Quantity of genomic dna in human cells - (Oct/18/2005 )

Hmm, this might be a fairly elementary question, but I'm curious if all human cells regardless of nuclei/cell size contain the same ug quantity of genomic DNA?

I guess I was always under the belief that smaller nuclei equated to fewer copies and subsequently less DNA, but a friend has tried to convince me otherwise. Can someone explain?

Unless it is a cell that underwent meiosis, or is undergoing mitosis, or is one of those special cells, eg, erythrocytes, thromboblastic cells, most cells in the human body have the same amount of DNA (i.e., the genomic DNA content / cell is the same). We are not counting mitochondrial DNA.

Smaller nuclei is usually a hallmark of differentiated cells with compact chromosomal structure, so DNA is more tightly bound than before. Usually large nuclei is to accomodate "looser" DNA so most areas are accessible to DNA/RNA polymerases, for higher rates of transcription or duplication (in highly proliferative cells).

Hope this helps. And if I am wrong in this, anyone, please correct me.

Thanks.

Oh, lets not forget to mention the loss of relatively small amounts of DNA due to recombinase activity in antibody producing cells.

If the human cell contains a nucleus, there should be the same number of chromosomes therefore the same amount of DNA.

The only human cells I know about that have greater amounts of DNA than normal are cancer cells that are > diploid (i.e. more than the usual pairs of chromosomes).

The only human cells with less DNA are enucleated cells like platelets or diseased cells where the chromosome has been damaged.

Size of the nucleus is dependent of the transcription activity in the nucleus...

I believe that a normal (diploid) mammalian nucleated cell contains around 6pg of DNA