Chapter 8, Problem 22DAP

(a)

Summary Introduction

To determine: Chargaff concluded that “no differences in composition have so far been found in DNA from different tissues of the same species” but a skeptic don’t agree by the data. How the data can be used to convince a skeptic.

Introduction:

Deoxyribonucleic acid (DNA) is a genetic material which is responsible for passing information from one generation to other. It is a double helical structure that consists of two parallel strands made up of nucleotides. Erwin Chargaff contributed in explaining the structure of DNA.

(b)

Summary Introduction

To determine: Whether Chargaff’s technique is capable of detecting a difference between the DNA of normal and a cancerous cell.

Introduction:

There are two types of nitrogenous bases: purines and pyrimidines. These bases pair with their complementary bases and form a nucleotide sequence. Adenine is linked to thymine with double hydrogen bond and guanine is linked to cytosine with triple hydrogen bond. The two nucleotides are joined together by the phosphodiester bond. To determine how these bases were composed in DNA, Chargaff devised new techniques to determine the base content of DNA. He gave Chargaff’s rule.

(c)

Summary Introduction

To determine: An argument based on the given data that supports “the base composition of DNA generally varies from one species to another”.

Introduction:

The amount of all bases adenine, guanine, cytosine and thymine is different in different organisms as the content of nucleotides is not fixed for different species. It is one of the conclusions of Chargaff’s rule.

(d)

Summary Introduction

To determine: An argument based on the given data, that supports “in all cellular DNAs, regardless of the species, $\text{A}+\text{G}=\text{T}+\text{C}$”.

Introduction:

In every living species, the amount of adenine is equal to the amount of thymine and the amount of guanine is equal to cytosine. It is one of the conclusions of Chargaff’s rule.

(e)

Summary Introduction

To determine: The way in which given data can be used to argue that wheat germ DNA is not a monotonous repeating sequence.

Introduction:

“Tetranucleotide hypothesis states that DNA is a monotonous tetranucleotide polymer and is not capable of having sequence information”. To disprove this theory, Chargaff took wheat germ DNA and treated it with deoxyribonuclease at different time intervals that represented different “core” sequences of wheat germ.