Presentation on theme: "AP Biology 2006-2007 DNA The Genetic Material AP Biology History of Genetic Science Create a time chart in your notebook- use the book to fill it in-20."— Presentation transcript:
AP Biology DNA The Genetic Material
AP Biology History of Genetic Science Create a time chart in your notebook- use the book to fill it in-20 min! Scientist(s)ExperimentDateConclusions 1850s Early 1950s 1953
AP Biology Scientific History The march to understanding that DNA is the genetic material Mendel (1857) T.H. Morgan (1908) Frederick Griffith (1928) Avery, McCarty & MacLeod (1944) Erwin Chargaff (1947) Hershey & Chase (1952) Franklin (Early 1950s) Watson & Crick (1953)
AP Biology Mendel’s laws of heredity Law of segregation each allele segregates into separate gametes Law of independent assortment genes on separate chromosomes assort into gametes independently EXCEPTION linked genes 1857
AP Biology Chromosomes related to phenotype T.H. Morgan working with Drosophila fruit flies associated phenotype with specific chromosome white-eyed male had specific X chromosome 1908 | 1933
AP Biology Genes are on chromosomes Morgan’s conclusions genes are on chromosomes but is it the protein or the DNA of the chromosomes that are the genes? initially proteins were thought to be genetic material… Why? 1908 | 1933
AP Biology The “Transforming Principle” 1928 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”
AP Biology The “Transforming Principle” Transformation = change in phenotype something in heat-killed bacteria could still transmit disease-causing properties live pathogenic strain of bacteria live non-pathogenic strain of bacteria mice diemice live heat-killed pathogenic bacteria mix heat-killed pathogenic & non-pathogenic bacteria mice livemice die A.B. C. D.
AP Biology DNA is the “Transforming Principle” Avery, McCarty & MacLeod purified both DNA & proteins separately from Streptococcus pneumonia bacteria which will transform non-pathogenic bacteria? injected protein into bacteria no effect injected DNA into bacteria transformed harmless bacteria into virulent bacteria 1944 What ’ s the conclusion? mice die
AP Biology Oswald AveryMaclyn McCartyColin MacLeod Avery, McCarty & MacLeod Conclusion first experimental evidence that DNA was the genetic material 1944 |
AP Biology 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 35 S in their protein coat 32 P in their DNA infected bacteria with labeled phages 1952 | 1969 Hershey Why use S ulfur vs. P hosphorus?
AP Biology Protein coat labeled with 35 S DNA labeled with 32 P bacteriophages infect bacterial cells T2 bacteriophages are labeled with radioactive isotopes S vs. P bacterial cells are agitated to remove viral protein coats 35 S radioactivity found in the medium 32 P radioactivity found in the bacterial cells Which radioactive marker is found inside the cell? Which molecule carries viral genetic info? Hershey & Chase
Blender experiment Radioactive phage & bacteria in blender 35 S phage radioactive proteins stayed in supernatant therefore viral protein did NOT enter bacteria 32 P phage radioactive DNA stayed in pellet therefore viral DNA did enter bacteria Confirmed DNA is “transforming factor” Taaa-Daaa!
AP Biology Hershey & Chase Alfred HersheyMartha Chase 1952 | 1969 Hershey
AP Biology Let the race begin! 1950s – scientific community racing to find 3-D structure of DNA Major players Erwin Chargaff James Watson & Francis Crick Linus Pauling Maurice Wilkins & Rosalind Franklin
AP Biology 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% 1947 That ’ s interesting! What do you notice? Rules A = T C = G
AP Biology Rosalind Franklin ( ) Wilkins & Franklin used X-ray crystallography to study DNA structure Diffraction pattern used to deduce 3-D shape of molecules DNA was helical in shape!
AP Biology Structure of DNA Watson & Crick developed double helix model of DNA other leading scientists working on question: Rosalind Franklin Maurice Wilkins Linus Pauling 1953 | 1962 Franklin WilkinsPauling
AP Biology Watson and Crick 1953 article in Nature CrickWatson
AP Biology DNA Structure Revealed 1953 – the puzzle pieces are assembled Watson put sugar-phosphate chain on the outside & nitrogen bases on the inside Sugar-phosphate backbone like the side ropes of a rope ladder. Pairs of nitrogen bases, one from each strand, form rungs The ladder forms a twist every ten bases Watson (age 25) & Crick (age 37) publish a 1 page paper in Nature Franklin’s name was not mentioned Hear from Watson Hear from Watson
Learning Check Summarize the evidence that DNA is the genetic material that allows traits to be passed on from one generation to the next
AP Biology Scientific History March to understanding that DNA is the genetic material Gregor Mendel (1857) Traits are carried from one organism to another T.H. Morgan (1908) genes are on chromosomes Frederick Griffith (1928) a transforming factor can change phenotype Avery, McCarty & MacLeod (1944) transforming factor is DNA Erwin Chargaff (1947) Chargaff rules: A = T, C = G Hershey & Chase (1952) confirmation that DNA is genetic material Watson & Crick (1953) determined double helix structure of DNA