Trans

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Trans is a Latin noun or prefix, meaning "across", "beyond" or "on the opposite side [of]" . It is the opposite of cis, which means "on the same side [of]".

  • In chemistry, a double bond (or ring) not subject to free rotation in which the greater radical on both ends is on the opposite side of the bond (or face of the ring) is called trans. Compare with cis.
In the diagram on the right, the hydrogen atoms are on opposite sides of the carbon chain. They cannot rotate to the same side of the molecule, as (unlike with a single bond) double bonds prevent this from happening. A similar phenomenon is seen in cyclic compounds (in which the atoms form a closed ring), where substituents can be on the same "face" of the ring (cis) or opposite faces (trans.)
See geometric isomerism for more on this topic. See also Trans fat.
  • In cell biology, external factors which act on a molecule are considered to act in trans. For example, proteins which are transcription factors bind to the DNA in trans to modify the rate of RNA transcription. Internal factors act in cis. For example, a specific promoter sequence which recruits RNA polymerase and thereby increases the rate of RNA transcription acts in cis.

Trans is also: