Interactive Explorer
DNA Structure
Explore the double helix, understand base pairing rules, follow DNA replication step-by-step, and test your knowledge with a built-in quiz.
Base Pairs
~3.2B
DNA Double Helix
The iconic structure discovered by Watson & Crick in 1953
Key Structural Features
Diameter
2 nm
Width of the double helix
Base pair spacing
0.34 nm
Distance between rungs
Full turn
10 bp / 3.4 nm
One complete helical turn
Chirality
Right-handed (B-DNA)
Most common form in cells
Strands
Antiparallel
5′→3′ opposite to 3′→5′
Bonds
Hydrogen bonds
2 (A-T) or 3 (C-G) per pair
Base Color Legend
A
Adenine
pairs with T
T
Thymine
pairs with A
C
Cytosine
pairs with G
G
Guanine
pairs with C
The Four Nucleotide Bases
DNA is built from four nitrogenous bases. Click any card to expand details.