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 the mechanism of 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
- substrate must collide in the correct orientation and speed for a reaction to occur

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

What is an intracellular enzyme

Answer 5

an enzyme that is produced and functions inside of cells

Question 6

Give an example of an intracellular enzyme

Answer 6

catalase
- converts hydrogen peroxide into water and oxygen, preventing any damage to cells and tissues

Question 7

What is an extracellular enzyme

Answer 7

an enzyme that is secreted by cells and catalyses reactions outside of cells

Question 8

Give an example of an extracellular enzyme

Answer 8

amylase
- hydrolyses starch into simple sugars
- secreted from the salivary glands and the pancreas, for the digestion in the mouth and small intestine

Question 9

Describe the lock and key theory

Answer 9

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

Question 10

Describe the induced fit theory

Answer 10

as substrate collides and binds with the enzymes active site, the enzyme molecule experiences a conformational change in shape of the active site
- oppositely charged groups help hold substrate and enzyme together
- this maximises the ability of the enzyme to catalyse the reaction

Question 11

What effect do enzymes have on the activation energy of a reaction

Answer 11

enzymes provide an alternative energy pathway with lower activation energy

Question 12

Why is enzymes lowering activation energy vital for biological reactions

Answer 12

without enzymes, extremely high temperatures or pressures would be needed to meet the energy of many biological reactions
- this would kill cells

Question 13

Give four factors that affect the rate of enzyme action

Answer 13

1)temperature
2) pH
3)enzyme concentration
4) substrate concentration

Question 14

Describe how temperature affects enzyme action

Answer 14

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

Question 15

Why do high temperatures denature enzymes

Answer 15

at a certain point, high kinetic energy and vibration of the enzyme molecule causes the weaker hydrogen bonds and ionic bonds to break
this changes the tertiary structure of the enzyme, changing the shape of its active site

Question 16

What is the Q10 temperature coefficient

Answer 16

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

Question 17

How to calculate Q10

Answer 17

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

Question 18

Describe how pH affects rate of enzyme action

Answer 18

below and above the optimum pH, excess amounts of H+ and OH- ions break the hydrogen and ionic bonds holding the tertiary structure together, altering the shape of the active site
- so enzyme-substrate complexes form less easily

Question 19

What is the pH of the stomach

Answer 19

pH 2
due to pepsin

Question 20

What is the pH of the liver

Answer 20

pH 11
due to arginase

Question 21

How does enzyme concentration affect the rate of enzyme activity

Answer 21

if there is an excess of substrate, increasing enzyme concentration will increase the rate of reaction as more active sites are available, increasing the frequency of enzyme-substrate complex formation
increasing enzyme concentration no longer has an effect as the substrate is the limiting factor (not in excess anymore)

Question 22

How does substrate concentration affect enzyme activity

Answer 22

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 23

What are coenzymes

Answer 23

organic molecules that bind to the active site, before or with the substrate
they are involved in carrying electrons or chemical groups between enzymes
coenzymes link different enzyme catalysed reactions into a sequence during metabolic processes e.g. respiration or photosynthesis

Question 24

Give an example of a source of coenzymes

Answer 24

vitamins

Question 25

What are cofactors

Answer 25

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 26

Give three examples of cofactors

Answer 26

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

Question 27

What are reversible inhibitors

Answer 27

molecules that reduce or stop enzyme activity temporarily

Question 28

What are competitive inhibitors

Answer 28

they have a similar shape to that of substrate molecules can compete with them to bind to the active site

Question 29

What effect does increasing the substrate concentration have on the rate of reaction, for competitive inhibitors

Answer 29

increasing the substrate will increase the rate of the reaction

Question 30

What are non competitive inhibitors

Answer 30

they bind to the enzyme at an alternative site, which results in a conformational change in the active site this prevents substrate from binding to it

Question 30

Explain the process of end-product inhibition

Answer 30

metabolic reactions can be controlled by using the end-product of a metabolic reaction as a non-competitive, reversible inhibitor 1) as the enzyme converts the substrate into product, the end product of the reaction chain binds to an alternative site on the enzyme 2) this changes the shape of the active site, preventing the formation of any further enzyme-substrate complexes 3) this slows down the reaction chain 4) the end product can detach from the enzyme and be used elsewhere, allowing the active site to reform to its normal shape

Question 31

What effect does increasing the substrate concentration have on the rate of reaction, for non-competitive inhibitors

Answer 31

increasing substrate concentration will not increase rate of reaction this is because the shape of the active site remains changed and enzyme-substrate complexes are still unable to form

Question 32

Give an example of a metabolic poison

Answer 32

ethylene glycol

Question 33

Explain how ethylene glycol works

Answer 33

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

Question 34

What are non-reversible inhibitors

Answer 34

they form covalent bonds with enzymes, inhibiting them permanently

Question 35

Why are non-reversible inhibitors dangerous

Answer 35

they result in the complete inactivation of the cell, which can cause biological reactions that require enzymes to completely stop

Question 36

How can enzyme inactivation be prevented

Answer 36

transcribing and translating the gene for that enzyme to produce more of the enzyme being inhibited - relatively slow process