Biochem Lecture 10

Question 1

What is an oxidoreductase?

Answer 1

Catalyzes oxidation-reduction reactions.

Question 2

What are transferases?

Answer 2

Catalyze transfer of C-, N-, or P- containing groups.

Question 3

What are hydrolases?

Answer 3

Catalyze cleavage of bonds by adding water.

Question 4

What are lyases?

Answer 4

Catalyze cleavage of C-C, C-S and certain C-N bonds.

Question 5

What are isomerases?

Answer 5

Catalyze racemization of optical or geometric isomers. Racemization is producing equal quantities of the enantiomers of a substance.

Question 6

What are ligases?

Answer 6

Catalyze formation of bonds between carbon and O,S,N coupled hydrolysis of high energy phosphates such as ATP.

Question 7

What is a cofactor with enzymes?

Answer 7

A small molecule required for the catalytic activity of an enzyme. They can be metal ions or coenzymes.

Question 8

What is a coenzyme?

Answer 8

When a cofactor is an organic molecule.

Question 9

What is a cosubstrate?

Answer 9

When a cofactor is only transiently associated.

Question 10

What is prosthetic group?

Answer 10

When the cofactor is permanently associated with a protein, such as a heme group in Hb.

Question 11

What is the difference between a holoenzyme and an apoenzyme?

Answer 11

Holoenzymes are the active enzyme-cofactor complex.

Apoenzymes lack the cofactor.

Question 12

What is a substrate?

Answer 12

It is the molecule undergoing the reaction with an enzyme.

Question 13

How do active site and substrate interact?

Answer 13

The active site has a 3d physical shape that is complimentary to the shape of the substrate. It is a physical and chemical attraction.

Question 14

What is the induced fit model for the binding of a substrate?

Answer 14

It says that the binding of a substrate distorts the shape of both the substrate and the enzyme. The active site becomes complimentary to the substrate after it is bound.

Question 15

Are enzymes stereo-specific?

Answer 15

They are. The right enantiomer is needed.

Question 16

What is the free energy of a molecule?

Answer 16

The amount of energy available to do work.

Question 17

What is the ground state of a molecule or substance?

Answer 17

The normal energy state of a molecule. The lower the free energy, the more stable a molecule is.

Question 18

How is the delta G of a reaction calculated?

Answer 18

Delta G= G-Products (minus) G-Reactants

Question 19

What kind of number will delta G be for an energetically favorable reaction?

Answer 19

It will be negative, which signifies that the products have less energy than the reactants.

Question 20

What is activation energy?

Answer 20

It is the energy needed to get from the energy state of the substrate to the energy level of the transition state. It is the energy needed to carry out a reaction. It takes energy to break bonds and make new ones, essentially.

Question 21

What does the rate of a reaction depend on?

Answer 21

It depends on the activation energy. The lower the energy needed for the reaction, the faster it will go.

Question 22

What does delta G tell us about a reaction?

Answer 22

1. Where the equilibrium point will be
2. If the reaction is energetically favorable
3. It does not tell anything about the rate of reaction

Question 23

How do enzymes speed up reactions?

Answer 23

They lower the activation energy and therefore increase the rate. They lower the energy of the transition state by stabilizing it. Enzymes often are more complimentary to the transition state than to the substrate.

Question 24

How is the net energy of a reaction changed when catalyzed vs uncatalyzed?

Answer 24

There is no difference in the overall delta G for a reaction whether a catalyst is used or not. This is because the beginning and final states remain the same. It is the transition state that is changed.

Question 25

How does penicillin work?

Answer 25

It binds covalently to glycopeptidyl transferase in bacteria (which catalyzes the formation of cell walls) and prevents it from working.

Question 26

What is catalysis by proximity?

Answer 26

Substrates need to be close to the enzyme in order to react. The higher the concentration of substrate, the faster the reaction will go.

Question 27

What is covalent catalysis?

Answer 27

Enzyme forms a transient covalent bond with the substrate. This is common for transferases.

Question 28

What is catalysis by strain?

Answer 28

The substrate is bound in such a way that it places strains the bonds and they are vulnerable to cleavage.

Question 29

What is acid-base catalysis?

Answer 29

An exchange of protons can occur between the substrate and the enzyme to carry out the reaction. Histidine is usually involved with this.

Question 30

How does the concentration of substrate and enzyme affect the rate of a reaction?

Answer 30

Increasing substrate will increase the rate until it reaches a Vmax for the conditions.
Increasing enzyme will increase the rate.

Question 31

What can slow down a reaction?

Answer 31

Denaturing of the enzymes through temperature or pH or heavy metals. Raised temperatures will initially speed up the reaction, but too high will denature the proteins.