Biological molecules - ENZYMES

Question 1

What happens to globular proteins (enzymes) if they are taken out of water?

Answer 1

If taken out of water, the protein will unravel and change shape, as the hydrophilic groups no longer have access to water.

Question 2

What is the induced fit model?

Answer 2

The substrate binds to the active site of the enzyme; the induced fit model tells us the tertiary structure of the enzyme changes, straining the chemical bonds in the substrate, lowering the activation energy.

Question 3

What do enzymes do? (2 marks)

Answer 3

They catalyse biological reactions - decrease activation energy by providing an alternative pathway.

Question 4

What is activation energy?

Answer 4

The energy needed to break bonds

Question 5

What are inhibitors?

Answer 5

Inhibitors prevent successful collisions - for example, different substrates will not be complementary to all enzymes; hence blocking the active sites.

Question 6

What are non-competitive inhibitors?

Answer 6

Non-competitive inhibitors are chemicals that bind to the enzyme and change its shape; eventually all enzymes will bind to non-competitive inhibitors.

Question 7

What are competitive inhibitors?

Answer 7

Competitive inhibitors have similar shapes to the substrate, hence competing with the substrate for the available active site. Competitive inhibitors are not permanently bound to the enzyme active site, however.

Question 8

What is an allosteric inhibitor?

Answer 8

Allosteric inhibitors slow down enzyme activity by deactivating the enzyme. An allosteric inhibitor is a molecule that binds to the enzyme at an allosteric site.

Question 9

Why do enzymes increase the rate of reaction? (PPQ)

Answer 9

Enzymes:
- Reduce activation energy
- Due to bending bonds//without the enzyme, very few substrates have sufficient energy for reaction

Question 10

Lyxose binds to the enzyme, and increases rate of reaction. Explain (PPQ)

Answer 10

• Binding alters the tertiary structure of the enzyme (if lyxose is acting as an inhibitor)
• Causing a change in the active site shape
• Hence more successful enzyme-substrate complexes formed

Question 11

Suggest two variables that need to be controlled when investigating the effect of temperature on an enzyme rate reaction? (PPQ)

Answer 11

• pH
• Concentration of enzyme
• Volume of enzyme

Question 12

What are immobilised enzymes and give one example.

Answer 12

Immobilised enzymes are enzymes that are trapped, for example an enzyme trapped in gel beads.

Question 13

Suggest one advantage of immobilised enzymes.

Answer 13

• The enzyme is reused
• It is a continuous process

Question 14

Galactose has a similar structure to part of the lactose molecule. Explain how galactose inhibits lactase. (PPQ)

Answer 14

• Galactose is a competitive inhibitor / attaches to the active site (of lactase)
• Fewer enzyme substrate complexes formed.

Question 15

Why are enzymes effective in small quantities?

Answer 15

Enzymes are biological catalysts; they can decrease the activation energy of a reaction without being used up, hence can be reused

Question 16

If one of the amino acids of the enzyme active site was changed, why would the enzyme stop functioning?

Answer 16

• The altered amino acid codes for a different protein to be created.
• This protein has a different 3D structure and shape meaning that it’s active site, where the substrate should bind, can no longer fit.
• An enzyme substrate complex is not achieved and so the enzyme cannot work.

Question 17

Compare competitive and non-competitive inhibitors

Answer 17

Similarities:
- Rate of reaction is slower than without an inhibitor
- Substrate cannot bind to the active site

Differences:
- Non competitive inhibitors bind to the allosteric site/competitive inhibitors bind to the active site
- Non competitive inhibitors alter the shape of the active site/competitive inhibitors block the active site
- Competitive inhibitors can still achieve the maximum rate of the reaction
- Competitive inhibitors are more likely to be reversible