Enzyme Kinetics Flashcards
What is the velocity of a reaction?
It is the rate of the reaction. Change in concentration of product or reactant per unit time. It is usually measured by the rate of formation of the product(s)
What is a second-order reaction?
A chemical reaction where the rate of reaction is proportional to the square of the concentration of one reactant
What is a first-order reaction?
A chemical reaction where the rate of reaction is proportional to the concentration of one reactant
Explain the shape of the [Concentration] vs Time graph
General trend: Rate of reaction increases at a decreasing rate and eventually comes to a plateau. This is because over time, as the [substrate] decreases (converted to product), the frequency of effective collision between the substrate and the active site of the enzyme decreases.
How will an increase in [substrate] affect the velocity of an enzyme-catalysed reaction?
The increase in [substrate] will increase the frequency of effective collision between the substrate and the active site of the enzyme. This will result in an increase in the velocity of the reaction. Hence, the initial gradient of the [concentration] vs Time graph will be steeper.
What is Vmax?
The theoretical maximum velocity of a reaction attainable when Enzyme (total) = Enzyme-substrate complex -> i.e. all the enzymes are saturated by the substrate.
Why is Vmax theoretical?
To attain Vmax, [E-total] = [ES complex]. However, in order to achieve that, we need to supply a very high concentration of substrate to shift the equilibrium to the right. Furthermore, it is unlikely that all the enzymes will be saturated (i.e. bounded to a substrate)
What are the disadvantages of the Michaelis-Menten plot?
[Substrate] may be too concentrated that it forms a precipitate during the reaction. Hence, it would be difficult to estimate Vmax -> Hence difficult to determine the value of Km (since the value of Km is the [S] when the velocity of the reaction is half-maximum)
What is Km?
value of Km is the [S] when the velocity of the reaction is half-maximum
It is also a measure of the affinity of the enzyme for its substrate. It is inversely related to the affinity to the substrate.
What is Kd (Dissociation constant)
Ratio of the [free enzyme and substrate] to the [enzyme-substrate complex]
What is Kcat?
The number of substrate molecules converted to product per unit time when the enzyme is saturated with the substrate. It measures the maximal catalytic activity of an enzyme. Kcat = Vmax/[E-total]
What is the catalytic efficiency of an enzyme?
It is the ratio of Kcat to Km. The higher the catalytic efficiency, the higher the v0.
What are enzyme inhibitors?
Enzyme inhibitors are molecules that bind to enzymes and decrease their activity.
What are the types of inhibitors?
Irreversible and reversible inhibition (Competitive, Uncompetitive and non-competitive inhibition)
What is irreversible inhibition/ suicide inhibition?
Occurs when the inhibitor forms covalent bonds with functional groups at the active site of the enzyme. This effectively decreases the amount of active enzymes, hence decreases Vmax. No change in Km (affinity of the enzyme) because Km = [E][S]/[ES], and [E] and [ES] are reduced by the same extent. This is because when the inhibitor binds to the enzyme, the number of free enzymes decreases, which means that the number of ES complex that can be formed will be decreased by the same extent.
The inhibitor neither dissociates the enzyme-inhibitor complex nor restore enzyme activity upon dialysis of he solution.
