CH 12.1 DNA The Genetic Material

1. CH 12.1 DNA The Genetic Material Learning Objectives: Summarize the experiments leading to the discovery of DNA as the genetic material. Diagram and Label the basic structure of DNA

2. Scientific History • The march to understanding that DNA is the genetic material • T.H. Morgan (1908) • Frederick Griffith (1928) • Avery, McCarty & MacLeod (1944) • Erwin Chargaff (1947) • Hershey & Chase (1952) • Watson & Crick (1953) • Meselson & Stahl (1958)

3. 1908 | 1933 Chromosomes related to phenotype • T.H. Morgan • working with Drosophila • fruit flies • associated phenotype with specific chromosome • white-eyed male had specific X chromosome

4. 1908 | 1933 Genes are on chromosomes • Morgan’s conclusions • genes are on chromosomes • but is it the proteinor the DNAof the chromosomes that are the genes? • initially proteinswere thought to be genetic material… Why? What’s so impressiveabout proteins?!

5. 1928 The “Transforming Principle” • Frederick Griffith • Streptococcus pneumonia bacteria • was working to find cure for pneumonia • harmless live bacteria (“rough”) mixed with heat-killed pathogenic bacteria (“smooth”) causes fatal disease in mice • a substance passed from dead bacteria to live bacteria to change their phenotype • “Transforming Principle”

6. The “Transforming Principle” mix heat-killed pathogenic & non-pathogenic bacteria live pathogenic strain of bacteria live non-pathogenic strain of bacteria heat-killed pathogenicbacteria A. B. D. C. mice die mice live mice live mice die Transformation=change in phenotype something in heat-killed bacteria could still transmit disease-causing properties

7. 1944 DNA is the “Transforming Principle” • Avery, McCarty & MacLeod • purified both DNA & proteins separately from Streptococcus pneumonia bacteria • which will transformnon-pathogenic bacteria? • injected protein into bacteria • no effect • injected DNA into bacteria • transformed harmless bacteria into virulent bacteria mice die What’s the conclusion?

8. 1944 | ??!! Avery, McCarty & MacLeod • Conclusion • first experimental evidence that DNA was the genetic material Oswald Avery Maclyn McCarty Colin MacLeod

9. 1952 | 1969 Hershey Confirmation of DNA • Hershey & Chase • classic “blender” experiment • worked with bacteriophage • viruses that infect bacteria • grew phage viruses in 2 media, radioactively labeled with either • 35S in their proteins • 32P in their DNA • infected bacteria with labeled phages Why useSulfurvs.Phosphorus?

10. Protein coat labeled with 35S DNA labeled with 32P Hershey & Chase T2 bacteriophages are labeled with radioactive isotopes S vs. P bacteriophages infect bacterial cells bacterial cells are agitated to remove viral protein coats Which radioactive marker is found inside the cell? Which molecule carries viral genetic info? 32P radioactivity foundin the bacterial cells 35S radioactivity found in the medium

12. Blender experiment • Radioactive phage & bacteria in blender • 35S phage • radioactive proteins stayed in supernatant • therefore viral protein did NOT enter bacteria • 32P phage • radioactive DNA stayed in pellet • therefore viral DNA did enter bacteria • Confirmed DNA is “transforming factor” Taaa-Daaa!

13. 1952 | 1969 Hershey Hershey & Chase Martha Chase Alfred Hershey

14. 1947 Chargaff • DNA composition: “Chargaff’s rules” • varies from species to species • all 4 bases not in equal quantity • bases present in characteristic ratio • humans: A = 30.9% T = 29.4% G = 19.9% C = 19.8% RulesA = T C = G That’s interesting!What do you notice?

15. Structure of DNA Now scientists agreed that DNA was in fact the genetic material…. But what did it look like? Let’s take a closer look at DNA.

16. 1953 | 1962 Structure of DNA • Watson & Crick • developed double helix model of DNA • other leading scientists working on question: • Rosalind Franklin • Maurice Wilkins • Linus Pauling Wilkins Pauling Franklin

17. 1953 article in Nature Watson and Crick Watson Crick

18. Rosalind Franklin (1920-1958)

19. DNA Stands for DeoxyribonucleicAcid

20. proteins DNA Nucleic Acids • Function: • genetic material • stores information • genes • blueprint for building proteins • DNA  RNA  proteins • transfers information • blueprint for new cells • blueprint for next generation

21. T G A C T A C A G G A T C

22. Nucleic Acids • Examples: • RNA (ribonucleic acid) • single helix • DNA (deoxyribonucleic acid) • double helix • Structure: • monomers = nucleotides DNA RNA

23. Nucleotides • 3 parts • nitrogen base(C-N ring) • pentose sugar(5C) • ribose in RNA • deoxyribose in DNA • phosphate(PO4)group Nitrogen baseI’m the A,T,C,G or Upart! Are nucleic acidscharged molecules?

24. Types of nucleotides Purine = AG Pure silver! • 2 types of nucleotides • different nitrogen bases • purines • double ring N base • adenine (A) • guanine (G) • pyrimidines • single ring N base • cytosine (C) • thymine (T) • uracil (U)

25. Nucleic polymer • Backbone • sugar to PO4 bond • phosphodiester bond • new base added to sugar of previous base • polymer grows in one direction • N bases hang off the sugar-phosphate backbone Dangling bases?Why is this important?

26. Pairing of nucleotides • Nucleotides bond between DNA strands • H bonds • purine :: pyrimidine • A :: T • 2 H bonds • G ::: C • 3 H bonds Matching bases?Why is this important?

27. DNA molecule Shape = Double helix • H bonds between bases join the 2 strands • A :: T • C ::: G