Chapter 21, Problem 34A

Interpretation Introduction

Interpretation:

Complementary base pairing between two individual strands of DNA must be described that forms the overall double helical structure. The involvement of complementary base pairing during replication of DNA must also be explained.

Concept Introduction:

DNA is the nucleic acid which has double helical structure. The two strands are connected through Watson-Crick base pairing with the help of hydrogen bonds.

Answer to Problem 34A

Two individual strands of DNA participate in hydrogen bonding to make the overall double helical structure of DNA.

During replication the base pairing is temporarily lost to unwind the DNA for daughter DNA strands generation.

Explanation of Solution

DNA has one aldopentose sugar which is 2-Deoxy-D-Ribose. Nitrogenous bases are Adenine (A, purine), Guanine (G, purine), Cytosine (C, pyrimidine) and Thymine (T, pyrimidine). There is one phosphate group. Between two strands there are hydrogen bonds.

A forms two hydrogen bond with T and G forms three hydrogen bonds with C as shown in the figure below. Thus the overall double helical structure of DNA is formed.

During replication the two DNA strands are separated. The hydrogen bond is not there now. The two individual strands now acts as a template and DNA polymerase helps to add the nucleotides one by one as per complementary sequence required. This time again the two strands become connected through hydrogen bonding and finally daughter DNA molecule is generated. This is the DNA replication process.