Enzymes

Question 1

What is an enzyme?

Answer 1

Enzymes are tertiary structure proteins that catalyse a wide range of reactions

Question 2

What is the function of enzymes?

Answer 2

Enzymes are biological catalysts so they lower the activation energy of a reaction

Question 3

Do enzymes get used up in reactions?

Answer 3

No

Question 4

What is the activation energy?

Answer 4

The minimum amount of energy required for a reaction to occur

Question 5

What part of an enzyme attaches to a substrate?

Answer 5

The active site

Question 6

Describe the shape of an active site

Answer 6

Specific and unique due to the sequence of amino acids

Question 7

Why is the unique shape of the active site in an enzyme important?

Answer 7

It ensures that enzymes can only bind to substrates that are complementary in shape

Question 8

What is the induced-fit model?

Answer 8

• Before the reaction the active site of an enzyme in not completely complementary to the substrate
• The active site will change shape as the substrate binds, forming an enzyme-substrate complex
• This distorts the bond in the substrate which leads to a reaction
• Once products are formed they are released and active site returns to its original shape

Question 9

What factors affect the rate of enzyme controlled reactions?

Answer 9

• Temperature
• pH
• Substrate concentration
• Enzyme concentration
• Competitive inhibitors
• Non-competitive inhibitors

Question 10

How does temperature affect enzyme controlled reactions?

Answer 10

As temperature increases the rate of reaction will increase due to more successful collisions between the substrate and the enzyme so more enzyme-substrate complexes form

However at too high a temperature there will be too much kinetic energy and the enzyme will denature and its active site will change shape resulting in enzyme-substrate complexes no longer being able to form as the active site is no longer complementary to the substrate

Question 11

How does pH affect enzyme controlled reactions?

Answer 11

• Too high/too low a pH will cause the enzyme to denature and its active site will change shape
• Enzyme-substrate complexes can no longer form as the active site is no longer complementary to the substrate

Question 12

How does substrate concentration affect enzyme controlled reactions?

Answer 12

• More substrate results in more successful collisions between the enzyme and the substrate
• More enzyme-substrate complexes are formed
• However the rate of reaction plateaus as enzyme concentration becomes the limiting factor as all active sites are saturated

Question 13

How does enzyme concentration affect enzyme controlled reactions?

Answer 13

• More active sites available so more successful collisions between the enzyme and the substrate
• More enzyme-substrate complexes are formed
• However the rate of reaction plateaus as substrate concentration becomes the limiting factor

Question 14

How do competitive inhibitors affect enzyme controlled reactions?

Answer 14

• They have a similar shape as the substrate and can bind to active site
• This prevents the substrate from binding to the enzymes active site
• If more substrate is added this will out-compete the inhibitor and knock them out of the active site

Question 15

How do non-competitive inhibitors affect enzyme controlled reactions?

Answer 15

• They bind to the enzyme away from the active site called the allosteric site
• This causes the active site to change shape and the substrate can no longer bind as the active site is no longer complementary to the substrate
• Enzyme-substrate complexes can no longer form