DNA is the blueprint of life. Your genetic code | Chegg.com - Free Printable

While I can't view or analyze images directly, I can help you answer the question based on the text you've provided. Here's a detailed explanation of the contributions each person made to the discovery of the structure of DNA:

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1. Erwin Chargaff (Austrian biochemist, Columbia University, New York, USA):

Erwin Chargaff made a crucial contribution through his biochemical analysis of DNA composition. He discovered what is now known as Chargaff’s Rules, which state that in DNA:

- The amount of adenine (A) equals the amount of thymine (T).
- The amount of guanine (G) equals the amount of cytosine (C).
- The total amount of purines (A + G) equals the total amount of pyrimidines (T + C).

These findings were essential because they suggested a specific pairing between the nitrogenous bases, which later helped Watson and Crick deduce the double helix structure with complementary base pairing.

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2. Rosalind Franklin and Maurice Wilkins (King’s College London, London, England, UK):

Rosalind Franklin and Maurice Wilkins worked at King’s College London and contributed significantly through X-ray crystallography.

- Rosalind Franklin produced high-quality X-ray diffraction images of DNA, most notably Photo 51, which revealed the helical structure of DNA. Her work provided critical data showing the dimensions and symmetry of the DNA molecule.
- Maurice Wilkins also conducted X-ray studies on DNA and was instrumental in encouraging collaboration between scientists. He shared some of Franklin’s data with James Watson and Francis Crick without her knowledge, which played a key role in their model-building.

Franklin’s precise data was vital for determining the helical nature of DNA, although she did not receive full recognition during her lifetime due to gender bias and lack of proper credit.

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3. James Watson and Francis Crick (University of Cambridge, Cambridge, England, UK):

James Watson and Francis Crick are widely credited with discovering the double helix structure of DNA in 1953.

- Using model building and integrating data from Chargaff’s rules and Franklin’s X-ray images (especially Photo 51), they proposed a three-dimensional model of DNA.
- Their model showed that DNA consists of two antiparallel strands forming a double helix, with the sugar-phosphate backbones on the outside and the nitrogenous bases paired in the center (A with T, G with C).
- This structure explained how DNA could be replicated and passed on genetically.

Their discovery was published in *Nature* in 1953 and revolutionized biology by providing the foundation for understanding genetics and molecular biology.

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Summary:

- Chargaff: Provided base-pairing rules.
- Franklin & Wilkins: Produced critical X-ray data revealing DNA’s helical structure.
- Watson & Crick: Built the correct model of the DNA double helix using all available data.

This collaborative effort, though marked by controversy over credit (especially regarding Franklin), ultimately led to one of the most important discoveries in science.

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