THE DIGESTION AND METABOLISM OF NUTRIENTS

This part describes the physicai and chemical processes by which an animal obtains nutrients from the chemical compounds that make up the foods ingested and explains how these nutrients are subsequently utilised. 

A key group of molecules required for both digestion and metabolism are the enzymes, and Chapter 7 provides details of their chemistry, mode of action and the factors affecting their activity. 

Once the digested molecules are absorbed, they are used to provide energy and to produce the proteins, fats and carbohydrates that are required by the body. Chapter 9 describes the metabolic processes by which cells utilise and transform molecules and how these processes are controlled. 

Each living cell contains hundreds of enzymes and can function efficiently only if the action of these enzymes is suitably coordinated. It is important to appreciate that within the cell, the enzymes exist in different compartments the cell is not a bag of randomly distributed enzymes. Thus, the enzymes used in the first stage of the oxidation of glucose (glycolysis) are present in the cytoplasm, whereas those involved in the formation of acetyl-CoA from pyruvate and its subsequent oxidation via the tricarboxylic acid cycle are found in the mitochondria (see Chapter 9). 

---