B3 - Enzymes and Mutations

Question 1

What do enzymes do?

Answer 1

Biological catalysts - speed up chemical reactions.
Most of these reactions, such as
• photosynthesis
• respiration
• protein synthesis
take place inside living cells.
Enzymes can be used to catalyse the same type of reaction many times.

Question 2

Describe how enzymes catalyse reactions.

Answer 2

• The substrate molecules fit into the active site ( enzyme - substrate complex ) which brings them together so they can form a bond. This makes a bigger molecule and leaves the enzyme free to catalyse another of these reactions.

Sometimes:
• A big substrate molecule fits into the active site and a bond breaks. Two smaller product molecules are made.

Question 3

How do different temperatures affect enzymes?

Answer 3

Low temp - enzyme and substrate molecules have less energy = do not move very fast = they do not collide very often -> rate of reaction is low.

High temp - enzyme and substrate molecules move more quickly = collide more often = a faster rate of reaction.

Too high - shape of enzyme’s active site changes.
Substrate molecule cannot fit into active site. Rate of reaction slows - eventually stops. Change = irreversible. The enzyme is denatured.

Question 4

What is the usual temperature coefficient of an enzyme and how do you work it out?

Answer 4

Many enzymes have a Q10 of about 2. This means that the rate of reaction doubles when the temperature is increased by 10 °C.

Q10 = rate at higher temperature ÷ rate at lower temperature

Question 5

What happens if the pH is not an enzymes optimum pH?

Answer 5

• The shape of the active site changes.
• The substrate molecules cannot fit into it.
• The enzyme has been denatured.

Question 6

What can mutations be caused by?

Answer 6

• Often it is a copying error when DNA is replicating itself
• chemicals, such as tar in tobacco smoke
• ionising radiation, such as X-rays and ultraviolet light.

Question 7

What happens when a gene mutates?

Answer 7

The sequence of its bases is changed. This changed gene may not now code for the protein it normally codes for. Instead, it may now code for a different protein, which has a different shape and may not be able to do its normal job.

Question 8

Why might some mutations be harmful?

Answer 8

It may cause:
• cells to keep on dividing (cancer)
• a particular enzyme not to work, causing a
serious illness
• slightly differently shaped haemoglobin molecules (sickle cell anaemia).