Biology Forum › Molecular Biology › Evidence of Hereditary material
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- April 21, 2005 at 1:57 pm #751
Mstar888ParticipantIs anyone familiar with the Frederick Griffith experiment and can help me with the questions?
- April 21, 2005 at 3:41 pm #21574Mstar888Participant
This experiment had to do with the mice and 2 kinds of bacteria, unencapsulated and capsulated. I need help with some of the questions, so if you could please reply, that would be great. An example would be:
Encapsulated (S-form) pneumococcal cells were heated, killed and then injected into mouse C. Mouse C continued to live and the autopsy revealed that no living S cells were found in the animal’s tissue.
Predict what would have happened to the mouse if the unencapsulated (R-form) cells had been heated and then injected. What would this step have represented in the experimental protocol?
If the mouse had been injected with heated unencapsulated (R-form) cells, the mouse could either die because by heating the cells, it could activate the harmful bacteria within the cell. Another possibility could be that the cell remains harmless regardless of heat. This step would have represented
This is what I wrote and where I left off. There are still more questions I need help on, so please reply. Thanks - April 21, 2005 at 6:54 pm #21579zami’87.Participant
Hi there! I only know that R-mouse lives.
S-mouse dies.S heated-mouse lives. S heated and then+ R mouse dies.It is important not to destroy genetic material by heating I think. - April 21, 2005 at 8:10 pm #21582canalonParticipant
Zami’87 is correct for the description of the results:
quote :R-mouse lives.
S-mouse dies.S heated-mouse lives. S heated and then+ R mouse diesThis experience is famous because it was the first to prove spontaneous transformation in bacteria.
The explanation is S-bacteria have in their genome something (chromosomal genes,plasmid), that allow them to kill mice, and is not present in R-bacteria. When R and dead S-bacteria are mixed together the R-bacteria are able to integrate in their genome this something that makes them pathogenic. This acquisition of external genetic material is called transformation. It is possible because heating kills the bacteria but do onot degrade their DNA.
To answer your specific question, you would not expect the mouse to die either with dead R-bacteria. This is the control that mice death is due to bacterial pathogenicity and is not a side effect of the bacterial heating and killing procedure.
- April 21, 2005 at 9:40 pm #21587zami’87.Participant
Hey can you explain me how the transformation occurs?That’s why I couldn,t totally understand the process. 😕
- April 22, 2005 at 3:49 pm #21606canalonParticipantquote zami’87.:Hey can you explain me how the transformation occurs?That’s why I couldn,t totally understand the process. 😕
A good introduction, although very short but with picture could be found here:
http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Search&db=books&doptcmdl=
GenBookHL&term=transformation+bacteria+AND+iga%5Bbook%5D+AND+100385%5Buid
%5D&rid=iga.section.1343[Line break inserted by Kyle]
More detailed explanations and figure can be found here for free:
]http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?CMD=search&DB=booksUse “transformation and bacteria” as key words
HTH
Patrick
- April 22, 2005 at 4:41 pm #21607zami’87.Participant
Thanks! Very clear! 😀
- April 22, 2005 at 8:47 pm #21616Mstar888Participant
Thanks for all your help, but what does it represent? Like does it show that regardless of heat, no mice can be killed by the R cell? Also, what is the difference between a prediction and a hypothesis? And, this is long, but I really don’t know how to answer it…
Predict the experimental results of the following protocols. Support your prediction with a hypothesis.
-Polysaccharide-digesting enzymes are used to digest the encapsulated polysaccharide coat of the heated S form of the bacteria. The treated bacteria are then placed with unencapsulated pneumonia cells, which are then injected into a mouse.
This is what I wrote: The mice would die because it’s the carbohydrate bing treated which isn’t the transforming principle according to Avery’s hypothesis. (Is this my prediction, if so, can someone help me with my hypothesis? Thanks)
-Heated encapsulated bacteria are treated with DNAase. The treated bacteria are then mixed with unencapsulated pneumonia cells, which are injected into a mouse.
-All proteins are extracted from the heated encapsulated bacteria. The bacteria are then mixed with unencapsulated pneumonia cells, which are injected into a mouse.
Based on the info provided (above, I’m guessing), suggest improvements to the experimental protocols.
Thanks again for the help. - April 22, 2005 at 9:44 pm #21618canalonParticipantquote Mstar888:Thanks for all your help, but what does it represent? Like does it show that regardless of heat, no mice can be killed by the R cell? Also, what is the difference between a prediction and a hypothesis? And, this is long, but I really don’t know how to answer it…
Predict the experimental results of the following protocols. Support your prediction with a hypothesis.
-Polysaccharide-digesting enzymes are used to digest the encapsulated polysaccharide coat of the heated S form of the bacteria. The treated bacteria are then placed with unencapsulated pneumonia cells, which are then injected into a mouse.
This is what I wrote: The mice would die because it’s the carbohydrate bing treated which isn’t the transforming principle according to Avery’s hypothesis. (Is this my prediction, if so, can someone help me with my hypothesis? Thanks)
-Heated encapsulated bacteria are treated with DNAase. The treated bacteria are then mixed with unencapsulated pneumonia cells, which are injected into a mouse.
-All proteins are extracted from the heated encapsulated bacteria. The bacteria are then mixed with unencapsulated pneumonia cells, which are injected into a mouse.
Based on the info provided (above, I’m guessing), suggest improvements to the experimental protocols.
Thanks again for the help.The result of the experience is that R-bacteria are normally innocuous for the mice, only the S-bacteria kill them. But if R-bacteria are mixed with dead S-bacteria, they can also kill. Conclusion: something in the dead S-cells transforms the R-cells in “killer bacteria”
You are now asked to make an hypothsesis on the nature of the transforming agent: it could be DNA, a protein or fragment of the broken polysaccharide capsule. You make 3 experiments that allow you to test for the effect of each of those different molecules.
From your biology knowledge you could supose that DNA could explain the transformation. That is making an hypothese on your experiment. The predictions that you could the make are: If I remove proteins or digest the polysaccharide coat DNA could still transform R-cells, hence the mice will die. But when I destroy DNA with the DNAse, the transforming agent is not present any more, hence the mouse will survive.
I do not really see which experimental protocol could be improved?
HTH anyway
Patrick
- April 23, 2005 at 2:43 pm #21628Mstar888Participantquote Canalon:quote Mstar888:Predict the experimental results of the following protocols. Support your prediction with a hypothesis.
-Polysaccharide-digesting enzymes are used to digest the encapsulated polysaccharide coat of the heated S form of the bacteria. The treated bacteria are then placed with unencapsulated pneumonia cells, which are then injected into a mouse.
-Heated encapsulated bacteria are treated with DNAase. The treated bacteria are then mixed with unencapsulated pneumonia cells, which are injected into a mouse.
-All proteins are extracted from the heated encapsulated bacteria. The bacteria are then mixed with unencapsulated pneumonia cells, which are injected into a mouse.
Based on the info provided (above, I’m guessing), suggest improvements to the experimental protocols.
Thanks again for the help.I do not really see which experimental protocol could be improved?
I agree, but it does say suggest improvememts. Oh well, thanks for all your help.
- April 24, 2005 at 9:04 pm #21646canalonParticipantquote Mstar888:I agree, but it does say suggest improvememts. Oh well, thanks for all your help.
Yep, but I am replying from my workplace, and do not have that much time to think of an improved experimental design. Surely you could do that by yourself, no?
Good Luck…
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