A dimer is a molecule or a group of molecules that consists of two often identical subunits, the monomers . In terms of size , molecular weight and complexity , the dimer is the simplest oligomer or polymer . The process of dimer formation is called dimerization .
Homodimers and heterodimers
Dimers are divided into:
- Homomers: the two monomers are identical
- Heterodimers: the two monomers are different, but often very similar.
The subunits in dimers can be linked to one another in different ways. The most common type is the covalent bond . Strongly polar compounds or proteins can also form non-covalent dimers, in which van der Waals , dipole , electrostatic and hydrophobic interactions as well as hydrogen bonds play a decisive role for cohesion.
- Atoms of the 1st ( hydrogen and lithium ), 5th ( nitrogen ) 6th ( oxygen ) and 7th main group ( halogens such as fluorine and chlorine ) of the periodic table form covalent homodimers.
- Complex of transition metals close sporadically together to form dimers. Usually the link takes place via a multiple binding.
- Some - mainly organic - compounds form homodimers through intramolecular hydrogen bonds , for example acetic acid .
- The most common dimers are different types of sugars ; z. B. sucrose is a heterodimer of a glucose and a fructose molecule and cellobiose is a homodimer of two glucose units. These dimers are called disaccharides (out of date double sugars ).
- Proteins can also consist of several polypeptide chains as di- or oligomers . Here then a dimer of a polymeric compound occurs, for example in the case of fumarases I or phytochromes .
- Especially with DNA , the mutagenic effect of UV light can cause a thymine dimer , i.e. a dimer between two adjacent thymine bases, which can lead to an error in replication.