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            Discuss enzymes under the following headings:.
             Enzymes are biological catalysts because they speed up chemical reactions without being affected themselves. They are composed of protein and have an active site, which is complementary in shape to the enzymes substrate. The primary structure of enzymes is a chain of amino acids linked by peptide bonds, this chain is called a polypeptide chain, and the secondary structure is where the chain folds to form the alpha helix. This folding is allowed by hydrogen bonds. The tertiary structure is further folding of this structure forming globular proteins.
             Enzymes either build up large molecules from smaller molecules, synthesis reactions, or break down large molecules into smaller molecules, degradation. Enzymes are specific, so only one substrate can fit into the active site, this is called the lock and key hypothesis.
             As the enzymes active site is complementary in shape to its substrate, the enzyme and substrate join together to form the enzyme-substrate complex, the enzyme then moves away from the products of the degradation process. Enzymes control biological pathways both inside and outside of cells, for example, food digestion enzymes.
             There are many factors that affect enzyme activity. Most enzymes of the body have an optimum p.H which is neutral or slightly alkaline with the exception of pepsin which has an optimum p.H at an acid p.H 2. Outside this narrow p.H range enzymes do not work as well and some become denatured and do not work at all. Another factor that affects enzyme activity is temperature. At low temperatures the reaction is slow and as the temperature increases so does the rate of reaction, until it reaches its optimum temperature where the enzymes activity has reached a maximum. As temperature then gets higher, the reaction rate slows and the enzyme finally denatures. Gene mutation also affects enzyme activity. These mutations can cause essential metabolic pathways to be stopped as the mutation codes for an "enzyme" of the wrong shape, or an "enzyme" is not present, an example of this is PKU.

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