B Enzymes

Question 1

What are the two main different types of enzymes?

Answer 1

1. Intracellular enzymes eg. catalase breaks down hydrogen peroxide in cells.
2. Extracellular enzymes eg. amylase breaks down starch.

Question 2

What does the lock and key model suggest?

Answer 2

Enzymes active sites and substrates have fixed, complementary shapes.

Question 3

What does the induced-fit model suggest?

Answer 3

• Enzymes active sites aren’t complementary, when the substrate starts to bind the active site changes shape to become complementary.
• This puts stress on the substrates bonds, making them easier to break and lowering activation energy.

Question 4

What are precursors?

Answer 4

• Enzymes that are produced in an inactive form.
• To become active, some precursors require cofactors (non-protein molecules).

Question 5

What are the three main types of cofactor?

Answer 5

1. Inorganic ions - bind temporarily to the enzyme to activate it. Eg. chloride ions are cofactors for amylase.
2. Coenzymes - organic molecules that temporarily bind to an enzyme eg. vitamins.
3. Prosthetic groups - molecules that are permanently bound to an enzyme eg. Zn2+ is a prosthetic group of carbonic anhydrase (enzyme that breaks down CO2).

Question 6

What are the factors affecting enzyme controlled reactions?

Answer 6

1. Enzyme concentration.
2. Substrate concentration.
3. Competitive inhibitors (complementary to the enzymes active site, lowering the probability of an enzyme-substrate complex forming, maximum rate of reaction is still reached as inhibitors do not permanently bind).
4. Non-competitive inhibitors (bind to the allosteric site, causing the active site to change shape, preventing an enzyme-substrate complex from forming, decreasing initial and maximum rate of reaction).
5. Temperature (high temperature breaks hydrogen bonds - denaturing enzyme).
6. pH (large change in pH can break hydrogen and ionic bonds).

Question 7

What is end-product inhibition?

Answer 7

Reversible inhibitors that regulate metabolic pathways as the final product of the pathway inhibits the enzymes involved.

Question 8

What is the temperature coefficient/Q10?

Answer 8

How much the rate of reaction changes when temperature is increased by 10 degrees celsius - usually 2.