Question 1

Which property of X-rays makes them particularly useful for studying the structure of DNA using X-ray crystallography?

Accepted Answer

Their wavelength is similar to the spacing between atoms in a crystal lattice, allowing for diffraction.

Question 2

Rosalind Franklin's Photo 51 was critical in determining which feature of DNA?

Accepted Answer

The double helical structure with a regular repeating pattern.

Question 3

Which equation is used to relate the angle of X-ray diffraction to the spacing between planes in a crystal, as applied in DNA studies?

Accepted Answer

$$n\lambda = 2d\sin	heta$$

Question 4

What was the significance of the 3.4 nm pitch observed in DNA's X-ray diffraction pattern?

Accepted Answer

It revealed the length of one complete turn of the DNA helix.

Question 5

Which of the following best describes the contribution of Maurice Wilkins to the discovery of DNA structure?

Accepted Answer

He provided key X-ray diffraction data that supported the helical structure of DNA.

Question 6

Why is the regularity of the X-ray diffraction pattern important in determining the structure of DNA?

Accepted Answer

It suggests a repeating, ordered structure such as a helix.

Question 7

Which Nobel Prize was awarded in 1962 for the discovery of the structure of DNA, and who were the recipients?

Accepted Answer

Nobel Prize in Physiology or Medicine; Watson, Crick, and Wilkins

Question 8

A student is analyzing an X-ray diffraction pattern of a DNA sample. If the distance between the spots on the pattern corresponds to 0.34 nm, what does this distance represent?

Accepted Answer

The distance between two adjacent base pairs.

Question 9

Which of the following statements about the electromagnetic spectrum is correct in the context of X-ray crystallography?

Accepted Answer

X-rays have shorter wavelengths than visible light, making them suitable for probing atomic structures.

Question 10

In the context of DNA structure, what is the significance of the major and minor grooves?

Accepted Answer

They allow proteins to interact with specific base sequences for gene regulation.

Question 11

Which experimental evidence most directly led Watson and Crick to propose the double helix model of DNA?

Accepted Answer

The X-ray diffraction patterns obtained by Franklin and Wilkins.

Question 12

If the wavelength of X-rays used in a crystallography experiment is $$1.54 \ 	ext{Å}$$ and the angle of diffraction is $$30^\circ$$, what is the distance $$d$$ between the planes in the crystal according to Bragg's Law ($$n=1$$)?

Accepted Answer

$$d = \frac{1.54}{2 \sin 30^\circ} = 1.54 \ 	ext{Å}$$

Question 13

Which of the following best explains why Rosalind Franklin did not share the Nobel Prize for the discovery of DNA's structure?

Accepted Answer

She had passed away before the Nobel Prize was awarded.

Question 14

Which feature of the DNA double helix is directly related to its function as a genetic material?

Accepted Answer

Complementary base pairing, allowing for accurate replication.

Question 15

A researcher observes that the X-ray diffraction pattern of a DNA sample changes after heating. What is the most likely explanation?

Accepted Answer

The double helix has denatured into single strands, disrupting the regular structure.

Question 16

Which of the following is NOT a conclusion drawn from the X-ray diffraction studies of DNA?

Accepted Answer

DNA is composed of amino acids.

Question 17

Which real-world application relies on the principles of X-ray crystallography discovered during DNA research?

Accepted Answer

Determining the structure of new pharmaceutical drugs.

Question 18

Which scientist is most closely associated with the first clear X-ray diffraction image of DNA, known as Photo 51?

Accepted Answer

Rosalind Franklin

Question 19

What is the main reason why X-ray crystallography requires the sample to be in a crystalline form?

Accepted Answer

Crystals provide a regular, repeating arrangement of molecules, necessary for producing interpretable diffraction patterns.

The Molecular Basis of Heredity: Discovery of DNA Structure

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