Chapter 26, Problem 26.23UKC

Interpretation Introduction

Interpretation:

The hydrogen bonding exists in structure and the sequence of each strand of DNA has to be predicted.

Concept Introduction:

Composition of nucleic acid: Nucleic acid is a polymer of nucleotides. Each nucleotide has three parts: a sugar, a nitrogenous base, and a phosphate group. Two nucleotides are joined by phosphate diester linkage where a free phosphate on 5’ carbon of one nucleotide and a free –OH group on 3’ carbon of another nucleotide.

Base pairing in DNA: The two strands of the DNA double helix run in the opposite directions- one in 5’ to 3’ direction and other from 3’ to 5’ direction. The hydrogen bonding between two strands enhances the stability of the DNA; where the alignment of hydrophobic nitrogenous bases in the interior and hydrophilic phosphate and sugar groups on the exterior also enhance the stability. Adenine and thymine gives a pair forming two hydrogen bonds and cytosine and guanine gives rise to another pair forming three hydrogen bonds.

Sugar: In both DNA and RNA, sugar portion is found. In DNA, the sugar is D-ribose, where at 2’hydroxyl group is absent and in RNA, the hydroxyl group is present at 2’.

Nucleotide: (Nucleoside + phosphate)

Nucleotides are the building blocks of nuclei acids; monomers of DNA and RNA polymers. At carbon-5’ of the ribose sugar, a phosphate group is added which is collectively known as nucleotide. Phosphate groups can be added to any of the nucleotide to form diphosphate or triphosphate.

Nitrogenous bases: Five types of nitrogenous bases (has unique one-letter code A, G, T, U, and C) are derived from two parent compounds called purine and pyrimidine. The purine derivatives are Adenine and Guanine are two fused nitrogen containing rings. The pyrimidine derivatives are Thymine, Cytosine, and Uracil has a six-membered nitrogen  ring.  Adenine, Guanine, Thymine, and Cytosine are the nitrogenous bases present in DNA. Adenine, Guanine, Cytosine and Uracil are the nitrogenous bases present in RNA.

Numbering the atoms in sugar and base rings:

In order to distinguish the atoms in the sugar of a nucleoside and atoms of a base ring, numbers without prime is used for atoms in the base ring and numbers with prime used for the atoms in the sugar ring.