Final answer:
A three-letter abbreviation or a single upper case letter represents an amino acid. Essential amino acids, such as isoleucine, leucine, and cysteine, must be consumed as they are not produced by the body. These codes are vital for expressing protein sequences and the genetic code.
Step-by-step explanation:
Each three-letter symbol or a single upper case letter represents an amino acid, for example, Leu stands for leucine. Amino acids are crucial for protein synthesis in the body, and while some can be produced by the organism itself, others must be obtained through the diet and are termed essential amino acids.
In humans, essential amino acids include isoleucine, leucine, and cysteine, among others, which vary from organism to organism. The genetic code utilizes a series of three-letter codes, wherein each triplet encodes an amino acid, ultimately determining the protein's structure. The one-letter code is handy when indicating long amino acid sequences in proteins, enhancing the clarity and simplicity of genetic and protein-related documentation.