DNA as the heriditary material ( Experiments ) Flashcards
(13 cards)
What was the aim of Griffith’s experiment?
To find out what carries genetic information — what causes transformation in bacteria.
What organisms were used in Griffith’s experiment?
Streptococcus pneumoniae bacteria (S and R strains) and mice.
What’s the difference between S and R strain?
S-strain has a polysaccharide capsule → virulent (causes disease). R-strain lacks capsule → non-virulent (harmless).
What happened when mice were injected with heat-killed S strain?
They survived — meaning heat-killed bacteria couldn’t cause disease.
What was the big twist in Griffith’s experiment?
When heat-killed S strain + live R strain were injected → mice died.
What did he find in the blood of dead mice?
Live S strain bacteria!
What was Griffith’s conclusion?
Some “transforming principle” from dead S strain turned R strain into deadly S strain. Transformation occurred.
What was the goal of Hershey and Chase’s experiment?
To confirm whether DNA or protein is the genetic material.
What organism and tool did they use?
Bacteriophage (virus that infects bacteria) and radioactive labeling.
What parts of the virus were labeled?
DNA was labeled with ³²P. Protein was labeled with ³⁵S.
What was the method?
They let the labeled viruses infect bacteria and then checked what entered the cell.
What did they find inside the bacterial cells after infection?
Only the radioactive phosphorus (DNA) entered the bacteria. Sulfur (protein) stayed outside.
What did Hershey & Chase conclude?
DNA is the genetic material, not protein.
