Proteins

Long chains of amino acids folded into precise three-dimensional shapes. Proteins are the body’s most versatile molecules — its primary “workers.”

Building blocks

Built from 20 standard amino acids, strung together in a sequence dictated by DNA. The sequence determines the fold, and the fold determines the job.

Roles

• Enzymes — speed up chemical reactions.
• Structural — collagen, keratin, and others give tissues strength and shape.
• Transport — hemoglobin carries oxygen; membrane proteins ferry substances across cell borders.
• Signaling — many hormones are proteins, as are the receptors that receive them.
• Defense — antibodies are proteins.
• Movement — actin and myosin drive muscle contraction.

Key idea

Almost everything the body does, as opposed to what it is made of, is carried out by proteins — and a protein’s function follows entirely from its shape.