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General Chemistry Principles, Patterns, and Applications, 2011

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Nucleic Acids<br />

Nucleic acids are the basic structural components of DNA (deoxyribonucleic acid) <strong>and</strong> RNA (ribonucleic<br />

acid), the biochemical substances found in the nuclei of all cells that transmit the information needed to<br />

direct cellular growth <strong>and</strong> reproduction. Their structures are derived from cyclic nitrogen-containing<br />

compounds called pyrimidines <strong>and</strong> purines, which can engage in hydrogen bonding through the lone<br />

electron pair on nitrogen (in pyrimidine <strong>and</strong> purine) or through the hydrogen of the amine (in purine):<br />

The same<br />

cyclic structures are found in substances such as caffeine, a purine that is a stimulant, <strong>and</strong> the antifungal agent<br />

flucytosine, a pyrimidine. (For more information on the structure of caffeine, see Chapter 3 "Chemical<br />

Reactions", Section 3.2 "Determining Empirical <strong>and</strong> Molecular Formulas".)<br />

When a pyrimidine or a purine is linked to a sugar by a bond called a glycosidic bond, anucleoside is formed.<br />

Adding a phosphoric acid group to the sugar then produces anucleotide (part (a) in Figure 24.25 "The<br />

Formation of Nucleic Acids"). The linkage of nucleotides forms a polymeric chain that consists of<br />

alternating sugar <strong>and</strong> phosphate groups, which is the backbone of DNA <strong>and</strong> RNA (part (b) in Figure 24.25<br />

"The Formation of Nucleic Acids").<br />

While the function of DNA is to preserve genetic information, RNA translates the genetic information in<br />

DNA <strong>and</strong> carries that information to cellular sites where proteins are synthesized. Many antibiotics<br />

function by interfering with the synthesis of proteins in one or more kinds of bacteria. Chloramphenicol,<br />

for example, is used against infections of the eye or outer ear canal; it inhibits the formation of peptide<br />

bonds between amino acids in a protein chain. Puromycin, which is used against herpes simplex type I,<br />

interrupts extension of a peptide chain, causing the release of an incomplete protein <strong>and</strong> the subsequent<br />

death of the virus.<br />

Figure 24.25 The Formation of Nucleic Acids<br />

Saylor URL: http://www.saylor.org/books<br />

Saylor.org<br />

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