In biochemistry, many proteins are actually assemblies of more than one protein (polypeptide) molecule, which in the context of the larger assemblage are known as protein subunits. In addition to the tertiary structure of the subunits, multiple-subunit proteins possess a quaternary structure, which is the arrangement into which the subunits assemble. Enzymes composed of subunits with diverse functions are sometimes called holoenzymes, in which some parts may be known as regulatory subunits and the core is often called the catalytic subunit. Examples of proteins with quaternary structure include hemoglobin, DNA polymerase, and ion channels. Other assemblies referred to instead as multiprotein complexes also possess quaternary structure. Examples include nucleosomes and microtubules. Changes in quaternary structure are called conformational changes. It is through such changes, which underlie cooperativity and allostery in "multimeric" enzymes, that many proteins undergo regulation and perform their physiological function. Biochemistry is the study of the chemistry of life, a bridge between biology and chemistry that studies how complex chemical reactions give rise to life. ... A representation of the 3D structure of myoglobin, showing coloured alpha helices. ... Peptides are the family of molecules formed from the linking, in a defined order, of various amino acids. ... A molecule is the smallest particle of a pure chemical substance that still retains its chemical composition and properties. ... In structural biology, a protein subunit or subunit protein is a single protein molecule that assembles (or coassembles) with other protein molecules to form a multimeric or oligomeric protein. ... In biochemistry, the tertiary structure of a protein is its overall shape. ... Ribbon diagram of the catalytically perfect enzyme TIM. An enzyme is a protein that catalyzes, or speeds up, a chemical reaction. ... In biochemistry, holoenzyme may refer either to the complete and operative form of an enzyme with multiple protein subunits or to the combination of an apoenzyme with its cofactor. ... 3-dimensional structure of hemoglobin. ... DNA polymerase 3D structure. ... Another, unrelated ion channeling process is part of ion implantation. ... A nucleosome is a unit made of DNA and histones. ... This article is in need of attention from an expert on the subject. ... Conformation generally means structural arrangement. ... In biochemistry, a macromolecule has cooperative binding if when binding a ligand, the affinity of the ligand for the molecule changes depending on the amount of ligand already bound. ... In biochemistry, an enzyme or other protein is allosteric if its activity or efficiency changes in response to the binding of an effector molecule at a so-called allosteric site. ...

The above definition follows a classical approach to biochemistry, established at times when the distinction between a protein and a functional, proteinaceous unit was difficult to elucidate. More recently, people refer to protein-protein interaction when discussing quaternary structure of proteins and consider all assemblies of proteins as protein complexes. A protein complex is a group of two or more associated proteins. ...

Quaternary Structures Types

Quaternary structures are described using numeric names that end in -meric. The first twenty quaternary structures types have formal names, the rest are composed of the number followed by -meric.

*No known examples

See also: primary structure -- secondary structure -- tertiary structure -- structural biology -- translation In chemistry, a monomer (from Greek mono one and meros part) is a small molecule that may become chemically bonded to other monomers to form a polymer. ... Sucrose, or common table sugar, is composed of glucose and fructose. ... Trimer might refer to: trimer (chemistry), a reaction product composed of three identical molecules trimer (biochemistry), a compound of three macromolecules non-covalently bound This is a disambiguation page: a list of articles associated with the same title. ... A tetramer is a protein with four subunits (tetrameric). ... This article does not cite its references or sources. ... Dodecameric is a term pertaining to protein quaternary structure, and describes a protein complex with 12 protein subunits (protein chains). ... Eicosameric refers to biological polymers or multimers having exactly twenty monomers (or 20 repeating components). ... A protein primary structure is a chain of amino acids. ... A representation of the 3D structure of the Myoglobin protein. ... In biochemistry, the tertiary structure of a protein is its overall shape. ... Structural biology is a branch of molecular biology concerned with the study of the architecture and shape of biological macromolecules--proteins and nucleic acids in particular—and what causes them to have the structures they have. ... Translation in the cytoplasm; tRNA carries amino acids which are added to the growing peptide chain in the ribosome. ...

External links

• The Macromolecular Structure Database (MSD) at the European Bioinformatics Institute (EBI) serves a list of the Probabable Quaternary Structure (PQS) for every protein in the Protein Data Bank (PDB).
• The Protein Interfaces, Surfaces and Assemblies (Pisa) server at the MSD.