Chapter 1: DNA: Its Discovery, Structure, and Mechanisms

Abstract

The Discovery of DNA At the base of every lifeform on earth lies the basic unit of heredity known as genes. More importantly, genes are segments of Deoxyribonucleic acid also known as DNA. DNA is a polymer by which all life on earth’s genetic information is contained. Before we explore the composition and functions of DNA first we will dive into the history around its discovery. Swiss-born scientist Friedrich Miescher began his formal education at the age of 17 at the University of Basel in Germany in 1862 and eventually graduated and passed his board exams in 1868. After a brief career in the medical field, Miescher pursued a new career path in the realm of research in the laboratory of Felix Hoppe-Seyler, a renowned physiologist and chemist known for establishing many principles of biochemistry. In his initial experiments, Miescher attempted to study lymphocytes but due to the logistics and technology of the time, couldn’t efficiently obtain samples. With guidance from his mentor, he began to collect samples of drainage from surgical bandages at the local hospital and isolating the cells within the pus. During his testing, Miescher determined the ingredients comprising the cytoplasm of the cells, protein and lipids. In the process of performing his experiments, Miescher observed the presence of a mysterious byproduct after the addition of acid to his solution of cells and adversely, its disappearance after the addition of a base. This precipitate was a rudimentary form of DNA. Due to the properties of this material, Miescher attributed its origination to the nucleus of the cells. Subsequently, Miescher developed a novel method for isolating the DNA for study involving a series of salt washes and solvent additions. To begin, cells from the surgical bandages were cleaned and separated from contaminants. Next, the cells were washed with a sodium sulfate solution. The cells were then filtered allowing for any other materials to be left behind. In order to split the cell nuclei from the cytoplasm, Miescher then used a series of washings with Hydrochloric acid solution over a number of weeks. These nuclei were then agitated in an ether solution to break down the lipids within the cytoplasm still tarnished by cytoplasm while leaving the clean, cytoplasm-free nuclei alone. Another important contribution to the realm of biochemistry and the establishment of the true structure of DNA was the work of Erwin Chargaff. In Chargaff’s experiments performed in the late 1940’s, he found that no organisms possessed the same order of nucleotides in their DNA and more importantly that the same exact DNA existed a similar amount of base pairs when comparing adenine (A) to thymine (T) and guanine (G) and cytosine (C). This was the first evidence of an equal distribution of purines (A + G) and pyrimidines (C +T) and the links in between the two. In addition to Chargaff’s contributions to the field, other major contributors included figures such as Maurice Wilkins and Rosalind Franklin with discoveries in the field of X-ray crystallography. Wilkins and Franklin most notably are attributed with the first image of DNA in an image revered as “Photo 51” depicting its helical structure. Despite this breakthrough, only Wilkins w