Question

question 4 of 26

which two statements describe the features of dna that were revealed by the combined experiments of franklin, watson, and crick?

a. the nitrogenous bases form specific pairs on the inside of the molecule.
b. the molecule is wrapped around proteins called histones.
c. the amount of adenine equals the amount of cytosine.
d. the shape of dna is a double helix.

Explanation:

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<reasoning>

Analyze the historical experiments

Using the DNA Structure knowledge point
Rosalind Franklin's X-ray diffraction data (Photo 51) demonstrated that DNA has a helical shape with a consistent width. Watson and Crick used this data, along with Chargaff's rules of base pairing, to build their 3D double-helix model. This model revealed that the nitrogenous bases point inward, forming specific hydrogen-bonded pairs (adenine with thymine, cytosine with guanine) inside the double helix.

Evaluate statement A

Using the DNA Structure knowledge point
Statement A is correct. The Watson-Crick model placed the hydrophobic nitrogenous bases on the inside of the double helix, paired specifically via hydrogen bonds.

Evaluate statement B

Using the DNA Structure knowledge point
Statement B is incorrect. The wrapping of DNA around histone proteins to form nucleosomes is a feature of eukaryotic chromosome packaging, which was discovered much later and not by Franklin, Watson, or Crick.

Evaluate statement C

Using the DNA Structure knowledge point
Statement C is incorrect. According to Chargaff's rules, the amount of adenine equals thymine (\(A = T\)), and the amount of cytosine equals guanine (\(C = G\)), not adenine to cytosine.

Evaluate statement D

Using the DNA Structure knowledge point
Statement D is correct. Franklin's X-ray diffraction images directly indicated a helical structure, and Watson and Crick's model confirmed it is a double helix.
</reasoning>

<answer>
<mcq-correct>A. The nitrogenous bases form specific pairs on the inside of the molecule.</mcq-correct>
<mcq-option>B. The molecule is wrapped around proteins called histones.</mcq-option>
<mcq-option>C. The amount of adenine equals the amount of cytosine.</mcq-option>
<mcq-correct>D. The shape of DNA is a double helix.</mcq-correct>
</answer>

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Answer:

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<reasoning>

Analyze the historical experiments

Using the DNA Structure knowledge point
Rosalind Franklin's X-ray diffraction data (Photo 51) demonstrated that DNA has a helical shape with a consistent width. Watson and Crick used this data, along with Chargaff's rules of base pairing, to build their 3D double-helix model. This model revealed that the nitrogenous bases point inward, forming specific hydrogen-bonded pairs (adenine with thymine, cytosine with guanine) inside the double helix.

Evaluate statement A

Using the DNA Structure knowledge point
Statement A is correct. The Watson-Crick model placed the hydrophobic nitrogenous bases on the inside of the double helix, paired specifically via hydrogen bonds.

Evaluate statement B

Using the DNA Structure knowledge point
Statement B is incorrect. The wrapping of DNA around histone proteins to form nucleosomes is a feature of eukaryotic chromosome packaging, which was discovered much later and not by Franklin, Watson, or Crick.

Evaluate statement C

Using the DNA Structure knowledge point
Statement C is incorrect. According to Chargaff's rules, the amount of adenine equals thymine (\(A = T\)), and the amount of cytosine equals guanine (\(C = G\)), not adenine to cytosine.

Evaluate statement D

Using the DNA Structure knowledge point
Statement D is correct. Franklin's X-ray diffraction images directly indicated a helical structure, and Watson and Crick's model confirmed it is a double helix.
</reasoning>

<answer>
<mcq-correct>A. The nitrogenous bases form specific pairs on the inside of the molecule.</mcq-correct>
<mcq-option>B. The molecule is wrapped around proteins called histones.</mcq-option>
<mcq-option>C. The amount of adenine equals the amount of cytosine.</mcq-option>
<mcq-correct>D. The shape of DNA is a double helix.</mcq-correct>
</answer>

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