Chapter 17, Problem 1Q

Summary Introduction

To review:

The deoxyribonucleic acid (DNA) molecule that denatures first on heating from the given two deoxyribonucleic acid (DNA) molecules, and the reason behind its early denaturation.

$\begin{array}{l}\text{5’-GCATTTCGGCGCGTTA-3’}\hfill \\ \text{3’-CGTAAAGCCGCGCAAT-5’ }\hfill \\ \text{5’-ATTGCGCTTATATGCT-3’}\hfill \\ \text{3’-TAACGCGAATATACGA-5’}\hfill \end{array}$

Introduction:

The deoxyribonucleic acid (DNA) molecule has a double helical structure that is stabilized by different forces. These forces include hydrophobic interactions, hydrogen bonds, base stacking, and electrostatic interactions.

Explanation of Solution

The second DNAmolecule denatures first because it has smaller number of guanine–cytosine (GC) base pairs, and thus less amount of GCcontent (37.64%).The GC content is measured by dividing the number of cytosine and guanine nucleotides present in deoxyribonucleic acid sequence by the total number of base pairs in the sequence.

The base stacking interactions in the second molecule are less than the interactions in the first molecule. The GC content for the first molecule is higher (56.25%), and the base stacking is stronger as well. A lower amount of heat energy is required to break down the hydrogen bonds and stacking interactions, in the second molecule, and it denatures earlier than the other DNAmolecule.

The base pairs in the deoxyribonucleic acid (DNA) molecule are joined by hydrogen bonds. There are 3 hydrogen bonds between guanine and cytosine while only 2 hydrogen bonds are present between adenine and thymine. The triple bond between guanine-cytosine is stronger than the double bond between adenine and thymine. More energy is required to denature the DNA molecule since ithas more guanine–cytosine base pairs.

Conclusion

It can be concluded that the second deoxyribonucleic acid molecule denatures first on heating because of comparatively weaker base stacking interactions and lower GCcontent.