The 4 bases found in DNA molecules are:

• adenine (A)
• guanine (G)
• cytosine (C)
• thymine (T)

A protein is an amino acid polymer - a chain of amino acids, usually several hundred. There are 20 possible amino acids - the sequence of amino acids determines the structure and function of a protein.
Proteins are made on ribosomes. Ribosomes are analogous to cassette tape players. They are machines that allow reading of the message (the cassette, analogous to mRNA) and conversion into output (the audible sound, analogous to the protein).

The DNA strands making up the 23 pairs of chromosomes in the cell are enormous molecules. They are entirely restricted from leaving the nucleus. Information in the DNA must be transferred from the nucleus to the ribosomes. The intermediary molecules in this transfer are RNA (ribonucleic acid) molecules.

The process can be divided into two parts:

• transcription in which a short portion of chromosomal DNA which codes for a single protein/polypeptide is used to make a RNA molecule - small enough to leave the nucleus.
• translation in which the RNA code is used to assemble the protein at the ribosome.