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A representation of the 3D structure of myoglobin, showing coloured alpha helices. This protein was the first to have its structure solved by X-ray crystallography by Max Perutz and Sir John Cowdery Kendrew in 1958, which led to them receiving a Nobel Prize in Chemistry.

A protein is a complex, high molecular weight organic compound that consists of amino acids joined by peptide bonds. Proteins are essential to the structure and function of all living cells and viruses. Many proteins are enzymes or subunits of enzymes. Other proteins play structural or mechanical roles, such as those that form the struts and joints of the cytoskeleton. Still more functions filled by proteins include immune response and the storage and transport of various ligandIn chemistry, a ligand is an atom, ion or functional group that is bonded to one or more central atoms or ions, usually metals generally through co-ordinate covalent bond. An array of such ligands around a centre is termed a complex. The central atom usuas. In nutrition, proteins serve as the source of amino acids for organismIn biology and ecology, an organism is a living being. The origin of life and the relationships between its major lineages are controversial. Two main grades may be distinguished, the prokaryotes and eukaryotes. The prokaryotes are generally considered tos that do not synthesize those amino acids natively.

Proteins are one of the classes of bio- macromolecules, alongside polysaccharidePolysaccharides are relatively complex "unsweet" carbohydrates. Polysaccharides are polymers made up of many monosaccharides joined together (hence poly saccharides). They are therefore very large, often branched, molecules. Properties include insolubilits and nucleic acidA nucleic acid is a complex, high-molecular-weight biochemical macromolecule composed of nucleotide chains that convey genetic information. The most common nucleic acids are deoxyribonucleic acid ( DNA) and ribonucleic acid ( RNA). Nucleic acids are founds, that make up the primary constituents of living thingsAlternate uses: see Life (disambiguation) and Living (disambiguation Life is a multi-faceted concept with no simple definition; this article is confined to the primary meanings in biology; articles on life in other senses are included in the article life. They are amongst the most actively studied moleculeIn science, a molecule is the smallest particle of a pure chemical substance that still retains its chemical composition and properties. A molecule consists of multiple atoms joined by shared pairs of electrons in a covalent bond''. It may consist of atom in biochemistry and were discovered by Jöns Jacob Berzelius, in 1838.

1 Structure

Main article: Protein structure

Proteins are amino acid chains that fold into unique 3-dimensional structures. The shape into a which a protein naturally folds is known as its native state, which is determined by its sequence of amino acids. Biochemists refer to four distinct aspects of a protein's structure:

Primary structure: the amino acid sequence
Secondary structure: highly patterned sub-structures— alpha helix and beta sheet—or segments of chain that assume no stable shape. Secondary structures are locally defined, meaning that there can be many different secondary motifs present in one single protein molecule
Tertiary structure: the overall shape of a single protein molecule; the spatial relationship of the secondary structural motifs to one another
Quaternary structure: the shape or structure that results from the union of more than one protein molecule, usually called subunit proteins subunits in this context, which function as part of the larger assembly or protein complex.

In addition to these levels of structure, proteins may shift between several similar structures in performing of their biological function. In the context of these functional rearrangements, these tertiary or quaternary structures are usually referred to as " conformations," and transitions between them are called conformational changes.

The primary structure is held together by covalent peptide bonds, which are made during the process of translation. The secondary structures are held together by hydrogen bonds. The tertiary structure is held together by primarily by hydrophobic interactions but hydrogen bonds, ionic interactions, and disulfide bonds are usually involved too.

The process by which the higher structures form is called protein folding and is a consequence of the primary structure. Although any unique polypeptide may have more than one stable folded conformation, each conformation has its own biological activity and only one conformation is considered to be the active, or native conformation.

The two ends of the amino acid chain are referred to as the carboxy terminus (C-terminus) and the amino terminus (N-terminus) based on the nature of the free group on each extremity.

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1 Structure

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