Chapter 9, Problem 27PDQ

Summary Introduction

To analyse:

The structure of the molecule by postulating a model, which is consistent with the given observations.

Given:

The discovery of a primitive eukaryote with a unique nucleic acid as a genetic material revealed the following observation:

(a) X-ray diffraction studies show a general pattern resembling DNA (deoxyribonucleic acid), but has somewhat different dimensions and is more irregular.

(b) On heating and monitoring the UV (ultraviolet) absorption at 260 nm (nanometer), a major hypochromic shift is observed.

(c) Base-composition analysis shows four bases with proportions given below:

(1) Adenine is 8%

(2) Hypoxanthine is 18%

(3) Guanine is 37%

(4) Xanthine is 37%

(d) About 25 percent of the sugars are ribose and 75 percent are deoxyribose.

Introduction:

Watson and Crick proposed the double-stranded structure of DNA using X-ray diffraction. Four nitrogenous bases were discovered in DNA, out of which two were purines and two were pyrimidines. Purines are guanine and adenine while pyrimidines are thymine and cytosine in DNA. In RNA (ribonucleic acid), uracil is present instead of thymine. Hyperchromicity is the increase in the absorption of UV light by any biomolecule after it gets denatured. Single-stranded DNA shows more absorption as compared to double-stranded DNA.