Enzymes

Question 1

Enzymes are biological catalysts.

State how a catalyst affects the rate of a reaction.

Answer 1

A catalyst increases the rate of a reaction

Question 2

What is a substrate?

Answer 2

The molecule changed in a reaction

Question 3

Name the part of an enzyme where substrate molecules bind.

Answer 3

Active site

Question 4

Enzymes have a ‘high specificity’ for their substrate.

Describe what this means.

Answer 4

Only one type of substrate will have a shape that is complementary to the shape of a specific enzyme’s active site

Question 5

Describe the ‘lock and key’ mechanism of enzymes.

Answer 5

• The substrate is the key
• The active site is the keyhole
• The enzyme is the lock

Question 6

Explain what happens when an enzyme begins to denature.

Answer 6

The shape of the enzyme’s active site changes, so a substrate will no longer fit

Question 7

List some factors that affect enzyme activity.

Answer 7

• Temperature
• pH
• Substrate concentration

Question 8

Explain the effect of temperature on enzyme activity.

Answer 8

• Increasing the temperature increases the rate at first
• If temperature gets too high, some of the bonds holding enzyme together break
• Enzyme begins to denature as active site changes shape

Question 9

(Exam-style question)

Answer 9

• If pH is too high or low, some of the bonds holding enzyme together break
• Enzyme begins to denature as active site changes shape

Question 10

(Exam-style question)

Explain why increasing the substrate concentration fails to affect the rate of an enzyme-controlled reaction after a certain point.

Answer 10

• After a certain point, all active sites on enzymes are full
• Increasing substrate concentration would not result in more substrate molecules entering active sites of enzymes
• Therefore, the rate of reaction is not affected