Why doesn't PCR shorten DNA by-products?

[K Niner]

Note: Question at bottom in blue.

In DNA replication the DNA polymerase reads the template strand 3'->5' (or synthesizes the new DNA strand 5'->3', whichever you prefer) starting after the primer. But at the very end of the lagging strand the final okazaki fragment either 1) can't be primed (due to the primer sequence not being the absolute last DNA bases of the end of the strand) or 2) the terminal primer can't be converted into DNA (b/c the typical DNA polymerases add DNA after the primer, and the DNA polymerases that replace the primer with DNA nucleotides require a 3' strand extending beyond the primer, which obviously is not present).

To remedy this, Eukaryotes have telomeres, telomerase, etc. to prevent the shortening of the DNA strands. Prokaryotes have ciruclar DNA that doesn't have this problem.

All this to say, why in PCR are the target strands of successive DNA replications not shortened? What am I missing in the PCR mechanism?

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[Kahr]

PCR doesn't have a leading and lagging strand, nor does it use RNA primers, okazaki fragments, etc. It only replicates continuously (like the leading strand), and uses DNA primers. I can only assume this resolves the issues mentioned in your paragraph.

However, I don't see anything about this in Campbell's, so it is likely beyond the scope of the DAT. Also, the DAT will typically ask you more something along the lines of: what is the purpose of PCR? what does PCR do?

 

[glo1984]

As Kahr has stated, PCR only serves to exponentially amplify SPECIFIC regions of DNA; ultimately creating a large amount of DNA from a very small amount. Thus producing significant amounts of pure DNA for many analytical techniques. Sequencing DNA is particularly trivial at best due to the ravishing potential by contaminants.

I highly recommend understanding the many analytical techniques and the different PCR reactions as this will aid in your understanding of DNA in general. But Kahr made a very good point, the DAT would only ask what PCR is and why it may be useful.