What is Cytosine?

Cytosine is among the five primary nitrogenous bases of which DNA and RNA and are being used in storage and transportation of genetic makeup within a cell. Adenine, guanine, thymine as well as uracil are the remaining four nucleobases.


Cytosine, thymine and uracil are derivatives of pyrimidine, and guanine and adenine are derivatives of purine. Cytosine has a nucleoside called cytidine. The complementary purine compounds guanine (G) and adenine (A) include hydrogen bonds of cytosine (C) and thymine (T) in DNA. The RNA adds uracil (U) rather than thymine to adenine. As a result, cytosine is available across both DNA and RNA, together with adenine and guanine, in DNA while only thymine is present whereas uracil is generally present instead of thymine in RNA. Cytosine forms three nitrogenous pair with guanine in the Watson-Crick model of DNA. From an engineering point of view, it is noteworthy that cytosine always bonds with guanine in DNA through three hydrogen bonds, whereas adenine only binds thymine with two hydrogen bonds. From a technical perspective, cytosine usually connects with DNA guanine by three hydrogen bonds, while adenine only attaches to thymine through two hydrogen bonds

"An image showing purines and pyrimidines."


A nucleotide is an organic molecule which is a DNA and RNA basic foundation. They also have roles in connection with organism, metabolic processes and reactions to the enzymes. There are three components of a nucleotide namely, a group of phosphates, 5-membered sugar and a base of a nitrogen. Adenine, cytosine, guanine, and thymine are the four nitrogen bases of DNA. Rather than thymine, RNA incorporates uracil as a nucleotide base. The genetic code is found in a nucleotide sequence for all living species. They also perform various other functions such as messengers other than simply genetic information storage molecules. The core detail carrying section of the nucleotide structure is the nitrogen base. They have various functional groups, with diverse interaction ability.

Discovery of Cytosine

Only detected in 1894, Cytosine was extracted from the tissues of calf thymus. In 1903, a model was suggested and the laboratory was sequenced the same year (and therefore verified). The use of cytosine in quantum computing has recently been reported. When the investigators at Oxford applied David Deutsch's algorithm on an NMRQC two-cubit (Nuclear Magnetic Resonance Quantum Computer) on cytosine particle, they used the first quantity mechanical characteristics to handle knowledge on August 1, 1998.

Properties of Cytosine

Cytosine has a chemical formula of C4H5N3O and is a molecular pyrimidine nucleobase. The molecular weight of cytosine is 111.10 g/moland the melting temperature is between 320 and 325 °C. It can be present in both the nucleic acids that is DNA as well as RNA. It can also be present in the nucleoside molecule which has nucleobase + deoxyribose or ribose sugar and nucleotide components which has nucleoside with phosphate groups.

Structure of Cytosine

Cytosine is a heterocyclic, aromatic ring which is a pyrimidine derivative, with linked to two replacements an amine group at fourth carbon and a keto group at second carbon. Heterocyclic molecules are organically produced substances, and have a ring structure of carbohydrates, including Sulphur, oxygen and sometimes nitrogen. A combined ring of unsaturated bond, a pair of electrons or empty orbitals when has a more power in stabilizing effect than the stability of the conjugation alone this property is known as aromaticity. Cytosine is full of nitrogen atoms as a nitrogen base where it has three linkages. It also has a carbon ring that gives it a property to be called a pyrimidine. On the other side, a purine has two carbon rings. Cytosine is linked to guanine in nucleic acids. Intrinsically unstable, though, it can transform into uracil through the process of spontaneous deamination. If DNA repair enzymes, like uracil glycosylase, which cleaves an uracil in DNA, not correct this situation it may result to a point mutation. Through the use of an enzyme known as DNA methyltransferase, cytosine can also be methylated into 5-methylcytosine.

Cytidine is a molecular sub-unit of cytosine and sugar containing ribose ribonucleic acid. The compound used in cells to incorporate cytidyl acid units into ribonucleic acids is the cytidine triphosphate (CTP) which is a cytidine and triphosphoric acid ester. CTP also responds to coenzymes that are involved in the development of phospholipids with alcohols containing nitrogen.

"An image showing cytosine."

Difference Between Cytosine, Uracil and Thymine

The nitrogenous bases cytosine, thymine, and uracil all belong to the group pyrimidine. By displaying a keto group in C2 position and an amine group in 4th position on its heterocyclic aromatic ring, cytosine can all be different from those other pyrimidines. It has a C 4 H 5 N 3 Ochemical formula. In comparison to thymine and uracil, cytosine forms complementary base pairs in both DNA and RNA with guanine whereas thymine and uracil are paired with adenine in DNA and RNA correspondingly.

"An image showing structure of cytosine, uracil and thymine."

Biological Importance

Cytosine is among the 5 main nucleotide bases, including thymine, uracil, guanine, and adenine, being the remaining. They form the core nucleotide bases of the genetic material. The genetic information for a given protein on the basis of nuclear sequence is contained in nucleic acids such as DNA and RNA molecules. In cellular metabolism, genetic inheritance, and existence of a species, nucleic acids are essential. Cytosine can be used as a co-factor to the enzymes in the form of cytidine triphosphate (CTP). Adenosine diphosphate (ADP) can be converted to ATP by transferring a phosphate. ATP is a high-energy enzyme used in various cells and major biological processes.

Biological Reactions

The cytosine nucleosides are in the form of cytidine and deoxycytidine. When they become phosphorylated with three units of phosphoric acids, gets converted to cytidine triphosphate (CTP) and the deoxycytidine triphosphate (dCTP). These are the nucleotide molecules that constitute RNA and DNA molecules.

Common Mistakes

The common students can make is while writing the number of bonds between nucleotide bases and writing the complimentary pairs. Nucleotide adenosine pairs with guanine with two bonds while cytosine pairs with thymine with three hydrogen bonds in DNA.

Practice Problems

What is specific to RNA: Cytosine, Uracil, Thymine



Context and Applications  

This topic is significant in the professional exams for both undergraduate and graduate courses, especially for,

  • B.Sc. in Chemistry, Biotechnology, Biochemistry and Biology
  • M.Sc. in Chemistry, Biotechnology, Biochemistry and Biology

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