BIOL 1010 Lecture Notes - Lecture 10: Arthur Kornberg, Petri Dish, Oswald Avery
DNA: The Genetic Material
October 16, 2014
Discovery of DNA as a Hereditary Model:
1. Miescher 1 isolates nuclein
2. Fred Griffith (1928) demonstrates transformation of bacteria
3. A decade later, Oswald Avery purifies the transforming principle, DNA
4. Hershey-Chase experiment shows that DNA=genes
5. Watson & Crick (1953) reported the structure of DNA
6. Meselson & Stahl (1958) determine DNA replication is semi-conservative
7. In 1960s, Arthur Kornberg and others deduce the molecular components of DNA
replication
Griffith wanted to make a vaccine against Diplococcus pnuemoniae, the causative agent of
pneumonia. He wished to kill the deadly bacterium by heating to make a safe vaccine.
• A harmless R-strain of D. pneumonia produced rough shaped colonies on a petri
plate
• A virulent S-strain of the bacterium produced smooth shaped colonies on a petri
plate
• Griffith used both strains in his experimental work
Griffith injected live and heat-killed D. pneumoniae into mice:
)nterpretation of Griffith’s Experiment:
• Q. Perhaps the heat-killed S-cells in the mixture in experiment #4 were not really
dead
A. In experiment #3, mice did not die
• Q. Perhaps, the R-cells in the mixture in experiment #4 had mutated into the killer
form
A. Not true; experiment #1 serves as a control
Conclusion from Griffith’s Experiment:
• The ability to cause infection has been transferred from the dead S-cells to the
harmless R-cells. The R-cells had been transformed a permanent change in the
hereditary system of the R-strain of the bacterium)
• What is the transforming principle- protein or DNA?
Transformation – changing the genetic makeup
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Viruses are composed of only nucleic acid (DNA/RNA) and protein.
Bacteriophage – attaches to a bacterium prior to infection
Hershey-Chase Experiment: The Theoretical Basis
• Protein contains sulphur, but lacks phosphorous. Protein can be specifically labeled
with radioactive sulphur (35S)
• DNA contains phosphorous, but lacks sulphur. DNA can be specifically labeled with
radioactive phosphorous (32P). By this method, either DNA or protein can be
detected in cells.
1. Let labeled bacteriophage attach and inject hereditary material
2. Knock off bacteriophage shells using a blender
3. Collect bacteria via centrifugation
4. Measure radioactivity of pellet (bacteria) and liquid (including shells)
DNA carries genes for bacteriophage propagation.
Therefore, DNA is the hereditary material of bacteriophage.
Chemical Structure of DNA
• The nucleotide is the building block of DNA. Nucleotides are joined together to form
a polymer of a DNA strand
• A nucleotide consists of:
o Five carbon ribose sugar group
o A phosphate group on ’ carbon of the ribose
o A base on the 1’ carbon of the ribose
• There are both purine and pyrimidine bases in DNA
o Adenine and guanine are DNA nucleotides with purine bases
o Thymine and cytosine are DNA nucleotides with pyrimidine bases
• Two Types of Nucleic Acids in cells:
1. Deoxyribonucleic Acid – DNA
o Double stranded
2. Ribonucleic Acid – RNA
o Single stranded
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Document Summary
Griffith wanted to make a vaccine against diplococcus pnuemoniae, the causative agent of pneumonia. Griffith injected live and heat-killed d. pneumoniae into mice: q. Perhaps the heat-killed s-cells in the mixture in experiment #4 were not really: q. Perhaps, the r-cells in the mixture in experiment #4 had mutated into the killer: not true; experiment #1 serves as a (cid:498)control(cid:499) harmless r-cells. Viruses are composed of only nucleic acid (dna/rna) and protein. Bacteriophage attaches to a bacterium prior to infection. Hershey-chase experiment: the theoretical basis: protein contains sulphur, but lacks phosphorous. Protein can be specifically labeled with radioactive sulphur (35s: dna contains phosphorous, but lacks sulphur. Dna can be specifically labeled with radioactive phosphorous (32p). Therefore, dna is the hereditary material of bacteriophage. Chemical structure of dna: the nucleotide is the building block of dna. Each dna strand has a (cid:887)" and 3" end: ex. (cid:887)"-gaattgac-3", dna polymerase enzyme that joins nucleotides together.
