Enzymes Kinetics Flashcards
Catalyst
provides an alternative pathway for the reaction in which the rate-determining step has a lower Gibbs activation energy
Temperature effect on catalyst
Rate constant is greater for the catalysed reaction, so the reaction is faster
Non-catalysed reaction
A single transition state, whereas the mechanism for the catalysed reaction involves the formation of an intermediate
Enzymes
- Protein molecules, catalyse a specific reaction, unchanged by the reactions they catalyse
Assumptions
Michaelis Menten model
- The enzyme binds a single substrate with two distinct steps.
- The substrate binds reversibly but product formation is irreversible
- Steady state approximation
Steady State Approximation
- 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
Lock and key model
- 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
Induced fit
- The tertiary structure of the protien to accomodate the substrate
- When product release active site returns to original shape
1st assumption equation
Differential rate equation for enzyme substrate complex
Rate of formation (k1) - rate of consumption (k2) = 0
- rate [E][S] - (k1- k2) [ES] = 0
2nd assuption made
Enzyme concentration
E0 - total concentration of enzyme
E - Free enzyme concentration
E0 = [ES] + [E]
Assumption 3
Concentration of substrate
- Much greater than the enzyme so [S] is usually constant
Concentration intial stage of enzyme substrate reaction
- Increase in enzyme substrate concentration and decrease in free enzyme concentration
Concentration final stage of enzyme substrate reaction
- Substrate concentration has been exhaused so there is a decrease in enzyme substrate concentation
- Increase in free enzyme concentration
Michaelis Menten equation
Rate of enzyme catalysed reaction = Vmax[S]/Km+[S]
Vmax
k2[E0]
Km
- Michaelis constant
- k2+k1/k1
When [S] is in large excess than Km the Michaelis equation is
- Vmax = k2 [E]0
- Rate of reaction independant to [s]
- [ES] = [E]0 so saturated
- 0 order with respect to [S]
When [S] is lower than Km the Michaelis equation is
- (k2 [E]0 [S])/Km
Rate of reaction increases linearly 1st order with respect to the substrate
Turnover number
- 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)
Km
- Substrate concentration at wich reaction velocity is half V max
- How tight enzyme binds to substrate
- Weak substrate > Km
- Good substrate < Km
Linweaver-burk equation
- 1/V = Km/Vmax[S] +1/Vmax
- Used to plot straight line graph eaiser to plot
