Protein
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| See Protein in Wikipedia, the free encyclopedia. |
A protein is a macromolecule made from a chain of amino acids, called a polypeptide until it is post-processed into a full protein. The order of amino acids is specified by the order of bases in the mRNA (messenger RNA) from which the protein was translated, which is in turn transcribed from DNA.
The structure of a protein is critical to its function. Determining structure is often very difficult, but detailed structures are needed for such areas as 'rational drug design' as well as just understanding how the protein functions. Generally it is recognized there are four levels of structure:
- primary: The actual order of the amino acids in the polypeptide chain
- secondary: various local structural motifs involving multiple amino acids, such as alpha-helix or beta-sheets
- tertiary: the final "folded" structure of a single protein
- quatenary: sometimes multiple protein monomers are complexed into a larger molecule, e.g. hemoglobin from two alpha and two beta proteins, and then modified with additional elements, such as the heme complex in hemoglobin
Proteins may undergo even further post-processing such as glycosylation to achieve their full activity.
Since proteins are the products of genes and can be produced as needed they have many functions in an organism. One of the most important is acting an as enzyme and thus catalyzing other biochemical reactions which then drive biological activity. As receptors proteins are also used to convey messages across cellular boundaries (the messengers often being proteins of another name, hormones) in multicellular organisms.
Paralleling the development of genomics the study of proteins has evolved its own set of high-throughput techniques now generally known as proteomics. Comparison of the proteome of organism provides additional clues about their evolutionary development. Most proteins found in homo sapiens have some sort of ancestor in earlier life-forms. Differences in proteins provides clues about how long ago different species diverged from each other, e.g. cytochrome.
