MOHAMED NASRELDIN

History of DNA1

In 1928, Fredrick Griffith, a British Biologist, did an experiment on mice

He injected two strains of bacteria into the mice

One was harmful, the other was harmless

“Transforming Factor”2

He injected Strain 1 (harmful) into the first mouse, it died

The second mouse, he injected Strain 2 (Harmless), it survived

The third mouse, He injected a heat treated Strain 1, the mouse survived

In the fourth mouse he injected a mixture of strain 2 and heat treated strain 1, the mouse died.

“Transforming Factor”3

“Transforming Factor”4

Since the fourth mouse died, Griffith concluded that there was a transforming factor.

The harmless strain transformed and became deadly.

“Transforming Factor”5

American BiologistTook Griffith’s experiments a step furtherWanted to find out what was the transforming

factor.Thought it might be Protein

Oswald Avery6

Treated Griffith’s mixture of heat-treated deadly strain and live harmless strain with protein-destroying enzymes

The bacteria grown from the mixture was still transformed

He concluded that Protein was not the transforming factor

Avery’s Experiments7

He then treated the mixture with DNA destroying enzymes

The bacteria colonies did not transformAvery concluded that DNA is the genetic

material

Avery’s Experiments8

Many scientists did not believe AveryStill believed Protein was the “transforming

factor” because DNA was too simpleFurther research had to be conducted

Further Experiments9

Wanted to make sure the transforming factor was DNA

Used viruses for testing

Hershey and Chase10

Knew that the phage had two components- DNA and Protein

They were not sure which one had the hereditary material

Made an experiment to determine which part of the phage it was DNA or the protein

Hershey and Chase11

For one batch, they used a radioactive isotope of sulfur (found only in Protein)

The other batch they used a radioactive isotope of phosphorus (found in DNA)

Hershey and Chase12

They concluded that DNA was the hereditary material

Their experiment convinced other scientists that DNA contains the genetic material

Hershey and Chase13

When the protein coats were labeled, the radioactivity was detected outside the cells

When DNA coats were labeled, the radioactivity was detected inside the cells

Hershey and Chase14

Bibliography

http://edu.glogster.com/media/4/14/58/61/14586124.jpg

http://www.csb.yale.edu/userguides/graphics/ribbons/help/dna_rgb.gif

http://www.mun.ca/biology/scarr/Chase_&_Hershey_1953.jpg

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The END16