cy·​to·​sine | \ ˈsī-tə-ˌsēn How to pronounce cytosine (audio) \

Definition of cytosine

: a pyrimidine base C4H5N3O that codes genetic information in the polynucleotide chain of DNA or RNA — compare adenine, guanine, thymine, uracil

Examples of cytosine in a Sentence

Recent Examples on the Web One serves as a template, laying down sequences of the four bases that make up DNA molecules: adenine (A), thymine (T), guanine (G) and cytosine (C). Lydia Denworth, Scientific American, "A Breakthrough in Genetic Medicine for Rare Diseases," 3 Mar. 2020 However, rather than the conventional duo of base pairs, adenine and uracil or cytosine and guanine, the molecules form hexamers, or six-membered rings. Quanta Magazine, "Chemists Seek Possible Precursor to RNA," 5 Feb. 2014 Part of this gene contains repeated segments for three of the letters of the DNA code—cytosine, adenine and guanine, which are known as CAG repeats. Bret Stetka, Scientific American, "Antisense Drugs for Huntington’s, ALS and Prion Diseases Could Meet the Dire Need for Brain Treatments," 15 Aug. 2019 Her team reported last year in Cell that many mRNA cytosine bases are acetylated. Ken Garber, Science | AAAS, "Hidden layer of gene control influences everything from cancer to memory," 1 July 2019 In a process called hydrolytic deamination, for example, the base cytosine spontaneously loses its amino group and becomes uracil. Quanta Magazine, "Ancient DNA Yields Snapshots of Vanished Ecosystems," 29 May 2019 In 1953, scientists proposed that DNA is structured as a double helix, with the chemical bases—adenine (A), cytosine (C), guanine (G), and thymine (T)—stacked up in pairs between two intertwining lengths of sugar and phosphate. Ryan Rossotto, National Geographic, "DNA, explained," 12 June 2019 For instance, with height, having a guanine base instead of a cytosine one in a particular DNA region might correlate with being 0.1 millimeter taller than average. Quanta Magazine, "New Turmoil Over Predicting the Effects of Genes," 23 Apr. 2019 To form the i-motif, the double helix untwists and then one of the strands bunches up with a bunch of cytosine molecules. Avery Thompson, Popular Mechanics, "Scientists Discover That the Double Helix Isn't the Only DNA Form," 24 Apr. 2018

These example sentences are selected automatically from various online news sources to reflect current usage of the word 'cytosine.' Views expressed in the examples do not represent the opinion of Merriam-Webster or its editors. Send us feedback.

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First Known Use of cytosine

1894, in the meaning defined above

History and Etymology for cytosine

International Scientific Vocabulary cyt- + -ose + -ine entry 2

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Time Traveler for cytosine

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The first known use of cytosine was in 1894

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Cite this Entry

“Cytosine.” Dictionary, Merriam-Webster, Accessed 14 Jul. 2020.

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More Definitions for cytosine


cy·​to·​sine | \ ˈsīt-ə-ˌsēn How to pronounce cytosine (audio) \

Medical Definition of cytosine

: a pyrimidine base C4H5N3O that codes genetic information in the polynucleotide chain of DNA or RNA — compare adenine, guanine, thymine, uracil

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