Download S strain

Ch 10-1 Discovery of DNA
Scientists thought if they could figure out how an organism’s molecules store hereditary info….they’d
get how these chromosomes function in heredity
Griffith’s Experiments
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British med officer dude Fred Griffith
o Studying s. pneumoniae
o Types of bacterium  STRAINS of bacterium
o Virulent – disease causing
 Griffith was trying to make a vaccine against virulent strain of the bacterium\
S strain – has capsule that
protects it from body’s
defense system.
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Smooth edged
colonies
R strain – no capsule –
Colonies of harmful (S) strain
colonies of harmless (R) strain
So this guy performed experiments to find out more about hereditary material
EXERIMENTS 1 & 2
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He injected either live R or S cells into mice.
Only S cells killed the mice!
EXPERIMENT 3
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Injected heat-killed S bacteria into mice, which survived
EXPERIMENT 4
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Injected both heat killed S cells and live R cells – both mice died
Rough colonies
Griffith concluded that HEAT-KILLED virulent bacterial cells release a hereditary factor which takes
disease- causing ability to live, harmless cells
Transformation – type of transfer of genetic material from one cell to another cell, or from
one organism to another.
Avery’s Experiments
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American researcher Oswald Avery
o Tested if tranforiming agent in Griffith’s experiment was protein, RNA, or DNA
o Used enzymes to separate each of 3molecules in heat killed S cells
 PROTEASE enzyme – for protein destroying
 RNase – for RNA
 DNase – for DNA
o Mixed separate 3 experi. Batches of heat-killed S cells with live R cells…injected mice!
Found that cells w/ no protein/RNA could turn R cells into S cells and kill the mice!
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Cells missing DNA didn’t transform R into S…
SOOOOOOO.. DNA is responsible for transformation in bacteria!!