The bonding of an enzyme to its substrate forms an enzyme-substrate complex. The catalytic action of the enzyme converts its substrate into the product or products of the reaction. Each reaction is extremely specific, distinguishing between closely related compounds, including isomers. For example, the enzyme sucrase will only act on sucrose and will not bind to any other disaccharide. The molecular recognition of enzymes is due to the fact that they are proteins, which are defined as being macromolecules with unique three-dimensional conformations. Therefore, the specificity of enzymes is a consequence of its shape which results from its amino acid sequence. The enzyme binds to the substrate at a region known as the active site, a groove on the surface of the protein. The active site of an enzyme is formed by a few of the enzyme’s amino acids while the rest of the protein molecules determine the configuration of the active site. The specificity of the enzyme is attributed to the shape of the active site and the shape of the substrate. When the substrate enters the active site interactions between its chemical groups and the amino acids of the protein cause the enzyme to change shape slightly in order to fit more tightly around the substrate. This induced fit brings chemical groups of the active site into positions that enhance their ability to catalyze the reaction. The substrate is held in the active site if the enzyme by weak interactions, usually hydrogen bonds.
When more substrate molecules are available they are able to access active sites of enzyme molecules more often. This in turn aids in speeding up the rate of the reaction. However, when concentration reaches a high enough point a problem arises because all enzyme active sites are already engaged. The high concentration of substrate saturates the enzyme and the rate of the reaction is determined by the rate at which the active site converts substrate to product. The only way to overcome saturation...
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