Nucleobases are the building blocks that make up the long chains of DNA and RNA molecules in their phosphorylated nucleotide form.

In the DNA, which forms ladder-like double strands, the four occurring nucleic bases form hydrogen bonds with the complementary base. The nucleobases consist of either a bicyclic purine or a monocyclic pyrimidine backbone.

What are nucleic bases?

The four nucleobases adenine, guanine, cytosine and thymine, as building blocks of the long DNA double helix molecular chains, form the constant pairings adenine-thymine (AT) and guanine-cytosine (GC).

The two bases adenine and guanine each consist of a modified bicyclic six-membered and five-membered ring of the purine skeleton and are therefore also called purine bases. The basic structure of the other two nucleobases, cytosine and thymine, consists of a heterocyclic aromatic six-membered ring, which corresponds to a modified pyrimidine skeleton, which is why they are also called pyrimidine bases. Since the RNA are usually present as single strands, there are initially no base pairings. This takes place only during replication via mRNA (messenger RNA).

The copy of the RNA strand consists of the complementary Nukleinbasen analogous to the second strand of DNA. The only difference is that thymine is substituted in the RNA by uracil. The DNA and RNA chain molecules are not formed by the nucleic bases in pure form, but they first connect in the case of DNA with the 5-sugar deoxyribose to the corresponding nucleoside. In the case of RNA, the sugar group consists of ribose. In addition, the nucleosides are phosphorylated with a phosphate radical to form so-called nucleotides.

The purine bases hypoxanthine and xanthine also found in DNA and RNA correspond to modified thymine. Hypoxanthine is formed from adenine by replacing the amino group (-NH3) with a hydroxy group (-OH), and xanthine is formed from guanine. Both nucleobases do not contribute to the transmission of genetic information.

Function, effect & tasks

One of the most important functions of the nucleobases from which the double strands of the DNA are built up is to show presence at the respectively provided position.

The order of the nucleobases corresponds to the genetic code and defines the type and sequence of amino acids from which proteins are assembled. This means that the most important function of the nucleic bases as part of the DNA consists of a passive, static, role that does not actively intervene in the metabolism and their biochemical structure is not changed during the reading process by messenger RNA (mRNA). This partly explains the longevity of the DNA.

The half-life of mitochondrial DNA (mtDNA), in which half of the initial binding between the nucleobases breaks down, is highly dependent on ambient conditions and varies between about 520 years in average conditions with positive temperatures and up to 150, 000 years in permafrost conditions,

As a component of RNA, the nuclein bases have a somewhat more active role. In principle, in the division of cells, the DNA duplexes are broken up and separated from each other to form a complementary strand, the mRNA, which forms the working copy of the genetic material and serves as a basis for the selection and sequence of the amino acids from which the provided proteins are assembled. Another nucleobase, the dihydrouracil, occurs only in the so-called transport RNA (tRNA), which is used for amino acid transport during protein synthesis.

A completely different function is performed by several nucleobases as part of enzymes that actively enable and control certain biochemical processes by catalytic means. The best known task fulfills adenine as a nucleotide in the energy balance of the cells. Here, adenine, as adenosine diphosphate (ADP) and adenosine triphosphate (ATP) and as a component of nicotinamide adenine dinucleotide (NAD), plays an important role as an electron donor.

Education, occurrence, properties & optimal values

Nucleobases in the non-phosphorylated form consist exclusively of carbon, hydrogen, and oxygen, which are ubiquitous and freely available. The body is therefore able to synthesize nucleobases itself, but the process is complex and energy consuming.

Therefore, the recovery of nucleic acids by way of recycling is preferred, for. As by the degradation of proteins in which certain compounds are included, which can be isolated with little energy or even with energy gain and converted into nucleic acids. Nucleic acids usually do not occur in pure form in the body, but usually as a nucleoside or deoxynucleoside with an attached ribose or Desoxyribosemolek├╝l. As part of the DNA and the RNA and as a component of certain enzymes, the nucleic acids or their nucleosides are additionally reversibly phosphorylated with one to three phosphate groups (PO4-).

A reference value for optimal supply of nucleic bases does not exist. A deficiency or an excess of nucleic bases can only be indirectly determined by certain disturbances in the metabolism.

Diseases & Disorders

The nature of the dangers, disorders, and risks associated with the nucleic bases are errors in the number and order on the DNA or RNA strands, resulting in a change in the coding for protein synthesis.

If the body can not remedy the error via its repair mechanisms, it will lead to the synthesis of biologically inactive or exploitable proteins, which in turn may lead to mild to severe metabolic disorders. It can z. B. genetic mutations that can cause symptomatic diseases from the outset on metabolic disorders, which may be incurable. But even with a healthy genome, replication of the DNA and RNA chains can lead to copying errors that affect the metabolism.

A known metabolic disorder in Purinhaushalt goes z. For example, to a gene defect on the x chromosome. Because of the genetic defect, the purine bases hypoxantin and guanine can not be recycled, which ultimately promotes the formation of urinary stones and in the joints gout.

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