Metabolic Strategies

<h1>Text Preview</h1> <p>The enzymes of organisms are arranged into highly coordinated processes called metabolic pathways.</p> <p>Some metabolic pathways degrade, or break down, molecules for energy. This process is known as catabolism. Other pathways use energy to synthesize complex molecules from simple ones. This process is called anabolism. Glycolysis, the breakdown of glucose, is a catabolic pathway, and the synthesis of glucose is an anabolic pathway. In catabolic processes, electrons are lost from energy-containing nutrients, and ATP is generated. In anabolic processes, carbon is reduced, and ATP is consumed.</p> <p>Some athletes take anabolic steroids because these drugs promote the synthesis of protein and muscle. This is the drug's anabolic effect. Anabolic steroid abuse has been associated with a wide range of adverse side effects. This is because steroid abuse disrupts the normal production of hormones in the body, causing both reversible and irreversible changes. </p> <p>The activities of enzymes in metabolic pathways are regulated. Energy is a scarce resource, and organisms that use energy more efficiently have a selective, or evolutionary, advantage. A useful analogy is the automobile. The gas-guzzling cars of the early 1970s were replaced with more fuel-efficient models in the 80s when gas prices skyrocketed and shortages were common. To prevent the waste of precious resources, all metabolic pathways are regulated. Regulation prevents unneeded metabolites from being made and then thrown away.</p> <p>Organisms have evolved diverse metabolic lifestyles. Chemotrophs obtain their energy by oxidizing molecules. Oxidation is the loss of electrons. When one molecule is oxidized, another must be reduced. In aerobic metabolism, oxygen ultimately accepts the electrons. In anaerobic metabolism, other molecules accept the electrons.</p> <p>In the presence of oxygen, yeast cells metabolize glucose to carbon dioxide and water. The water is formed by the reduction of molecular oxygen. Under anaerobic conditions, yeast cells ferment pyruvate to ethanol. Less energy is produced under anaerobic conditions. We also resort to anaerobic metabolism when oxygen is limited. For example, vigorous exercise can lead to anaerobic metabolism, which builds up lactate in our tissues. When we rest and oxygen levels are replenished, the lactate is slowly converted back into glucose. </p> <p id="TextCopyright">Copyright 2006 The Regents of the University of California and Monterey Institute for Technology and Education</p>