Question

The number of base pairs/turn of two different DNA is 10 and 12 respectively. The pitch of the helix is 3.6nm and 2.8nm respectively. what should be vertical rise/base-pair of each DNA?

Answer 1

Ans. Pitch is the vertical distance taken to complete a turn i.e. 360⁰.

# The vertical rise/ spacing or rise per bp is the distance between adjacent base pairs.

# While taking a complete turn (the distance of a pitch), the sum of vertical rise between specified number of bases per turn must be equal to the pitch.

# DNA 1: Given-

Pitch = 3.6 nm. That is, a complete turn of helix spans a vertical distance of 3.6 nm between the start and end point of the complete turn.

Base pairs per turn = 10. That is, there are 10 bp in a complete turn of the helix.

Now,

            Rise per bp = Pitch / No. of bp per turn = 3.6 nm / 10 = 0.36 nm

# DNA 2: Given- pitch = 2.8 nm                ; base pairs/ turn = 12

Now,

            Rise per bp = Pitch / No. of bp per turn = 2.8 nm / 12 = 0.23 nm