1.4.2: Enzymes

Question 1

Describe the lock and key model

Answer 1

• Active site is a fixed shape
• Due to random collisions the substrate collides and attaches to the enzyme
• Forming enzyme substrate complex
• Active site distorts substrate and lowers the activation energy
• Products are released and active site ready to be reused

Question 2

Describe the induced fit model

Answer 2

• Active changes shape to become complementary to substrate
• Distorts bonds in substrates and lowers the activation energy
• Products are removed and active site changes to original shape

Question 3

What are the 5 factors affecting enzymes?

Answer 3

1) Temperature
2) pH
3) Substrate concentration
4) Enzyme concentration
5) Inhibitors

Question 4

How does temperature increase enzyme activity?

Answer 4

• Enzyme and substrate increase their kinetic energy so they’re more likely to successfully collide and react
• Rate of reaction increases as temperature increases
• More enzyme substrate complexes form per second

Question 5

How does extreme temperature affect enzyme activity?

Answer 5

1) Enzymes has lots of kinetic energy
2) Weak H bonds and ionic bonds between R groups between amino acids break causing a change in specific tertiary structure which may change the shape of the active site
3) Substrate no longer complementary to enzyme meaning less enzyme substrate complexes formed
4) Enzyme is denatured

Question 6

What happens to enzyme if pH changes?

Answer 6

• Charge on R groups from amino acids is altered
• Ionic bonds from tertiary structure are changed
• Active site changes, substrate is no longer complementary and doesn’t bind
• Less enzymes substrate complexes and rate of reaction decreases

Question 7

Increasing substrate concentration on rate

Answer 7

• Increases as more active sites are filled and increased rate of reaction due to more enzyme substrate form
• Rate of reaction stops increases as active sites become saturated. Enzyme concentration is now limiting factor

Question 8

What are competitive inhibitors?

Answer 8

• Similar structure to substrate
• Bind to active site and prevent substrate from binding temporarily
• Fewer enzyme substrate complexes per second
• Reduce the rate of reaction
• Some product still formed but takes longer
• Overcome by increasing substrate concentration

Question 9

What are non-competitive inhibitors?

Answer 9

• Bind away from active site called allosteric site
• Causes change to shape of active site so substrate can’t bind
• Fewer enzyme substrate complexes formed
• Rate of reaction decreases
• Not overcome by increasing substrate concentration