Start with a decent tour of the basics, from Learn.Genetics.

Class presentation is here (click shadowed images for animations and movies):

Essential Biology: 3.3 (SL Only) DNA Structure

Essential Biology: 3.3 & 7.1 (HL) DNA Structure

Here’s a decent video from BBC AS Guru with David Suzuki:

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And here’s a very stylized video of DNA structure from Hybrid Medical Animation. See if you can narrate it:

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The story of the discovery of the double-helix structure is a good example international collaboration and competition, and led to the Nobel prize for Crick, Watson and Wilson (who we never hear about). You’ve got to feel for Rosalind Franklin – her work was key in their discovery and she wasn’t cited for it until after her death.

Here’s a great video, though the presenter sound like he has a mouth full of marbles: