Griffth (Proof of DNA as Genetic Material)

8/19/2019 Griffth (Proof of DNA as Genetic Material)

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Much of the first half of

the century microbiologistsattempted to identifyorganisms responsible fordisease.

Griffith and Avery, McCloud & McCarthy providethe first evidence for DNA as the genetic material

Oswald Avery


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What is Pneumococcus?

The Pneumococcus is a bacteria that causesserious infections in adults and children, includingpneumonia, blood infections, and meningitis. Thisbacteria is also the number one cause of sinusitis

and ear infections.Fred Griffith

anted to ma!e a vaccine against"treptococcus pneumoniae, hich caused a type

of pneumonia.#hough he failed in ma!ing thevaccine he stumbled on a demonstration of thetransmission of genetic instructions by aprocess e no call transformation.


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#he $ bacteria ere harmless, but the " bacteria erelethal hen in%ected into mice.

e found that the bacterium had to forms hen gronon agar plates, a smooth '"( and a rough '$( form.

eat)!illed " cells ere also harmless)the same effectseen by *asteur.

oever, surprisingly hen live $ cells ere mi+ed ith !illed" cells and in%ected into mice the mice died, and thebacteria rescued from the mice had been transformed into" type.

#his e+periment strongly implied that genetic materialhad been transferred from the dead to the live cell. -tas hard to be certain of this, or to !no hat thematerial as in this crude e+periment.


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"i+teen years later the team of Avery, Maceodand McCarty revisited this e+periment andattempted a more definitive e+periment.

A favorite hypothesis of the /012s as that thegenetic instructions in chromosomes as protein.

oever,chemical analysis of DNA had begun to

suggest that it might be a more interesting moleculethan had been supposed.

Avery, Maceod and McCarty repeated Griffith3s

e+periment using purified DNA molecules and gotthe same transformation of $ cells into " cells.


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Avery,Macleod and McCarty 4s

e+periment


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An explanation of Grith's results came inthe 1!"'s #ith the #or$ of %s#ald A&er,(olin )ac*eod and )acln )c(art. Theseresearchers suggested that something inthe heat treated + bacteria transformed the

tpe bacteria into li&ing +. -n order todemonstrate #hat the transforming agent#as, the too$ li&e and heat treated + andmixed it #ith t#o enmes/


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protease #hich destros protein00noticefrom the image that the mouse still died,indicating that something other thanprotein #as the transforming agent.

2ase #hich destros 2A00notice from theimage that the mouse li&ed, indicating that2A is re3uired for the transformatione&ent.

-n short, these researchers demonstratedthat 2A, and not protein, #as the

transforming agent.


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-n fact, it is unli!ely that either Griffith or Avery hadany real feeling for ho important their or! ouldultimately become. -nstead, each focused only onansering a very specific 5uestion. Griffith ondered,

Can bacteria change from one type to another6 andshoed that they could. Avery as!ed, 7hat substancema!es them change6 and found that it as DNA. 8et,by as!ing simple 5uestions and designing elegante+periments to anser them, Griffith and Avery laid the

groundor! for a scientific revolution that neither couldhave imagined.


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Source :http://mywebpages.comcast.net/biologycentury

/pages/dna1.html

http://www.accessexcellence.org /

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Griffth (Proof of DNA as Genetic Material)