91Ó°ÊÓ

Discuss the contributions of Francis Crick, James Watson, and Rosalind Franklin to the discovery of the structure of DNA. a. Rosalind Franklin used X-ray diffraction methods to demonstrate the helical nature of DNA, while Watson and Crick formulated the double stranded structural model of DNA. b. Rosalind Franklin, Watson and Crick first employed the technique of X-ray diffraction to understand the storage of DNA. Since it did not work out, Watson and Crick then ran experiments to ascertain the DNA structure. c. Rosalind Franklin, Watson and Crick used X-ray diffraction methods to demonstrate the helical nature of DNA, while Rosalind Franklin formulated the double stranded structural model of DNA. d. Watson and Crick used X-ray diffraction methods to demonstrate the helical nature of DNA, while Rosalind Franklin formulated the double stranded structural model of DNA.

Step by step solution

01

- Understanding Rosalind Franklin's Contribution

Rosalind Franklin used X-ray diffraction methods to show that DNA had a helical structure. Her famous Photo 51 provided crucial evidence for the helical nature of DNA.

02

- Understanding Watson and Crick's Contribution

James Watson and Francis Crick formulated the double-helix model of DNA. They used information, including Franklin's X-ray diffraction data, to build their model, revealing that DNA is composed of two strands that coil around each other.

03

- Analyzing Option A

Option A correctly states that Rosalind Franklin used X-ray diffraction to demonstrate the helical nature of DNA, and Watson and Crick formulated the double-stranded structure of DNA.

04

- Analyzing Option B

Option B incorrectly states that all three scientists first used X-ray diffraction and that Watson and Crick ran other experiments afterward, which is not accurate.

05

- Analyzing Option C

Option C incorrectly credits Rosalind Franklin with formulating the double-stranded structural model of DNA, whereas that was Watson and Crick's contribution.

06

- Analyzing Option D

Option D incorrectly credits Watson and Crick with demonstrating the helical nature of DNA through X-ray diffraction, which was actually done by Rosalind Franklin.

07

- Conclusion

Based on the analysis, Option A is the correct answer as it accurately reflects the contributions of Rosalind Franklin, James Watson, and Francis Crick.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Rosalind Franklin

Rosalind Franklin was a pioneering scientist whose work with X-ray diffraction was critical to uncovering the structure of DNA. X-ray diffraction is a technique where X-rays are directed at a sample, in this case, DNA, and the way the X-rays scatter can reveal details about the sample's structure. Franklin's key contribution was her capturing of what is known as Photo 51. This particular X-ray diffraction image provided clear evidence that DNA had a helical structure.
Her meticulous approach and expertise in X-ray crystallography were instrumental in building a foundational understanding of DNA. Despite facing challenges due to the male-dominated field of science at the time, her work remains invaluable to the discovery of DNA's structure.

Watson and Crick

James Watson and Francis Crick are credited with formulating the double-helix model of DNA. Using insights derived from Rosalind Franklin's X-ray diffraction images, particularly Photo 51, they were able to deduce that DNA is made up of two strands that twist around each other to form a helix.
Before their groundbreaking model, the structure of DNA was a topic of considerable speculation among scientists. Watson and Crick's model not only identified the helical structure but also explained how genetic information is stored and replicated, transforming our understanding of molecular biology.

• They proposed that the two strands are antiparallel.
• They identified base-pairing rules: Adenine pairs with Thymine, and Cytosine pairs with Guanine.

Their work was revolutionary and earned them, along with Maurice Wilkins, the Nobel Prize in Physiology or Medicine in 1962.

X-ray diffraction

X-ray diffraction played a pivotal role in understanding the structure of DNA. This method involves directing X-rays at a crystal, in this case, fibers of DNA, and then analyzing the pattern of the X-rays that are scattered by the sample.
When Rosalind Franklin used this technique, she was able to gather data that identified the helical nature of DNA. The scattered X-rays create a diffraction pattern that can be analyzed to reveal detailed structural information. Specifically, Franklin's Photo 51 showed an X-shape, indicating a helical structure.
This method was crucial for providing evidence that could be used to construct a physical model. Without X-ray diffraction data, Watson and Crick would not have had the crucial information needed to propose the double-helix structure.

Double helix model

The double helix model of DNA, formulated by James Watson and Francis Crick, stands as one of the most significant scientific discoveries of the 20th century. Their model described DNA as consisting of two strands that coil around each other, forming a shape known as a double helix. Each strand is composed of nucleotides, which include a sugar-phosphate backbone and nitrogenous bases.
They proposed specific base-pairing rules, which state that Adenine (A) pairs with Thymine (T) and Cytosine (C) pairs with Guanine (G). This discovery explained how DNA replicates and stores genetic information reliably.

• The two strands are held together by hydrogen bonds between the paired bases.
• The antiparallel nature of the strands means they run in opposite directions.
• This model clarified how genetic material is passed down and expressed in living organisms.

The double helix was a monumental step in molecular biology and opened new avenues for genetic research, ultimately leading to our current understanding of genetics and heredity.