Chapter 12.3, Problem 12.9CT

(a)

Interpretation Introduction

Interpretation:

For the given set of DNA strands, the error in the base pairing has to be found and circled.

Concept Introduction:

The four major nitrogen-containing bases are:

Adenine:

It is represented with the letter “A”

Guanine:

It is represented with the letter “G”.

Thymine:

It is represented with the letter “T”.

Cytosine:

It is represented with the letter “C”.

Complementary bases:

• • Adenine is the complementary base of Thymine
• • Cytosine is the complementary base of Guanine.
• • In DNA, Adenine always makes a double bond with thymine ($A=T$) and cytosine always makes triple bond with guanine $\left(G\equiv C\right)$

(b)

Interpretation Introduction

Interpretation:

Wheather the mismatched pair in DNA strands are more stable or less stable than a correct pair have to be found.

Concept Introduction:

Hydrogen bonding between complementary bases:

• • The bases of nucleotides of one DNA strand makes hydrogen bonding with their respective complementary bases of the nucleotides of the other DNA strand. This hydrogen bonding keeps the two DNA strands of a DNA helix rigid and stable.
• • Adenine is the complementary base of Thymine and it makes two hydrogen bonds with Thymine. Hence, two hydrogen bonds exist between Adenine and Thymine which has been represented by the double lines in between them.

• • Cytosine is the complementary base of Guanine and it makes three hydrogen bonds with Guanine. Hence, three hydrogen bonds exist between Cytosine and Guanine which has been represented by the triple lines in between them.