Question

The physical dimensions for DNA is described by
I. The nitrogen bases are 0.34 nm from one another, moving $5^{\prime }$ to $3^{\prime }$.
II. The diameter of the strand is 20 nm.
III. The two strands run antiparallel.

• A. I only
• B. II only
• C. III only
• D. I and II
• E. I and III

Answer 1

Answer: (E)

I and III

The two antiparallel polynucleotides chains, of DNA are coiled around same axis, while bases are present at right angle to the axis. Since one complete turn of the double helix is 3.4 nm long and each of which has 10 base pairs, the distance between two consecutive base pairs 0.34 nm. Same orientation of all phosphodiester linkages along the chain imparts each linear nucleic acid strand a specific polarity and distinct 5’ and 3’ ends. The two DNA strands are antiparallel, and have opposite polarity. This means that 5’ phosphate of one strand faces 3’hydroxyl group of other strand and that the 5’ phosphate groups of two strands are present in opposite position. Diameter of strand is 20 angstrom.
So, the correct answer is option E.