2.1.4 Enzymes

Question 1

Properties of enzymes

Answer 1

• globular proteins
• includes a ‘cleft’ - active site
• specific to one type of substrate
• unchanged at the end of the reaction

Question 2

Describe how enzymes break down substrates

Answer 2

substrate binds to the complementary active site of the enzyme, forming an enzyme-substrate complex
- bond between substrate breaks and products are released
- enzyme remains unchanged

Question 3

What is an anabolic reaction

Answer 3

enzymes building up molecules

Question 4

What is a catabolic reaction

Answer 4

breaking down molecules

Question 5

Describe the lock and key theory

Answer 5

shape of the active site is complementary to the shape of the substrate molecule
enzyme has a specifically shaped active site

Question 6

Describe the induced fit theory

Answer 6

as substrate collides and binds with the enzymes active site, the enzyme molecule changes shape
- oppositely charged groups help hold substrate and enzyme together

Question 7

Factors that affect the rate of enzyme action

Answer 7

temperature
pH
enzyme concentration
substrate concentration

Question 8

Describe how temperature affects enzyme action

Answer 8

increase in temperature
increase in kinetic energy
increase in collisions between enzymes and substrates
- so more enzyme substrate complexes formed
- so more products

Question 9

What is the Q10 temperature coefficient

Answer 9

the increase in the rate of a process when the temperature is increased by 10*C
- between 2 and 3 for most enzymes

Question 10

How to calculate Q10

Answer 10

rate of reaction at T + 10C / rate of reaction at TC

Question 11

Describe how pH affects rate of enzyme action

Answer 11

below and above the optimum pH, excess amounts of H+ and OH- ions break the hydrogen and ionic bonds holding the tertiary structure together, changing the shape of the active site

Question 12

What is the pH of the stomach

Answer 12

pH 2
trypsin/pepsin

Question 13

What is the pH of the liver

Answer 13

pH 11
arginase - liver

Question 14

How does enzyme concentration affect the rate of enzyme activity

Answer 14

if there is an excess of substrate, increasing enzyme concentration will increase the rate of reaction
increasing enzyme concentration no longer has an effect as the substrate is the limiting factor (not in excess anymore)

Question 15

How does substrate concentration affect enzyme activity

Answer 15

at low substrate concentration, there are not enough molecules to occupy the active sites
increasing substrate concentration eventually no longer has an effect as all active sites are occupied/saturated (no longer limiting)

Question 16

What are coenzymes

Answer 16

organic molecules that bind to the active site, before or with the substrate
- may be involved in more than one reaction
- often carry substances between enzymes in a reaction sequence
- temporary

Question 17

What are cofactors

Answer 17

inorganic metal ions
- they affect charge distribution and consequently enzyme shape and shape of the active site
- usually speed up the formation of ESC’S
- prosthetic groups

Question 18

Examples of cofactors

Answer 18

iron required for catalase function
chlorine ions for amylase
zinc requires for alcohol dehydrogenase

Question 19

What are competitive inhibitors

Answer 19

• usually fit into the active site of the enzyme, shaped like substrate
• block substrate from binding
• effects are reversible as they only bind temporarily
• degree to which they inhibit enzyme action is dependant on substrate concentration

Question 20

What are non competitive inhibitors

Answer 20

• dont bind to the active site, but alters the shape of the active site when binding to the enzyme
• substrate may still be able to bind, but active site doesnt catalyse reaction
• reversible or permanent
• degree to which they inhibit enzyme action is not dependant on substrate concentration

Question 21

Give an example of a metabolic poison

Answer 21

ethylene glycol

Question 22

Explain how ethylene glycol works

Answer 22

substance is broken down into oxalic acid by alcohol dehydrogenase (produced in the liver)
oxalic acid poisoning causes rapid chronic kidney failure and death