Lecture 17 Flashcards
What were Chargaff’s 2 significant findings?
- A=T and G=C
- the composition of DNA varies between species
What is the outline of Chargaff’s discovery about DNA?
That A and T bases were found in the same number, as were G and C bases.
What was Chargaff’s solution based on his 2nd rule?
As there is significant DNA variation between species, DNA is feasible to be the genetic material.
What were the 2 strains of bacterium that Griffth identified?
- S strain: smooth cells, pathogenic
- R strain: rough cells, non pathogenic
What makes the S strain pathogenic and the R strain not?
The S strain has a polysaccharide capsule which protects it from detection of the hosts immune system, the R strain does not have this capsule
What experiment did Griffth do ?
The transforming principle.
- injected rats with living and dead S strain and living R strain to see which ones would live and what would be in their system
What happened when rat injected with living S strain?
Dies
- S strain found
What happened when rat injected with living R strain?
Mouse healthy
- R strain not found
What happened when mouse injected with S strain that’s dead?
Mouse healthy
- S strain not found
What happens when mouse injected with dead S strains and living R strains?
Mouse dies
- S strains found
What was the conclusion from Griffth’s experiment?
Information that determines a bacteria’s strain and virulence must be encoded in a non-living chemical, as this information can be transferred from dead to living bacteria
Griffth’s conclusion
A chemical substance (transforming principle), is the bearer of genetic information. (Cautious to say DNA)
What did Avery want to find out?
What was the chemical substance in Griffth’s experiments?
What was Avery’s experiment?
He heat killed S strain in a beaker
- added enzymes to remove RNA, proteins, and DNA
- to see which one would have only R strain present
What happened when RNase added?
S strain and small amount of R strain present
