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Cytosine (/ ˈ s aɪ t ə ˌ s iː n,-ˌ z iː n,-ˌ s ɪ n / [2] [3]) (symbol C or Cyt) is one of the four nucleotide bases found in DNA and RNA, along with adenine, guanine, and thymine (uracil in RNA). It is a pyrimidine derivative, with a heterocyclic aromatic ring and two substituents attached (an amine group at position 4 and a keto group ...
Base pairing: Two base pairs are produced by four nucleotide monomers, nucleobases are in blue. Guanine (G) is paired with cytosine (C) via three hydrogen bonds, in red. Adenine (A) is paired with uracil (U) via two hydrogen bonds, in red. Purine nucleobases are fused-ring molecules. Pyrimidine nucleobases are simple ring molecules.
Catalytic RNA molecules were discovered in the early 1980s, leading to a 1989 Nobel award to Thomas Cech and Sidney Altman. In 1990, it was found in Petunia that introduced genes can silence similar genes of the plant's own, now known to be a result of RNA interference. [80] [81]
Well-studied biological nucleic acid molecules range in size from 21 nucleotides (small interfering RNA) to large chromosomes (human chromosome 1 is a single molecule that contains 247 million base pairs [18]). In most cases, naturally occurring DNA molecules are double-stranded and RNA molecules are single-stranded. [19]
Double-stranded RNA forms an A-type helical structure, unlike the common B-type conformation taken by double-stranded DNA molecules. The secondary structure of RNA consists of a single polynucleotide. Base pairing in RNA occurs when RNA folds between complementarity regions. Both single- and double-stranded regions are often found in RNA molecules.
The two DNA strands are known as polynucleotides as they are composed of simpler monomeric units called nucleotides. [2] [3] Each nucleotide is composed of one of four nitrogen-containing nucleobases (cytosine [C], guanine [G], adenine [A] or thymine [T]), a sugar called deoxyribose, and a phosphate group.
The team also detected adenine, guanine, cytosine, thymine and uracil — all five of the biological nucleobases, or components that make up the genetic code in DNA and RNA. “These organic ...
This nucleotide contains the five-carbon sugar deoxyribose (at center), a nucleobase called adenine (upper right), and one phosphate group (left). The deoxyribose sugar joined only to the nitrogenous base forms a Deoxyribonucleoside called deoxyadenosine, whereas the whole structure along with the phosphate group is a nucleotide, a constituent of DNA with the name deoxyadenosine monophosphate.