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Adenine

Abbreviations: A, Ade
German: Adenin

1 Definition

Adenine as one of the four organic nucleobases is a basic building block of DNA and RNA. It is, however, also a part of various other biologically relevant molecules, for example adenosine triphosphate (ATP), NADH and FADH2.

2 Structure

Adenine is a 6-aminopurin which is made up of an aromatic six-membered carbon ring which is adjacent to a five-membered ring. The carbon atoms 1, 3, 7, and 9 in the ring structure are substituted by four nitrogen atoms. The C6 atom binds an amino group.

3 Function

In the double-strand molecules of the DNA helix, Adenine can form two hydrogen bonds with the opposite thymine molecule via one of the hydrogen atoms bound to the amino group of C6 and via the free electron pair of the ring's N1 atom. In RNA molecules, however, adenine is paired through two hydrogen bonds with a uracil molecule.

Adenine can form an N-glycosidic bond with the C1 atom of ribose via its N9 atom of the five-membered ring. The product is a nucleoside, in this case adenosine. If adenine binds to deoxyribose the resulting nucleoside is deoxyadenosine.

In further steps the adenosine molecule can be phosphorylated on the C5 of its ribose part. Depending on the amount of phosphate, the resulting nucleotide is called:

  • Adenosine monophosphate (AMP),
  • Adenosine diphosphate (ADP) or
  • Adenosine triphosphate (ATP)

Corresponding molecules are formed when the phosphates bind to deoxyadenosine (dAMP, dADP, dATP).

4 Synthesis and metabolism

The human organism is capable of synthesizing adenine by itself. Because this metabolic pathway is very energy-consuming the body can reuse the purine derivative adenine from the nucleotide salvage pathway, cut it from nucleic acid molecules meant for degradation and attach ribose whenever necessary.

The degradation of adenine results in hypoxanthine and continues to uric acid.

5 Pathophysiology

Disturbances of the nucleotide salvage pathway, especially defects of the hypoxanthine-guanine phosphoribosyltransferase (HGPRT) enzyme, result in the pathology of Lesch–Nyhan syndrome.
Elevated levels of metabolized adenine result in an unphysiological amount of uric acid (hyperuricemia) which can crystallize in the kidneys, the efferent urinary tract or in bradytrophic tissues (especially articular capsules), which leads to urinary stones or gout.

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