NEET BIOLOGY

Detailed explanation-1: -In an idealized DNA molecule the twist is 36 degrees, meaning that if you rotate one base pair by 36 degrees and move it up the helix by 0.34 nm, you will occupy the position of the next base pair. Thus, the distance or rise along the axis of the double helix is 0.34 nm between 2 consecutive base pairs.

Detailed explanation-2: -The distance between two consecutive base pairs is about 0.34nm, that is one turn consisting of 34 Å. One complete turn takes about 360° consisting of 10 bp hence the distance between two successive base pairs is 36°. So, the deflection of pitch angle is 36° therefore the correct answer is option C.

Detailed explanation-3: -The diameter of the B-DNA is 20 Angstroms, and the distance between base pairs is 3.4 Angstroms or 0.34 nm. The base pairing of opposite strands is stereochemically selective, adenine always pairing with thymine, and guanine with cytosine.

Detailed explanation-4: -The crystallographic studies shows that the pitch angle is approximately 38 deg., less than the corresponding zero-twist angle of 41.8 deg., which is consistent with the suggested principle for transcription.

Detailed explanation-5: -The bend angle at the kink angle was close to 120°. A few kinks with intact base pairs were also observed. The simulations were unable, however, to reproduce the known structure of the double helix accurately: DNA helical repeat in the simulated structure was equal to 12 bp/turn rather than 10.5 bp/turn (9).