What is Protein?
[[File:Myoglobin.png|thumb|right|A 3D diagram of the protein [[myoglobin]] showing turquoise [[alpha helix|alpha helices]]. This protein was the first to have its structure solved by [[X-ray crystallography]]. Towards the right-center among the coils, a [[heme]] group (shown in grey) with a bound [[oxygen]] molecule (red)]] '''Proteins''' are long-chain [[molecule]]s built from small units known as [[amino acid]]s, which are joined in a sequence by [[peptide bond]]s. Every sequence of amino acids becomes a specific final shape, allowing living things to use proteins as tiny machines to do work. They are [[biochemistry|biochemical]] [[Chemical compound|compounds]].They have one or more [[polypeptide]]s folded into a round or [[fibrous protein|fibrous]] shape.<ref>See [[protein structure]] for more on this topic.</ref> A polypeptide is a single linear [[polymer]] chain of [[amino acid]]s. The [[sequence]] of amino acids in a polypeptide comes from the [[DNA sequence]] of a [[gene]].<ref>see [[Translation (genetics)]] and [[RNA splicing]] for a fuller account.</ref> The [[genetic code]] specifies 20 standard amino acids. Shortly after synthesis, some amino acids are chemically modified. This alters the folding, stability, activity, and function of the protein. Sometimes proteins have non-peptide groups attached, as [[Cofactor (biochemistry)|cofactor]]s. Proteins are essential to all [[cell (biology)|cell]]s. Like other biological [[macromolecule]]s ([[polysaccharide]]s and [[nucleic acid]]s), proteins take part in virtually every process in cells: # Many proteins are [[enzyme]]s that [[catalysis|catalyze]] (help to happen) biochemical reactions and are vital to [[metabolism]]. # Other proteins have structural or mechanical functions, such as in muscle and in [[cell]]s. The [[cytoskeleton]] is a system of [[scaffolding]] that keeps cell shape. # Other proteins are important in [[Signal transduction|cell signaling]], [[antibody|immune response]]s, and [[cell division]] == Formation == Proteins are formed by a pro