DNA - Deoxyribonucleic Acid

A protein molecule is one or more chains of amino acids (in a particular order) joined together by a peptide bond, and each chain of amino acids is called a polypeptide.
The specific order of the amino acids is stored in a gene and is recalled during protein synthesis.
Proteins have many functions:
They are enzymes (biological catalysts)
They are essential constituents of all cell membranes
They have a structural function (e.g. collagen in tendon, ligament and bone)
They are hormones
They are antibodies
They have a transport function (e.g. haemoglobin)
Protein Synthesis is the manufacture of proteins inside a cell. It occurs in two stages:

TRANSCRIPTION

The instructions for protein synthesis are found within the sequence of bases on the DNA. However, DNA is too large to exit the nucleus, so instead a strand of mRNA is formed. The DNA unwinds and opens up, exposing the bases. One strand only acts as a template for mRNA formation as free nucleotides move in and bond in a complimentary fashion - Cytosine and Guanine pair up as per usual, but Adenine on the DNA will pair with Uracil instead of Thymine.
The enzyme RNA Polymerase joins the bases together. Once mRNA formation is complete, it detaches from the DNA and moves into the cytoplasm. The DNA reforms.

TRANSLATION

tRNA molecules carrying specific amino acids bind to the mRNA strand. Ribosomes move along the strand connecting the amino acids together and detaching them from the mRNA. A chain of amino acids is termed a polypeptide. Once the amino acid is detached from the tRNA, the tRNA may detach from the mRNA, pick up another amino acid, and the process may repeat itself if the cell requires more than one copy of the polypeptide.

Each set of three bases on the mRNA strand is called the codon. The three bases on the tRNA molecule are known as the anti-codon. Because there are only 20 different amino acids, there are more than enough codon combinations to code for each amino acid, and have some sequences spare for "start" and "terminate" commands. In total, there are 64 different combinations (4 x 4 x 4).

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