Explaining the DNA structure
The DNA double helix contains two sequences of nucleotide code letters than run along the molecule. Untwist the spiral and DNA can be seen as two parallel strands. That's why its sometimes called the double helix. Unzip the strands and you have two linear sequences of the letters A C G and T. The precise order of the letters along the molecule carries the coded instructions. These are the equivalent of binary 1s and 0s in a computer, one strand is a complementary image of the other an a will always pair with T and C with G so if you know the sequence of one strand you can work out the sequence of the other. It dawned on Watson and Crick that this complementary copy of the code was the key to understanding how genetic information could be passed on. So the essence of life could be explained with chemistry, there were no mysterious life forces.
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15676. DNA helix
Image depicting DNA helix model and table.
15530. DNA replication: how genetic information is passed on, 3D animation with narration
The structure of DNA, that Watson and Crick discovered, suggests how genetic information is passed on.
16434. Video 19: James Dewey Watson, clip 3
DNA as a double helix.
15539. DNA base pairs
DNA base pairs
15493. The double helical structure of DNA, 3D animation with no audio
Animation of 2D DNA model becoming three dimensional.
Because it contains the directions for assembling the components of the cell, DNA is often thought of as the "instruction book" for assembling life.
15015. Francis Crick and James Watson in Cambridge.
1953 picture of Francis Crick (L) and James Watson (R) walking along the backs of King's College in Cambridge.
15677. DNA helix model closeup
Image of DNA helix model (closeup).
16433. Video 19: James Dewey Watson, clip 2
DNA as a regular, repeating structure -- a helix.