3. Enzymes

Question 1

Define enzyme

Answer 1

An enzyme is a biological catalyst. It is a protein that speeds up chemical reactions but remains unchanged at the end of the reaction.

Question 2

What type of proteins are enzymes?

Answer 2

globular proteins

Question 3

What is the lock and key hypothesis?

Answer 3

the substrate is a complementary shape to the active site of the enzyme, and the enzyme is specific to the substrate.

Question 4

What is the induced fit hypothesis?

Answer 4

the substrate is a complementary shape to the active site of the enzyme, but not an exact fit. The enzyme or the substrate can slightly change shape to fit perfectly.

Question 5

What is activation energy?

Answer 5

the energy needed for the reaction to take place, enzymes allow reactions to take place with reduced activation energy.

Question 6

What affects enzyme action? (4)

Answer 6

1) temperature
higher temperature –> more kinetic energy –> increased enzyme activity

2) pH
mention optimum pH

3) enzyme concentration
more active sites to bind to, increase enzyme activity
- effective until there’s no more substrate left

4) substrate concentration
more substrate to bind with active sites will increase enzyme activity
- effective until all active sites are occupied

Question 7

Define Vmax

Answer 7

Vmax is the maximum rate of reaction.

Question 8

Define Km

Answer 8

Km is half Vmax, used to measure the affinity of the enzyme for its substrate

Question 9

Lower Km…

Answer 9

…higher affinity

Question 10

What is enzyme inhibition?

Answer 10

Inhibition reduces the rate of activity of an enzyme

Question 11

What is competitive inhibition, and is it reversible?

Answer 11

competitive inhibitor has a similar shape to the substrate and occupies the active site

reversible by increasing the concentration of the substrate

Question 12

What is non-competitive inhibition, and is it reversible?

Answer 12

non competitive inhibitor binds to the allosteric site, though it can change the shape of the active site and inhibit the substrate binding to the active site.

reversible, but increasing substrate concentration has no effect

Question 13

What is one way to control metabolic reactions using inhibition?

Answer 13

End product inhibition

Question 14

What are immobilised enzymes?

Answer 14

enzymes that have been fixed to a surface, or trapped within beads of agar gel, such as immobilised enzyme lactase inside alginate beads

Question 15

What are the advantages of enzyme immobilisation?

Answer 15

– uncontaminated end product
– reusable
– more tolerant to temperature and pH changes because enzymes held firmly in shape and not fully exposed by agar gel