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Anatomy of the molecule
The stretch in the helix is real DNA from the pair above. Hover a feature to trace it on the molecule.
Sugar–phosphate backbone
Deoxyribose sugars alternate with phosphates, joined by phosphodiester bonds. The charged phosphates face the water.
Major groove 2.2 nm
The wide gap between the backbones. Transcription factors read base edges here without opening the helix.
Minor groove 1.2 nm
The narrow gap on the sugar side of each pair. AT-rich runs narrow it further.
Base pairs, hydrogen bonds 0.34 nm
A–T share 2 hydrogen bonds, G–C share 3. Pairs stack 0.34 nm apart and turn 34.3° each.
5′ → 3′, antiparallel
Strand 1 runs 5′→3′ from one end, its partner from the other. Polymerase only builds 5′→3′.
A = Tadenine (purine) with thymine (pyrimidine), 2 hydrogen bonds
G ≡ Cguanine (purine) with cytosine (pyrimidine), 3 hydrogen bonds
A long plate with a divider is a two-ring purine; a short plate is a one-ring pyrimidine, so every rung spans the same 2.0 nm. Amber pairs differ between the two organisms.
Copy it
Every cell copies this gene before it divides. Uncurl the helix to watch both strands template new partners, then curl the copies back.
Write your own
Type any stretch of DNA and the helix rebuilds as you type. The partner strand writes itself: A pairs with T, G pairs with C.
The partner strand writes itself: A pairs with T, G pairs with C.