​​Subtopic 1.4: Nucleosides and nucleotides 

Nucleosides and nucleotides are involved in the preservation and transmission of the genetic information of all living creatures. In addition, they play roles in biological energy storage and transmission, signaling and regulation of various aspects of metabolism.​
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These molecules can be divided into two major families:
  • Purines: are two-ring structures (adenine and guanine);
  • Pyrimidines: are one ring structure (thymine, cytosine and uracil). 
Picture
Figure 11. Structure of purines and pyrimidines

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The unique structure and interaction of these molecules serve as the fundamental building block of RNA and DNA molecules and allow fundamental processes of DNA replication and protein synthesis to occur.

Components of Nucleotides:
  • Nitrogenous base: The nitrogenous base of a nucleoside or nucleotide may be either a purine or a pyrimidine.
  • Carbohydrate: The carbohydrate component of nucleosides and nucleotides is usually the sugar ribose for RNA molecules and deoxyribose for DNA molecule
  • Phosphate Group: One or more phosphate groups (PO4−3) may be attached to the carbon 5 of the carbohydrate molecule. 
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Figure 12. Example of structure of nucleotide: Adenosine triphosphate