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Lecture 12

BLG 151 Lecture 12: Chapter 13 part-1 notes

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Ryerson University
BLG 151
Martina Hausner

Microbiology Chapter 13: Bacterial Genome Replication and Expression 13.1 Experiments Using Bacteria and Viruses Demonstrated that DNA is the Genetic Material What is Genetics?  Study of structure and function of hereditary material and the mechanisms by which organisms pass traits from one generation to the next  Microbial genetics?  Use of microorganisms to study genetics Terminology and Concepts  Genome  All DNA present in a cell or virus  Bacteria and archaea generally have one set (haploid – 1N)  Eukaryotes have two sets (diploid – 2N)  Genotype  Specific set of genes an organism possesses  Phenotype  Collection of observable characteristics Discovery of DNA as Genetic Material  1928 – Fred Griffith  1944 – Avery, McLeod and McCarty  1952 – Alfred Hershey and Martha Chase DNA as Genetic Material  Griffith in 1928 observed the change of non virulent organisms into virulent ones via “transformation”  MacLeod and McCarty in 1944 showed that the transforming principle was DNA Griffith’s Experiments  Worked with Streptococcus pneumonia  Used different strains of the bacteria to show pathogenic trait caused death in mice  Showed pathogenic trait could be passed onto non pathogenic bacteria  “transforming factor” – what is it? Avery, McLeod and McCarty’s Experiments  Repeated Griffith’s experiment with more advanced biochemistry  Showed “transforming factor” was DNA  Earlier experiments done by Avery, MacLeod, and McCarty had shown that only DNA extracts from S cells caused transformation of R cells to S cells. To demonstrate that contaminating molecules in the DNA extract were not responsible for transformation, the DNA extract from S cells was treated with RNase, DNase, or protease, and then mixed with R cells. Only treatment of the DNA extract from S cells with DNase destroyed the ability of the extract to transform the R cells DNA as Genetic Material – Proof with Radioactivity Experiments  Hershey and Chase, 1952, used bacteriophage T2 infection as model 32 35  DNA labeled with P; protein coat labeled with S  Only DNA entered cell but both new DNA and protein coats synthesized in new viruses indicating DNA had genetic information for both of these viral components  In both experiments, phage progeny were produced. Thus blender treatment did not interfere with the infection process. A) When E.coli was infected with a T2 35 phage containing S protein, after centrifugation most of the radioactivity remained in the supernatant where the sheared-off phage particles were located.
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