Difference Between Nucleotide and Nucleoside

It is extremely essential to understand the key differences between a nucleotide and a nucleoside to differentiate between the two. While both are essentially the foundation of nucleic acid, the molecular composition is highly varying, with nucleotides containing sugar, base and a phosphate group, and nucleosides containing only sugar and a base. Additionally, a nucleotide occurs before the formation of DNA and RNA, but a nucleoside occurs before the formation of a nucleotide. 

Nucleotide

Compounds consisting of a nitrogenous base and a phosphate group which is attached to a pentose sugar, which can be either deoxyribose or ribose, is called a nucleotide. The pentose sugar with 5’ carbon can have anywhere between one to three phosphate groups. The nitrogenous base, however, can be either pyrimidine or a purine. 

While guanine and adenine are known to be purine bases, thymine, uracil and cytosine are pyrimidine bases. 

The Table Below shows Examples of Nucleotides that Correspond to their Nitrogenous Bases. 

Nitrogenous Bases

Corresponding Examples

Guanine

GMP, GDP, GTP, dGMP, dGDP, dGTP, and dGTP

Adenine

AMP, ADP, ATP, dAMP, dADP, dATP, and ddATP

Cytosine

CMP, CDP, CTP, dCMP, dCDP, dCTP and ddCTP

Thymine

TMP, TDP, TTP, dTMP, dTDP, dTTP and ddTTP

 

Nucleotides are widely used as energy sources- while ATP has biochemical usage, GTP is where the energy source is derived during protein synthesis. In the endocrine system and the nervous system, there can be seen the involvement of cyclic AP in signal transduction. Dideoxynucleotides often help in sequencing for chain termination. Also, for the regulation of the gene expression, LNA, PNA and morpholino are crucial for the sugar backbone in RNA. 

Nucleoside

A nucleoside is any nucleotide that does not have a phosphate group but is bound to the 5’ carbon of the pentose sugar. A nucleotide always contains a nucleoside that binds the one to three phosphate groups. 

A nucleoside is always composed of a pentose sugar and a nitrogenous base, which are the same as a nucleotide would have. Examples of nucleosides include cytidine, uridine, guanosine, inosine thymidine, and adenosine. A beta-glycosidic bond binds the 3’ position of the pentose sugar to the nitrogenous base. 

Nucleosides are used as anticancer and antiviral agents. 

Nucleotide vs. Nucleoside 

A nitrogenous base is attached to a sugar and somewhere between one to three phosphate groups in case of a nucleotide. A nitrogenous base is covalently attached to sugar which is either ribose or deoxyribose, however, there is no presence of the phosphate group here in case of a nucleoside. 

Nucleotide = Sugar + Base + Phosphate

Nucleoside = Sugar + Base

Nucleotides have various functions in the field of biology:

  • The DNA and RNA acts as a place for data storage

  • ATP in nucleotides provides energy

  • Helps in co-enzyme catalysis

  • The cAMP or ATP act as allosteric regulators, thereby helping chemical communication among cells and also helps in regulating metabolism 

  • These are the building blocks of life

The building blocks of RNA and DNA are nucleotides. It consists of a chain of nucleotides which are linked together to create a sugar and phosphate backbone with prominent nitrogenous bases. 

Difference Between Nucleotide and Nucleoside

Nucleotide 

Nucleoside

Nucleotides are built of a nitrogenous base, a sugar and a phosphate group when it comes to chemical composition. 

Nucleosides are built of a nitrogenous base and a sugar, however, without the phosphate group when it comes to chemical composition. 

To this day, malfunctioning nucleotides are one of the major reasons behind cancer. 

Nucleosides, on the other hand, are used for medicinal purposes, mostly as anti-cancer agents and against various viruses. 

Nucleotide = Sugar + Base + Phosphate

Nucleoside = Sugar + Base

Common examples of nucleotides include adenosine, cytidine, guanosine, uridine, thymidine and inosine with the inclusion of phosphate groups. 

Examples of nucleotides also include adenosine, cytidine, guanosine, uridine, thymidine and inosine, however, there is no presence of phosphate groups.