DNA: The Secret of Life Jan 8, 2008 Genetics and Society Biol/ Phil 2510

1. DNA: The Secret of LifeJan 8, 2008Genetics and SocietyBiol/ Phil 2510

2. DNA: The Secret of Life • What is Life? • History of the question • DNA: the modern answer

3. Questions everyone asks Who am I? Where did I come from? How are we different from each other? Will I get cancer? What will my children look like? Who was in this room an hour ago? Why do I love who I love?

4. Feb 28, 1953 Two guys walk into a bar and say they have the answer.

5. But let’s start at the beginning

6. Question-What is Life?

7. Vitalism Vitalism is the idea that living organisms possess an inner force or energy that gives them the property of life. Vitalists say that there is a property that distinguishes life from non-life.

8. Can you think of an example of vitalist thought you have heard of?

9. Materialism Materialism says life has a physical basis. Living matter is made of the same components as non-living matter.

10. Materialism in the 1800s 1828 Friedrich Wohler synthesizes urea from inorganic materials Substances normally produced by living organisms are chemical compounds that can be made by non-living sources 1897 Hans and Eduard Buchner show that fermentation can be accomplished in a cell free system. Fermentation, a reaction carried out by living organisms, is a chemical, not a vital process

11. Heredity Around 1900, the debate begins to focus on heredity. Why are pandas not people?

12. Why are pandas not people? How would a vitalist answer this question? How would a materialist?

13. Mendel’s laws show the rules of heredity (1866, rediscovered in 1900) Inheritance occurs in packets of information

14. Properties of a physical unit • You can see it • You can move it from one place to another • You can change it with other physical processes

15. Developments in the 20th century 1933: Thomas Hunt Morgan wins the Nobel prize for demonstrating that chromosomes are the fundamental unit of inheritance. Demonstrated that here is an observable, physical nature to cellular information http://www.biol.unlp.edu.ar/historianobel-genetica.htm http://www.cofc.edu/~bernardoj/Genetics%20Lab/212Lhome.html

16. X Breed mutant flies Look at their chromosomes The experiment

17. Observed Traits can often be inherited together. There are the same number of trait groups as there are chromosomes. In rare cases when chromosomes are not inherited normally, the traits are also not inherited normally. Inheritance is on chromosomes- things you can see in a microscope.

18. Properties of a physical unit • You can see it • You can move it from one place to another • You can change it with other physical processes

19. Developments in the 20th century 1944: Avery, McCarty and McLeod published a paper that stated "Deoxyribonucleic acid (DNA) plays a central role in determining specific characteristics in the course of reproduction. " There is a chemical substance, DNA, that holds genetic information http://genetics.gsk.com/history.htm

20. The experiment + Pneumonia Bacteria (S)

21. The experiment + Pneumonia Bacteria (R)

22. The experiment + Pneumonia Bacteria (R) Plus DNA from Pneumonia Bacteria (S) DNA alone is enough to make R into S

23. Properties of a physical unit • You can see it • You can move it from one place to another • You can change it with other physical processes

24. Developments in the 20th century 1946: Hermann Müller wins a Nobel Prize for his work on the genetic effects of radiation. The information can be changed through physical processes http://nobelprize.org/nobel_prizes/medicine/laureates/1946/muller-bio.html

25. X-rays Broken chromosomes Mutant chromosomes Mutant offspring The experiment

26. Properties of a physical unit • You can see it • You can move it from one place to another • You can change it with other physical processes

27. Heredity has a physical basis Inheritance is on chromosomes. You can see them. DNA can carry new traits into an organism. You can hold it in your hand. Traits can be changed by physical processes. You can change it by hitting it with a hammer.

28. The BIG Question How does DNA make an organism? Surely there will be something more to DNA than chemistry. Vitalism??

29. What did we know about DNA? • It contains sugar, phosphate and nitrogen-containing bases • There are 4 bases- A, C, G, T

30. Rosalind Franklin

31. X-rays DNA crystal Photographic film The Experiment

33. X-ray diffraction from DNA crystal Showed that DNA is a double helix Showed that the bases are on the inside More info on this at: http://www.pbs.org/wgbh/nova/photo51/

34. Francis Crick and Jim Watson (1953)

35. The Experiment

37. Watson-Crick DNA Model (1953) • Antiparallel double helix • DNA bases in the middle • Sugar Phosphate backbone running along the outside

38. Watson-Crick DNA Model (1953) • Antiparallel double helix • DNA bases in the middle • Sugar Phosphate backbone running along the outside • Bases are paired with each other

39. What was the secret of life?

40. DNA bases can only pair one way A T G C This is called complementarity

41. Complementarity Complementarity allows the hereditary information to be copied digitally. Question: Why is digital copying an advantage?

42. DNA can be very accurately copied There have been hundreds of billions of cell divisions since you were a single fertilized egg. How many cell divisions have happened on Earth in the last hour?

43. DNA can be very accurately copied This DNA sequence is still recognizable since the last common ancestor of these animals.

44. Why is this a big deal? • When you know where the information is stored, you can: • Read it

45. Why is this a big deal? • When you know where the information is stored, you can: • Read it • Change it

46. The chemical structure of DNA is yet another blow to vitalism What Next?

47. Francis Crick Francis Crick worked in his later years to understand the neurobiological basis of consciousness. “You’, your joys and your sorrows, your memories and your ambitions, your sense of personal identity and free will, are in fact no more than the behavior of a vast assembly of nerve cells…” How does this relate to vitalism? 1916-2004 http://biology.plosjournals.org/perlserv/?request=get-document&doi=10.1371/journal.pbio.0020419

48. Postscript

49. Watson, Crick and WilkinsNobel Prize 1962

50. Where was Rosalind Franklin? Rosalind Franklin (1920 - 1958)