Enzymes

Question 1

Enzymes

Answer 1

Enzymes are proteins that catalyse reactions. The chemical reactants that enzymes bind to are called substrates. Enzymes lower the amount of activation energy often making reactions happen at a lower temperature.

Question 2

Active site

Answer 2

They catalyse specific reactions.
The active site has a specific shape for each enzyme.
Substrates with a complementary shape to the active site of an enzyme can bind to form an enzyme-substrate complex.
The shape of the active site is determined by the tertiary structure of the polypeptide.

Question 3

The lock and Key theory

Answer 3

The model proposes that the enzyme and substrate fit together perfectly.
The substrate is a key fitting into a lock (the enzyme).

Question 4

Induced fit model

Answer 4

more dynamic interaction between enzyme and substrate.
as an enzyme and substrate come together, their interaction causes a small shift in the enzyme’s structure.
The shift means that the enzyme and substrate can bind to form an enzyme-substrate complex and catalyse a reaction.
This model is now more widely accepted.

Question 5

Reaction rate is influenced by the relative enzyme and substrate concentrations

Answer 5

Substrate concentration

Increasing the concentration of the substrate increases the numbers of substrate molecules that can form enzyme-substrate (ES) complexes at any one time.
This increases the initial rate of reaction but when all the enzyme molecules are engaged in ES complexes the rate cannot increase any further.
The rate will then plateau because the enzyme is said to be saturated.

Question 6

Inhibitors

Answer 6

Inhibitors are chemicals that slow down the rate or stop the reaction altogether.

Question 7

Competitive inhibitors

Answer 7

similar in shape to the usual substrate and affect the active site directly, blocking access for the formation of ES complexes.

Increasing the substrate concentration can compensate for the effects of a competitive inhibitor as there is no permanent damage to the shape of the active site.

Question 8

Factors affecting enzyme activity

Answer 8

Temperature
PH
Substrate concentrations
Enzyme concentrations

Question 9

Non competitive inhibitors

Answer 9

Bind to another site on the enzyme.
Alter the active site structure so enzyme-substrate complexes cannot form.

Question 10

Competitive Inhibitors

Answer 10

Bind directly to the active site.
Block access for substrates so enzyme-substrate complexes cannot form.