Enzymes-1

Question 1

Where on an enzyme does catalysis occur?

Answer 1

The active site

Question 2

What do **proteolytic **enzymes catalyse?

Answer 2

Proteolysis (hydrolysis of a peptide bond)

Question 3

What small molecules are sometimes present in enzymes and essential for some enzymes to work?

Answer 3

Cofactors

Question 4

What is an enzyme without its cofactor called?

Answer 4

An apoenzyme

Question 5

What is an enzyme with its cofactor called?

Answer 5

A holoenzyme

Question 6

Apoenzyme + cofactor =

Answer 6

Holoenzyme

Question 7

What are the two subdivisions of cofactors?

Answer 7

1. Metals
2. Coenzymes

Question 8

What are tightly bound coenzymes called?

Answer 8

Prosthetic groups

Question 9

Define free energy (G)

Answer 9

A thermodynamic property that is a measure of useful energy , or the energy that is capable of doing work

Question 10

What happens in a reaction that has -ΔG?

Answer 10

It is spontaneous

Question 11

What happens in a reaction that has +ΔG?

Answer 11

It is not spontaneous

Question 12

What is the difference in energy between the substrate and the transition state?

Answer 12

The activation energy

Question 13

The active site of an enzyme is the region that binds the ________ (and the _______, if any). It also contains the residues that directly participate in the ________ and _________ of bonds. These residues are called the _________ _______.

Answer 13

The active site of an enzyme is the region that binds the **substrates **(and the cofactor, if any). It also contains the residues that directly participate in the **making **and **breaking **of bonds. These residues are called the catalytic groups.

Question 14

What are some of the generalisations that can be made about the active sites of enzymes?

Answer 14

• the active site has a three-dimensional cleft
• the active site takes up a small portion of the total volume of the enzyme
• active sites are unique microenvironments
• substrates are bound to enzymes by multiple weak attractions
• the specificity of binding depends on the precisely defined arrangement of atoms in an active site

Question 15

What is the velocity of an enzyme catalysed reaction?

Answer 15

The amount of product formed in a given amount of time, or the amount of substrate that disappears in a unit of time

Question 16

What is the Michaelis-Menten equation?

Answer 16

Question 17

What is the Michaelis constant, K_M?

Answer 17

Question 18

How can K_M be worked out from a V₀/[S] graph?

Answer 18

Question 19

Define V_max

Answer 19

The point at which there is a maximal turnover of product from an enzyme, i.e. the enzyme is fully saturated with substrate

Question 20

Define K_M

Answer 20

A constant that describes the amount of substrate needed to half saturate an enzyme. A high K_Mmeans a lot of substrate is needed to saturate an enzyme.

Question 21

What K_cat?

Answer 21

A constant that describes the turnover number of an enzyme

Question 22

What is a Lineweaver-Burk plot?

Answer 22

A plot of 1/V₀ versus 1/[S].

Can be used to determine V_max as the y intercept is 1/V_max

Question 23

What are the two main types of inhibition of an enzyme?

Answer 23

1. Reversible
2. Irreversible

Question 24

What are the three types of reversible enzyme inhibition?

Answer 24

1. Competitive
2. Noncompetitive
3. Uncompetitive

Question 25

How does competitive inhibition affect V_max and K_M?

Answer 25

V_max is unchanged

K_M is decreased

Question 26

How does uncompetitive inhibition affect V_max and K_M​?

Answer 26

V_max is decreased

K_M is decreased

Question 27

How does noncompetitive inhibition affect V_max and K_M​?

Answer 27

V_max is decreased

K_M is unchanged