How does autoradiography detect replication?

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Discussion Overview

The discussion centers on the mechanism of autoradiography in detecting DNA replication, particularly in the context of using radioactive nucleotides. Participants explore the methodology and clarify misconceptions related to the process.

Discussion Character

  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant describes autoradiography as producing dark bands on film to indicate the location of radioactive substances, specifically in the context of Southern blotting.
  • Another participant suggests that incorporating radioactive DNA nucleotides into cells during replication allows for the detection of radioactivity in DNA, indicating which cells were replicating during that time.
  • A later reply corrects the initial description of autoradiography, emphasizing that the radiation from radionuclides, such as 32P, is what blackens photographic plates, and that 3H thymidine is specifically used to reveal and localize DNA replication.

Areas of Agreement / Disagreement

Participants express differing views on the specifics of how autoradiography works, particularly regarding the role of radioactive nucleotides and the process of detecting replication. The discussion remains unresolved with multiple competing explanations presented.

Contextual Notes

There are limitations in the initial understanding of autoradiography as it relates to Southern blotting and the specific use of radionuclides for detecting replication. The discussion highlights the need for clarity on the mechanisms involved and the types of radioactive substances used.

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Homework Statement
Which among the following is the best method to determine if the nuclear DNA is being replicated?
Relevant Equations
a. Phase-contrast microscopy
b. Thin layer chromatography
c. Gel electrophoresis
d. Autoradiography
Ans: d.
I'm aware that in autoradiography a film is produced which display the exact location of radioactive substances (for e.g. labeled probe in southern blotting ) as dark bands by passing X-ray through the sample (southern blot).

But I do not understand, how does autoradiography detects replication?
 
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The classic method would be to add radioactive DNA nucleotides to the cells for some amount of time, then wash them away. Cells that were undergoing DNA replication during the time period where the radioactive nucleotides were present will have radioactivity incorporated into their DNA while cells not undergoing DNA replication would not have radioactivity in their DNA.
 
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Thank you.
 
Mistaken to say 'as dark bands by passing X-ray through the sample (southern blot)'. It is the radiation coming from radionuclides (e.g. 32P incorporated into probe polynucleotides not into any replicating DNA in the case of Southern blots) that blacken the photographic plates made to lie on top. To reveal and localise cell, tissue, chromosome replication 3H thymidine is used. exercise suggests you could probably benefit by checking back how these things really work and correcting/refining your understanding for which there will subsequently be numerous applications.
 
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