Cytosine: What is it? History, Chemical Reactions, Theoretical Aspects and Properties

It is one of the four main bases found in deoxyribonucleic acid and ribonucleic acid, along with adenine , guanine and thymine .

It is a pyrimidine derivative, with a heterocyclic aromatic ring and two substituents attached (an amino group in the 4-position and a keto group in the 2-position). The nucleoside of the cytosine is cytidine. In the Watson-Crick base pairing, it forms three hydrogen bonds with guanine.

Cytosine is one of the five main nucleobases used to store and transport genetic information within a cell in the nucleic acids DNA and RNA. The other four nucleobases are adenine, guanine, thymine and uracil.

Cytosine, thymine and uracil are derivatives of pyrimidine, while guanine and adenine are derivatives of purine. The nucleoside of the cytosine is cytidine.

In DNA, cytosine (C) and thymine (T) form hydrogen bonds with their complementary purine derivatives, guanine (G) and adenine (A). In RNA, the complement of adenine is uracil (U) instead of thymine.

Therefore, cytosine, along with adenine and guanine, is present in both DNA and RNA, while thymine is generally observed only in DNA and uracil only in RNA.

In the mating of Watson-Crick bases, the cytosine forms three hydrogen bonds with guanine. From the point of view of the structure, it is notable that cytosine, with its three binding sites, only adheres to guanine in DNA, whereas adenine, with two sites for hydrogen bonding, only adheres to the thymine.

The way in which these hydrogen bonds hold the strands of the nucleic acid together to form the double helix, and at the same time allow the strands to “decompress” for replication and transcription, is simply amazing from the design point of view .

Cytosine can also be part of a nucleotide that is not related to DNA or RNA.

Like cytidine triphosphate (CTP), it can act as a cofactor for enzymes and can transfer a phosphate to convert adenosine diphosphate (ADP) to adenosine triphosphate (ATP). ).

History of cytosine

Cytosine was discovered and named by Albrecht Kossel and Albert Neumann in 1894 when it was hydrolyzed / isolated from the tissues of the calf thymus. A structure was proposed in 1903, and was synthesized (and thus confirmed) in the laboratory in the same year.

Cytosine recently found use in quantum computing.

The first time the properties of quantum mechanics were used to process information occurred on August 1, 1997, cytosine was used in an early demonstration quantum information processing when researchers from the University of Oxford implemented David Deutsch’s algorithm. Jozsa

It was implemented in a two-cubic NMRQC (Quantum Nuclear Magnetic Resonance Computer) of two qubits, based on the cytosine molecule.

In March 2015, NASA scientists reported the formation of cytosine, along with uracil and thymine, from pyrimidine under laboratory conditions similar to space conditions, which is interesting because pyrimidine has been found in meteorites, although its origin is unknown.

Chemical reactions

Cytosine can be found as part of DNA, as part of RNA or as part of a nucleotide.

Like cytidine triphosphate (CTP), it can act as a cofactor for enzymes and can transfer a phosphate to convert adenosine diphosphate (ADD) to adenosine triphosphate (ADT). ).

In DNA and RNA, cytosine is combined with guanine. However, it is inherently unstable and can be transformed into uracil (spontaneous deamination). This can lead to a point mutation if it is not repaired by DNA repair enzymes, such as uracil glycosylase, which cleaves a uracil in DNA.

When it is in third place in an RNA codon, cytosine is synonymous with uracil, since they are interchangeable as the third base. When it is found as the second base in a codon, the third is always interchangeable. For example, UCU, UCC, UCA and UCG are all serines, regardless of the third base.

The cytosine can also be methylated in 5-methylcytosine by an enzyme called DNA methyltransferase or be methylated and hydroxylated to form 5-hydroxymethylcytosine.

Active enzymatic deamination of cytosine or 5-methylcytosine by the APOBEC family (apolipoprotein B mRNA editing enzyme, similar to catalytic polypeptide) of cytosine deaminases could have beneficial and detrimental implications in various cellular processes, as well as in the evolution of the organism.

The implications of deamination on 5-hydroxymethylcytosine, on the other hand, remain less understood.

Theoretical aspects of cytosine

Cytosine has not been found in meteorites, suggesting that the first strands of RNA and DNA had to look elsewhere to obtain this basic element.

The cytosine probably formed within some parent bodies of meteorites, however it did not persist within these bodies due to an effective deamination reaction in uracil.

Properties

Cytosine is a pyrimidine derivative, with a heterocyclic aromatic ring and two substituents attached (an amino group at position four and a keto group at position two).

Heterocyclic compounds are organic compounds (those containing carbon) that contain a ring structure that contains atoms in addition to carbon, such as sulfur, oxygen or nitrogen, as part of the ring.

Aromaticity is a chemical property in which a conjugated ring of unsaturated bonds, solitary pairs or empty orbitals exhibits a stronger stabilization than would be expected with the stabilization of the conjugation alone.

In organic chemistry, a substituent is a substituted atom or group of atoms instead of a hydrogen atom in the original chain of a hydrocarbon.

In DNA and RNA, cytosine is combined with guanine. However, it is inherently unstable and can be transformed into uracil (spontaneous deamination). This can lead to a point mutation if it is not repaired by DNA repair enzymes, such as uracil glycosylase, which cleaves a uracil in DNA.

Cytosine can also be methylated in 5-methylcytosine by an enzyme called DNA methyltransferase.