Chapter 26.3, Problem 4P

Interpretation Introduction

Interpretation: The hydrogen bond acceptor (A), hydrogen bond donor (D) or both (D/A) should be indicated on the functional groups of the five heterocyclic bases in nucleic acids.  It is also indicated that to show how base pairing would be affected if the bases existed in the enol form.

Concept introduction:

A parent DNA molecule consists of two poly nucleotide chains held together by bonds between complementary nitrogen bases.

A base is nitrogen containing heterocyclic compound which is found in DNA and RNA.

There are mainly five nitrogen bases.

1. (1) Adenine
2. (2) Guanine
3. (3) Cytosine
4. (4) Thymine
5. (5) Uracil

Hydrogen bond is a type of attractive (dipole-dipole) interaction between an electronegative atom and a hydrogen atom bonded to another electronegative atom.

In DNA, hydrogen bonding is the chemical interaction that underlies and connects the base pairing.  The DNA hydrogen bonds are responsible for holding together the double helix structure.

Enol is a tautomer which exhibiting a special type of functional isomerism namely tautomerism.

Tautomerism is a special type of functional isomerism in which isomers are in dynamic equilibrium with each other.