Enzymes Kinetics

Question 1

Catalyst

Answer 1

provides an alternative pathway for the reaction in which the rate-determining step has a lower Gibbs activation energy

Question 2

Temperature effect on catalyst

Answer 2

Rate constant is greater for the catalysed reaction, so the reaction is faster

Question 3

Non-catalysed reaction

Answer 3

A single transition state, whereas the mechanism for the catalysed reaction involves the formation of an intermediate

Question 4

Enzymes

Answer 4

• Protein molecules, catalyse a specific reaction, unchanged by the reactions they catalyse

Question 5

Assumptions

Michaelis Menten model

Answer 5

• The enzyme binds a single substrate with two distinct steps.
• The substrate binds reversibly but product formation is irreversible
• Steady state approximation

Question 6

Steady State Approximation

Answer 6

• This means the [ES] remains constant.
• Rate of formation of ES = Rate of consumption of ES
• Only be applied when the first step of the reaction is significantly slower than subsequent step in an intermediate-forming consecutive reaction

Question 7

Lock and key model

Answer 7

• Hydrophobic area of the compound binds to the hydrophobic area of the enzyme
• Positively charged area of subrate bind to negative areas of active site
• Conplementory shape

Question 8

Induced fit

Answer 8

• The tertiary structure of the protien to accomodate the substrate
• When product release active site returns to original shape

Question 9

1st assumption equation

Differential rate equation for enzyme substrate complex

Answer 9

Rate of formation (k1) - rate of consumption (k2) = 0
- rate [E][S] - (k1- k2) [ES] = 0

Question 10

2nd assuption made

Enzyme concentration

Answer 10

E0 - total concentration of enzyme
E - Free enzyme concentration
E0 = [ES] + [E]

Question 11

Assumption 3

Concentration of substrate

Answer 11

• Much greater than the enzyme so [S] is usually constant

Question 12

Concentration intial stage of enzyme substrate reaction

Answer 12

• Increase in enzyme substrate concentration and decrease in free enzyme concentration

Question 13

Concentration final stage of enzyme substrate reaction

Answer 13

• Substrate concentration has been exhaused so there is a decrease in enzyme substrate concentation
• Increase in free enzyme concentration

Question 14

Michaelis Menten equation

Answer 14

Rate of enzyme catalysed reaction = Vmax[S]/Km+[S]

Question 15

Vmax

Answer 15

k2[E0]

Question 16

Km

Answer 16

• Michaelis constant
• k2+k1/k1

Question 17

When [S] is in large excess than Km the Michaelis equation is

Answer 17

• Vmax = k2 [E]0
• Rate of reaction independant to [s]
• [ES] = [E]0 so saturated
• 0 order with respect to [S]

Question 18

When [S] is lower than Km the Michaelis equation is

Answer 18

• (k2 [E]0 [S])/Km
  Rate of reaction increases linearly 1st order with respect to the substrate

Question 19

Turnover number

Answer 19

• Number of substrate molecules converted into the product by the enzyme in a unit time
• When enzyme is fully saturated with substrate
• Measure of enzyme capacity and efficiency
• k2 = Vmax/[E]0 (s^-1)

Question 20

Km

Answer 20

• Substrate concentration at wich reaction velocity is half V max
• How tight enzyme binds to substrate
• Weak substrate > Km
• Good substrate < Km

Question 21

Linweaver-burk equation

Answer 21

• 1/V = Km/Vmax[S] +1/Vmax
• Used to plot straight line graph eaiser to plot