Essential Amino Acids
The biosynthesis of proteins requires the presence of all the constituent amino acids. If one of the 20 amino acids is missing or in short supply, protein biosynthesis is inhibited. Some organisms, such as Escherichia coli, can synthesize all the amino acids they need. Other species, including humans, must obtain some amino acids from dietary sources. The essential amino acids in human nutrition are listed in Table 23.1. The body can synthesize some of these amino acids, but not in sufficient quantities for its needs, especially in the case of growing children. This last point applies particularly to children’s requirement for arginine and histidine. Amino acids are not stored (except in proteins), and dietary sources of essential amino acids are needed at regular intervals. Protein deficiency, especially a prolonged deficiency in sources that contain essential amino acids, leads to the disease kwashiorkor. The problem in this disease, particularly severe in growing children, is not simply starvation but the breakdown of the body’s own proteins.
Humans cannot produce some amino acids in sufficient quantities to meet their metabolic needs. These are called essential amino acids.
The essential amino acids must be obtained from dietary sources.