What is a nucleotide?

A nucleotide is the basic building block of DNA and RNA, consisting of three components:

Nucleotide = Phosphate Group + Sugar + Nitrogenous Base

• Sugar: Deoxyribose in DNA; ribose in RNA
• Nitrogenous bases in DNA: A, T, G, C (in RNA, Thymine → Uracil)
• Base pairing: A–T and G–C (via hydrogen bonds)

Think of nucleotides as letters DNA is the sentence written from those letters.

Summary: A nucleotide is the structural unit of DNA/RNA, consisting of a phosphate group, a sugar, and one of four nitrogenous bases.