Lab Manual - eScience Labs

Lab 9: Enzymes
is the pocket where the substrate aaches and where the reacon occurs. Aer the enzyme/substrate
complex forms and catalysis occurs, the “new” substrate is released from the acve site, and the enzyme
can repeat the process. Enzymes levels are not reduced or altered during the reacon. This
means they are efficient and can be used repeatedly.
Enzymes determine the rate at which the reacon occurs (not how it occurs). Their acvity is affected
by temperature, pH, enzyme and substrate concentraon, and other chemicals that may be present
(such as salts, which can change the protein structure).
Variaons in temperature and alkalinity can change the shape of the proteins, such as enzymes, which
makes them inacve (they can no longer bind to their substrate). The pH can alter charge of the protein,
once again changing its shape and rendering them inacve.
The concentraons of both the enzyme and substrate determine the reacon rate (Figure 2). Remember
that high reacon rates do not always translate into rapid me of compleon (it also depends on
the amount of substrate!).
Figure 2: Substrate Saturaon Curve
Acvators are chemicals that bind to the acve site of the enzyme
and help it to bind to the substrate. They are somemes
called cofactors or organic coenzymes.
Inhibitors are chemicals that interfere with the binding of the
substrate to the enzyme. There are two types:
Many drugs and poisons are enzyme
inhibitors. For example, aspirin
inhibits an enzyme that leads to
inflammaon.
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