Question

The reason for the double helical structure of DNA is the operation of:
A. electrostatic attractions
B. van der Waals forces
C. dipole-dipole forces
D. hydrogen bonding

Answer 1

For this problem, we have to study the structure of DNA in brief so that we can determine the actual backbone of the DNA which consists of a nitrogenous base, pentose sugar but they are attached with the help of a bond.

Complete step by step answer:
- In the given question, we have to explain the bond which is responsible for the helical structure of the DNA.
- As we know that DNA is also known as Deoxyribonucleic acid is the main source of the genetic material of human beings.
- The DNA mainly consists of a long chain of nucleic acids also known as nucleotides which are made up of a phosphate sugar, a sugar group and four nitrogenous groups.
- There are four nitrogenous groups in the DNA molecule that is adenine, guanine, cytosine and thymine.
- These nitrogenous bases are attached with the pentose sugar as it consists of five carbon atoms known as pentose sugar.
- The nitrogenous bases are held together with the help of hydrogen bonds. As among them, adenine makes 2 hydrogen bonds with thymine only.
$\text{Sugar - A = T - Sugar}$
- Whereas the cytosine makes 3 hydrogen bonds with the guanine only.
$\text{Sugar - C }\equiv \text{ G - Sugar}$
- Due to which the two strands of the DNA are held together in a spiral or helical pattern.
So, the correct answer is “Option D”.

Note: Watson and Crick gave the model of the DNA in which it is explained the helical pattern of the DNA. Also, both the strands of the DNA are opposite to each other that's why they are known as antiparallel strands.