Chapter 14 - General principles of metabolism

Abstract

This chapter focuses on the general principles of metabolism. Once the food has been digested and absorbed, the various nutrients are distributed to the tissues via the blood and, having passed through the cell membranes, are exposed to the metabolic machinery of the cell. The aim of this machinery is to release some of the energy contained in the nutrients and convert it into a form that can be used for the various functions of the cell, and to use the rest of the material for the synthesis of substances that the body needs for its growth and activities. To do this, the food materials are subjected to a variety of metabolic processes, each of which involves a well-defined sequence of reactions. Nearly every step is catalyzed by a different enzyme and results in a small but specific chemical change. This field of intermediary metabolism constitutes a major part of biochemistry. Metabolism may be divided into three areas. Catabolism deals with the breakdown of materials with the release of energy. Anabolism covers the processes by which complex substances are built up from simple precursors, and this utilizes much of the energy released during the course of catabolism. Between the clearly defined anabolic and catabolic pathways lies a central area of metabolism in which various simple compounds are interconverted.