Enzyme Classification

Question 1

[Mnemonic]

LI’L HOT

(how to remember the six enzyme classes)

Answer 1

LI’L HOT

Ligase

Isomerase

Lyase

Hydrolase

Oxidoreductase

Transferase

Question 2

What do oxidoreductases catalyze?

Answer 2

Oxidation-reduction reactions (the transfer of electrons).

Example: A + B: ⇔ A: + B

Question 3

What do transferases catalyze?

Answer 3

The transfer of functional groups.

Example: A + BX → AX + B

Question 4

What do hydrolases catalyze?

Answer 4

Hydrolysis reactions

Ex. A + H₂0 → B + C

Question 5

What occurs during a hydrolysis reaction?

Answer 5

Water breaks a compound into two different molecules.

Question 6

What do lyases catalyze?

Answer 6

Cleaves a single molecule into two products

(without hydrolysis or oxidation)

Example: A → BC

Question 7

What do isomerases catalyze?

Answer 7

Isomerism reactions

Examples:

1. A → B
2. glucose-6-p → fructose-6-p

Question 8

What is isomerism?

Answer 8

The rearrangement of bonds (or atoms) within a molecule to yield different isomers.

Question 9

What do ligases catalyze?

Answer 9

Ligation (joining) using ATP

Example: A + B → AB

Question 10

What is the difference between a kinase and phosphatase?

Answer 10

Kinase: adds a phosphate group

(phosphorylation)

Phosphatase: removes a phosphate group

(dephosphorylation)

Question 11

What is the difference between a synthase and a synthetase?

Answer 11

Synthase: forms covalent bonds WITHOUT energy input

Synthetase: forms covalent bonds WITH energy input