Enzyme Study Questions
o enzyme: a protein molecule that catalyzes chemical reactions without itself being destroyed or altered o catalyst: a substance that increases the rate of a chemical reaction but is not consumed or changed by it. o substrate: a substance upon which the enzyme acts. o denaturation: the partial or total alteration of the structure of a protein without change in covalent structure by the action of certain physical procedures (heating, agitation) or chemical agents. Any disruption of the protein structure that is accompanied by a loss of activity o cofactor: nonprotein molecules that must bind to a particular enzyme before a reaction occurs (natural reactant – usually a metal ion or a coenzyme) o coenzyme: a diffusible, heat-stable substance of low molecular weight that when combined with an inactive protein called an apoenzyme forms an active compound or a complete enzyme called a holoenzyme o apoenzyme: the protein part of an enzyme
o prostheticgroup: the coenzyme bound tightly to the enzyme o holoenzyme: the functional compound formed by the combination of an apoenzyme and its appropriate coenzyme o zymogen: Some enzymes, mostly digestive enzymes, are originally secreted from the organ of production in a structurally inactive form o activation energy: the energy required for a molecule to form an activated complex; in an enzyme-catalyzed reaction, corresponds to the formation of the activated enzyme substrate complex o enzyme-substrate complex (E-S): a molecule of substrate is bound to the active center of the enzyme molecule o active site: where the initial binding of substrate and enzyme occurs o absolute specificity: meaning that the enzyme combines with only one substrate and catalyzes only the one corresponding reaction o group specificity: they combine with all substrates containing a particular chemical group o first-order kinetic reaction: a reaction in which the rate of reaction is proportional to the concentration of substrate o zero-order kinetic reaction: a reaction in which the rate is independent of the concentration of substrate, and depends on enzyme concentration only o activator: Inorganic cofactors, such as chloride or magnesium ions; They increase the catalytic activity of an enzyme when it binds to a specific site. o inhibitor: interfere with the reaction, decrease the rate of reaction; can be either reversible or irreversible o competitive inhibitor: binds to the active site of an enzyme and competes with substrate for the active site o noncompetitive inhibitor: binds an enzyme at a place other than the active site so no competition between inhibitor and substrate, examples are heavy-metal ions such as lead and mercury o uncompetitive inhibitor: binds to the enzyme-substrate complex so that increasing substrate concentration results in more ES complexes to which the inhibitor binds and thereby increases the inhibition so there is no product. o Fixed time reaction: the amount of change produced by the enzyme is measured after the reaction is stopped (usually by inactivating the enzyme with a weak acid) at the end of a fixed time interval and a measurement is made of the amount of reaction that has occurred. o continuous monitoring method: the reaction is monitored continuously, usually of absorbance change every 30 or 60 seconds. Continuous measurements are preferred because any deviation from linearity is readily observable. o isoenzyme: one of a group of related enzymes catalyzine the same reaction but having different molecular structure and characterized by varying physical, biochemical, and immunological properties; subunit of the enzyme o NAD: nicotinamide adenine dinucleotide, example of a coenzyme o...
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