DNA Helix Structure (2D) — Base Pairing & Major/Minor Grooves

Helix

Rotation speed 1.0

Unwind 0.00

Click any rung to mutate that base pair.

Base pairing

Adenine (A) — pairs with T, 2 H-bonds

Thymine (T) — pairs with A, 2 H-bonds

Guanine (G) — pairs with C, 3 H-bonds

Cytosine (C) — pairs with G, 3 H-bonds

Live Readouts

Base pairs shown

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GC content

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A–T pairs

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G–C pairs

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Total H-bonds

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bp per turn

10.5

How it works

This flattened companion to the 3D DNA helix simulator draws the same structure as a scrolling ladder: two antiparallel sugar-phosphate backbones traced as out-of-phase sinusoids, joined by rungs built from real Watson-Crick base pairs. Because real B-DNA backbones are not diametrically opposite around the helix axis, the two strands here sit at an angular offset of about 130° on one side and 230° on the other — the wider gap reads as the major groove (~22 Å across in real DNA), the narrower one as the minor groove (~12 Å). A full turn spans 10.5 base pairs and rises about 34 Å (3.4 nm) along the axis, so this diagram completes one visible turn roughly every 10-11 rungs.

Each rung is generated from an actual base sequence, not colored at random: adenine (A) always pairs with thymine (T) through two hydrogen bonds, and guanine (G) always pairs with cytosine (C) through three — one extra bond that makes GC-rich DNA measurably more thermally stable. Click any rung to mutate just that base pair and see its identity and bond count; the unwind slider progressively separates the two strands into a flat ladder, mimicking how helicase opens the double helix ahead of replication.

x1(y) = cx + R·cos(θ(y,t))
x2(y) = cx + R·cos(θ(y,t) + offset)
offset ≈ 130°..230° (major/minor groove asymmetry)
pair(A) = T (2 H-bonds), pair(G) = C (3 H-bonds)
10.5 bp/turn, ~34 Å pitch

Click a rung to mutate it · drag sliders to unwind or change speed

Major / minor groove
shown by rung-gap width