I wonder if each cell possess only one strand of DNA which according to my book is more than "7 feet" long(if uncoiled), then why does human has 46 chromosomes which are actually coiled chromatin (DNA wrapped around histone proteins)? Does DNA break into parts and form 46 chromosomes during cell division (I am just guessing I am not sure about it)?

  • $\begingroup$ I think you are misusing the term "strand". "filament" instead? Or perhaps, you have the "chromatin string" in mind? Can you clarify it in your question, please? $\endgroup$ – alec_djinn Sep 26 '16 at 19:15
  • $\begingroup$ I am referring to DNA molecule (entire chain of polypnucleotide) or you can say how many chains of deoxy ribonucleic acid are found in each cell? $\endgroup$ – AksaK Sep 26 '16 at 19:24
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    $\begingroup$ Referring to this picture en.wikipedia.org/wiki/DNA#/media/File:Lambda_repressor_1LMB.png the DNA molecule is composed of the red strand and the blue strand. A chromosome is composed of one DNA molecule or two DNA strands. $\endgroup$ – alec_djinn Sep 26 '16 at 21:07
  • $\begingroup$ So that means if one chromosome is composed of one DNA molecule and there are 46 chromosomes therefore 46 DNA molecules are present in each DNA. Right? $\endgroup$ – AksaK Sep 27 '16 at 5:15
  • $\begingroup$ Yes, in each diploid human cell there are 46 molecules of DNA $\endgroup$ – alec_djinn Sep 27 '16 at 6:28

Human cells contain 23 pairs of chromosomes (46 chromosomes in total). Each chromosome is formed by 2 strands of DNA tied by hydrogen-bonds to each other making the classic DNA double helix (double-stranded DNA). So, in total there are 46*2=92 strands of DNA in each diploid human cell! Gametes contain half of the chromosomes, so half of the strands as well.

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  • $\begingroup$ Ah yeah, if you consider each plus and minus as a strand then the number doubles, good point! $\endgroup$ – Joe Healey Sep 27 '16 at 9:20
  • $\begingroup$ @JoeHealey — although the OP probably was misusing strand, and his major concern was how many copies of each dsDNA chromosome there were. $\endgroup$ – David Sep 3 '17 at 16:30

Each chromosome is present twice in every cell (excluding sperm and eggs, where only one of each is acquired in meiosis). So yes, that is 46 'strands' of DNA wrapped around histones as you said.

During mitosis each chromatid is replicated, and then in anaphase the sister chromatids are separated in to each daughter cell.

Any basic high school/university text book will have a good diagram of this.

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  • $\begingroup$ So you mean human cell have 46 DNA strands which are coiled to form chromosomes? $\endgroup$ – AksaK Sep 26 '16 at 16:19
  • $\begingroup$ Yes exactly (with the exception of the gametes as I mentioned, which are haploid rather than diploid). $\endgroup$ – Joe Healey Sep 26 '16 at 16:26

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