DNA The Genetic Material AP Biology 2006 2007

DNA The Genetic Material AP Biology 2006 -2007

Scientific History § The march to understanding that DNA is the genetic material T. H. Morgan (1908) u Frederick Griffith (1928) u Avery, Mc. Carty & Mac. Leod (1944) u Erwin Chargaff (1947) u Hershey & Chase (1952) u Watson & Crick (1953) u Meselson & Stahl (1958) u AP Biology

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

1908 | 1933 Genes are on chromosomes § Morgan’s conclusions genes are on chromosomes u but is it the protein or the DNA of the chromosomes that are the genes? u § initially proteins were thought to be genetic material… Why? What’s so impressive about proteins? ! AP Biology

The “Transforming Principle” § Frederick Griffith u 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 u a substance passed from dead bacteria to live bacteria to change their phenotype u § AP Biology “Transforming Principle” 1928

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

1944 DNA is the “Transforming Principle” § Avery, Mc. Carty & Mac. Leod u purified both DNA & proteins separately from Streptococcus pneumonia bacteria § which will transform non-pathogenic bacteria? u injected protein into bacteria § no effect u injected DNA into bacteria § transformed harmless bacteria into virulent bacteria mice die AP Biology What’s the conclusion?

Avery, Mc. Carty & Mac. Leod 1944 | ? ? !! § Conclusion u first experimental evidence that DNA was the genetic material Oswald Avery AP Biology Maclyn Mc. Carty Colin Mac. Leod

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

Hershey & Chase Protein coat labeled with 35 S DNA labeled with 32 P T 2 bacteriophages are labeled with radioactive isotopes S vs. P bacteriophages infect bacterial cells are agitated to remove viral protein coats Which radioactive marker is found inside the cell? Which molecule carries viral genetic info? AP Biology 35 S radioactivity found in the medium 32 P radioactivity found in the bacterial cells

AP Biology

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

Hershey & Chase AP Biology Martha Chase 1952 | 1969 Hershey Alfred Hershey

Chargaff § DNA composition: “Chargaff’s rules” varies from species to species u all 4 bases not in equal quantity u bases present in characteristic ratio u § humans: A = 30. 9% T = 29. 4% G = 19. 9% C = 19. 8% AP Biology That’s interesting! What do you notice? Rules A = T C = G 1947

1953 | 1962 Structure of DNA § Watson & Crick u developed double helix model of DNA § other leading scientists working on question: w Rosalind Franklin w Maurice Wilkins w Linus Pauling AP Biology Franklin Wilkins Pauling

1953 article in Nature Watson and Crick Watson AP Biology Crick

Rosalind Franklin (1920 -1958) AP Biology

But how is DNA copied? § Replication of DNA u base pairing suggests that it will allow each side to serve as a template for a new strand “It has not escaped our notice that the specific pairing we have postulated immediately suggests a possible copying mechanism for the genetic AP Biology material. ” — Watson & Crick

Models of DNA Replication § Alternative models u become experimental predictions conservative P 1 2 AP Biology Can you design a nifty experiment to verify? semiconservative dispersive

Semiconservative replication 1958 § Meselson & Stahl u u label “parent” nucleotides in DNA strands with heavy nitrogen = 15 N label new nucleotides with lighter isotope = 14 N “The Most Beautiful Experiment in Biology” Make predictions… 15 N/15 N parent strands AP Biology parent replication

Predictions 14 N/14 N 1 st round of replication 2 nd round of replication 15 N/15 N 1 15 N/15 N 2 15 N parent AP Biology strands 15 N/14 N semiconservative dispersive conservative 14 N/14 N P 15 N/14 N 14 N/14 N 15 N/14 N semiconservative dispersive conservative

Meselson & Stahl Matthew Meselson Franklin Stahl Matthew Meselson AP Biology

Scientific History § March to understanding that DNA is the genetic material u T. H. Morgan (1908) § genes are on chromosomes u Frederick Griffith (1928) § a transforming factor can change phenotype u Avery, Mc. Carty & Mac. Leod (1944) § transforming factor is DNA u Erwin Chargaff (1947) § Chargaff rules: A = T, C = G u Hershey & Chase (1952) § confirmation that DNA is genetic material u Watson & Crick (1953) § determined double helix structure of DNA u AP Biology Meselson & Stahl (1958) § semi-conservative replication

The “Central Dogma” § Flow of genetic information in a cell transcription DNA replication AP Biology translation RNA protein

Science …. Fun Party Time! Any Questions? ? AP Biology 2006 -2007

Ghosts of Lectures Past (storage) AP Biology 2006 -2007

Semiconservative replication 1958 § Meselson & Stahl u u label “parent” nucleotides in DNA strands with heavy nitrogen = 15 N label new nucleotides with lighter isotope = 14 N “The Most Beautiful Experiment in Biology” parent 15 N/15 N parent strands AP Biology replication

Semiconservative replication 1958 § Make predictions… u u u AP Biology 15 N strands replicated in 14 N medium 1 st round of replication? where should the bands be? 2 nd round?