How do nucleotides and nucleosides differ?


English: nucleotide

1 definition

As Nucleotide is the name given to the basic chemical building blocks of DNA and RNA. They consist of a nucleoside, which contains a special sugar molecule and one of four specific bases, and at least a phosphate group on the 5'-hydroxyl group of the pentose:

2 chemistry

Nucleotides are compound molecules in which pentose bonds with different substituents. Following the numbering of the carbon atoms of the pentose ring, the carbon atom at which the N-glycosidic bond with the base takes place is called the C1 atom and counts from there along the neighboring carbon atoms to the C5 atom. At the C5 atom there is an ester bond between a hydroxyl group of the sugar, which is involved in the structure of the nucleoside (without a phosphate group), and phosphoric acid.

In the case of the nucleoside triphosphates, there is not only one phosphate group on this ester bond, but a total of three phosphate residues linked to one another via an energy-rich phosphoric acid anhydride bond on the C5 atom of the sugar molecule. Phosphoric anhydrides can be split in their function as high-energy bonds with energy gain. The anhydride bond can be used, for example, to lengthen a nucleotide chain as part of DNA replication as an energy source for the DNA ligase reaction. The best example of this principle is provided by ATP, which, in addition to its property as a trinucleotide, is used by the organism as a universal energy substrate.

While the phosphoric anhydride bond is one of the high-energy bonds, this does not apply to the phosphoric acid ester bond, via which the carbon structure of the pentose is connected to the phosphate residues.

3 systematics

Depending on the number of phosphate groups, a distinction is made between three types of nucleotides:

  • Nucleoside + 1 phosphate group = nucleoside monophosphate (NMP)
  • Nucleoside + 2 phosphate groups = nucleoside diphosphate (NDP)
  • Nucleoside + 3 phosphate groups = nucleoside triphosphate (NTP)

The following table gives an overview of the human nucleotides:

Depending on the type of pentose, a distinction is made between ribonucleotides and deoxyribonucleotides. While deoxyribonucleotides occur in DNA, RNA is characterized by ribonucleotides.

In addition to their function as a genetic storage molecule, DNA nucleotides primarily fulfill functions as energy carriers and molecular activators.