What is a Nucleotide

The nucleotide is the base unit of nucleic acids DNA and RNA. Several nucleotides join together to form chains of nucleotides or polynucleotides that make up the structure of DNA and RNA.

There are 2 types of nucleotides: ribonucleotides that make up ribonucleic acid or RNA deoxyribonucleotides that make up deoxyribonucleic acid or DNA.

nucleotide structure

basic structure of a nucleotide showing phosphate group, sugar and nitrogenous base

The structure of nucleotides is made up of 3 parts:

  • Nitrogen base: is a ring structure that contains nitrogen, can be purines or pyrimidines. Purines are adenine (A) or guanine (G) and pyrimidines are cytosine (C), thymine (T) and uracil (U).
  • 5 carbon sugar: It is also called pentose. In RNA the nucleotide has a ribose, in DNA it has a deoxyribose. The sugar carbon atoms are each named 1′ (one prime), 2′ (two prime), 3′ (three prime), 4′ (four prime), and 5′ (five prime). The nitrogenous bases are bonded to the 1′ carbon and the 5′ phosphate groups.
  • Phosphate group: made up of phosphorus and oxygen.

Nucleotide and nucleic acids

The nucleotide is the base unit of nucleic acids (DNA and RNA). Each nucleic acid contains 4 nitrogenous bases, a 5-carbon sugar, and a phosphate group.

The nitrogenous bases of deoxyribonucleic acid (DNA) are: Adenine (A), Guanine (G), Cytosine (C) and Thymine (T).

The nitrogenous bases of ribonucleic acid (RNA) are: Adenine (A), Guanine (G), Cytosine (C) and Uracil (U).

The 5-carbon sugar in DNA is called deoxyribose and the 5-carbon sugar in RNA is called ribose.

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nucleotide and nucleoside

The nucleoside is made up of the nitrogenous base and the 5-carbon sugar or pentose. It differs from the nucleotide in that it does not have a phosphate group.

The nitrogenous base can be Adenine (A), Guanine (G), Cytosine (C) (for DNA and RNA) Thymine (T) (for DNA) or Uracil (U) (for RNA) and the sugar can be deoxyribose for DNA or ribose for RNA.