What Are Nucleosides and Nucleotides

DNA is an enormous molecule that stores our genetic information, whereas RNA serves in the transcription and translation of this information, which is then expressed through the synthesis of proteins. 

In this chapter, we will first examine the DNA molecule in detail to gain an understanding of its structure and function. We start by examining the structure of nucleosides and nucleotides and the manner in which these monomers are covalently bonded to form nucleic acids. Then we explore how genetic information is encoded on molecules of DNA, the function of the three types of ribonucleic acids, and, finally, how the primary structure of a DNA molecule is determined. 

Nucleic acid A biopolymer containing three types of monomer units heterocyclic aromatic amine bases derived from purine and pyrimidine, the monosaccharides D-ribose or 2-deoxy-D-ribose, and phosphate. 

A nucleoside is a compound containing a pentose, either D-ribose or 2-deoxy-D-ribose bonded to a heterocyclic aromatic amine base by a /3-Atglycosidic bond (Section 17.4A). Table 20.1 gives the names of the nucleosides derived from the four most common heterocyclic aromatic amine bases. 

A nucleotide is a nucleoside in which a molecule of phosphoric acid is esterified with a free hydroxyl of the monosaccharide, most commonly either the 3 -hydroxyl or the 5 -hydroxyl. A nucleotide is named by giving the name of the parent nucleoside. 

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A distinguishing feature of the substances listed previously is the presence or absence of a phosphate group or groups, again underscoring the prominent role of phosphates in life processes. As a point of departure, it may be noted that what are called nucleotides form the monomeric units of the polymers that comprise nucleic acids, and are thereby connected to the composition of DNA and RNA (Voet and Voet, 1995, pp. 795, 796). The loss of a phosphate group or groups yields what is called a nucleoside. 

What are the structures and components of the nucleotides The monomers of nucleic acids are nucleotides. An individual nucleotide consists of three parts—a nitrogenous base, a sugar, and a phosphoric acid residue— all of which are covalently bonded together. The bases are bonded to the sugars, forming nucleosides. 

UDP and UTP are selective agonists of certain of the P2Y receptors. It is not yet clear what factors control the release of uridine nucleotides into the extracellular space. UTP can be formed from UDP in the extracellular space by the action of the enzyme nucleoside diphosphokinase, which catalyzes the transfer of the -phosphate of nucleoside triphosphates to nucleoside diphosphates, e.g., ATP + UDP —> ADP + UTP. 

First, mobile phase and column we saw that most of the small molecule separations could be made on a C18 column in An/buffer water, with the exception of charged molecules and carbohydrates, which are too water soluble. We saw a range of polarity from fat-soluble vitamins, steroids, triglycerides, chlorinated pesticides eluting in 60-80% An/water, to carbamate, phosphate pesticides, anticonvulsants, antidepressants at 40-50% An/water, to nucleosides, nucleotides, aspirin, and water-soluble vitamins at 5-10% An/water. If you know something about the compound s structure or its solubility, you have a good clue as to what mobile phase can be used for its separation. 

Phosphodiester bonds are what make up the backbone of DNA and RNA molecules. These bonds provide the linkage that holds together the individual nucleotides or nucleosides in DNA and RNA. Enzymes called polymerases catalyze their formation (DNA polymerases for DNA and RNA polymerases for RNA). Take a look at the picture below to see the chemical structure of a phosphodiester bond. 

What would happen if one adds a fake nucleoside to the reaction medium of reverse transcriptase Note that we talked about nucleotides above, but we are here using word nucleoside. This is not a typographical error. A compound that consists of base (A, G, C, and T or U) and ribose (without phosphate) is called nucleoside. When this fake nucleoside is bound at the end of a growing DNA, the DNA cannot elongate further, because a phosphate group is necessary to connect two nucleosides. The fake nucleoside can also block the proper nucleotide binding site on the enzyme. Thus, it can inhibit the enzyme activity. This could stop production of DNA that is a copy of the gene RNA. 

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