Structure of purine and pyrimidine nucleotides

 Purine and pyrimidine nucleotides are essential building blocks of nucleic acids, such as DNA and RNA. Here’s an overview of their structure:

Purine Nucleotides

Purines are larger, double-ringed structures composed of a fused six-membered and five-membered ring. The most common purines are adenine (A) and guanine (G).

1. Adenine (A)
   • Structure: Adenine consists of a six-membered ring fused to a five-membered ring. It has the molecular formula C₅H₅N₅. The ring structure has alternating double bonds and contains nitrogen atoms at positions 1, 3, 7, and 9.
2. Guanine (G)
   • Structure: Guanine also consists of a six-membered ring fused to a five-membered ring, with the molecular formula C₅H₅N₅O. It has nitrogen atoms at positions 1, 3, 7, and 9, with an additional carbonyl group (=O) at position 6 on the six-membered ring.

Pyrimidine Nucleotides

Pyrimidines are smaller, single-ring structures. The most common pyrimidines are cytosine (C), thymine (T) in DNA, and uracil (U) in RNA.

1. Cytosine (C)

   • Structure: Cytosine is a single six-membered ring structure with the molecular formula C₄H₅N₃O. It contains nitrogen atoms at positions 1 and 3, and an amino group (-NH₂) attached to carbon 4, with a carbonyl group (=O) at carbon 2.

2. Thymine (T)

   • Structure: Thymine is also a single six-membered ring with the molecular formula C₅H₆N₂O₂. It has nitrogen atoms at positions 1 and 3, a carbonyl group at positions 2 and 4, and a methyl group (-CH₃) attached to carbon 5.

3. Uracil (U)

   • Structure: Uracil is similar to thymine but lacks the methyl group. It has the molecular formula C₄H₄N₂O₂, with nitrogen atoms at positions 1 and 3, and carbonyl groups at positions 2 and 4.

Nucleotide Structure

A nucleotide consists of three components:

1. Nitrogenous Base (Purine or Pyrimidine)
2. Pentose Sugar (Ribose in RNA or Deoxyribose in DNA)
3. Phosphate Group(s) (One or more phosphate groups are attached to the 5' carbon of the sugar)

• Nucleoside: A nucleotide without the phosphate group, consisting of just the nitrogenous base and the sugar.

When a phosphate group is added to a nucleoside, it forms a nucleotide. These nucleotides then link together via phosphodiester bonds to form the backbone of DNA or RNA strands.