UNIT 3 DNA - THE HEREDITARY MATERIAL Flashcards
who discovered the dna molecule
in 1869, freidrich miescher
hy isolating the nuclei of wbcs, he extracted an acidic molecule he claled nuclein. (aka nucleic aicd)
before dna was established as the genetic matieral in cells, scientists knew:
- there was a connection between chromosomes and inherited traits
- the genetic material had to control the production of enzymes and proteins
- the genetic material had to be able to replicate itself with accuracy and still allow mutations to occur
dna or protein?
scientists knew that chromosomes werecomposed of proteins and nucleic acids.
proteins were known to be composed of 20 amino acids.
- nucleic acids were composed of only four bases
whatd griffith do
fredrick griffiths experiments with strep in 1928 helped to establish dna as the material of heredity.
two forms of bacterium were used:
one variety, the s strain had a capsule like a cell wall
the other variety, the r strain did not have a capsule
griffiths tests
Griffith injected mice with s-strain and r-strain.
The mice lived through the r-strain and died through the s-strain.
The mice lived thru heat injected s-strain
The mice died with a mix of s-strain and r-strain.
what were his conclusions
the s strain had somehow passed on its deadly properities to the live, non pathogenic r strain.
he called this the transforming principle: something from the heat killed s strain must have transformed the living r strain to make em deadly
identifying dna avery macleod and mccarthy
oswald avery and his group built on griffiths work to identiy the molecules in the s strain that caused the ransformation. avery, macleod, and mccarthy prepd identical extracts of the heat killed s strain and subjected each extract to one of 3 enzymes:
1 that destroys proteins
one that destroyed rna
one that destroys dna
avery and cos results
each enzyme treated extract was then mixed with live r strain cells.
the only extract that did not allow transformations of the r strain to the pathogenic s strain was the one treated with the dna destroyed enzyme.
avery and his colleagues concluded that dna was the hereditary material.
inspite of evidence, many sicnetists at the time still believed that the more compledx proteins were the hereditary material.
what did hershey and chase rule out
in 1952, american alfred hershey and martha chase ruled out protein as the hereditary material.
what was their experiment
hershey and chase used two diff radioactive isotopes to track each molecule (25s for proteins and 32p for dna)
- in the first experiment: a virus with dna radioacively labelled with 32p was allowed to infect bacteria. after agitation and separaion, radioactivity was found in the bacteria pellet but in the liqud medium
what was their second experiment
a virus with its protein coat radioactively labelled wit h35s was allowed to infect bacteria. after agitation adn seperation, raidoactivity was found in the liquid medium but not in the bacteria pellet.
what did this mean
the hersheychase experiments setlled the matter of which molecule is in the genetic material.
the results provided conclusive evidence that viral dna was trasferred to the bacterial cells adn that viral dna held the gneetic information needed for viruses to reproduce.
