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A dimer is a chemical or biological entity consisting of two structurally similar subunits called monomers, which are joined by bonds, which can be strong or weak.

Organic chemistry

Molecular dimers are often formed by the reaction of two identical compounds e.g.: 2A → A-A. In this example, monomer "A" is said to dimerise to give the dimer "A-A". An example is Diaminocarbenes, which dimerise to give tetraaminoethylenes:

2 C(NR₂)₂ → (R₂N)₂C=C(NR₂)₂

Acetic acid forms a dimer in the gas phase, the monomer units are held together by hydrogen bonds. Under special conditions, most OH-containing molecules form dimers, e.g. the water dimer.

Dicyclopentadiene is a unsymmetrical dimer of two cyclopentadiene molecules have reacted to give the product. Upon heating, it "cracks" to give identical monomers:

C₁₀H₁₂ → 2 C₅H₆

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.

Biochemistry

In biochemistry and molecular biology, dimers of macromolecules like proteins and nucleic acids are often observed. The dimerization of identical subunits is called homodimerization; the dimerization of different subunits or unrelated monomers is called heterodimerization. Most dimers in biochemistry are not connected by covalent bonds with the exception of disulfide bridges. An example of this would be the enzyme reverse transcriptase, which is made of two different amino acid chains.

Examples

• • DNA
  • Antibodies
    • Receptor tyrosine kinases
  • Transcription factors
    • Leucine zipper motif proteins
    • Nuclear receptors
  • 14-3-3 proteins
  • G protein-coupled receptors
  • G protein βγ-subunit dimer
  • Kinesin
  • Triosephosphateisomerase (TIM)
  • Alcohol dehydrogenase
  • Factor XI
  • Factor XIII
  • Toll-like receptor
  • Fibrinogen

See also

• Monomer
• Trimer
• Tetramer
• Heteromer
• Oligomer
• Polymer
• Dimer model

References

• "IUPAC "Gold Book" definition". Retrieved 2009-04-30.

1. "Structure-Activity Relationships of - 3'-spiro-5' '-(4' '-amino-1' ',2' '-oxathiole-2' ',2' '-dioxide)thymine Derivatives as Inhibitors of HIV-1 Reverse Transcriptase Dimerization". J. Med. Chem. 49 (16): 4834–4841. 2006. doi:10.1021/jm0604575. {{cite journal}}: Unknown parameter |authors= ignored (help)

• Chemical compounds