The nucleotide is named according to the nitrogenous base it contains.

Adenine (A) and guanine (G) are double-ringed purines, and cytosine (C) and thymine (T) are smaller, single-ringed pyrimidines. There are four types of nitrogenous bases in DNA.

The building blocks of DNA are nucleotides, which are made up of three parts: a deoxyribose (5-carbon sugar), a phosphate group, and a nitrogenous base ( Figure 9.3). Now let’s consider the structure of the two types of nucleic acids, deoxyribonucleic acid (DNA) and ribonucleic acid (RNA). (credit a: modification of work by Marjorie McCarty b: modification of work by NIH) Scientist Rosalind Franklin discovered (b) the X-ray diffraction pattern of DNA, which helped to elucidate its double helix structure. Figure 9.2 Pioneering scientists (a) James Watson and Francis Crick are pictured here with American geneticist Maclyn McCarty. In 1962, James Watson, Francis Crick, and Maurice Wilkins were awarded the Nobel Prize in Medicine for their work in determining the structure of DNA. This meant they were always paired in some way. Chargaff had shown that of the four kinds of monomers (nucleotides) present in a DNA molecule, two types were always present in equal amounts and the remaining two types were also always present in equal amounts. Watson and Crick also had key pieces of information available from other researchers such as Chargaff’s rules. Watson and Crick were able to piece together the puzzle of the DNA molecule using Franklin’s data ( Figure 9.2). In Wilkins’ lab, researcher Rosalind Franklin was using X-ray crystallography to understand the structure of DNA. The patterns give important information about the structure of the molecule of interest.

X-ray crystallography is a method for investigating molecular structure by observing the patterns formed by X-rays shot through a crystal of the substance. Pauling had discovered the secondary structure of proteins using X-ray crystallography. Other scientists, such as Linus Pauling and Maurice Wilkins, were also actively exploring this field. In the 1950s, Francis Crick and James Watson worked together at the University of Cambridge, England, to determine the structure of DNA.

Describe how eukaryotic and prokaryotic DNA is arranged in the cell.

By the end of this section, you will be able to:

Free download nucleic acid structure