Lecture 1. Enzyme Essentials

Question 1

Carbonic anhydrase increases the forward rate of which reaction?

Answer 1

CO₂ + H₂O ⇌ HCO₃⁻ + H⁺

Question 2

Without carbonic anhydrase, how fast is the forward rate of reaction?

Answer 2

0.1 molecules per second

Question 3

With carbonic anhydrase, how fast is the forward rate of reaction?

Answer 3

1,000,000 molecules per second

Question 4

What are the names of RNA molecules that operate as enzymes?

Answer 4

Ribozymes

Question 5

What can catalytic power be demonstrated by?

Answer 5

The ‘turnover number’ or ‘catalytic constant’ kcat

Question 6

What does kcat mean?

Answer 6

Number of molecules of ‘substrate’ that one enzyme molecule can convert in 1 second

Question 7

What are the reactants in an enzyme-catalysed reaction known as?

Answer 7

Substrates

Question 8

What are substrates converted to in an enzyme-catalysed reaction known?

Answer 8

Products

Question 9

What are cofactors?

Answer 9

Small molecules not part of the enzyme but which are
required for activity

Question 10

Examples of cofactors

Answer 10

Metal ions, organic molecules, co-enzymes and prosthetic groups

Question 11

What is an apoenzyme?

Answer 11

An enzyme lacking an essential cofactor
or coenzyme

Question 12

What is the complete machinery of an enzyme and its cofactors called?

Answer 12

Holoenzyme

Question 13

How many classes of enzyme are there?

Answer 13

6

Question 14

What are EC 1 enzymes and what do they do?

Answer 14

Oxidoreductases - oxidation/reduction

Question 15

What are EC 2 enzymes and what do they do?

Answer 15

Transferases - transfer of a group

Question 16

What are EC 3 enzymes and what do they do?

Answer 16

Hydrolases - water cleaves a bond

Question 17

What are EC 4 enzymes and what do they do?

Answer 17

Lyases - Non-hydrolytic cleavage, addition or removal of groups

Question 18

What are EC 5 enzymes and what do they do?

Answer 18

Isomerases - intramolecular rearrangement

Question 19

What are EC 6 enzymes and what do they do?

Answer 19

Ligases - join two molecules

Question 20

Example of an oxidoreductase

Answer 20

Lactate dehydrogenase

Question 21

Example of a transferase

Answer 21

Hexokinase

Question 22

Example of a hydrolase

Answer 22

Glucose-6-phosphate

Question 23

Example of a lyase

Answer 23

Carbonic anhydrase

Question 24

Example of an isomerase

Answer 24

Triose-phosphate isomerase

Question 25

Example of a ligase

Answer 25

Amino-acyl tRNA synthetases

Question 26

What does specificity imply?

Answer 26

Enzymes recognise and bind substrates in an enzyme

Question 27

What proteinases are not highly specific?

Answer 27

Papain and savinase

Question 28

What does trypsin hydrolyse and where?

Answer 28

Trypsin hydrolyses peptide bonds at the C-terminal side of lysine or arginine

Question 29

What does chymotrypsin hydrolyse and where?

Answer 29

Chymotrypsin hydrolyses peptide bonds at the C-terminal side of phenylalanine, tyrosine or tryptophan

Question 30

What does thrombin hydrolyse?

Answer 30

Thrombin hydrolyses the arginine-glycine bond

Question 31

What is the name of the part of the enzyme that interacts with the substrate?

Answer 31

The active site

Question 32

What determines the activity and specificity of the enzyme?

Answer 32

The structure and the chemistry of the active site

Question 33

What is the current model used by scientists to represent the active sites?

Answer 33

The induced fit model

Question 34

What does the active site bind to?

Answer 34

Transition states

Question 35

What is a transition state?

Answer 35

The highest energy state

Question 36

What is the activation barrier?

Answer 36

The difference in energy between the reactant(s) and the transition state

Question 37

What do enzymes lower?

Answer 37

The activation barrier speeding up reactions

Question 38

What is the enzyme-substrate complex also known as?

Answer 38

The Michaelis complex