It is estimated that the human body may contain over two million proteins, coded for by only 20,000 - 25,000 genes. The total number found in terran biological organisms is likely to exceed ten million, but nobody knows for sure. Data is available on just over a million of them, taken mainly from information found in the over 100 genomes that have been fully sequenced.
The field that analyzes proteins in general and aims to exhaustively characterize all of those in the human body is called proteomics. Many see the next logical step after the completion of the Human Genome Project to be the initiation of a Human Proteome Project. The Human Proteome Organization was founded to pursue this goal.
Proteins are long molecular chains made from the 20 basic building blocks of life, amino acids. The longest known one, titin, also known as connectin, contains 26,926 amino acids. Titin is found in muscle and contributes to its passive stiffness. Because the 20 amino acids can be connected up in arbitrary sequences, the total space of possible proteins is exponential, with a value of approximately 2050,000 — a tremendous number. Within this space there may be cures for every disease or ailment, but locating them in such a vast number is a profound computational and theoretical challenge.
The word protein comes from the Greek prota, meaning "of primary importance." This is a suitable name, as their central importance in the human body can not be overestimated. All biological organisms can be seen fundamentally as protein structures filled with water and sometimes supported by mineralized tissues called bone. For almost every one, there is another that can break it down. They sometimes coalesce into mutually cooperative units called complexes, which perform useful biological functions. Every section of useful genetic information, found in DNA and some RNA, codes for a corresponding protein that goes on to fulfill a useful biological role.
