This article is about a class of molecules. A representation of the 3D structure of the protein myoglobin showing turquoise α-helices. Protein kcal per g protein was the first to have its structure solved by X-ray crystallography.
Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residues. A linear chain of amino acid residues is called a polypeptide. A protein contains at least one long polypeptide. 30 residues, are rarely considered to be proteins and are commonly called peptides. Once formed, proteins only exist for a certain period and are then degraded and recycled by the cell’s machinery through the process of protein turnover. A protein’s lifespan is measured in terms of its half-life and covers a wide range. Like other biological macromolecules such as polysaccharides and nucleic acids, proteins are essential parts of organisms and participate in virtually every process within cells.
Proteins were recognized as a distinct class of biological molecules in the eighteenth century by Antoine Fourcroy and others, distinguished by the molecules’ ability to coagulate or flocculate under treatments with heat or acid. Proteins were first described by the Dutch chemist Gerardus Johannes Mulder and named by the Swedish chemist Jöns Jacob Berzelius in 1838. Early nutritional scientists such as the German Carl von Voit believed that protein was the most important nutrient for maintaining the structure of the body, because it was generally believed that “flesh makes flesh. The difficulty in purifying proteins in large quantities made them very difficult for early protein biochemists to study. Hence, early studies focused on proteins that could be purified in large quantities, e. In the 1950s, the Armour Hot Dog Co. Linus Pauling is credited with the successful prediction of regular protein secondary structures based on hydrogen bonding, an idea first put forth by William Astbury in 1933.
The first protein to be sequenced was insulin, by Frederick Sanger, in 1949. With the development of X-ray crystallography, it became possible to sequence protein structures. The bond itself is made of the CHON elements. Most proteins consist of linear polymers built from series of up to 20 different L-α- amino acids. The peptide bond has two resonance forms that contribute some double-bond character and inhibit rotation around its axis, so that the alpha carbons are roughly coplanar. The words protein, polypeptide, and peptide are a little ambiguous and can overlap in meaning. Protein is generally used to refer to the complete biological molecule in a stable conformation, whereas peptide is generally reserved for a short amino acid oligomers often lacking a stable 3D structure.
Proteins are assembled from amino acids using information encoded in genes. Each protein has its own unique amino acid sequence that is specified by the nucleotide sequence of the gene encoding this protein. The process of synthesizing a protein from an mRNA template is known as translation. Short proteins can also be synthesized chemically by a family of methods known as peptide synthesis, which rely on organic synthesis techniques such as chemical ligation to produce peptides in high yield.
The crystal structure of the chaperonin, a huge protein complex. A single protein subunit is highlighted. Three possible representations of the three-dimensional structure of the protein triose phosphate isomerase. Left: All-atom representation colored by atom type. Middle: Simplified representation illustrating the backbone conformation, colored by secondary structure.
Most proteins fold into unique 3D structures. The shape into which a protein naturally folds is known as its native conformation. Although many proteins can fold unassisted, simply through the chemical properties of their amino acids, others require the aid of molecular chaperones to fold into their native states. Primary structure: the amino acid sequence. Secondary structure: regularly repeating local structures stabilized by hydrogen bonds.