Active Site
Biological systems are dependent on the proper functioning of enzymes. Specific enzymes act to aid specific reactions. Enzymes achieve this specificity through differences in the shape and composition that reflect genetic differences (i.e., differences in the genetic code that carry instructions to construct the enzyme). A region of the enzyme molecule termed the active site achieves an important component of specificity. The active site is a specific region of the enzyme molecule that bonds only with a limited number of molecules (substrates) to form the enzyme-substrate complex.
The binding of a specific substrate (or a limited number of substrates) to a specific region of the enzyme molecule is also termed the "lock and key" mechanism of proteins. Only specific keys (substrates) can fit into and properly interact with an active site on an enzyme molecule. The broadness with which an enzyme can act within a biological system or reaction depends on how many different substrates may properly interact with the active site on an enzyme.
Enzymes are proteins. Because they are proteins, their basic or primary structure consists of a linked chain of amino acids, the order of which is directly determined the genetic code in the gene that carries the instructions for the enzyme.
Enzymes are catalysts that are capable of allowing the body to carry out complex chemical reactions at modest body temperatures. Without being altered themselves, enzymes also control the rate of reactions and, in so doing, control the amount of product (e.g., hormone, protein, etc) produced.
As early as 1894, Emil Fischer identified enzymes that were capable of recognizing very small mirror image like difference in the shapes of molecules. Modern researchers use studies of active sites to investigate the function of proteins on the molecular level. A key component of this research includes the use of sophisticated genetic techniques to identify and map active site regions. Alterations in active sites can be determined by changes in the amount or type of products produced by biochemical reactions. The goal of many studies is to trace such reactive changes back to a specific structural changes that, in turn, can be traced back to specific alterations (mutations) in the DNA within the gene that codes for the primary structure of the enzyme (the amino acid sequence of the enzyme). Mutations at the genetic level may ultimately translate into direct changes in the active site and thus alter the functional ability of the enzyme. Although mutations that occur in regions of the gene that code for regions of the enzyme not a part of the active site may also ultimately result in a non-functional or impaired enzyme, these changes are usually due to changes in the shape (tertiary structure) of the enzyme or a change in enzyme biochemistry (e.g., participation in acid-base reactions, etc).
Geneticists and biochemists use mutational analysis to study enzymes and active site functions. Sophisticated mathematical techniques can help link specific enzyme molecular geometry with matching substrate structure.
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