Proteins

The proteins are the building materials for living cells. They contain carbon, hydrogen, and oxygen like the carbohydrates and lipids, but they also contain nitrogen and often sulfur and phosphorus.

Protein molecules are often very large and are made up of hundreds to thousands of amino acid units. The 20 amino acids are combined in different ways to make up the 100,000 or so different proteins in the human body. Some of these proteins are in solution in the blood and other fluids of the body, and some are in solid form as the framework of tissue, bone and hair. Shipman, et al. suggests that they make up about 75% of the dry weight of our bodies.

Proteins can be characterized as extremely long-chain polyamides. The amides contain nitrogen, and nitrogen composes about 16% of the protein atomic content. These proteins are created in the body by condensation of amino acids under the influence of enzyme catalysts, using patterns or direction from the nucleic acids in the cells.

The amino acid units in a protein molecule are held together by peptide bonds, and form chains called polypeptide chains. The sequencing of the 20 amino acids forms a kind of alphabet for expression of the type of protein, leading to a very large number of types of proteins.