Amino acids are necessary for protein synthesis. Some must be supplied specifically in the diet (the essential amino acids) since the tissues are unable to synthesis them. The reminder or non-essential amino acids are also supplied in the diet, but they can be formed from intermediates by transamination using the amino nitrogen from other surplus amino acids. After deamination, excess amino nitrogen is removed as urea, and the carbon skeletons that remain after transamination (Figure 8.5).

1. are oxidised to CO₂ via citric acid cycle,
2. form glucose (gluconeogenesis) and
3. form ketone bodies.

In addition to their requirement for protein synthesis, the amino acids are also the precursors of many other important compound. Examples: Purine, pyrimidine, and hormones such as epinephrine and thyroxine.

Figure 8.5 Overview of Amino Acid Metabolism