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[sahy-tuh-seen, -zeen, -sin]
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noun Biochemistry.
  1. a pyrimidine base, C4H5N3O, that is one of the fundamental components of DNA and RNA, in which it forms a base pair with guanine. Symbol: C

Origin of cytosine

< German Cytosin (1894); see cyto-, -ose2, -ine2
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018
British Dictionary definitions for cytosine


  1. a white crystalline pyrimidine occurring in nucleic acids; 6-amino-2-hydroxy pyrimidine. Formula: C 4 H 5 N 3 OSee also DNA, RNA
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

Word Origin and History for cytosine


1894, from German cytosin (1894), from cyto- "cell" + -ose + chemical suffix -ine (2). "The name cytosine (due to Kossel and Neumann) is misleading. Cytosine is not, like adenosine and guanosine, a nucleoside but the sugar-free base." [Flood]

Online Etymology Dictionary, © 2010 Douglas Harper

cytosine in Medicine


  1. A pyrimidine base that is an essential constituent of RNA and DNA.
The American Heritage® Stedman's Medical Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.

cytosine in Science


  1. A pyrimidine base that is a component of DNA and RNA, forming a base pair with guanine. Chemical formula: C4H5N3O.
The American Heritage® Science Dictionary Copyright © 2011. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.