Molecular 0, DNA molecule of heredity. Flashcards
Describe and explain the Griffith experiment and explain what it proved?
v=· Griffith attempted to find vaccine for pneumonia using this experiment
Griffith experimented with two strains of streptococcus pneumonia
VIRULENT S-STRAIN = Virulent s-strain has a smooth coating protection which protects the bacteria from the immune system of the recipient allowing bacteria to attack cells causing disease
A-VIRULENT S-STRAIN= j Has rough coating (so no coating) therefore no protection, so it’s killed by immune system therefore its unable to infect the recipient
How does the griffith experiment work.
1)S-strain
Mouse LIVED
As expected, mouse lived as live R-strain are killed by immune system
2) R-strain
Mouse DIES
Expected results mouse dies as it develops pneumonia
3) Heat- killed R-strain
Mouse LIVED
Heat kills live bacteria inside coating therefore bacteria cannot infect host
4)Heat-killed R-strain + S-strain
Mouse DIES
Unexpected results as the S-train virulent bacteria are dead and r-strain should not be infecting.
However, mouse is dead showing R-strain acquired some deadly component from S-virulent strain and transformed into r-strain infecting and killing host
What did the AVERY Macleod Mccharty experiment prove?
The Avery–MacLeod–McCarty experiment was an experimental demonstration that demonstrated DNA is the substance that causes bacterial transformation, in an era when it had been widely believed that it was proteins that served the function of carrying genetic information
Describe and explain Avery- Macleod - Mcarty experiment.
· The AMM experiment expanded on Griffiths experiment identifying NUCLEIC ACIDS as molecule of inheritance
1. In the AMM experiment scientists ran for experiments based on Griffith experiment of R-strain + S-Strain Heat killed bacteria given to mice
2. In each experiment a key component: PROTEIN/DNA/RNA was removed
if the mouse still died when one of the components was taken away it showed that the BIOMOLECULE was not the Transforming principle
Results;
1) Control Group = Heat killed R strain + S-strain, mouse dies
2) Protein removed using protease= mouse still dies, there protein are not the heredity material
3) Heat killed R-strain + S-strain BUT RNA is removed = Mouse still dies, Rna is not the molecule of heredity
4) Heat killed R- strain + S-strain but DNA is removed = Mouse LIVES, which means DNA is molecule of heredity as it was removed the transformational principle did not take place in-between the bacteria.
How do BACTERIOPHAGE work?
BACTERIOPHAGE: H-C used bacteriophages as they have useful properties such as QUICK REPRODUCTION and contain ONLY proteins and nucleic acids.
Bacteriophage naturally reproduce by attaching to the outer membrane of host-cell and then inject their genetic material into the host HIJACKING the internal working of the cell. DNA from the bacteriophage causes the host cells to start producing identical copies of the original BACTERIOPHAGE inside the cell and then explodes and releases all the bacteriophages which infect even more cells.
Describe and explain the Hershey and chase experiment.
Experiment A: bacteriophages A’s protein coat was radioactively labelled,
* Experiment B: Bacteriophages B DNA was radioactively labelled
* These were each used to infect cells in experiments A and B.
* Centrifugation of both infected cells in experiment A and B, to get pellet which would contain bacterial cell content (nucleus and etc.)
* In experiment A where protein were labelled: the radioactivity was NOT detected in the pellet, but only in the general liquid which indicated that protein were not the material for gene heredity so therefore they are not in the pellet as they have not been absorbed by the nucleus inside the cell. Hence Radioactivity was only detected in SUPERNATANT LIQUID but not in the pellet where the nucleus is so therefore where hereditary material should have been
* In experiment B where DNA was labelled: Radioactivity detected In the pellet ( as this is where the inside of the bacterial cells, infected by the BACTERIOPHAGES is)
* This shows DNA is molecule of heredity, as it was absorbed by bacteria through BACTERIOPHAGES and it infected other cells as bacteriophages are viral.
Hershey and Chase experiment.
HC used bacteriophages to show that DNA is the molecule of heredity.
Bacteriophage A= Protein are radioactively labelled in this using SULPHUR 35 isotope which is NOT found in DNA so DNA is not labelled, because bear in mind bacteriophage contain only protein and nucleic acid.
Bacteriophage B= DNA is radioactively labelled, using PHOPHORUS 32
In both experiment bacteriophages are mixed with bacteria they can replicate inside bacteria.
Sample is the centrifugated and if supernatant is radioactively labelled it indicated the molecule of heredity.
Exp A= Protein labelled, no radioactivity in supernatant, only in pellet which means protein did not enter bacterial cell so they are not molecule of heredity
Exp B= Supernatant shows a lot of radioactivity, indicating DNA did enter bacteria and causes replication of the bacteriophage.
