Topic 1---A: Biological molecules- 6. Enzymes

Question 1

What are enzymes?

Answer 1

They are proteins that speed up chemical reactions by acting as biological catalysts.

Question 2

What components do enzymes have?

Answer 2

• Active site (specific shape) which is part of the enzyme
• Substrate molecules which is the substance the enzyme interacts with (active site binds to substrate)

Question 3

What is activation energy?

Answer 3

The energy that needs to be supplied before a chemical reaction will start.

Question 4

How do enzymes speed up reactions?

Answer 4

• They lower the amount of activation energy that’s needed.
• Often making reactions happen at lower temperatures
• Speeding up the rate of reaction

Question 5

What gets formed when a substrate fits into the enzymes active site?

Answer 5

Enzyme-substrate complex which is what lowers the activation energy.

Question 6

What are the two reasons why enzyme-substrate complexes lower the activation energy?

Answer 6

• If 2 substrate molecules need to be joined, being attached to the enzyme holds them close together which reduces any repulsion between the molecules so they can bond more easily.
• If the enzyme is catalysing a breakdown reaction, fitting into the active site puts a strain on bonds in the substrate so the substrate molecule breaks up more easily.

Question 7

What are the two models of enzyme action?

Answer 7

• Lock and key model
• Induced fit model

Question 8

Lock and key model

Answer 8

• This is where the substrate fits into the enzyme in the same way that a key fits into a lock.
• Active site and substrate have a complementary shape.

Question 9

Why did scientists modify the old lock and key model and come up with the induced fit model?

Answer 9

• Evidence showed that the enzyme-substrate complex changed shape slightly to complete the fit.
• This locks the substrate in even more tightly to the enzyme.

Question 10

Induced fit model

Answer 10

• In the presence of a substrate, the active site undergoes a change in shape to allow a better fit between the active site and substrate.
• Forming an enzyme-substrate complex.

Question 11

What happens after the products are released from the enzyme?

Answer 11

The active site returns to it’s original shape and can bind to the next substrate molecule.

Question 12

Enzyme properties (how are they specific?)

Answer 12

• There related to their tertiary structure.
• Their very specific so they can only usually catalyse one reaction as only one complementary substrate will fit into the active site.
• The active sites shape is determined by the enzymes tertiary structure which is determined by the enzymes primary structure.
• Each different enzyme has a different tertiary structure and so a different shaped active site.
• If the substrate doesn’t match the active site an enzyme-substrate complex won’t be formed so the reaction can’t be catalysed.

Question 13

What happens if the tertiary structure of a protein is altered?

Answer 13

• The shape of the active site will change.
• Substrate won’t fit into the active site so an enzyme-substrate complex can’t be formed.
• Enzyme will no longer be able to carry out its function (catalysing reactions).

Question 14

How is the tertiary structure of an enzyme altered?

Answer 14

By changes in pH or temperature

Question 15

How is the primary structure of a protein determined?

Answer 15

• By a gene
• If a mutation occurs in that gene, it could change the tertiary structure of the enzyme produced.

Question 16

Intracellular

Answer 16

Enzyme action within cells

Question 17

Extracellular

Answer 17

Enzyme action outside cells

Question 18

What is the main difference between the lock and key model and the induced fit model?

Answer 18

In the lock and key model:
- The active site has a fixed shape that is complementary to the substrate.
But in the induced fit model:
- The active site has to change shape slightly to allow the substrate to bind slightly.