Chapter 4, Problem 3Q

Summary Introduction

To review:

The consequence of the differences in purine to pyrimidine ratio between deoxyribose nucleic acid (DNA) and ribonucleic acid (RNA) sets in the given data.

Given:

Purine to pyrimidine ratio of DNA and RNA in the tissues of some organisms is provided in the Tables 1 and 2.

Table 1: Purine to pyrimidine ratio of DNA in different organisms.

Organism and the tissue from which DNA is extracted	Ratio of purine to pyrimidine in DNA
Herring sperm pyrimidines ratio	1
Rat bone marrow	1
Human sperm	1
Escherichia coli	1.04
Yeast	1

Table 2: Purine to pyrimidine ratio of RNA among different organisms.

Organism and the tissue from which RNA is extracted	Ratio of purine to pyrimidine in RNA
Rat liver	0.91
Carp muscle	1.03
Yeast	1.24
Rabbit liver	0.87
Cat brain	1.15

Introduction:

Purine and pyrimidine form an important part of DNA and RNA structures. The combination of different purines and pyrimidines in a DNA defines the genetic constitution of a given cell. The genetic code is an ultimate source of protein expression. The combination of purine and pyrimidine, therefore, indirectly affects the types of proteins expressed in different organisms.

In DNA, purines are A (adenine) and G (guanine), and pyrimidines are T (thymine) and C (cytosine). The RNA does not act as the source of genetic code (except for a few viruses) because it is more reactive and unstable as compared to DNA. In RNA, the uracil is present instead of thymine.