mRNA is synthesised from DNA via a process called transcription which in turn leave the nucleus and travels to the ribosomes on the rough endoplasmic reticulum before being converted into a protein by a process called translation. Proteins are made up of chains of amino acids.
The human genome is 3.3 billion base pairs in length. Compare that to the bacteria Pseudomonas aeruginosa which has 6.4 million base pairs. A base pair is A or T or G or C. In DNA, which has a double helix, (two strands attached together) these are:
A – Adenine binds to Thymine -T
T – Thymine binds to Adenine – A
G – Guanine binds to Cytosine – C
C – Cytosine binds to Guanine – G
DNA encodes for everything thing you are in the form of genes of which the human genome encodes for between 20,000 to 25,000 protein encoding genes. Your genes are capable of producing proteins which perform functions in your body including deciding your eye colour, hair colour, insulin production, immune system etc…Your 46 chromosomes are found in every cell in your body but not all the genes are switched on or activated in every cell. The cells in your eye do not need to activate proteins that would normally be found active in your liver and your liver would not activate the genes that control eye colour but the information for both is in every cell. When genes are activated in cells mRNA is produced from the DNA (a process called transcription) and this mRNA travels to the ribosomes to be turned into proteins (a process known as translation). mRNA has 4 base pairs but is only single stranded (unlike DNA) and has Uracil (U) instead of Thymine (T).
Human Amylase enzyme (which is found in your saliva and helps break down starch) has a gene size of 1544 base pairs and produces a protein 511 amino acids long. It takes 3 base pairs to encode/make an amino acid. You can see the final structure of the protein here:
http://www.rcsb.org/pdb/explore/jmol.do?structureId=4GQQ&opt=3&jmolMode=JAVA