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Name: Anonymous
Status: Student
Age: N/A
Location: N/A
Country: N/A
Date: July 2003


Question:
If you spread out a strand of DNA, how long would it be?



Replies:
As described in the "Chromosomal DNA and Its Packaging" section of the on-line textbook, Molecular Biology of the Cell @ NCBI

( http://www.ncbi.nlm.nih.gov/books/bv.fcgi?tool=bookshelf&call=bv.View..Show Section &searchterm=human&rid=cell.section.1607#1608 ):

"Every million "letters" (nucleotides) take up a linear distance of only 3.4 × 10E5 nm (0.034 cm)....The [haploid] human genome...contains about 3 x 10E9 nucleotide pairs, organized as 24 chromosomes (22 different autosomes and 2 different sex chromosomes), and thus consists of 24 different DNA molecules - each containing from 50 × 10E6 to 250 x 10E6 nucleotide pairs of DNA. DNA molecules of this size are 1.7 to 8.5 cm long when uncoiled, and even the slightest mechanical force will break them once the chromosomal proteins have been removed."

Thus, using the conversion factor of 0.034 cm per million (10E6) nucleotides, the uncoiled length of the total human genome would be approximately 102 cm, or 40 inches. This is pretty impressive if you consider that "A typical [dipoid] human cell thus contains ...about 6 × 10E9 nucleotide pairs of DNA....By comparison, 6 x 10E9 letters..would occupy more than a million pages [of a typical book].", as described in the Molecular Biology of the Cell at NCBI. The "Chromosomal DNA and Its Packaging" section also explains the nature of haploid vs. diploid chromosomal organization, if you need some clarification

( http://www.ncbi.nlm.nih.gov/books/bv.fcgi?tool=bookshelf&call=bv.View..Show Section &searchterm=human&rid=cell.section.1607#1608 ).

Thanks for the great question,

Jeff Buzby, Ph.D.
CHOC Research Institute



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