Protein
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This article is about a class of molecules. For protein as a nutrient, see Protein (nutrient). For other uses, see Protein (disambiguation).
[ندعوك للتسجيل في المنتدى أو التعريف بنفسك لمعاينة هذه الصورة]
A representation of the 3D structure of the protein myoglobin showing colored alpha helices. This protein was the first to have its structure solved by X-ray crystallography. Towards the right-center among the coils, a prosthetic group called a heme group is shown colored largely in green.
Proteins ([ندعوك للتسجيل في المنتدى أو التعريف بنفسك لمعاينة هذه الصورة] /ˈproʊˌtiːnz/ or /ˈproʊti.ɨnz/) are biochemical compounds consisting of one or more polypeptides typically folded into a globular or fibrous form, facilitating a biological function.
A polypeptide is a single linear polymer chain of amino acids bonded together by peptide bonds between the carboxyl and amino groups of adjacent amino acid residues. The sequence of amino acids in a protein is defined by the sequence of a gene, which is encoded in the genetic code. In general, the genetic code specifies 20 standard amino acids; however, in certain organisms the genetic code can include selenocysteine and—in certain archaea—pyrrolysine. Shortly after or even during synthesis, the residues in a protein are often chemically modified by posttranslational modification,
which alters the physical and chemical properties, folding, stability,
activity, and ultimately, the function of the proteins. Sometimes
proteins have non-peptide groups attached, which can be called prosthetic groups or cofactors. Proteins can also work together to achieve a particular function, and they often associate to form stable protein complexes.
Like other biological macromolecules such as polysaccharides and nucleic acids, proteins are essential parts of organisms and participate in virtually every process within cells. Many proteins are enzymes that catalyze biochemical reactions and are vital to metabolism. Proteins also have structural or mechanical functions, such as actin and myosin in muscle and the proteins in the cytoskeleton, which form a system of scaffolding that maintains cell shape. Other proteins are important in cell signaling, immune responses, cell adhesion, and the cell cycle. Proteins are also necessary in animals' diets, since animals cannot synthesize all the amino acids they need and must obtain essential amino acids from food. Through the process of digestion, animals break down ingested protein into free amino acids that are then used in metabolism.
Proteins may be purified from other cellular components using a variety of techniques such as ultracentrifugation, precipitation, electrophoresis, and chromatography; the advent of genetic engineering
has made possible a number of methods to facilitate purification.
Methods commonly used to study protein structure and function include immunohistochemistry, site-directed mutagenesis, nuclear magnetic resonance and mass spectrometry.
Contents
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- 1 Biochemistry
- 2 Synthesis
- 2.1 Chemical synthesis
