Think of the shape of a molecule. What image pops into your head? Probably the double-helix shape of DNA. It is so familiar that when you see a double helix, you immediately think of DNA.
The double-helix shape of DNA was discovered by Francis Crick and James Watson in 1953. They won the Nobel Prize for their efforts, work that was helped out by a few other people, including Rosalind Franklin, who used x-rays to help figure out the structure of DNA. X-rays are very powerful and they are used to look at your teeth or maybe a broken bone because x-rays can penetrate skin.
If molecules are crystallized, then their shape can be figured out using x-rays. Think about a pool table and hitting one ball into another. The ball that you hit might go in one direction and if you are a really good pool player you can guess where the ball might go. Figuring out the shape of a molecule using x-rays is kind of like that because the way that the x-rays bounce off a molecule can be predicted. It is called x-ray diffraction. Watson and Crick used an x-ray that Rosalind Franklin took to help uncover the structure of DNA.
The shape of DNA, like every other molecule, is determined by the atoms and the bonds between the atoms.