Nucleotide Structure: Building Blocks of DNA and RNA

A nucleotide is the fundamental monomer of nucleic acids (DNA and RNA). Each nucleotide consists of three covalently bonded components:

Three Components

1. Pentose Sugar:
   • DNA: Deoxyribose (lacks oxygen at 2' carbon)
   • RNA: Ribose (has hydroxyl group at 2' carbon)
2. Phosphate Group: Phosphoric acid residue linking to the 5' carbon of the sugar; forms the backbone via phosphodiester bonds
3. Nitrogenous Base: Attached to the 1' carbon of the sugar
   • Purines (double-ring): Adenine (A), Guanine (G)
   • Pyrimidines (single-ring): Cytosine (C), Thymine (T) in DNA; Uracil (U) replaces thymine in RNA

Polymerization

Nucleotides link via phosphodiester bonds between the 3' hydroxyl of one sugar and the 5' phosphate of the next, forming a directional strand (5'→3'). This creates polynucleotides—DNA's double helix or RNA's single-stranded structures.

Beyond Genetics

Nucleotides also serve as:

• Energy carriers (ATP, GTP)
• Enzyme cofactors (NAD+, FAD, CoA)
• Second messengers (cAMP, cGMP)
• Allosteric regulators

The sequence of nitrogenous bases encodes genetic information, making nucleotides the molecular basis of heredity and protein synthesis.