01/23 DNA as genetic material Flashcards
what is a negative control
in an experiment it is something that has no effect and acts as a consistent baseline
what is a positive contorl
in an experiment, it is something that consistently shows an effect
what is the purpose of controls
when using experimental groups, we can see/mimic the effect/no effect of the controls and they must be done everytime to serve as a baseline
what were the controls in the Griffin Experiment
The rough strain was the negative control
- consistently had no effect
- no isolated bacteria were isolated from the mouse
The living smooth strain was the positive control
- consistently had an effect (killing the mouse)
- isolated smooth bacteria from the dead mouse
what were the treatment groups in the griffin experiment
the heat killed smooth strain and the heat killed smooth strain + living R strain
what treatment group emulated the positive control in the griffin experiment
the heat killed smooth strain + the living R strain killed the mouse and left isolated smooth bacteria
what treatment group emulated the negative control in the griffin experiment
the heat killed smooth strain had no effect and no bacteria were found in the mouse
how was the R strain and heat-killed S strain mixture able to kill the mouse
the R strain was somehow transformed by the hereditary material in the S strain
what was the basis of the Avery, MacLeod, and McCarty Experiments
they wanted to know what was the transforming material (DNA, RNA, Protein, Carb, or Lipids)
describe how the four criteria of genetic material were utilized in the transformation of the rough strains to smooth strains in griffins experiments
the bacterial cells acquired the “information” to make the capsule
“variation” existed in the ability to make a capsule
the information required to create a capsule is “replicated” and “transmitted” from mother and daughter cells
In the Avery et al experiments, they used smooth cell extracts of DNA RNA or protein and introduced them to the rough strain. Were these extracts pure? Why or why not
No, these were not pure. They used rough cuts of enriched extracts for the samples, there was still some remnants of the other components in it
in the Avery et al experiments, which smooth extract was able to transform the rough strain into the smooth strain
the enriched DNA extract
what is in the extracts added to the R rough cells
DNA RNA and protein
why do we add an antibody to the R+S extract mixture?
the antibody attaches to the rough cells that did NOT transform into smooth cells. This allows them to be centrifuged into a pellet and the subsequent supernatant liquid can be plated to grow smooth cells
why do we add an enzyme to the extract mixture in the Avery experiment
the enzyme will destroy a targetted molecule (DNAase-> DNA, RNAase–> RNA, protease–> protein)
the addition of which enzyme caused the treatment to emulate the negative control
DNAase, this revealed that DNA is the genetic material as the rough cells were not able to transform or grow smooth strains without the DNA
Treatment with DNAase caused the destruction of genetic material which led to the inability to transform the rough strain into the smooth strain. When the sample was plated, the results looked like the negative control.
True or False
True
, when we treated with DNAase, the enzyme broke down the DNA molecules which contained the information necessary for the rough cells to undergo transform into the smooth cells. When we centrifuge the tubes, all of the rough cells will fall into the pellet and there would be no smooth cells in the supernatant to grow the resulting bacteria
What is a bacteriophage comprised of
it is comprised of DNA and protein
how does a bacteriophage function
it binds to specific binding proteins and injects its genetic material into the cell.
the genetic material hijacks the cells machinery and directs it to replicate the viral genome and proteins, resulting in the replication of more bacteriophages within the cell
the bacterium will be lysed (broken open) to release the newly formed phage progeny
what was the hypothesis to the Hershey and Chase experiment
only the genetic material is injected and isotope labeling will reveal if it is DNA or protein
What is a radioactive isotope? why is it used?
a radioactive isotope are atoms with unnatural amounts of neutrons that will decay and give off detectable alpha and beta particles
in the Hershey and Chase experiment, why did they use P32 for DNA and S35 for protein ?
Phosphate is an essential part of DNA as it is the essential component of the phosphate backbone
Sulfer is most commonly found in protein and not DNA
why would P32 not show up in the protein?
phosphorus is not native in protein but can be added later
describe the first step in the Hershey experiment
radioactive P35 and S32 were placed into SEPARATE bacteria samples with bacteriophage, through replication the radioactive isotopes were incorporated into the proteins or DNA that make up the bacteriophage
what was the second step of the Hershey experiment
the bacteriophage were removed from the samples and introduced into NEW Ecoli bacteria and allowed to incubate for a short period of time
What is the attachement phase in the Hershey experiment
it is the short period of incubation where the radioactive phage’s were allowed to bind an inject their genetic material into the cells
After letting the bactereophage inject their genetic material, why did they blend the samples? (hershey exp)
they used to blender to sheer off the bacteriophage from the cells
this allowed the “ghost” phage’s to go into the supernatant liquid and the cells were centrifuged into a pellet
If we didn’t use the blender for the Hershey experiment, what would have happened to the radioactive results? where would P32 and S35 be?
if you do not use the blender, the phages will not be sheered off and all of the radioactivity will be in the pellet and NOT be detected in the supernatant
this means the graph would be very low
what does it mean when we call a bacterophage a “ghost”
it means it has delivered its genetic material into the cell
When analyzing the results of the hershey experiment, what do we analyze? the pellet or the supernatant?
we are analyzing the supernatant with a scintillation counter which allows us to quantitatively count the radioactivity NOT IN THE CELL
this is what was NOT injected into the cell
if DNA is the genetic material, what results do we expect from the Hershey experiment
if DNA is the genetic material, we expect the majority of the P35 to be in the cell (low concentration in the supernatant)
since protein is NOT the genetic material, where would be expect the S35 to be in the Hershey experiment?
we would expect it to be in the supernatant liquid.
it was not injected into the cell, therefore it will remain on the outside and not be in the bacterial pellet
what did the graph results from the Hershey experiment show?
it showed the % of radioactivity in the supernatant liquid.
If the percentage was low, that means the remaining amount of radioactivity is in the pellet cell (was injected)
why did the P32 sample not show 0% radioactivity for the supernatant
1) incomplete infection,
- not all of the bacteriophages fully delivered their P32, some remains in the supernatant
2.) too light of centrifuging
- if they vortexed it too hard, the cells would lyse and release everything but this means that not all of the phages may have been removed
Why does the S35 test not show 100% concentration in the supernatant
the blender might not have been 100% effective, some of the bacteriophages with S35 may be attached and are in the pellet
what was the overall result of the hershey experiment
since most of the S35 was in the supernatant and the majority of the P32 was in the pellet, this concludes that the P32 labeled DNA entered the bacteria and is the genetic material
what happened when the bacteria were lysed to release the phage progeny from the prior labeled bactereopage?
the cells that were originally exposed to the P32 labeled phage released a new progeny of phage that were also radioactive
the cells that were originally exposed to the S35 labeled phage released a new progeny of phage that were not radioactive since none of the radioactive labeled proteins entered the cell
If it turned out that protein was the genetic material, then which of the following would be seen during Hershey and Chase’s experiment?
A. Radioactive sulfur would be seen primarily in the pellet and not in the supernatant
B. Radioactive phosphorous would be seen primarily in the supernatant
C. Radioactive sulfur would be seen in the bacteriophage that lyse out of the infected bacteria
A, B, C
