enzyme kinetics Flashcards
What does a catalyst do?
Catalyst: provides an alternative pathway
for the reaction in which the rate-
determining step has a lower Gibbs
activation energy than that of the non-
catalysed reaction
How does rate differ based on temperature?
At a given temperature, the rate
constant is greater for the
catalysed reaction, so the reaction is
faster
How does the reaction process differ based on if its catalysed or not?
Non-catalysed reaction proceeds through a single transition state,
whereas the mechanism for the catalysed reaction involves the
formation of an intermediate
What are enzymes?
Enzymes: protein molecules, catalyse a specific reaction, unchanged by
the reactions they catalyse
What are the two steps of an enzyme catalysed reaction?
*The first step is reversible
This and other factors affect the kinetics of enzyme reactions
*The second step is irreversible
Describe properties of enzyme bonding and process
- The enzyme binds a single substrate (the model assumes cofactors are already
bound) - There are two distinct steps. The substrate binds reversibly but product
formation is irreversible - A steady state approximation applies (quantitative analysis of the kinetics
of enzyme-catalysed reactions)
What happens after the start of an enzymic reaction (rate)?
- Very soon after the start of an enzymatic reaction a ‘steady state’ situation
is reached. This means the [ES] remains constant.
Rate of formation of ES = Rate of consumption of ES (conversion to E + P)
How does E & ES change in the initial reaction phase?
n the initial phase of the reaction: [E] ↓ and [ES] ↑
[ES] and [E] remain steady over most of the reaction time.
Only at the end of the reaction, when [S] is exhausted, does [ES] decline
What is the Michaelis menten equation?
V (rate of reaction) = max(S)/Km+ (s)
What are some properties to understand of the MM equation?
The velocity (rate) of an enzyme catalysed
reaction increases in a non-linear fashion
Vmax or (rate)max=maximum velocity the reaction
can achieve. It is equal to K2[E]0
KM=the Michaelis constant. It is (
k2 +
k-1)/k1
How does the enzyme differ based on (S)? + vmax rate
The enzyme is said to be saturated. If the [S] increases, no more enzyme–
substrate complexes can be formed, and the rate of the reaction is independent
of [S]
Vmax=maximum rate that a given enzyme can achieve, indicates the velocity of
the reaction when the enzyme active site is saturated and indicates the
maximum number of moles of S that can be processed in a unit of time (mol s-1)
How is rate affected by S?
Rate of the reaction is independent of the [S].The rate of reaction remains constant at the maximum value, Vmax, and the reaction is zero order with respect to [S]
How does the equation change when S is larger than KM?
V = Vmax = k2
How does the equation change when S is very small?
V = Vmax (S)/Km = K2 (E)0 (S)/Km
What is the turnover number?
The number of substrate molecules converted into product by an enzyme
molecule in a unit time when the enzyme is fully saturated with substrate
It is related to Vmax and is equivalent to the rate constant
k2. It is a comparative measure of enzyme capacity or enzyme efficiency
What is the equation for the turnover number?
turnover number = K2 = Vmax/ E0 (s-1)
What is KM?
KM= substrate concentration ([S]) at which the
reaction velocity is half of V maximum (Vmax/2)
What does KM indicate?
KM gives an indication of how tightly the enzyme
binds its substrate
How does km differ in weak substrates vs good substrates?
Weak substrate, large
KM: a high [S] is needed to
achieve Vmax/2 (and even more to reach Vmax!)
Good substrate, low
KM: Only a low [S] needed to
reach Vmax
What is the line weaver burk equation?
1/V = KM/V~~~S+ 1/Vmax
