Lesson 15 - Product time graphs continued & factors affecting enzyme controlled reactions

Question 1

For an enzyme to catalyse a reaction, it must…

Answer 1

• Come into physical contact with a substrate(s)
• The substrate must be complementary to the active site
  = SUCCESSFUL COLLISION!

Question 2

What is activation energy?

Answer 2

The minimum energy required for molecules to react (breaking existing bonds/making new ones)

Question 3

What determines the shape of an enzyme’s active site?

Answer 3

Tertiary structure – held in place by selection of bonds – ionic/disulphide/hydrogen (which is in turn determined by amino acid sequence (primary structure))

Question 4

Name 4 factors that could affect the rate of enzyme action?

Answer 4

Temperature
pH
Enzyme concentration
Substrate concentration

Question 5

Formula for rate of reaction

Answer 5

change in product/change in time

Question 6

Enzyme concentration against rate of reaction graphs:

Answer 6

• begins with 0 rate of reaction
• as enzyme concentration increases, RoR increases
• after a point, the graph plateaus, meaning the RoR stays constant and substrate concentration is the limiting factor

Question 7

Substrate concentration against rate of reaction graphs:

Answer 7

• begins with 0 rate of reaction
• as substrate concentration increases, RoR increases
• after a point, the graph plateaus, meaning the RoR stays constant and enzyme concentration is the limiting factor

Question 8

Define a limiting factor

Answer 8

A factor is limiting when an increase in its value causes an increase in the rate of reaction

Question 9

what is V-max

Answer 9

the maximum velocity (ie rate) at which the enzyme catalysed the reaction – happens when all enzyme active sites are saturated with substrate

Question 10

What is pH?

Answer 10

A measure of its hydrogen ion concentration (H+)

The pH of a solution is calculated using the formula:
e.g. a hydrogen ion concentration [H+] of 1 x 10-9 therefore has a pH of 9

Question 11

Why do scientists measure the initial rate of reaction of enzyme-catalysed reactions?

Answer 11

they measure the rate at the start of a reaction before any factors, e.g. substrate concentration, have had time to change.

Question 12

Temperature against rate of reaction graphs:

Answer 12

• increase in KE, molecules move faster, more successful collisions, more E-S complexes and faster RoR
• the peak of the curve, optimum temperature. (Highest KE before denaturation)
• enzyme denatures, change in shape of enzyme’s active site. It’s no longer complementary to substrate, can’t bind, no E-S complexes, decrease in RoR

Question 13

pH against rate of reaction graphs:

Answer 13

• a peak on the graph: optimum pH
• on either side of the peak, the enzyme denatures. Which means its no longer complementary to substrate, can’t bind, no E-S complexes formed, so a decrease in rate of reaction