Uncompetitive: bind ES complex only, compete NOT at active site, lowers Vmax

Mixed: binds either E or ES, compete NOT at active site, affect Km and Vmax

Question 6

Name four ways that enzymes are regulated.

Answer 6

1. Allosteric regulation
2. Covalent modification of enzyme
3. Binding of another regulatory protein
4. Protelytic cleavage of enzyme to activate

Question 7

How is an enzyme regulated by a feedback loop?

Answer 7

When a downstream product of a pathway acts as a regulator of an enzyme from earlier in that pathway

Question 8

What is the prominent example of covalent modification of an enzyme?

Answer 8

Phosphorylation

or dephosphorylation; in response to intra/extra-cellular signals and/or conditions

Question 9

What is a cofactor?

Answer 9

A substance that needs to be present in addition to an enzyme; often a metal

Question 10

What is a coenzyme?

Answer 10

A small molecule that donates a chemical group to the enzyme that will be used in the reaction