B3. Enzymes

Question 1

Define ‘enzymes’

Answer 1

Proteins that function as biological catalysts – they speed up chemical reactions but are themselves unchanged. Their action relies on their shape, as their substrate molecule (s) fit into their active site as in the lock & key hypothesis.

Question 2

What are catalysts?

Answer 2

Proteins produced by organisms that speed up a chemical reaction and remain unchanged at the end of the reaction.

Question 3

Properties of enzymes

Answer 3

• They are all proteins.
• Each enzyme catalyses one reaction.
• They can be used again and again.
• They are influenced by temp.
• They are influenced by pH.

Question 4

Describe the effects of temperature on enzyme activity

Answer 4

• As temperature increases, the chance of chance of substrate molecules and enzymes colliding also increases, so the rate of reaction goes up.
• This continues to an optimum (best) temperature for an enzyme. For most human enzymes the optimum temperature is 37C (body temperature).
• Above this temperature, the bonds holding the enzyme together start to break so it changes shape
• This deforms the active site, so enzyme and substrate cannot fit together – the enzyme has been denatured. Most enzymes denature above 50oC.

Question 5

Describe the effect of pH on enzyme activity

Answer 5

• The pH of a solution is how acidic or alkaline it is.
• Most human enzymes have an optimum pH of 7 (neutral). Some exceptions:
  Pepsin, a protease in the stomach has an acidic optimum (pH 2);
  Lipase in the duodenum has an alkaline optimum (pH 9)
  Salivary amylase in the mouth prefers a slightly-acidic pH of 6.8.
• Extreme of pH affect the shape of enzymes, denaturing them.