Nucleotide vs Nucleoside
Nucleosides and nucleotides are same type of molecules with a small structural difference. However, this structural difference makes a huge difference in the functioning of the two molecules.
Nucleotide is the building block of two crucial macromolecules (nucleic acids) in living organisms called DNA and RNA. They are the genetic material of an organism, and are responsible for passing genetic characteristics from generation to generation. Further, they are important to control and maintain cellular functions. Other than these two macromolecules, there are other important nucleotides. For example, ATP (Adenosine tri phosphate) and GTP are important for energy storage. NADP and FAD are nucleotides, which act as cofactors. Nucleotides like CAM (cyclic adenosine monophosphate) are essential for cell signaling pathways.
A nucleotide is composed of three units. There is a pentose sugar molecule, a nitrogenous base and phosphate group/s. Depending on the type of pentose sugar molecule, nitrogenous base and the number of phosphate groups, nucleotides differ. For example, in DNA, there is a deoxyribose sugar and in RNA, there is a ribose sugar. There are mainly two groups of nitrogenous bases as pyridines and pyrimidines. Pyrimidines are smaller heterocyclic, aromatic, six-member rings containing nitrogens at 1 and 3 positions. Cytosine, thymine, uracil are the examples for pyrimidine bases. Purine bases are much larger than pyrimidines. Other than the heterocyclic aromatic ring, they have an imidazole ring fused to that. Adenine and guanine are the two purine bases. In DNA and RNA, complimentary bases form hydrogen bonds between them. That is adenine: thiamine/ uracil and guanine: cytocine are complimentary to each other. The phosphates are linked to the –OH group of carbon 5 of the sugar. In the nucleotides of DNA and RNA, normally there is a one phosphate group. However, in ATP, there are three phosphate groups. The linkages between phosphate groups are high energy bonds. Primarily, there are eight types of nucleotides in DNA and RNA.
• Deoxy adenosine mono phosphate
• Deoxy guanosine mono phosphate
• Deoxy cytidine mono phosphate
• Deoxy thymidine mono phosphate
• Adenosine mono phosphate
• Guanosine mono phosphate
• Cytidine mono phosphate
• Uridine mono phosphate
Above eight nucleotides are the basic types. And other nucleotides can be derivatives of these. Nucleotides can be linked to each other to form a polymer. This linkage occurs between the phosphate group of a nucleotide with a hydroxyl group of the sugar. By making this kind of phosphodiester bonds, macromolecules like DNA and RNA are formed.
Nucleosides are groups in which a sugar molecule (usually ribose or deoxy ribose sugar) is linked to a nitrogenous base via a beta-glycosidic bond. If a phosphate group is attached to the nucleoside, then it will become the corresponding nucleotide. So a nucleotide can also be written as a “nucleoside mono phosphate.” When nucleic acids are digested by nucleotidases enzymes, nucleosides are formed. Nucleosides have anticancer or antiviral properties.
Difference Between Nucleotide and Nucleoside
- The main difference between the two is nucleoside lacks a phosphate group. Other parts like the sugar molecules and nitrogenous bases are common to both.
- Normally, in living cells nucleotides are the functional units, not nucleosides.