Chapter 8, Problem S3.2BYB

Summary Introduction

To determine:

The structure of DNA.

Introduction:

The DNA is a double helical structure in which the two strands are complementary to each other. The strands are made up of the nitrogenous bases: purines and pyrimidine. The DNA act as genetic material that stores all the biological information of the individual.

Explanation of Solution

DNA is a polynucleotide composed of many nucleotides. A nucleotide molecule is composed of three units. These three units are nitrogen base, a pentose sugar, and a phosphate group. The nitrogen bases present in the DNA are adenine, guanine, cytosine, and thymine. Pentose sugar is deoxyribose.

The structure of B-DNA was given by Watson and Crick in 1953 through X-ray diffraction technology. The points of the Watson - Crick Model of DNA are as follows:

• DNA is a double helical strand of nucleotides.
• The strands of a DNA molecule run anti-parallel to each other. One strand runs in the $5\text{'}\to 3\text{'}$ direction and the other in the $3\text{'}\to 5\text{'}$ direction.

• Phosphodiester bonds form the backbone of the DNA.

• Adenine pairs with thymine by 2 hydrogen bonds, whereas cytosine pairs with guanine by 3 hydrogen bonds.

Conclusion

The structure of DNA is made up of two strands that form a helical structure when they combine through base pairs. The nitrogenous base pairs involved in DNA structure are: cytosine, thymine, adenine, and guanine.