DNA & RNA DNA

Griffith & Transformation 1928 Studying Natural Bacterial Pneumonia caused by: Streptococcus pneumoniae Smooth (pathogenic) Rough (non-pathogenic) S. pneumonia in sputum Notice capsule Gram Positive Diplococci

Streptococcus pneumonia Type 3 VERY Mucoid Optochin Disc

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

Mice Died Transformation Mixed Heat Killed Smooth With Rough Live Bacteria. Mice Died Autopsy Revealed Lungs Full Of Smooth Strain of Bacteria HOW?? Rough Bacteria Don’t Kill!

Griffiths Transformation

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

Avery & DNA 1944 Repeated Griffith’s Work Then Did Experiments to Find Out What Was Transforming the Bacteria By Treating The Extract From Heat Killed Smooth Bacteria To Destroy Specific Types Of Compounds

Treated Extract To Destroy Transformation Still Occurred Avery & DNA Treated Extract To Destroy Proteins Lipids Carbohydrates RNA Transformation Still Occurred

Transformation Did NOT Occur Avery & DNA Then They Treated The Extract & Destroyed The DNA Transformation Did NOT Occur DNA Was The Transforming Factor

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.

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

Hershey-Chase Experiment 1952 Studied Virus Particles, Especially Bacteriophages Martha Chase & Alfred Hershey

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

Proteins Contain No Phosphorous Radioactive Markers Grew Viruses In Cultures Containing Radioactive Phosphorus ( 32P ) and Radioactive Sulfur ( 35S ) Proteins Contain No Phosphorous DNA Contains No Sulfur

Nearly All The Bacteria Contained Therefore DNA Contained Genes 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

Hershey-Chase Bacteriophage (virus that infects bacteria) Outer, Protein Coat Contains Sulfur – No Phosphorus E. coli bacteria (infected by Bacteriophage) Bacteriophage DNA injected into the E. coli Bacteriophage DNA contains Phosphorous but NO Sulfur

Hershey-Chase

DNA, not Protein. Hershey - Chase Key Concept: Hershey and Chase concluded that the genetic material of the bacteriophage was: DNA, not Protein.

The Structure of DNA X-Ray Diffraction Rosalind Franklin Early 1950’s Doesn’t Show Structure But Provides Clues DNA Twisted In Coils Two Strands Nitrogenous Base In Center

Photo 51

The Double Helix Watson & Crick A Double Helix Building 3 Dimensional Models 1953 Saw Franklins X-ray Work Immediately Recognized What The Structure Had To Be: A Double Helix

The Structure of DNA Scientists still didn’t know: How information was carried between generations How genes were structured How genes were copied

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

The Structure of DNA There are 4 Nitrogenous Bases in DNA The 4 Bases are two types: Purines which are Double Ring Molecules Adenine Guanine Pyrimidines which are Single Ring Molecules Cytosine Thymine

Purines Pyrimidines

Watson & Crick Key Concept: Watson & Crick’s Model of DNA was a Double Helix, in which Two (2) Strands were wound around each other.

The Structure of DNA Phosphate/Deoxyribose Form Sides of the DNA Ladder Nitrogenous Bases Forms Rungs of DNA Ladder

Explained Chargaff’s Rule 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

Double Helix