Answer:
1) nitrogen bases
2) the 1950’s; microscope
3) DNA and protein
4) nucleotides
5) X-ray diffraction
6) ball-and-stick model-building
7) 25 April 1953
8) was critical to Watson and Crick
9) adenine-timine; guanine-citosine
10) double helix
11) base pairs
12) G with C and A with T
13) 1953
14) died
15) unwound
16) synthesized; a new molecule
Explanation:
Nitrogenous bases are used to construct nucleotides. Until the discovery of the helical shape of the DNA molecule, were only possible to identify the genetic material (chromosomes) by the microscope. Chromosomes are composed of DNA and proteins (histones). Nucleotides are the building blocks of the DNA molecule. The X-ray diffraction data obtained by Rosalind Franklin were used to decipher the DNA structure. The ball-and-stick is a molecular model where atoms are represented by spheres and bonds are represented by rods. Chargaff's rules indicate that the content of cytosine is equal to guanine and adenine is equal to thymine. Rosalind Franklin died of ovarian cancer in 1958. The double-stranded DNA molecule must be unwound and then the DNA strands serve as templates to synthesize identical DNA molecules.