What evidence did Watson and Crick have at their disposal in 1953? What was their approach in arriving at the structure of DNA?

Video transcript

Hi, everyone. Let's take a look at this practice problem together. What was the diameter of the double helix according to the Watson Crick model for DNA. The answer options are a two nanometers B 20 nanometers C 200 nanometers and D 2000 nanometers. Now recall that DNA is a double helix. We should know that and we know that it has a constant diameter throughout that diameter is two nanometers. Let's look at why the diameter is constant. Recall that in DNA double helix structure, there is Char Goff's rule and his role is about the nucleotides. It states that an adenine is always bonded with thymine and guanine is always bonded to cytosine. Now also recall that adenine and guanine are pines and purines have a double ring structure. Thymine and cytosine are pines, pines have a single ring structure. So a purine is always bonded with a Perine and that ensures the double helix diameter remains stabled throughout at two nanometers. Therefore, the correct answer is a two nanometers. All right, everyone. I hope you found this helpful and I'll see you soon for the next practice problem.