Building Blocks of Proteins

Like carbohydrates and lipids, proteins contain the elements carbon (C), hydrogen (H) and oxygen (O), but in addition they also always contain nitrogen (N).

Sulphur is often present as well as iron and phosphorus. Before understanding how proteins are constructed, the structure of amino acids should be noted. The diagram below shows the general structure of an amino acid.

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Just like the earlier carbohydrate and lipid molecules ‘R’ represents groups such as –CH₃ and –C₂H₅. There are about 20 commonly found amino acids but you will not need to know them all. Instead, learn the basic structure shown above.

How is a protein constructed?

The process begins by amino acids bonding together. The diagram shows two amino acids being joined together by a peptide bond.

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When many amino acids join together a long-chain polypeptide is produced. The linking of amino acids in this way takes place during protein synthesis.

There are around 20 different amino acids. Organisms join amino acids in different linear sequences to form a variety of polypeptides, then build these polypeptides into complex molecules, the proteins. Humans need eight essential amino acids as adults and ten as children, all the others can be made inside the cells. The sequence of amino acids along a polypeptide is controlled by another complex molecule, DNA