Biology 9th Chap 7 : Topic 3 - Maryam Publications

Biology Chapter 7 : Topic 3

Mechanism of Enzyme Action

1 / 15

What is the first step in the mechanism of enzyme action?

A) Release of enzyme

B) Breakdown of enzyme

C) Binding of substrate to the active site of the enzyme

D) Formation of products

2 / 15

The region of an enzyme where a substrate binds is called the:

A) Catalyst site

B) Active site

C) Reaction center

D) Protein site

3 / 15

Which term describes the temporary combination formed when an enzyme binds to its substrate?

A) Catalyst-substrate complex

B) Enzyme-product complex

C) Enzyme-substrate complex

D) Protein complex

4 / 15

According to the lock-and-key model, the substrate fits into the enzyme because:

A) The substrate supplies energy.

B) Both are made of proteins.

C) Their shapes are complementary.

D) The enzyme changes into the substrate.

5 / 15

What happens immediately after the enzyme-substrate complex is formed?

A) The substrate leaves unchanged.

B) The substrate is converted into product(s).

C) The enzyme becomes inactive permanently.

D) The enzyme is destroyed.

6 / 15

Which sequence correctly represents enzyme action?

A) Enzyme → Product → Substrate

B) Substrate → Product → Enzyme

C) Product → Substrate → Enzyme-substrate complex

D) Enzyme + Substrate → Enzyme-Substrate Complex → Product(s) + Enzyme

7 / 15

After the reaction is completed, the enzyme:

A) Is destroyed.

B) Remains unchanged and can be reused.

C) Changes into another enzyme.

D) Becomes part of the product.

8 / 15

Why does an enzyme usually act on only one type of substrate?

A) It produces energy.

B) It contains DNA.

C) It can move freely in cells.

D) It has a specific active site shape.

9 / 15

Which diagrammatic relationship best represents enzyme action?

A) Enzyme + Product → Substrate

B) Substrate + Product → Enzyme

C) Enzyme + Substrate → Enzyme-Substrate Complex → Product(s) + Enzyme

D) Product + Enzyme → Substrate

10 / 15

In the lock-and-key analogy, the enzyme represents the:

A) Key

B) Product

C) Catalyst inhibitor

D) Lock

11 / 15

In the lock-and-key analogy, the substrate represents the:

A) Active site

B) Product

C) Lock

D) Key

12 / 15

A substrate fails to bind to an enzyme because its shape does not match the active site. Which characteristic of enzymes does this demonstrate?

A) Reusability

B) Specificity

C) Catalysis

D) Denaturation

13 / 15

What is the main function of the enzyme-substrate complex?

A) To store energy permanently

B) To form new enzymes

C) To provide a site where the reaction occurs more easily

D) To destroy the substrate immediately

14 / 15

During enzyme action, the substrate is:

A) Unchanged throughout the reaction

B) Converted into an enzyme

C) Destroyed without forming products

D) Converted into product(s)

15 / 15

Which statement best explains why enzymes speed up reactions?

A) They provide permanent energy to cells.

B) They become products themselves.

C) They increase activation energy.

D) They lower the activation energy required for the reaction.

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