Question

which of the following characteristics of the structure of dna was determined directly from x-ray diffraction photographs of crystallized dna?
○ the double helical structure
○ the length of a given dna molecule
○ the sequence of nucleotides
○ the frequency of a versus t nucleotides

Explanation:

X - ray diffraction is a technique that can reveal the overall shape and symmetry of a molecule. The double - helical structure of DNA was deduced from the X - ray diffraction pattern (the famous "Photo 51" taken by Rosalind Franklin). The length of a DNA molecule (which can be very long and varies depending on the organism and chromosome) is not directly obtained from X - ray diffraction of crystallized DNA in the sense of a specific measurement for a "given" molecule in the way the structure is. The sequence of nucleotides (which is a linear order of A, T, C, G) and the frequency of A versus T (which is related to base - pairing rules and was known from Chargaff's rules, not from X - ray diffraction) cannot be directly determined from X - ray diffraction of the overall DNA crystal structure. X - ray diffraction gives information about the repeating pattern and overall shape, which in the case of DNA is the double - helix.

Answer:

the double helical structure