AI Tutor
If you uncoiled the DNA inside a single human cell, it would stretch over two meters, yet it is built entirely from repeating microscopic subunits called nucleotides.
Every nucleotide functions like a precision chemical module, engineered from three distinct components that govern both structural assembly and genetic information storage.
What specific chemical parts make up this universal molecular building block?

The Anatomy of a Nucleotide

A nucleotide consists of a five-carbon pentose sugar, a nitrogen-rich nitrogenous base attached to carbon 1β€²1', and one to three phosphate groups attached to carbon 5β€²5'.
Biochemists label the sugar's carbons with prime marks (1β€²1' through 5β€²5') to distinguish them from the numbered ring atoms of the nitrogenous base.
The identity of the sugar defines the nucleic acid class: ribose possesses a hydroxyl group (βˆ’OH-OH) at the 2β€²2' carbon, whereas deoxyribose contains only a hydrogen atom (βˆ’H-H) at 2β€²2'.
Nitrogenous bases fall into two structural families: double-ring purines (adenine and guanine) and single-ring pyrimidines (cytosine, thymine in DNA, and uracil in RNA).
How do these individual nucleotide units covalently bind to form an unbroken, resilient structural chain?

Forming the Phosphodiester Backbone

Nucleic acids assemble via a condensation reaction where the nucleophilic 3β€²3' hydroxyl group (βˆ’OH-OH) of the growing strand attacks the innermost Ξ±\alpha-phosphate of an incoming nucleoside triphosphate.
This nucleophilic attack creates a phosphodiester linkageβ€”a single phosphate atom forming two covalent ester bonds to connect the 3β€²3' carbon of one sugar to the 5β€²5' carbon of the next.