CIS

'Cis' is a Latin noun or prefix, meaning "on the same side [of]" or "on this side [of]". It is the opposite of ''trans'', which means "on the opposite side".

★ In chemistry, a double bond (or ring) in which the greater radical on both ends is on the same side of the bond (or face of the ring) is called '''cis'''. Compare with ''trans''. In the diagram on the right, both hydrogen atoms (and both fluorine atoms) are on the same side of the carbon chain. As the carbons are joined by a double bond, these cannot rotate around the molecule. See Geometric isomerism.

★ In genetics, '''cis-''' is a prefix used in terms such as "cis-regulation" to signify the co-location of two or more genes on the same chromosome of a homologous pair. The action of molecules is also described in these terms (see Cis-acting).

★ In molecular and cellular biology, Internal factors act ''in 'cis''' (''i.e.'', intramolecular). For example, a specific promoter sequence which recruits RNA polymerase and thereby increases the rate of RNA transcription acts ''in cis''. External factors which act on a molecule (''i.e.'', intermolecular interactions) 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.

★ In geography, placenames beginning with '''Cis-''' convey the meaning "on this side of". Examples include Ciskei (referring to the Kei River), Cisleithania (Leitha), Cisalpine Gaul (Alps), Cisjordan (used for the British Mandate of Palestine, the West Bank and Israel interchangeably). The antonym is ''Trans-''.

★ In astronomy cislunar means: in outer space between the Earth and the Moon. Translunar is its antonym. Similarly, a Trans-Neptunian object is a celestial object orbiting the Sun outside the orbit of Neptune, and Cis-Neptunian objects are at or before Neptune's orbit.

★ In medicine and sociology, cisgender and cissexual are the opposite of transgender and transsexual, respectively. Both describe people whose gender identity matches their physical and/or assigned sex.

★ In nutrition a cis fat is an unsaturated fatty acid whose hydrogen atoms are on the same side, as opposed to an unsaturated trans fat whose hydrogen atoms are on opposite sides. The difference in shape makes cis fats less likely to congest in the bloodstream and thus less dangerous than trans fats.