The Rate of Enzyme Reactions

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BIOL 130-017

Room: B2 151

Time: Wed 930AM - 12:20AM

Date of Experimentation: 11/04/09

The Rate of Enzyme Reactions


The purpose of this lab was to investigate what factors affect the direction of an enzyme reaction. The variables tested in this experiment were substrate concentration, enzyme concentration and reaction time.  Enzymes are important biological catalysts that are required to drive chemical reactions for normal cell function. A catalyst is a substance which promotes chemical change without being consumed in the reaction. (Hasselberger, F.X. 1978) They are also important metabolic mediators, responsible for every reaction in the cell. (Karp, G. 2007) In this experiment two types of enzymes were used to test the variables of the experiment. The enzymes were salivary amylase and phosphorylase.

Enzymes are used to accelerate the rates at which a favourable chemical reaction proceeds, however there are factors that affect the effectiveness of the enzyme activity.  First, all of the chemical reactions take place at an active site. This is the part of the enzyme molecule that is directly involved with the binding of the substrate.  Substrates are reactants bound by an enzyme. (Kuby, S.A. (1991).

When the substrate concentration increases, the rate of enzyme activity will increase as well. This is because there are more interactions between the substrate and enzyme molecules. However, gradually a maximum will be reached and at this point the rate of enzyme activity will remain constant. This is when all the available enzyme, is saturated with substrate,  has been converted to ES, enzyme substrate complex. (Karp,G. 2007) The rate then becomes independent of substrate concentration. (Hasselberger, F.X. 1978)  When the enzyme concentration increases, the rate of enzyme activity would also increase on one condition, there would have to be an excess of substrates for the enzymes to react with. If there wasn't any excess amount of substrates, then the rate of enzyme activity wouldn't change. Therefore, the reaction must be independent of the substrate concentration. (Hasselberger, F.X. 1978)


In the following experiment, two tests were carried out using two different enzymes. Salivary amylase is a digestive enzyme found in saliva and is involved with the digestion of starch molecules, breaking off maltose molecules from the ends of starch chains using water molecules. This process is called hydrolysis, a chemical reaction in which water molecules are used to break down a compound. After the food is swallowed, salivary amylase is carried to the stomach and intestines, where it aids other digestive enzymes (Shadan, S. 2007) Salivary amylase was used as a starch indicator in this experiment. Different concentrations of this enzyme was added to test tubes that contained different solutions. The iodine test was then used to test for the presence of starch.  The Benedict test was then used to test for reducing sugars.

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        The second enzyme phosphorylase also acts on starch however it breaks down glucose molecules using phosphoric acid. This process is called phosphorolysis, when the chemical reaction uses phosphoric acid to break down molecules. The difference between salivary amylase and phosphorylation is the water concentration doesn't affect the direction of the enzyme activity. During phosphorlysis, the energy from the breaking the bonds between glucose-glucose is used to create glucose-1-phosphate. Therefore, the direction of the enzyme reaction is determined by the concentrations of reactants and products. (Fesht, A., 1977) In the experiment, glucose-1-phosphate and lguose were used to indicate the presence of ...

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