Enzymes rev aug '08

Enzymes rev aug '08 - Enzymes Laboratory 4 Introduction A...

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Enzymes Laboratory 4 Introduction A cell has literally thousands of reactions occurring within its environment every minute. These reactions are not individual random events; rather they are chains of reactions, networked, that occur in response to a need. Therefore if product W is required, the chain of reactions A---E must occur as well as X---Z . I / / F-- G-- H / / A---- B---->C---->D----> E + --------- W X--- Y-- Z The sum of all chemical reactions within an organism defines metabolism. A given chain of chemical reactions is called a metabolic pathway. 1
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Molecules are held together by covalent bonds. It took energy to create these bonds and that energy is stored in the bonds. Energy stored is released when the bonds are broken. However it takes additional energy to break those bonds. Think of a match. It has stored chemical bond energy in the molecules on its tip. These do not spontaneously combust rather friction energy is used to initiate the chemical reaction. This start up energy is termed the energy of activation or E a . Now think of the thousands of reactions occurring per minute in a cell. It takes time and considerable energy for these to occur. Too much time and too much energy are involved to effectively and efficiently support life. It takes time to build up to the energy levels need to reach E a and the heat by- 2
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product can be harmful to the cell. Enzymes solved the heat and time problems. Enzymes , usually proteins, are substances that act as biological catalysts ( they speed up chemical reactions) for chemical reactions. Enzymes work by lowering the amount of energy it takes to start up or trigger a chemical reaction. Since less energy is required it not only reduces the heat by-product but also speeds up the chemical reaction because it takes less time (1/10,000) to reach the lower E a . Every biological chemical reaction within a cell requires an enzyme . Thus in the above example, the reaction A---B requires an enzyme; B----C also requires an enzyme but it is different from the enzyme catalyzing A---B. The cells different reactions require different enzymes. However if a bacteria 3
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has an enzyme structurally the same as one found in humans, then that enzyme most likely performs the same task in both organisms. In chemical reactions such as AB A+B, AB is termed the reactant and A & B are called products. In enzyme equations, e.g. AB---e--- A + B + e , AB is termed a “substrate” . Thus a substrate is a molecule that binds with an enzyme and undergoes chemical modification. A product is the result of the substrate change into a new type of molecule. Note that e, the enzyme , appears both before and after the reaction occurs . That’s because an enzyme is neither changed nor destroyed by the reaction. The enzyme is immediately reusable, some recycling more than a million times per minute, a very effective use of a resource. Enzyme equation: substrate + enzyme
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This note was uploaded on 06/06/2011 for the course BIO 110 taught by Professor Phil during the Fall '08 term at South Carolina.

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Enzymes rev aug '08 - Enzymes Laboratory 4 Introduction A...

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