ENZYMES Enzymes function as organic catalysts A catalyst

ENZYMES

§ Enzymes function as organic catalysts. A catalyst is a chemical involved in, but not changed by, a chemical reaction. Many enzymes function by lowering the activation energy of reactions. By bringing the reactants closer together, chemical bonds may be weakened and reactions will proceed faster than without the catalyst.

§ Enzymes are proteins. The functioning of the enzyme is determined by the shape of the protein. The arrangement of molecules on the enzyme produces an area known as the active site within which the specific substrate(s) will "fit". It recognizes, confines and orients the substrate in a particular direction.

§ Temperature: Increases in temperature speeds up enzyme mediated reactions, but only to a point. When heated too much, enzymes (since they are proteins dependent on their shape) become denatured. § Thermolabile enzymes, such as those responsible for colour camouflage of the Arctic fox, work better (or work at all) at lower temperatures. § Changes in p. H will also denature the enzyme by changing the shape of the enzyme. Enzymes are also adapted to operate at a specific p. H or p. H range.

§ Competitive Inhibition works by the competition of the regulatory compound and substrate for the binding site. If enough regulatory compound molecules bind to enough enzymes, the pathway is shut down or at least slowed down.

§ Noncompetitive Inhibition occurs when the inhibitory chemical, which does not have to resemble the substrate, binds to the enzyme other than at the active site. Irreversible Inhibition occurs when the chemical either permanently binds to or massively denatures the enzyme so that the tertiary structure cannot be restored. Nerve gas permanently blocks pathways involved in nerve message transmission, resulting in death. Penicillin, the first of the "wonder drug" antibiotics, permanently blocks the pathways certain bacteria use to assemble their cell wall components.