Download BIOLOGY 207 - Dr.McDermid Lecture #1: DNA is the Genetic Material

BIOLOGY 207 - Dr.McDermid
Lecture #1:
DNA is the Genetic Material
Reading: Griffiths et al, 7th Edition: Ch.8 pp 241-244 (No problems assigned)
Concepts:
1. What were the key experiments that lead us to the conclusion that DNA is the Genetic
Material?
a. Griffiths -1928
b. Avery, MacLeod, & McCarty - 1944
c. Hershey & Chase - 1952
2. Are there exceptions?
What is the most likely genetic material?
Protein?
DNA?
Frederick Griffith, 1928 (Figure 8-1)
Streptococcus pneumonia,
- pneumonia in humans, kills mice
2 strains:
smooth (S)
rough (R)
a) S-strain cells ‡ inject mouse ‡
b) R-strain cells ‡ inject mouse ‡
c) heat killed S-strain cells ‡ inject mouse ‡
d) heat killed S-strain cells + R-strain live cells
‡ inject mouse ‡
Conclusion:
- something in the S-cell debris could convert (transform) R -> S
- "Transforming Principle"
- potential assay
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Figure 8-1 from the text
Avery, MacLeod & McCarty - 1944 Figure 8-2
Identifying the transforming factor
Heat-killed S cells
Purify Components
Chemical
analysis
DNA
Add to Live R cells
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Heat-killed S cells
Purify Components
Protease
Chemical
analysis
RNase
DNA
DNase
Add to Live R cells
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Hershey & Chase - 1952
Figure 8-3
Bacteriophage (bacterial virus) T2
Radioisotope
32P to follow DNA; P not found in protein
35S labels protein; S not found in DNA
Results
35S protein ->
32P DNA ->
Conclusion:
If DNA is the hereditary material then:
1) How do cells replicate their DNA?
2) How is genetic information stored?
3) How do mutations occur?
1953 - DNA Structure
Watson and Crick
Are there exceptions to DNA as the
genetic material?
1) RNA viruses
2) Prions
- Creutzfeldt-Jakob disease
- elk wasting disease (mad elk disease)
- novel infectious agent
- Stanley Prusiner
- prions consist only of protein
- PrPc - PrPSc - PrPSc converts PrPc to PrPSc
Figure 8-3 from text
- PrPSc ‡ uv or ionizing radiation ‡
- PrPSc ‡ protein degradation ‡
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