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Amino acids are the basic building blocks of proteins and serve as biological molecules in their own right with a variety of functions. Amino acids are often categorized as essential or non-essential, depending on the ability of the body to manufacture each amino acid versus requirement for ingestion from the diet. Although several hundred amino acids exist, 20 play a predominant role in the human body. Each amino acid has a characteristic R-group that determines its chemical nature and, therefore, how it will interact with other amino acids, other molecules, and with its environment.

Amino acids link together via peptide bonds to form peptides and proteins. These peptides and proteins fold into their final three-dimensional shape as the result of hydrophobic, hydrophilic, hydrogen bonding, and ionic bonding forces (among others) that result from the other amino acids in the peptide chain, including the characteristics of their R-groups. Proteins may be categorized as enzymes, structural proteins, motor proteins, and transport/channel proteins. The specific roles of amino acids and proteins in the synthesis of other molecules and in the functions of organ systems and the human bodies will be explored in detail in subsequent chapters.



Amino acids are the basic building blocks of proteins. Twenty amino acids make up proteins in living organisms; several hundred more amino acids perform specialized functions in human and non-human biology. Amino acids are often described as

  • Essential (must be obtained directly from food)

  • Non-essential (the human body is able to produce them on its own).

There is some debate about the exact definitions of these terms, but 8–10 amino acids are usually deemed essential and 10–12 are non-essential (see Table 1-1).

TABLE 1-1.

Amino Acids—R-Group Classifications

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