Proteins, Amino Acids, and Nitrogen Metabolism

Animals require proteins, which are large nutrients made up of amino acids, in their diets. The body can make some amino acids, but others (essential amino acids) need to be provided by the diet. The ingested proteins go through digestion via various digestive enzymes to produce amino acids and peptides that are absorbed and transported via specific transporters. The whole body protein pool is determined by the balance between the processes of protein synthesis and degradation, which are under the control of hormonal, nutritional, and neuronal factors. Protein and amino acids play crucial roles in cellular and body weight homeostasis from regulation of appetite and food intake, metabolic reactions to cellular signaling within and between cells as well as energy production for survival. This chapter aims to discuss protein and amino acid metabolisms and provide a summary of current progress in the field.