Transcript 12-1 DNA
Chapter 12 DNA & RNA Section 12-1 DNA FOOTHILL HIGH SCHOOL SCIENCE DEPARTMENT Griffith & Transformation • 1928 • Studying Natural Bacterial Pneumonia caused by: S. pneumonia in sputum Notice capsule Gram Positive Diplococci – Streptococcus pneumoniae • Smooth (pathogenic) • Rough (non-pathogenic) FOOTHILL HIGH SCHOOL SCIENCE DEPARTMENT Streptococcus pneumonia Type 3 VERY Mucoid Optochin Disc FOOTHILL HIGH SCHOOL SCIENCE DEPARTMENT Griffith’s Experiments • Injected Mice –Smooth – Mice Died –Rough – Mice Didn’t Get Sick –Heat Killed Smooth – Mice Didn’t Get Sick • Illness Not Caused By Poison FOOTHILL HIGH SCHOOL SCIENCE DEPARTMENT Transformation Mixed Heat Killed Smooth With Rough Live Bacteria. –Mice Died –Autopsy Revealed Lungs Full Of Smooth Strain of Bacteria HOW?? FOOTHILL HIGH SCHOOL SCIENCE DEPARTMENT Griffiths Transformation FOOTHILL HIGH SCHOOL SCIENCE DEPARTMENT Transformation • Heat Killed Smooth Bacteria – Still Contained The Information On How To Become Smooth – And Could Transmit That Info – And Transform Rough Bacteria To The Smooth (Pathogenic) Form FOOTHILL HIGH SCHOOL SCIENCE DEPARTMENT Avery & DNA • 1944 • Repeated Griffith’s Work • But Treated The Extract From Heat Killed Smooth Bacteria To Destroy Specific Types Of Compounds FOOTHILL HIGH SCHOOL SCIENCE DEPARTMENT Avery & DNA Treated Extract To Destroy Proteins Lipids Carbohydrates RNA Transformation Still Occurred FOOTHILL HIGH SCHOOL SCIENCE DEPARTMENT Avery & DNA Then They Treated Extract & Destroyed DNA Transformation Did NOT Occur DNA Was The Transforming Factor FOOTHILL HIGH SCHOOL SCIENCE DEPARTMENT Avery & DNA Key Concept Avery and other scientists discovered that DNA stores and transmits the genetic information from one generation of an organism to the next generation. FOOTHILL HIGH SCHOOL SCIENCE DEPARTMENT Hershey-Chase Experiment • 1952 • Studied Virus Particles, Especially Bacteriophages Martha Chase & Alfred Hershey FOOTHILL HIGH SCHOOL SCIENCE DEPARTMENT Hershey-Chase Experiment • Bacteriophages – Composed of DNA or RNA – and a Protein Coat – Figured Whichever Part Entered The Bacteria – Carried The Genes • Used Radioactive Markers FOOTHILL HIGH SCHOOL SCIENCE DEPARTMENT Radioactive Markers • Grew Viruses In Cultures Containing – Radioactive Phosphorus ( 32P ) and – Radioactive Sulfur ( 35S ) Proteins Contain No Phosphorous DNA Contains No Sulfur FOOTHILL HIGH SCHOOL SCIENCE DEPARTMENT Radioactive Markers Therefore: If The Interior Of The Bacteria Contained: ( 32P ) Then DNA Contained Genes ( 35S ) Then Protein Contained Genes Nearly All The Bacteria Contained ( 32P ) Therefore DNA Contained Genes FOOTHILL HIGH SCHOOL SCIENCE DEPARTMENT Hershey-Chase FOOTHILL HIGH SCHOOL SCIENCE DEPARTMENT Hershey - Chase Key Concept: Hershey and Chase concluded that the genetic material of the bacteriophage was: DNA, not Protein. FOOTHILL HIGH SCHOOL SCIENCE DEPARTMENT The Structure of DNA • Scientists still didn’t know: –How information was carried between generations –How genes were structured –How genes were copied FOOTHILL HIGH SCHOOL SCIENCE DEPARTMENT The Structure of DNA • DNA is a long Molecule of repeating nucleotides • Each nucleotide has 3 parts: – 5 Carbon Sugar (Deoxyribose) – 1 Phosphate Group – 1 Nitrogenous Base FOOTHILL HIGH SCHOOL SCIENCE DEPARTMENT The Structure of DNA • There are 4 Nitrogenous Bases in DNA • The 4 Bases fit into two groups or types: – Group 1 Purines • Adenine • Guanine – Group 2 Pyrimidines • Cytosine • Thymine FOOTHILL HIGH SCHOOL SCIENCE DEPARTMENT Purines Pyrimidines FOOTHILL HIGH SCHOOL SCIENCE DEPARTMENT The Structure of DNA DNA Backbone Sugar & Phosphate Groups Nitrogenous Bases Stick Out & Join Sideways FOOTHILL HIGH SCHOOL SCIENCE DEPARTMENT The Structure of DNA Chargaffs Rules – Discovered That Certain Nucleotides Were Always Present In The Same Percentages: – Adenine & Thymine – Guanine & Cytosine – % In Each Species Different – Nobody Knew Why FOOTHILL HIGH SCHOOL SCIENCE DEPARTMENT The Structure of DNA • X-Ray Diffraction – Early 1950’s – Rosalind Franklin – Doesn’t Show Structure But Provides Clues • DNA Twisted In Coils • Two Strands • Nitrogenous Base In Center FOOTHILL HIGH SCHOOL SCIENCE DEPARTMENT Photo 51 FOOTHILL HIGH SCHOOL SCIENCE DEPARTMENT The Double Helix • Watson & Crick – Building 3 Dimensional Models – 1953 Saw Franklins X-ray Work – Immediately Recognized What The Structure Had To Be: The Double Helix FOOTHILL HIGH SCHOOL SCIENCE DEPARTMENT Watson & Crick Key Concept: Watson & Crick’s Model of DNA was a Double Helix, in which Two (2) Strands were wound around each other. FOOTHILL HIGH SCHOOL SCIENCE DEPARTMENT Double Helix FOOTHILL HIGH SCHOOL SCIENCE DEPARTMENT Watson & Crick • Discovered The Double Helix • Held Together By Hydrogen Bonds Between The Nitrogenous Bases • Base Pairing A:T and G:C Explained Chargaff’s Rule FOOTHILL HIGH SCHOOL SCIENCE DEPARTMENT