voet 03 - 3 Nucleotides, Nucleic Acids, and Genetic...

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3 Nucleotides, Nucleic Acids, and Genetic Information This chapter introduces you to the structure and function of nucleotides and their polymers, ribonucleic acid (RNA) and deoxyribonucleic acid (DNA). The chapter begins with a discussion of the various kinds of nucleotides and the large variety of their functions in cellular processes. The nucleic acid polymers, RNA and DNA, are the primary players in the storage, transmission, and decoding of the genetic material. Scientists use a variety of powerful techniques to characterize and manipulate DNA from any organism. This chapter discusses the sequence- specific cleavage of DNA by restriction endonucleases; DNA sequencing; amplification of DNA by cloning in unicellular organisms such as bacteria and yeast; and the in vitro amplification of DNA by the polymerase chain reaction. Essential Concepts Nucleotides 1. Of the four major classes of biological molecules (amino acids, sugars, lipids, and nucleotides), nucleotides are the most functionally diverse. They are involved in energy transfer, catalysis, and signaling within and between cells, and are essential for the storage, decoding, and transmission of genetic information. 2. Nucleotides are composed of a nitrogenous base linked to a ribose sugar to which at least one phosphate group is attached. The eight common nucleotides, which are the monomeric units of RNA and DNA, contain the bases adenine, guanine, cytosine, thymine, and uracil. 3. The best known nucleotide is the energy transmitter adenosine triphosphate (ATP), which is synthesized from adenosine diphosphate (ADP). Transfer of one or two of the phosphoryl groups of ATP is an exergonic process whose free energy can be used to drive an otherwise nonspontaneous process. Introduction to Nucleic Acid Structure 4. Nucleic acids are polymers of nucleotides in which phosphate groups link the 3 and 5 positions of neighboring ribose residues. This linkage is called a phosphodiester bond because the phosphate is esterified to the two ribose groups. The phosphates are acidic at biological pH and so the polynucleotide is a polyanion.
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Chapter 3 Nucleotides, Nucleic Acids, and Genetic Information 26 5. Nucleic acids are inherently asymmetric, so that one end (with a 5 phosphate) is different form the other end (with a 3 hydroxyl). This asymmetry, or polarity, is critical for the information storage function of nucleic acids. In fact, all linear biological molecules show this kind of polarity. 6. The structure of DNA was determined by Francis Crick and James Watson in 1953. Key information used to build their model included the following: (a) DNA has equal numbers of adenine and thymine residues and equal numbers of cytosine and guanine residues (called Chargaff’s rules). (b)
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voet 03 - 3 Nucleotides, Nucleic Acids, and Genetic...

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