In: Chemistry
Wrapping double-helical DNA around histone octamers condenses the DNA by a factor of 7. Higher order chromatin structures condense this DNA even further. During metaphase, the DNA is compacted by a factor of 1 × 104. How many centimeters would the naked double-helical DNA from a 50 Mb chromosome stretch? (Note: Assume the DNA remains in the B-form, which has a rise per base pair of 0.34 nm.)
A. 0.017cm
B. 0.17 cm
C. 0.68 cm
D. 1.7 cm
E. 6.8 cm
Correct option A: 0.017 cm
Length of fully extended (naked) 50 Mb chromosome stretch = 50 x106 bases x 0.34 nm
= 17.0 x 106 nm [1nm = 10-9 m]
= 1.7 x 10-2 m = 0.017 cm [1 m = 100 cm]
Rise per base pair means the vertical distance (elevation) between two adjacent bases as they rise along the helix. It gives the length of the naked DNA itself.