Question

The deflection of pitch angle between two successive steps (rungs) of DNA is
a) 72°
b) 54°
c) 36°
d) 18°

Answer 1

Hint: Deoxyribonucleic Acid (DNA) carries the genetic information for development growth and function for most of the living organisms and also present in viruses. It is a double helix chain that means two polynucleotide coils around each other. This coiling forms a shape called a Double Helix.

Complete answer:
DNA is a double helix structure that is made of polynucleotide. Each polynucleotide in turn consists of many nucleotides consisting of phosphate groups, 5-carbon sugar and a nitrogenous base. Nitrogenous base and 5–carbon sugar together constitute nucleosides.
Nitrogenous base consists of adenine, cytosine, guanine, and thymine. In case of RNA thymine is replaced by uracil. Adenine pairs with thymine with the help of 2 hydrogen bonds and cytosine pairs with guanine with the help of 3 hydrogen bonds.
5-carbon Sugar is deoxy as in DNA, and ribose in RNA. Which gives the name of a genetic molecule, that is deoxyribonuclease and ribonuclease. These sugars combine with Phosphate and form a sugar-phosphate backbone. These bonds are covalent in nature hence stronger than hydrogen bonds also they give rigidity to the structure.
The most common structure of DNA is double helix coiled structure which helps them to fit in small places as in cells. Each turn consists of 10 base pairs. Pitch is the number of base pairs in one helical turn. 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.

Note:
There are different types of DNA. A-DNA, B-DNA, Z-DNA depending upon the type of Conformation. The most common DNA that is found in every organism is B-DNA and has right-handed helix.