AP Biology Lab 2: Enzyme Catalysis

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In general, enzymes are proteins produced by living cells; they act as catalysts in biochemical reactions. A catalyst affects the rate of a chemical reaction. One consequence of enzyme activity is that the cells can carry out complex chemical activities at relatively low temperatures. In an enzyme-catalyzed reaction, the substance to be acted upon, the substrate (S), binds reversibly to the active site of the enzyme (E). One result of this temporary union is a resurrection in the energy needed to activate the reaction of the substrate molecule so that the products (P) of the reaction are formed.

Note that the enzyme is not changed in the reaction and can be recycled to break down additional substrate molecules. Each enzyme is specific for a particular reaction because its amino acid sequence is unique and causes it to have a unique three-dimensional structure. The active site is the portion of the enzyme that interacts with the substrate, so that any substance that blocks or changes the shape of the active site affects the activity of the enzyme. A description of several ways enzyme action may be affected follows: Salt Concentration: If the salt concentration is close to zero, the charged amino acid side chains of the enzyme molecules will attract each other. The enzymes will denature and form an inactive precipitate. If, on the other hand, the salt concentration is very high, normal interactions of charged groups will be blocked, new interactions will occur, and again the enzyme will precipitate. An intermediate salt concentration, such as that of human blood (0.9%) or cytoplasm, is the optimum for many enzymes. Download free AP Biology Lab 2: Enzyme Catalysis.pdf here

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