Chemistry · Ch 14 — Biomolecules
Composition and Structure of Nucleic Acids
Composition and Structure of Nucleic Acids
Nucleic acids are biopolymers of nucleotides. Controlled hydrolysis of either DNA or RNA yields three types of component: a nitrogenous base, a pentose sugar and a phosphate group.
Nitrogen bases. These are nitrogen-containing organic compounds that are derivatives of two parent ring compounds, pyrimidine and purine. Both DNA and RNA contain the same two major purine bases, adenine (A) and guanine (G). Both DNA and RNA also share one of their two pyrimidine bases, cytosine (C), but the second pyrimidine base differs between the two nucleic acids: it is thymine (T) in DNA and uracil (U) in RNA.
Pentose sugar. Nucleic acids contain two different pentose sugars. The recurring deoxyribonucleotide units of DNA contain 2'-deoxy-D-ribose, while the ribonucleotide units of RNA contain D-ribose; in the nucleotides of both DNA and RNA, the pentose is present in its closed, five-membered β-furanose ring form.
Phosphate group. Phosphoric acid forms a phosphodiester bond between successive nucleotides in the chain. Based on how many phosphate groups a given nucleotide carries, nucleotides are classified as mononucleotides, dinucleotides or trinucleotides. …
What this figure shows. The ring structures of the two parent heterocycles, purine (a fused six- and five-membered nitrogen ring, numbered 1-9) and pyrimidine (a single six-membered nitrogen ring, numbered 1-6), together with their five biologically important derivatives: the two purine bases adenine (a 6-amino-purine) and guanine (a 6-oxo-2-amino-purine), and the three pyrimidine bases thymine (5-methyluracil, found only in DNA), cytosine (4-amino-2-oxo-pyrimidine, found in both) and uracil (2,4-dioxo-pyrimi …
What this figure shows. Two furanose-ring structures drawn side by side for comparison: D-ribose, carrying an -OH group at the 2' carbon (the sugar used in RNA), and 2'-deoxy-D-ribose, carrying only an -H at the 2' carbon in place of that -OH (the sugar used in DNA) -- the single 2'-OH/2'-H difference that gives deoxyribonucleic acid its name. …
Worked out. A three-step build-up scheme in words: Sugar + Base combine to give a Nucleoside; Nucleoside + Phosphoric acid combine to give a Nucleotide (a single unit of a nucleic acid); and n Nucleotides link together to give a Polynucleotide, i.e. the complete DNA or RNA chain -- the stepwise assembly hierarchy that the surrounding prose describes. …