A nucleotide is the building block for nucleic acids.
Nucleotides are formed from three partners connected by covalent bonds :
The nucleotides that determine the sequence in DNA are actually deoxynucleotides. The pentose which makes them up as a ribose, in which the OH group in position 2nd is replaced by a hydrogen atom (a deoxyribose). There are fourDNA nucleotides, depending on the type of nitrogen base:
In RNA, the nucleotides are formed from a ribose with an OH group in the 2nd position. The nucleotide varies depending on the bound nitrogen base:
The order of the nucleotides determines the succession of bases in the nucleic acid forming the genetic message. The bases in DNA are involved in hydrogen bonds which are responsible for the double helix formation (two bonds between adenine and thymine, and three between guanine and cytosine). In RNA, the OH group located on the ribose may be involved in biological molecular reactions (ribozyme).
In addition to this role of forming more complex molecules, nucleotides are also energy carriers. ATP, or adenosine triphosphate, is therefore the energy molecule par excellence, in particular generated by the metabolic pathways (glycolysis). ATP can then be used (hydrolysed into ADP or adenosine diphosphate, by losing a phosphate) by enzymes to carry out reactions within the cell.
A nucleotide is defined by its nitrogen base, its sugar, and the number of phosphates. © Wikimedia, public domain