Chapter 12, Problem 43A

Summary Introduction

To explain:

The joining together of bases in DNA as per the description given by Person W and Person C in their excerpt

Introduction:

Using Person F’s data, Person W and Person C measured the width of the helix and the spacing of the bases. Together they built a model of the double helix that conformed to other scientists’ research. The data was used by Person W and Person C to solve the structure of DNA. The data indicated that DNA was a double helix formed by two strands of nucleotides twisted around each other.

Answer to Problem 43A

The bases are joined together by hydrogen bonds.

Explanation of Solution

According to Person W and Person C’s model of DNA, there are two chains of nucleotides that are held together by the nitrogenous bases. The planes of the bases are perpendicular to the fiber axis. The bases are joined together by weak hydrogen bonds. They form pairs with one base from one chain hydrogen bonded to a single base from the other chain. There are two types of bases; purines and pyrimidines. Adenine andguanine are purines, while thymine and cytosine are pyrimidine bases. One purine base always pairs with a pyrimidine base.