Chapter 26, Problem S25.1BYB

Summary Introduction

To determine:

The structural characteristics of a DNA molecule.

Introduction:

DNA was first observed by a German biochemist named Friedrich Miescher in 1869. It was not until 1953 that James Watson, Francis Crick, Maurice Wilkins, and Rosalind Franklin figured out the structure of DNA is a double helix, which they realized could carry biological information.  Watson, Crick and Wilkins were awarded the Nobel Prize in medicine in 1962 "for their discoveries concerning the molecular structure of nucleic acids and its significance for information transfer in living material."

Explanation of Solution

Nucleic acids are polymers of similar subunits known as nucleotides. A nucleotide is composed of three different molecules, a phosphate group, a sugar, and a nitrogen base. The basic building block of DNA and RNA is the nucleotide.

DNA consists of two polynucleotide chains wound around each other. They are wound around each other in such a way that they resemble a twisted ladder which is referred to as the double helix. The backbone of each of these strands is a repeating pattern of a 5-carbon sugar and a phosphate group. Each sugar is attached to one of the four nitrogen-containing bases: Adenine, Thymine, Guanine, or Cytosine.

The sugar present in the nucleotide is deoxyribose, hence the name deoxyribonucleic acid (DNA). In the double helix DNA structure, all four bases are confined to the inside of the double helix, held in place by hydrogen bonds linking complimentary bases on the two strands. The sugar-phosphate backbone of DNA is present on the outside of the double helix.

Adenine and thymine are paired by two hydrogen bonds, whereas cytosine and guanine are paired by three hydrogen bonds. The bases are stacked up as a ladder and the hydrophobic bonding between the bases gives the DNA molecule stability.

Conclusion

DNA is made up of small units known as nucleotides. Each nucleotide contains a phosphate group, a sugar group, and a nitrogen base.