Draft: Enzyme Kinetics

The rate of a reaction is measured as the change in concentration of product(s) per unit time. For most biological mechanisms, product increases too slowly to be effective. Enzymes are needed, which speed up the reaction rate. In the presence of enzymes, the concentration of products increases fastest at the beginning and then decreases over time as substrates are used. The rate of the reaction eventually levels off and remains constant when the mechanism reaches an equilibrium. Kinetic experiments assess the initial velocity/rate of a reaction because this is when the concentration of subtrates is approximately constant, there are minimal product(s), and the enzyme-substrate complex is most rapidly formed. The initial velocity of a reaction can be found by determining the initial slope of a [products]/time graph. To analyze an enzyme's activity, the initial velocity at different subtrate concentrations is measured, keeping the amount of enzyme constant throughout. The initial velocities of these reactions are plotted against the concentration of subtrate. It can usually be seen that the change in initial velocity increases the fastest at the beginning and levels off as the concentration of subtrate increases. This is because when the concentration of subtrate reaches a certain concentration, the enzymes are saturated, and the reaction is going the fastest it can go. This is known as the maximum velocity.