1. The Race to Discover the Structure of DNA

2. A Brief History of DNA
1865 Gregor Mendel publishes his work on plant breeding with the notion of "genes" carrying transmissible characteristics
1869 "Nuclein" is isolated by Johann Friedrich Miescher
in the laboratory of Hoppe-Seyler
1892 Meischer writes to his uncle "large biological molecules composed of small repeated chemical pieces could express a rich language in the same way as the letters of our alphabet"
1920 Recognition of the chemical difference between DNA and RNA
Phoebus Levene proposes the "tetranucleotide hypothesis"
1938 William Astbury obtains the first diffraction patters of DNA fibres

3. A Brief History of DNA
1944 Oswald Avery (Rockefeller Institute) proves that DNA carries the
genetic message by transforming bacteria

4. A Brief History of DNA
1950 Erwin Chargaff develops “Chargaff’s Rules”, A=T and C=G

5. Who will make history by discovering the structure of the DNA molecule?

6. The Players
Linus Pauling discovers the basic structure of the protein molecule at Cal Tech in Soon after he starts to model DNA.
Maurice Wilkins and Rosalind Franklin begin studying the structure of DNA using X-ray crystallography by 1951 at King’s college
In that year James Watson joined Francis Crick as researchers in the Cavendish laboratory under the supervision of Max Perutz and Sir Lawrence Bragg
Bragg and Perutz had been studying complex proteins for some time, also using X-ray techniques

7. Linus Pauling’s DNA

8. Sir Lawrence Bragg Bragg was in charge of the Cavendish laboratory
Unwritten standards at the time dictated that scientists not compete with colleagues on projects
DNA was Wilkins project, Bragg told Watson and Crick to cease work
Watson and Crick push ahead anyway

9. King’s College London

10. Maurice Wilkins – Kings College, London

11. Rosalind Franklin (in Paris)

12. Rosalind Franklin
Rosalind Franklin went to one of the few girls’ schools in London that taught physics and chemistry
She received a chemistry degree from Newham College, Cambridge in 1941.
Awarded Ph.D. in chemistry in 1945 from Cambridge
Worked in Paris ( ) and began working with X-ray diffraction techniques.
Was hired to do research at Kings College in London

13. Wilkins and Franklin
Wilkins considered Franklin his lab assistant, this was not the case
There was bad blood between Wilkins and Franklin
Franklin takes first X-rays of DNA
It was Wilkins that provided Franklin’s data to Crick and Watson
Franklin was not credited in Watson and Crick’s paper

14. The Famous “Photo 51”

15. Watson wrote… "The instant I saw the picture my mouth
fell open and my pulse began to race....
the black cross of reflections which
dominated the picture could arise only
from a helical structure... Mere inspection of the X-ray picture gave several of the vital helical parameters."

16. Important investigations into the structure of DNA were done by Pauling, Wilkins and Franklin.
It was Crick and Watson who were able to pull everything together and make a correct model

17. Watson and Crick

18. James D. Watson Francis H. Crick Maurice H. F. Wilkins What about?
1962: Nobel Prize in Physiology and Medicine
James D.
Watson
Francis H.
Crick
Maurice H. F.
Wilkins
What about?
Rosalind Franklin

19. 1953 Watson and Crick are the first to publish the correct structure of DNA
1958 Franklin dies
1962 Watson, Crick, and Wilkins are awarded the Nobel Prize in Medicine
1967 Watson publishes The Double Helix, his account of the discovery
Watson’s account reveals he and Crick may have violated ethical norms for scientists

20. The Double Helix Harvard University Press refused to publish the book
Crick, Wilkins, and others objected to Watson’s book claiming it misrepresented the truth
Watson’s portrayal of women in general and Franklin in particular was demeaning and at times simply untrue

21. It has not escaped our notice …
It has not escaped our notice that the specific pairing we have postulated suggests a possible copying mechanism for the genetic material.
It has not escaped our notice …

22. Chapter 16
Section 1 What Does DNA Look Like?
Objectives
List three important events that led to understanding the structure of DNA.
Describe the basic structure of a DNA molecule.
Explain how DNA molecules can be copied.

23. The Pieces of the Puzzle
Chapter 16
Section 1 What Does DNA Look Like?
The Pieces of the Puzzle
DNA stands for deoxyribonucleic acid. DNA is the genetic material that determines inherited characteristics.
Nucleotides: The Subunits of DNA DNA is made of subunits called nucleotides. A nucleotide consists of a sugar, a phosphate, and a base.

24. The Pieces of the Puzzle, continued
Chapter 16
Section 1 What Does DNA Look Like?
The Pieces of the Puzzle, continued
Chargaff’s Rule Erwin Chargaff found that the amount of adenine in DNA always equals the amount of thymine, and the amount of guanine always equals the amount of cytosine.
Franklin’s Discovery Chemist Rosalind Franklin was able to make images of DNA molecules by using X-ray diffraction.

25. The Pieces of the Puzzle, continued
Chapter 16
Section 1 What Does DNA Look Like?
The Pieces of the Puzzle, continued
Watson and Crick’s Model James Watson and Francis Crick used Chargaff’s and Franklin’s research to build a model of DNA.
The model, which looked like a long, twisted ladder, eventually helped explain how DNA is copied and how it functions in the cell.

26. DNA’s Double Structure
Chapter 16
Section 1 What Does DNA Look Like?
DNA’s Double Structure
The Double Helix The shape of DNA is known as a double helix.
The two sides of the ladder are made of alternating sugar parts and phosphate parts.
The rungs of the ladder are made of a pair of bases.

27. Chapter 16
Section 1 What Does DNA Look Like?

28. Chapter 16 Making Copies of DNA
Section 1 What Does DNA Look Like?
Making Copies of DNA
How Copies Are Made During replication, a DNA molecule is split down the middle, where the bases meet. The bases on each side of the molecule are used as a pattern for a new strand.
When Copies Are Made DNA is copied every time a cell divides. Each new cell gets a complete copy of all the DNA.

29. Making Copies of DNA, continued
Chapter 16
Section 1 What Does DNA Look Like?
Making Copies of DNA, continued