Enzyme Kinetics Flashcards
The velocity (v) of a simple reaction is measured by the disappearance of reactant (A) or by the appearance of product (P) per unit time, and is a function of the concentration of reactant. What is the equation for this?
v = d[P]/dt = -d[A]/dt = k[A]
give the velocity equation for a zero order reaction
v= k
give the velocity equation for a first order reaction
v = k[A]
give the velocity equation for a second order reaction
v = k[A]^2
What are the assumptions of the michaelis-menten equation?
- use only initial velocities, then [P] = 0 and therefore k4 can be ignored
- [ES] is constant, the “steady state” assumption
What is the michaelis-menten equation?
v = Vmax [S] / Km + [S]
When does Vmax = K3 [Etotal]
When [S] is very high, the enzyme will be saturated with S such that [ES] = [Etotal]
What does it mean in terms of saturation, for an enzyme to be at Vmax
since the enzyme is saturated with S, adding more S will not result in an increase in activity - this represents Vmax
Km = ?
(k3 + k2) / k1
At very low [S], the change in velocity with [S] approximates a linear response. This region is ____-____ order kinetics
pseudo-first
At very high [S], the velocity approaches Vmax in an asymptotic fashion. This region represents ____-____ order kinetics (the v no longer varies with an increase in [S]
pseudo-zero
The Km equals the [S] at which the velocity is what?
one-half maximum
Enzymes with lower Km, are said to have a ___ affinity for their substrates than enzymes with a higher Km
greater
A lower Km means a lower Km means a lower concentration of S is required to achieve what?
1/2 Vmax
Since Km represents (k3 + k2) / k1, a low Km means ___ of ES is more rapid than the ___ of ES
S + E -> ES -> E + P
formation; breakdown
In most cases, k3 is the ___ ____ step in catalysis, and therefore may be called kcat, or the turnover number
rate limiting
If one knows the Vmax, and [Etotal], the value of kcat can be calculated and will be what?
the moles of product formed per mole of enzyme per unit time, at maximum velocity
give the equation for the lineweaver-Burk plot
reciprocal of michaelis-menten
1/v = (Km/Vm)(1/S) + 1/Vm
What is the slope of the line in a lineweaver-burk plot? Y intercept? X intercept?
(m) = Km/Vm ; 1/Vm; -1/Km
