Chapter 14- Part 1 Discovery of DNA Flashcards
Many scientists believed that ____ were most like hereditary molecule.
Protein
Several experiments, proved DNA not protein is genetic material.
What did the hammerling experiment determine?
Discovered hereditary information is stored in the cells nucleus.
Describe the hammerling Reciprocal graft experiment:
Cells of green alga were cut into peices and observed.
He interchanged two different types of alga bases (containing the nucleus) but inserted the stem of a different type.
The alga’s type of cap and color was corresponded with that of the nuclues, not of the stem.
Thus nuclues in the base determines type of cap regenerated.
Who conducted the transformation experiment that could genetically transform bacteria (transformation)? What were those bacteria?
Fredrick Griffith in 1928.
Two strains of streptococcus pneumonia:
- Smooth strain(s) is highly infective (virulent) which quickly causes pneumonia and killing mice. Capsule might have caused it. Pathogenic.
- Rough Strain (R) is nonvirulent and does not kill mice: non-infective, non-pathogenic.
What two bacterium did Griffith’s experiment study?
Two strains of streptococcus pneumonia:
- Smooth strain(s) is highly infective (virulent) which quickly causes pneumonia and killing mice. Capsule might have caused it. Pathogenic.
- Rough Strain (R) is nonvirulent and does not kill mice: non-ineffective, non-pathogenic.
What were the results of Experiment 1 in Griffiths experiment?
First, griffith, injected Mice with live S cells (control to show effect of S strain)
Results: Mice die, Live S cells in their blood(live s bacterium propagated inside organism), shows S cells are virulent and pathogenic.
What were the results of Experiment 2 in Griffiths experiment?
Second, Griffith injected live R cells into mice (control to show effect of R cells)
Results: Mice live. No live R cells in their blood; shows R cells cells are virulent.
Capsule is responsible for virulence of S strain.
In Griffith’s experiment, what is responsible for S train virulence?
The capsule is responsible of the S strain.
What were the results of Experiment 3 in Griffiths experiment?
In his third experiment, he injected mice with Heat-Killed S cells (control to show effect of S cells)
Results: Mice Live. No Live S cells in their blood; shows that live S cells are necessary to be virulent to mice.
What were the results of Experiment 4 in Griffiths experiment?
In his 4th experiment, Mice injected with heat-killed S cells plus live R cells.
Expectation: mice will live
Results: Mice Die. Live S cells in their blood shows that living R cells can be convereted into virulent S cells with SOME FACTOR [transforming principle] present in and derived from dead S cells.
In Griffith’s experiment, what happened when mice were injected with both heat-killed S cells and live R cells?
Mice Died. Live S cells were found in the blood which indicated that R cells can somehow be converted to virulent S cells by a transforming principle.
Who discovered the chemical nature of the transforming principle in Griffith’s experiment?
1940s- Oswald Avery, McLeoid, and McCorty
Discovered it was DNA.
Detail Avery’s Experiment.
Avery broke down heat-killed S bacteria and destroyed one class of molecules: proteins, DNA, or RNA.
When Proteins or RNA were destroyed, the extract still transformed live R cells to virulent S cells.
But when DNA was destroyed, no transformation occurred thus the TRANSFORMING PRINCIPLE was DNA.
What did Avery’s Experiment Discover.
When DNA was erased from S bacteria, R bacteria no longer transformed.
Thus, DNA had to be the transforming principle in Griffith’s Experiment.
In a nutshell, what did Avery’s experiment discover?
Avery removed all lipid and proteins from bacteria and found no reduction in transforming activity. DNA destroyed all transforming activity.
What did the Hershey-Chase, 1953 experiment do in a nutshell?
They labled DNA and proteins with radioactive isotope tracers and determined hereditary information was DNA not protein.
Describe the organism studied in the Hershey-Chase experiment.
Bacteriophages are viruses that can infect the bacterium [E.coli.]
This virus has a protein “head” [capsule] and a DNA core. A bacteriophage infects when the virus injects DNA into a bacterial cell.
Here they used radioactive 35 S to mark the protein and 32 P to mark the DNA.
35 S marked proteins like methonine and cystine.
What did Hershey and Chase want to determine?
Which of these molecules [DNA or proteins] is the genetic material that is injected into the bacteria.
What is a virus?
Infectious agent made of DNA or RNA surrounded by a protein coat. Reproduces only in a host cell, using host cell materials.
What “phage” did Hershey and Chase study?
T2 bacteriophage which consists only of a core of DNA surrounded by proteins.
Bacteriophage DNA was labeled with what?
Radioactive phosphorus
32P
Bacteriophage proteins were labled with what?
Radioactive sulfur
35 S
Detail the Hershey-Chase Experiment.
Two cultures of phages were created. One marked proteins with 35 S. The other marked phage DNA with 32 P.
Cultures of E.Coli were infected with one specific type.
These radioactive molecules were tracked.
These phages infected E.Coli by injecting their DNA to reproduce using the cell’s mechanism.
Then through MECHANICAL FORCES, the phage “coat” without the DNA is discarded.
These cultures were then blended and centrifuges to separate cells from virus.
The results were as follows: With the 35 S, protein marked phages, less than 1% of radioactivity in progeny phages. [Supernatant with coats were radioactive and the pellet with bacteria with Viral DNA not. progeny]
The 32 P marked culture showed >30% progeny radioactivity [pellet with progeny bacteria was radioactive and supernatant with coat not having any]
Result: 32P which was used in phage-infected cells and in progeny phages show DNA is genetic material.
What was the conclusion of the hershey-chase experiment?
A tangible amount of 32 P used to label DNA was found in phage-infected cells and later progeny phages indiciated DNA IS the genetic material.
35S used to label proteins, was found in phage coats after infection, but not within the infected cell or in progeny phages, showing proteins are not genetic material.
What was in the pellet and supernantant of the culture contaning 35S labeled phages?
The supernatant had radioactive phage coats with the pellet had no instance of radioactivity in affected E.coli and later progeny stages.
What was in the pellet and supernantant of the culture contaning 32P labeled phages?
The supernantant containing coats had no radioactivity while the pellet with infected bacturium had significant ammounts of radioactivity along with radioactivity in progeny phages proving DNA is the genetic material.
