Thread: Where is DNA made?

Hi there folks,

First time positing. Hope to be around for a while!

I've checked all over the net and in my textbook, but I can't quite understand. I understand DNA is kept in the nucleus in most cells, but where is it made? Since DNA is not always kept in the nucleus, it seems right that it is not always made in the nucleus. Can anyone help?

Thanks!
GDT

Rather than asking where DNA is "made" it would better to ask where is it replicated since the cell does not make DNA from scratch. Rather, it synthesises new DNA strands using pre-existing strands as a template.

The short answer would be: In eukaryotic cells (those with a nucleus) DNA replication takes place within the nucleus.

The longer answer would require listing the exceptions to the above rule. DNA occurring outside of the nucleus is only found in a few specialised circumstances that I can think of:

1) So-called cytoplasmic-DNA. This would be the small DNAs that are found in organelles such as plastids and mitochondria.
2) In some anucleate cells. That is, cells that have no nucleus.
3) During the later stages of cell division the nucleus is broken down, so that'd be a case of DNA not in the nucleus also.
4) The DNA of DNA viruses and other weird things that can be trafficked to and from the nucleus and cytoplasm.

Thank you very much Zwirko, I understand.

Could you clear something else up please? I understand that the DNA strands unwind for replication. You then have half of the "ladder", so to speak. But then where do the other nitrogen bases come from to replicate the DNA? Are they floating around the nucleus waiting to be added?

Thanks again,
GDT

That's correct, the raw materials for DNA synthesis can be found throughout the cell including the nucleus. They are also used by, and created by, many metabolic pathways, so you can basically find them everywhere in the cell.

They're found bound to phosphate in the cytoplasm, ATP and GTP also have important functions in the cell besides being used as building blocks of DNA (as Zwirko said)

The nucleotides themselves are synthesized through fairly complex pathways, to make it simple your body makes them out of sugar and amino acids.

Edit: I had to take an entire biochem class on nucleic acid chemistry, it still gives me nightmares.

If I can extrapolate (perhaps incorrectly) then my original concept of DNA not being "made" has brought us to the fact that DNA is always replicated.

So somewhere down the line the first DNA strand had to originate from somewhere. Does this then bring us to a debate about soupy ponds of acids in the precambrian?

GDT