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Lecture 12

BLG 151 Lecture 12: Chapter 13 part-1 notes
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by OneClass1324334 , Fall 2016
5 Pages
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Department
Biology
Course Code
BLG 151
Professor
Martina Hausner
Lecture
12

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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?
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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
DNA labeled with 32P; protein coat labeled with 35S
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 phage
containing 35S protein, after centrifugation most of
the radioactivity remained in the supernatant where
the sheared-off phage particles were located.
B) When a T2 phage containing 32P DNA was
mixed with the host bacterium, after centrifugation
the radioactive DNA was in the pellet where the
cells were located. Thus DNA was carrying the
virus’s genetic information
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Description
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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