Enzymes and the Rate of Reaction
1
Wanak
Introduction: Metabolism is the sum total of chemical reactions in the body that are necessary for the
maintenance of life. Enzymes are large protein molecules that can speed up, and control chemical reactions that
would otherwise virtually never occur at normal body temperature, 37°C. Thousands of chemical reactions are
occurring in the human body every moment of life, and each of these reactions is controlled by a particular
enzyme.
The molecule with which an enzyme reacts is called a substrate. Enzymes are very specific; they react only with
their unique substrate. When enzymes were discovered, fast chemical reactions in the body (which took place
slowly in test tubes) could be explained. Enzymes speed up biochemical reactions by lowering the energy of
activation of their substrates.
Catalase is an enzyme which converts hydrogen peroxide into water and oxygen. The substrate for catalase is
hydrogen peroxide (H2O2)--is a product of cellular metabolism which can poison cells. If hydrogen peroxide
were allowed to build up even over a short period of time it would kill the cell. This is why hydrogen peroxide is
used to kill bacteria on open cuts. Catalase has to work very quickly to ensure that hydrogen peroxide
concentrations remain low. Catalase acts quickly; one molecule of it can deal with six million molecules of
hydrogen peroxide in one minute. This same reaction can be catalyzed by iron. However, to achieve the same
speed there would need to be about six tons of iron.
The Rate of Reaction of an enzyme can be measured to determine how fast the enzyme is
converting substrate into product. A rate is the speed at which something occurs during a
certain time period. Examples include 60 miles/hour, 20 mL per second (20 mL/sec) and 1.5
µl per minute (1.5 µl/min). Rates are calculated using the formula to the right, where Y is the dependant variable
and X is the independent. The 1 and 2 represent the first or second values you are cal