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?
There are two distinct steps in 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
