Enzye Kinetics Flashcards
1
Q
Zero order
A
- rate of reaction is independent of (reactant or substrate) but proportional to (catalyst or enzyme)
2
Q
First order rate
A
- proportional to concentration of reactant to first power
3
Q
Second order reaction
A
- rate proportional to conc. Of 2 substrates or of 1 to 2nd power
- v=k[S1][S2]
4
Q
Pseudo first order
A
- rate appears to depend on concentration of only one substrate
- S1 + S2—-> P
- if [S2] is very high and [S1] is very low, the rate will be proportional to [S1] only
5
Q
How do enzymes lower activation energy
A
- by stabilizing transition state complexes
- no effect on Keq
6
Q
Michaelis-Menten
A
- v= Vmax[S]/ Km + [S]
- assumes formation of enzyme-substrate complex
- It assumes that the ES complex is in rapid equilibrium with free enzyme
- breakdown of ES to form products is slower than formation of ES and breakdown of ES to re-form E and S
7
Q
Saturation effect
A
- at low substrate concentration in enzyme catalyzed reactions the velocity slopes off from first order to zero order kinetics at high substrate concentrations
- in first order substrate-enzyme collision is rate limiting
- In zero-order portion the enzyme is saturated and the rate limiting step is occurring on the enzyme surface
8
Q
Lineweaver-Burk Equation
A
1/V0 = Km/Vmax X 1/[S] + 1/Vmax
9
Q
Km
A
- small = tight binding, high = weak binding
- different pH’s and temperatures result in different Km’s
- the value of Km approximate the physiological concentration of the true substrate in many cases
- allows for substrate control and elimination
10
Q
Turnover number
A
- kcat
- number of substrate molecules converted to product per enzyme molecule per unit of time
- measure of enzymes maximal catalytic activity
11
Q
Enzyme Efficiency comparison
A
- if the enzyme is saturated with S, the one with highest k2 is most efficient. But living cells don’t normally have saturated enzymes
- best enzyme is one with the highest k2/Km
- kcat/Km: specificity constant
12
Q
Effect of pH on enzyme activity
A
- enzymes have optimum pH’s
- depends on acid-base behavior of AA in active sites
- Extreme pH levels will produce denaturation
13
Q
Effect of Temperature on Enzyme Activity
A
- increases with temperature
- doubles with 10 degree rise
- most enzymes denatured at 70 degrees
14
Q
Sequential Reactions (single displacement)
A
- substrates must combine with the enzyme to form a ternary complex before catalysis can proceed
15
Q
Ping-pong mechanisms (double-displacement)
A
- one or more products are released from the enzyme before all the substrates have been added
