Describe the various facets of the concept of enzyme specificity.
Unlike an inorganic catalyst, an enzyme typically is able to interact with only one type of reactant, referred to as the substrate, and speed up only one of the numerous possible reactions the substrate could undergo. An enzyme's extreme specificity is due to the fact that each type of enzyme has its own distinctive three-dimensional contours, determined by the enzyme's tertiary and quaternary structures. Its contours limit the number of substrates with which it can react to those substrates that spatially "fit" the enzyme's surface. The part of the enzyme to which the substrate binds is called the active site. It is important to note that an enzyme's active site may undergo conformational changes during bonding that improve the fit and the reactivity of the substrate. The enzyme and substrate are held together by polar hydrogen bonds and hydrophobic interactions. The formation of bonds between an enzyme and its substrate depends on the exposed R groups of the amino acids that form the enzyme's active site. R groups can be polar, non polar, or electrically charged, and the corresponding substrate must be compatible in order to bond. A non polar substrate will not bond with a polar or a charged active site even if otherwise spatially suited; conversely, a polar or a charged substrate will not bond with a non polar active site. In addition, some enzymes require the presence of coenzymes, nonproteinaceous molecules that remain
