How does autoradiography detect replication?

[TytoAlba95]

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?

 

[Ygggdrasil]

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.

 

[TytoAlba95]

Thank you.

 

[epenguin]

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. Excercise 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.