Biology / Unit 6 Bio 1209 short lesson, about 20 seconds
The Double Helix's Overall Structure
Captions available
The idea
DNA's double helix is a uniform, right-handed twist of two antiparallel, base-paired strands, roughly two nanometers wide along its length.
In practice
One full turn of the helix spans about ten base pairs, regardless of which bases make up that turn.
Where people slip
The helix's width and turn spacing stay constant everywhere — only the base sequence varies from one stretch of DNA to another.
Your place on the trail
Every lesson rests on earlier ones and opens later ones. Tap any to jump.
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