Cytosine

Description

Cytosine is pyrimidine; along with adenine and guanine they account for the fi ve nucleic acid bases. Pyrimidines are heterocyclic single-ringed compounds based on the structure of pyrimidine. Cytosinelike adenine and guanine, form nucleosides and nucleotides in RNA and DNA. When the bases combine with ribose, a ribonucleoside forms; and when it attaches to deoxyribose, a deoxyribosenucleoside is formed. Names of the nucleoside are summarized in Table 29.1.these in turn combine with phosphoryl groups, in a process called phosphorylation, to form their respective nucleotides that form nucleic acids.the nucleotides can be tri, di, and mono phosphate nucleotides similar to the way in which adenine forms ATP, ADP, and AMP.

Chemical Properties

White Solid

History

Cytosine is first isolated by hydrolysis of calf thymus tissue by Albrecht Kossel (1853–1927) and A. Neumann during 1893–1894. Thymine’s structure was published in 1900 and confi rmed over the next several years when it was synthesized by several investigators. In 1903, cytosine was synthesized by Henry Lord Wheeler (1867–1914) and Treat B. Johnson, confirming its structure. Uracil was first isolated in 1900 from yeast nucleic acid found in bovine thymus and herring sperm.the methylation of uracil produces thymine; thymine is also called 5-methyluracil because methylation takes place at the fi fth carbon in uracil to produce thymine.

Uses

Widely distributed in nature; constituent of nucleic acids

Uses

Cytosine is a nucleoside used for proteomics research. It is also used as an enzyme substrate or precursor of effector molecules such as cytosine sugars.

Uses

Cytosine has been used:

• for the preparation of nucleobase solutions
• as a standard for high-performance liquid chromatography (HPLC)
• for the estimation of global methylation rate
• for nucleoside 5′-triphosphate (NTP) synthesis
• purification

Definition

ChEBI: An aminopyrimidine that is pyrimidin-2-one having the amino group located at position 4.

Definition

cytosine: A pyrimidine derivative.It is one of the principal componentbases of nucleotides and the nucleicacids DNA and RNA.

Definition

A nitrogenous base found in DNA and RNA. Cytosine has the pyrimidine ring structure.

Biological Functions

Cytosine is one of the five nitrogenous bases that make up the genetic code in DNA and RNA. Nucleic acids are essential in heredity, cellular function, and biological reactions. Cytosine can also be methylated by adding a methyl (CH3) group at the C5 position and, in this modified form, plays a vital role in epigenetics. Moreover, cytosine can be transformed into other bases, such as uracil, further elevating the importance of this nitrogenous base in epigenetics. In its epigenetically modified form, cytosine associates with changes in the cellular and developmental process, neuron cell development, and human tumor development. Cytosine, in the form of cytidine triphosphate (CTP), may be used as an enzyme co-factor. Transferring a phosphate can convert adenosine diphosphate (ADP) to ATP. ATP is a high-energy molecule that is involved in a variety of cellular functions and essential biological reactions.

General Description

Pharmaceutical secondary standards for application in quality control, provide pharma laboratories and manufacturers with a convenient and cost-effective alternative to the preparation of in-house working standards.

Biochem/physiol Actions

Cytosine (C) is one of the four main bases found in DNA and RNA, along with adenine, guanine, and thymine (uracil in RNA).

Purification Methods

Cytosine crystallises from H2O as the monohydrate which loses water on heating above 100o. Its solubility in H2O is 0.77%. UV: max 267nm ( 6,100) in H2O pH 8.8 and 275nm ( 10,400) in 0.1N HCl. [Hilbert & Johnson J Am Chem Soc 52 1152 1930, Hilbert et al. J Am Chem Soc 57 552 1935, Beistein 25 III/IV 3654.]

Structure and conformation

Cytosine is a pyrimidine containing a single heterocyclic aromatic ring, a keto group at C2, and an amine group at C4. The molecule is planar in shape. Cytosine can form three hydrogen bonds with guanine. Due to these three hydrogen bonds, the cytosine-guanine base pair has an overall higher boiling point and greater bond strength than the adenine-thymine base pair. The high melting point makes the cytosine-guanine base-pair much more resistant to denaturation. The double strand of DNA breaks down into its single constituent strands due to high temperatures.