Proteins Are Combinations of Amino Acids What Are Amino Acids

We now know that all proteins are collections of amino acids. Said another way, amino acids are the "building blocks" of proteins. Although the final functional form of some proteins may contain minerals or other nonprotein components, the basis for these proteins is still amino acids.

All amino acids have the same basic design, as shown in Figure 6.1. There is both a nitrogen-containing amino portion and carboxylic acid portion attached to a central carbon atom. The presence of both an amino and an acid portion on each molecule led to the name amino acid

Amino group

Acid portion

Side chain

Figure 6.1 Basic components of amino acids. An amino acid contains a central carbon atom (C) with the following attachments: amino group, carboxyl (carboxylic acid) group, hydrogen (H), and a side chain (R group).

for this family of molecules. There is also a hydrogen atom attached to the central carbon, as well as a mysterious "R" group.

Twenty amino acids serve as the building blocks of protein; ten of them are dietary essential.

The R group denotes the portion of an amino acid that will be different from one amino acid to the next. The R portion of an amino acid may be as simple as a hydrogen atom, as in glycine, or much more complex to include carbon chains and rings, acid or base groups, and even sulfur (S). The structure of the twenty amino acids used to make protein is shown in Figure 6.2.

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