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I have went through Lehinger ( biochemistry book) and cooper ( cell Biology) but i didn't find my answer. plese help me

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closed as unclear what you're asking by David, John, another 'Homo sapien', James, The Last Word Aug 21 '18 at 16:56

Please clarify your specific problem or add additional details to highlight exactly what you need. As it's currently written, it’s hard to tell exactly what you're asking. See the How to Ask page for help clarifying this question. If this question can be reworded to fit the rules in the help center, please edit the question.

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    $\begingroup$ Your question isn't very clear; could you please elaborate? $\endgroup$ – Astrolamb Aug 6 '18 at 19:37
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The (very) basic answer to your question about in-vitro vs. in-vivo primer usage is:

  1. In-vivo - Although either (DNA or RNA primers) can be used for in-vivo primer extension biochemistry, DNA primers are not available (not made) in living cells. Therefore all natural in-vivo primer chemistries utilize RNA primers.

  2. In-vitro - DNA primers are easily synthesized, inexpensive, functional, and substantially more stable (less likely to be degraded). DNA primers are therefore primarily used for most in-vitro purposes (i.e. PCR and other in-vitro primer extension applications).

Beyond that, all other reasons (complex evolutionary reasons vs. human choices in-vitro); involving subtle differences between RNA and DNA chemistry, structure, and function, similarly can play a role. The links below may be helpful to address some of these differences.

https://en.wikibooks.org/wiki/Structural_Biochemistry/Nucleic_Acid/Difference_between_DNA_and_RNA

https://en.wikipedia.org/wiki/Primer_(molecular_biology)

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Generally speaking, initiation of DNA replication in vivo at a defined origin of replication, requires an enzyme with DNA primase activity. DNA primase is a DNA-dependent RNA polymerase that generates short RNA primers that are used to prime DNA synthesis by the DNA polymerase holoenzyme at a so-called replication fork.

The classical polymerase chain reaction (PCR), on the other hand, is a way for humans to use an in vitro method to amplify relatively large amounts of double-stranded DNA from a specific fragment, using a DNA template target and two artificial, single-stranded DNA oligonucleotide primers (along with dNTP substrates, buffer, Mg++, a thermostable DNA polymerase, and a programmable thermocycler).

So the goals, or outcomes, of the two processes that you are trying to compare seem vastly different to me. Replicating a chromosome is presumably to keep an organism alive, and reproducing, and dividing, to produce progeny. Amplifying a desired DNA fragment is a tool to allow some subsequent process or assay to occur.

Your question does not have a clear sense (to me). There is no stated requirement for biochemical reactions created by human scientists to in any way be limited, or constrained by reactions that occur inside a living cell.

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