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Building the helix
Models are built using a basic repetitive structure. Three pieces
are required, the 135 degree green connectors, the white rods, and the
blue rods. The green connectors serve as the deoxyribose sugar units of
the helix backbone. Phosphodiester bonds linking the sugar units are
represented by the white rods. Hydrogen bonded base pairs are
represented by blue rods.
The connections for the simplest model are illustrated below. The double
helix is composed of two backbones held together by hydrogen bonded
bases. Each backbone is formed by joining green connectors in a chain
using the white rods attached to the outer slots. The backbones are
cross linked with the blue rods. Blue rod attachment should be at the
third slot of the green connectors on each chain. Because the chains are
anti-parallel, on one chain attachment should be at the  third slot from
the left and on the other chain, third slot from the right.
- Follow the arrows above to produce the segment pictured below.
When the second blue rod is attached, the two backbones will start to
twist around each other.