What are the types of nucleobases?



Nucleobase is the abbreviation of “basic group” in chemistry. Most of the basic groups in organic matter contain nitrogen atoms and are called nitrogenous bases. Amino (-NH2) is the simplest nitrogenous base.
Nucleobases, also known as nucleobases and nitrogenous bases in biochemistry, are nitrogen-containing compounds that form nucleosides, which are components of nucleotides. Monomers such as bases, nucleosides and nucleotides constitute the basic building blocks of nucleic acids.
Nucleobases can form base pairs and stack with each other, so they are an important part of long-chain helical structures such as ribonucleic acid (RNA) and deoxyribonucleic acid (DNA).

Brief description of species and discovery process
discovery process
There are five common nucleobases in organisms, namely adenine (A), guanine (G), cytosine (C), thymine (T) and uracil (U), which were synthesized in 2019. 4 kinds of nucleobases, American scientist StevenA. Benner named these 4 new members “Z”, “P”, “S”, “B” (As the name implies, among the first five nucleobases, adenine and guanine belong to purines. family (abbreviated as R), they have a bicyclic structure. Cytosine, uracil, thymine belong to the pyrimidine family (Y), and their ring system is a six-membered heterocycle. They are also called major or standard nucleobases. They are the basic units that make up the genetic code, where the nucleobases A, G, C, and T are found in DNA, while A, G, C, and U are found in RNA. Notably, thymine has one more than uracil The 5-position methyl group increases the accuracy of genetics. The compound formed by the nucleobase linked to the 1-position carbon atom of ribose or deoxyribose by a covalent bond is called a nucleoside. The nucleoside is then combined with a phosphoric acid to form Nucleotides, the phosphate group is attached to the 5th carbon atom of the five-carbon sugar).

New nucleobase
Methylcytosine (mC): Derived from C, is the primary cause of epigenetic mechanisms. As an important epigenetic modification, mC is involved in gene expression regulation, X-chromosome inactivation, genomic imprinting, long-term silencing of transposons and carcinogenesis.
Methyladenine (mA), whose main role is to determine the nature of the epigenome, and thus plays an important role in the life process of cells. Algae, worms, and flies all have mA. The main function of mA is to regulate the expression of certain genes, therefore, constitute a new epigenetic mark.
The newly discovered nucleobases are also: 5-cytosine methyl, 5-hydroxymethylcytosine (5-hmC), 5-cytosine formyl (5-formylcytosine) and 5-cytosine carboxyl (5-carboxylcytosine) )
A total of 21 nucleobase species have been discovered as of 2020.

Nucleobase pairing
In a typical double helix DNA, each nucleobase pair contains one purine and one pyrimidine: A pairs with T through 2 hydrogen bonds, C pairs with G or Z pairs P or S pairs B through 3 hydrogen bonds key is connected. These purine-pyrimidine pairings are called nucleobase complementarity, and the nucleobases that connect the two strands of DNA are often likened to rungs in a ladder. Part of the reason for the pairing between purines and pyrimidines is steric constraints, as this pairing combination makes the DNA helix a geometry of constant width. A-T and C-G pairings form double or triple hydrogen bonds between the amine and carbonyl groups of complementary nucleobases.

Modified nucleobases
DNA and RNA molecules also contain other non-primary nucleobases that are modified after nucleic acid strand formation. Most of these nucleobases are derivatives formed by methylation or other chemical modifications at different positions of the above-mentioned purine or pyrimidine bases. The most common modified nucleobase in DNA is 5-methylcytosine (m5C). There are many modified nucleobases in RNA, including those contained in the nucleosides pseudouridine (Ψ), dihydrouridine (D), inosine (I), and 7-methylguanosine (m7G). .
Hypoxanthine and xanthine, two of the many modified nucleobases produced by mutagenic treatment, are both produced by deamination (replacement of an amine group with a carbonyl group). Hypoxanthine is derived from adenine and xanthine is derived from guanine.

Synthetic nucleobase
In medicine, several nucleoside analogs are used as anticancer and antiviral agents. Viral polymerases bind these compounds to non-primary nucleobases. Nucleoside analogs taken by patients enter the body and are converted into nucleotides and activated in cells.