Enzymes

Question 1

Why are enzymes effective in small amounts

Answer 1

Reused repeatedly

Question 2

Problems with lock and key model

Answer 2

Wrongly portrays all enzymes as inflexible and does not explain why they lower activation energy

Question 3

Induced fit model

Answer 3

• active site of enzyme does not fit its substrate exactly
• enzyme flexible so changes shape of active site to fit substrate
• applies strain and DISTORTS bonds in substrate (lowering Ea)

Question 4

ROR - increasing temperature

Answer 4

• increases kinetic energy
• more successful collisions
• more enzyme substrate complexes

Question 5

ROR - temperature too high

Answer 5

• enzymes denature
• hydrogen bonds in active site break
• change of shape of active site

Question 6

ROR - sudden changes in pH

Answer 6

• extreme pH changes away from optimum
• ionisation of R groups changes with [H+]
• disrupts hydrogen and ionic bonds
• active site denatured

Question 7

ROR - concentration

Answer 7

• limiting factor
• some active sites are free
• active site saturation
• maximum capacity of active sites reached

Question 8

Competitive Inhibitor

Answer 8

• similar shape to substrate
• compete to bind to active site
• blocks substrate from active site
• increasing concentration of substrate limits effect of inhibitor

Question 9

Non-competitive Inhibitor

Answer 9

• attach to allosteric site of enzyme
• alters the shape of enzyme so no longer complementary to substrate
• concentration of substrate has no effect on inhibitor as they are not competing for the same binding site

Question 10

Suggest why enzymes are kept in an inactive form

Answer 10

• allow metabolic control
• control rate of reaction
• protect cell from damage

Question 11

Explain why increasing concentration of enzyme increases rate of reaction

Answer 11

• more activate sites available
• higher frequency of successful collisions between active site and substrate
• more enzyme substrate complexes formed

Question 12

Suggest why it is an advantage that an enzyme with different roles is found at slightly different pHs to its optimum

Answer 12

• shape of active site must adjust to accommodate different shapes
• slight changes in pH alter shape of active site
• enzyme can digest more than one protein

Question 13

Suggest why enzymes are often found at pHs other than their optimal pH

Answer 13

• many enzymes must work together
• they work at different rates
• enzyme activity can be controlled by pH