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Gihan E-H Gawish, MSc, PhD Ass. Professor Molecular Genetics and Clinical Biochemistry Molecular Genetics and Clinical BiochemistryKSU SECOND WEEK.

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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:

1 Gihan E-H Gawish, MSc, PhD Ass. Professor Molecular Genetics and Clinical Biochemistry Molecular Genetics and Clinical BiochemistryKSU SECOND WEEK

2  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

3 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 Streptococcus pneumoniae iosci10v/bis10v/media/c h09/griffith.html om/college/biology/a nimations/ch12a01.h tm

4 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.

5 DETERMINED THAT “IIIS” DNA WAS THE GENETIC MATERIAL RESPONSIBLE FOR GRIFFITH’S RESULTS. 2- Avery, McCarty, & MacLeod (1944) Identified DNA as the transforming agent

6 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  om/cooper/4e/animati ons0401.html om/cooper/4e/animati ons0401.html

7 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?

8 Hershey-Chase Experiment Life cycle of virulent T2 phage: Animation

9 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. and Chase Experiment Conclusion: DNA (not protein) is the genetic material.

10 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 Fraenkel-Conrat & Singer RNA as a genetic material


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