Chapter 13, Problem 1RQ

Summary Introduction

To Draw:

The structure of a DNA double strand.

Introduction:

DNA (deoxyribonucleic acid) is the genetic material present in the cells of living organisms. It is basically a nucleic acid or a polymer of nucleotides. It is a double helix strand of nucleotides. Both the strands of a DNA molecule run anti-parallel to each other.

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:

1) DNA is a double helical strand of nucleotides.

2) The strands of a DNA molecule run anti-parallel to each other. One strand runs in the direction and the other in the direction.

3) Phosphodiester bonds form the backbone of the DNA.

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

Conclusion

DNA is the genetic material found in every living organism, except retroviruses. DNA is a polynucleotide formed from adenine, guanine, thymine, and cytosine. Pentose sugar in DNA is deoxyribose sugar and it is a double helical structure.