Enzymes

Question 1

What is a co-factor?

Answer 1

An additional non-peptide component of an enzyme

Question 2

What is a co-enzyme?

Answer 2

A complex organic or metalloorganic co-factor

Question 3

What are precursors to many enzymes?

Answer 3

Vitamins

Question 4

What is a prosthetic group?

Answer 4

A covalently bound cofactor

Question 5

What is a holoenzyme?

Answer 5

A complete, catalytically active enzyme

Question 6

What is an apoenzyme?

Answer 6

Protein portion of holoenzyme

Question 7

What does an oxidoreductase catalyze?

Answer 7

Transfer of electrons

Question 8

What type of reaction does a transferase catalyze?

Answer 8

Group transfer reactions

Question 9

What does a hydrolase catalyze?

Answer 9

Hydrolysis reactions

Question 10

What reaction do lyases catalyze?

Answer 10

Addition or removal of groups to break or form double bonds

Question 11

What type of reaction is catalyzed by an isomerase?

Answer 11

Transfer of groups within molecules to yield isomeric forms

Question 12

What do ligases catalyze?

Answer 12

Formation of C-C, C-S, C-O and C-N bonds by condensation reactions coupled to ATP cleavage

Question 13

What is the transition state?

Answer 13

The highest energy level of the reaction coordinate diagram

Question 14

At the transition state, what is the probability of forming reactants vs. products?

Answer 14

Equal

Question 15

What is activation energy?

Answer 15

Change in free energy from reactants to transition state

Question 16

How do enzymes speed up a reaction?

Answer 16

By lowering the activation energy

Question 17

What determines the rate of a reaction at a given temperature?

Answer 17

Activation energy

Question 18

The higher the activation energy the ___ the reaction rate.

Answer 18

Slower

Question 19

Where on an enzyme does the substrate bind?

Answer 19

The active site

Question 20

How many amino acids are present at the active site?

Answer 20

10 or fewer

Question 21

What is the specific environment that an active site provides?

Answer 21

• 3-D entity
• Shape and components of active site are related to those of substrates
• Usually either a cleft or crevice on the surface of the enzyme
• Water is usually excluded
• Usually a non-polar environment, so amino acid side chains can become highly active

Question 22

How do enzymes reduce the activation energy?

Answer 22

• There is “loaned” energy from weak, non-covalent interactions between the substrate and the active site
• Each interaction releases a small amount of energy that can be offset against activation energy

Question 23

What is the binding energy?

Answer 23

The sum of the energies released by the substrate-active site ineraction

Question 24

What is wrong with the lock and key hypothesis?

Answer 24

It creates an energy well, and more energy is needed to get to the transition state

Question 25

What are 3 common types of catalysis involving function groups?

Answer 25

1. Acid base 2. Covalent 3. Metal ion

Question 26

What is catalysis?

Answer 26

The speeding up of a reaction by an enzyme - the active site can provide functional groups that interact transiently with the substrates

Question 27

What can serve as proton donors/acceptors in active sites?

Answer 27

Acidic side chains Basic side chains Hydroxyl amino acid side chains

Question 28

What is covalent catalysis?

Answer 28

When a transient covalent link is formed between the enzyme and substrate or intermediate

Question 29

What is metal ion catalysis?

Answer 29

Metal ions, either tightly bound to the enzyme or taken up with the substrate, create ionic interactions with the substrate and help orient and/or stabilized the charged transition state

Question 30

What is chymotrypsin?

Answer 30

A Serine protease that hydrolyses peptides on the carboxyl side of aromatic side chain residues

Question 31

Chymotrypsin is a good example of what?

Answer 31

Transition state stabilization

Question 32

By what means does chymotrypsin cleave peptides?

Answer 32

Using both covalent catalysis and general acid-base catalysis

Question 33

What are the two major stages of peptide cleavage by chymotrypsin?

Answer 33

1. Acylation | 2. Deacylation

Question 34

What occurs in acylation?

Answer 34

- Peptide bond is cleaved - Peptide fragment from C-termal end is released - Ester linkage formed between peptidyl carbonyl carbon of the N-terminal peptide and serine 195 of the enzyme

Question 35

What occurs in deacylation?

Answer 35

- Ester linkage is hydrolyzed - Peptide fragment is released - The enzyme is regenerated