Presentation on theme: "Gihan E-H Gawish, MSc, PhD Ass. Professor Molecular Genetics and Clinical Biochemistry Molecular Genetics and Clinical BiochemistryKSU SECOND WEEK."— Presentation transcript:
Gihan E-H Gawish, MSc, PhD Ass. Professor Molecular Genetics and Clinical Biochemistry Molecular Genetics and Clinical BiochemistryKSU SECOND WEEK
Griffith’s Experiment Avery’s Experiment Hershey-Chase Experiment DNA as the Genetic Material 3 Characteristics of “The Genetic Material”: Must be a stable form containing information about cell form and function Must replicate accurately Must be able to change/evolve
Comment: - Griffith concluded that the live R had been transformed to S by picking up the genetic material from the dead S and using that material to repair the damaged gene in the R strain Objective: Determine the viability of the smooth strain was required for pathogenicity 1- Frederick Griffith’s Transformation Experiment - 1928 Streptococcus pneumoniae http://trc.ucdavis.edu/b iosci10v/bis10v/media/c h09/griffith.html http://nortonbooks.c om/college/biology/a nimations/ch12a01.h tm
Frederick Griffith’s Transformation of Bacteria non-pathogenic R strain changed to pathogenic S strain by something in the heat-killed S strain sample But identity of transforming agent was not identified A change in genotype (genetic makeup) and phenotype (appearance) due to the assimilation of a foreign substance (now known to be DNA) by a cell. http://www.sinauer.com/cooper/4e/animations0402.html
DETERMINED THAT “IIIS” DNA WAS THE GENETIC MATERIAL RESPONSIBLE FOR GRIFFITH’S RESULTS. 2- Avery, McCarty, & MacLeod (1944) Identified DNA as the transforming agent
Avery, et al. Experiment purified various classes of molecules from heat-killed S strain bacteria added to R strain (non- pathogenic) tested for conversion to pathogenicity showed DNA to be transforming agent Much resistance to that idea genes of bacteria not thought to be similar in composition and function to those of more complex organisms also couldn’t imagine how DNA could contain the genetic information http://www.sinauer.c om/cooper/4e/animati ons0401.html http://www.sinauer.c om/cooper/4e/animati ons0401.html
Bacteriophage 3- Hershey-Chase Experiment, 1952 = Virus that attacks bacteria and replicates by invading a living cell and using the cell’s molecular machinery. Structure of T2 phage: DNA & protein Phage made of DNA & protein What enters cell and allows production of new phage?
Hershey-Chase Experiment Life cycle of virulent T2 phage: Animation
Hershey-Chase Experiment Procedure: 1.Set-up two replicates: Label DNA with 32 P Label Protein with 35 S 2.Infected E. coli bacteria with two types of labeled T2 Observation 32 P is discovered within the bacteria and progeny phages, whereas 35 S is not found within the bacteria but released with phage ghosts. http://Hershey and Chase Experiment Conclusion: DNA (not protein) is the genetic material.
Used 2 viral strains to demonstrate RNA is the genetic material of Tobacco Mosaic Virus (TMV) Observation Closely related plant viruses made of an RNA molecule encased in a spiral of protein One coat protein could encapsulate the other RNA and still function properly during infection Gierer & Schramm TMV Experiment - 1956 Fraenkel-Conrat & Singer - 1957 RNA as a genetic material