Dimer

Dimer may refer to:

Dimerous refers to plants with organ arrangement based on the number 2: see merosity.

See also

Protein dimer

In biochemistry, a dimer is a macromolecular complex formed by two, usually non-covalently bound, macromolecules such as proteins or nucleic acids. It is a quaternary structure of a protein.

A homodimer is formed by two identical molecules (a process called homodimerisation). A heterodimer is formed by two different macromolecules (called heterodimerisation).

Most dimers in biochemistry are not connected by covalent bonds. An example of a non-covalent heterodimer is the enzyme reverse transcriptase, which is composed of two different amino acid chains. An exception is dimers that are linked by disulfide bridges such as the homodimeric protein NEMO.

Some proteins contain specialized domains to ensure dimerization (dimerization domains).

Examples

Dimer (chemistry)

A dimer (/ˈdaɪmər/) (di-, "two" + -mer, "parts") is an oligomer consisting of two structurally similar monomers joined by bonds that can be either strong or weak, covalent or intermolecular. The term homodimer is used when the two molecules are identical (e.g. A-A) and heterodimer when they are not (e.g. A-B). The reverse of dimerisation is often called dissociation.

Noncovalent dimers

Carboxylic acids form dimers by hydrogen bonding of the acidic hydrogen and the carbonyl oxygen when anhydrous. For example, acetic acid forms a dimer in the gas phase, where the monomer units are held together by hydrogen bonds. Under special conditions, most OH-containing molecules form dimers, e.g. the water dimer.

Borane ("BH₃") occurs as the dimer diborane (B₂H₆), due to the high Lewis acidity of the boron center.

Excimers and exciplexes are excited structures with a short lifetime. For example, noble gases do not form stable dimers, but do form the excimers Ar₂*, Kr₂* and Xe₂* under high pressure and electrical stimulation.