cytosine

American  

[sahy-tuh-seen, -zeen, -sin] / ˈsaɪ təˌsin, -ˌzin, -sɪn /

noun

Biochemistry.

1. a pyrimidine base, C 4 H 5 N 3 O, that is one of the fundamental components of DNA and RNA, in which it forms a base pair with guanine. C

---

cytosine British  

/ ˈsaɪtəsɪn /

noun

1. a white crystalline pyrimidine occurring in nucleic acids; 6-amino-2-hydroxy pyrimidine. Formula: C 4 H 5 N 3 O See also DNA RNA

---

cytosine Scientific  

/ sī′tə-sēn′ /

1. A pyrimidine base that is a component of DNA and RNA, forming a base pair with guanine. Chemical formula: C ₄ H ₅ N ₃ O.

---

Etymology

Origin of cytosine

< German Cytosin (1894); see cyto-, -ose ², -ine ²

Example Sentences

Importantly they also discovered all five nitrogenous bases — adenine, guanine, cytosine, thymine, and uracil — that are necessary to build DNA and RNA.

From Salon • Jan. 30, 2025

These include 14 of the 20 amino acids that life on Earth uses to build proteins and all four of the ring-shaped molecules that make up DNA - adenine, guanine, cytosine and thymine.

From BBC • Jan. 29, 2025

Nucleotides are composed of three distinctive parts: a sugar molecule, a phosphate group and one of the four nucleobases adenine, thymine, guanine and cytosine.

From Science Daily • Mar. 8, 2024

Rather than inducing random changes in the virus’ RNA genome, the drug is more likely to cause specific nucleic acid substitutions, with guanine switching to adenine and cytosine to uracil.

From Science Magazine • Feb. 1, 2023

“Suddenly I became aware that an adenine thymine pair was identical in shape to a guanine cytosine pair...no fudging was required to make the two types of base pairs identical in shape.”

From "The Gene" by Siddhartha Mukherjee