![]() Gosling were also using X-ray diffraction to understand the structure of DNA (Figure 4). At the same time, British researchers Rosalind Franklin (1920–1958) and her graduate student R.G. Pauling had earlier discovered the structure of protein α helices, using X-ray diffraction, and, based upon X-ray diffraction images of DNA made in his laboratory, he proposed a triple-stranded model of DNA. In 1952, American scientist Linus Pauling (1901–1994) was the world’s leading structural chemist and odds-on favorite to solve the structure of DNA. ![]() Other scientists were also actively exploring this field during the mid-20th century. The X-ray diffraction pattern of DNA shows its helical nature. Pyrophosphate is subsequently hydrolyzed, releasing the energy used to drive nucleotide polymerization.įigure 4. The two unused phosphate groups from the nucleotide triphosphate are released as pyrophosphate during phosphodiester bond formation. The resulting strand of nucleic acid has a free phosphate group at the 5ʹ carbon end and a free hydroxyl group at the 3ʹ carbon end. To construct the sugar-phosphate backbone, the two terminal phosphates are released from the dNTP as a pyrophosphate. During the polymerization process, deoxynucleotide triphosphates (dNTP) are used. Phosphodiester bonding between nucleotides forms the sugar-phosphate backbone, the alternating sugar-phosphate structure composing the framework of a nucleic acid strand (Figure 3). Individual nucleoside triphosphates combine with each other by covalent bonds known as 5ʹ-3ʹ phosphodiester bonds, or linkages whereby the phosphate group attached to the 5ʹ carbon of the sugar of one nucleotide bonds to the hydroxyl group of the 3ʹ carbon of the sugar of the next nucleotide. Nitrogenous bases within DNA are categorized into the two-ringed purines adenine and guanine and the single-ringed pyrimidines cytosine and thymine. A nucleoside comprises the five-carbon sugar and nitrogenous base.įigure 2. The carbon atoms of the five-carbon deoxyribose are numbered 1ʹ, 2ʹ, 3ʹ, 4ʹ, and 5ʹ (1ʹ is read as “one prime”). ![]() The three components of a deoxyribonucleotide are a five-carbon sugar called deoxyribose, a phosphate group, and a nitrogenous base, a nitrogen-containing ring structure that is responsible for complementary base pairing between nucleic acid strands (Figure 1). Nucleotides that compose DNA are called deoxyribonucleotides. The building blocks of nucleic acids are nucleotides. In this section, we will discuss the basic structure and function of DNA. In Mechanisms of Microbial Genetics, we will discuss in detail the ways in which DNA uses its own base sequence to direct its own synthesis, as well as the synthesis of RNA and proteins, which, in turn, gives rise to products with diverse structure and function. The base sequence of deoxyribonucleic acid (DNA) is responsible for carrying and retaining the hereditary information in a cell. ![]() Each nucleic acid strand contains certain nucleotides that appear in a certain order within the strand, called its base sequence. Like other macromolecules, nucleic acids are composed of monomers, called nucleotides, which are polymerized to form large strands. In this chapter, we will discuss a fourth class of macromolecules: nucleic acids. In Microbial Metabolism, we discussed three classes of macromolecules: proteins, lipids, and carbohydrates.
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