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L7 - DNA as Genetic Material
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Lecture by Dr David Chambers
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L7 – DNA as Genetic MaterialSlide 4 – What is the genetic material?
• 1865: Mendel defined genes
- Factors passed from parents to progeny that determine the characteristics of the
progeny (genotype)
- Units that are passed on from one generation to another
• Early 20th century: characteristics (genotype) determined by proteins
Slide 5 – What molecules store genetic information?
Slide 6 – Nucleic acids are the genetic material
• 1928: Griffith
• 1944: Avery
• 1952: Hershey and Chase
• Conclusions:
- DNA carries genetic information (in all organisms)
- DNA is chemically distinct from the substances it can produce
Slide 7 – Griffith pneumococcus experiment
• S: smooth strain (if cultured on agar bacteria plate, smooth-looking bacteria colony)
• R: rough strain (rough-looking bacteria colony)
• Heat-killed: heat treated
• Heat-killed S strain transformed R strain to living S strain
• Transforming principle: genetic material conferred different identity onto R strain
, Slide 8 – Avery pneumococcus experiment
• Griffith (1928): rough bacteria transformed by a heat-stable component of smooth
bacteria
• Avery (1944): isolated cytosol of heat-killed smooth bacteria
- Treated with DNase (removes DNA)
- Treat with trypsin (removes protein)
• DNA: transforming principle
• If you remove DNA from heat killed S strain before mixing with R strain, you can’t kill
mouse and recover living S strain
- Cannot transform R strain
• If you remove proteins and mix it with R strain, previous sequence of events doesn’t
happen
Slide 9
• Genetic information carried by nucleic acids (contain phosphorus), not proteins (contain
sulphur)
• Bacteriophages: viruses that infect bacteria, replicate cells
- Only composed of nucleic acids and proteins
• Infection of bacteria, find out what material makes it into the bacterial cell
• Always find radioactive nucleic acids in bacteria and never proteins
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