Microbiology

Microbiology Study Guide

2.3 Metabolism: Basic Methods of Metab lism and En rgy Conversion Microbial life can exist only where molecules and cells remain organized. Energy is needed by all microorganisms to maintain organization. Every activity taking place in microbial cells involves both a shift of energy and a measurable loss of energy. Unfortunately, the transfers of energy in living systems are never completely efficient. For this reason, more energy must be taken into the system than is necessary to simply carry out the actions of microbial life. Catalysts are substances that speed up chemical reactions but remain unchanged during the reactions. Catalysts work by lowering the required amount of activation energy for the chemical reaction. In microorganisms, the catalysts are enzymes. Enzymes Chemical reactions in microorganisms operate in the presence of enzymes. A particular enzyme catalyzes only one reaction, and thousands of different enzymes exist in a microbial cell to catalyze thousands of different chemical reactions. The substance acted on by an enzyme is called its substrate . The products of an enzyme-catalyzed chemical reaction are called end products . All enzymes are composed of proteins. When enzymes function, a key portion of the enzyme called the active site interacts with the substrate. The active site closelymatches themolecular configuration of the substrate, and after this interaction has taken place, a shape change at the active site places a physical stress on the substrate. This physical stress aids the alteration of the substrate and produces the end products. After the enzyme has performed its work, the product or products drift away. The enzyme is then free to function in the next chemical reaction. Enzyme-catalyzed reactions occur extremely fast. With some exceptions, enzyme names end in “-ase.” For example, the microbial enzyme that breaks down hydrogen peroxide to water and hydrogen is called catalase. Other well-known enzymes are amylase, hydrolase, peptidase, and kinase. Factors that Influence Enzyme Activity There are a number of factors that determine the rate of reaction between the enzymes and catalysts. Some of these factors include the presence of chemicals, concentration of substrate, and the acidity and temperature of the environment. For instance, the reaction between the enzymes and catalyst increases as the temperature in the environment rises. This is because enzymes are actually the substances of proteins, which under high temperature, brings about a change in its structure and thus makes them inactive. Enzymes that are altered and inactive during heat is called denatured. Enzymes operate in metabolic pathways that signify their operation in a sequence of chemical reactions occurring inside a cell. Out of these multiple chemical reactions, the reaction between one enzyme and its catalyst is treated as one reaction. The metabolic reactions can be categorized in two types, catabolism and anabolism. When the large complex molecules in the cell are broken down and

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