![]() ![]() Hydrogen atoms are not shown - their locations are implied. The color code for atom type is as follows: carbon - yellow, nitrogen - blue, oxygen - red, phosphorous - pink. The model is shown in stick form, where the sticks represent bonds, and atoms are centered at the ends or junctions of the sticks. ![]() Below, left: Examples of experimentally-observed base-pair strucures. ( Note: In a DNA sequence, T replaces U.)Ībove: Structural formulas for the two canonical Watson-Crick base pairs. (for base-pairing in a double-stranded structure) is GCAU. Thus, the sequence in the figure would be written as AUGC and its reverse complement In RNA sequences, G pairs with C and A pairs with U. Base pairingīase pairing provides the chemical complementarity that underlies replication. The four common ribonucleotides of RNA - along with their base components -Īre adenylate, which contains the base adenine (A) uridylate, which contains uracil (U), guanylate, containing guanine (G), and cytidylate With the first letter listed the 5' end and the last letter listed the 3' end. The directionality of the chain is indicated, with the 5' end at the top and the 3' end at the bottom.īy convention, a polynucleotide sequence can be represented by the single letter symbol for a base, Symbolic representations of the four common bases of ribonucleotidesĪnd RNA molecules to the right of the chemical structure. Left: Structural drawing of a polyribonucleotide, along with Or deoxyribose) and the 3' position (3' OH attached directly to the ring) of the sugar part of the backbone. There is a directionality to the chain that is specified notationally as the 5'→3' orģ'→5' directions, by reference to the 5' position (hydroxymethylene group exo to the aldopentose ring of ribose The chain can be extended to arbitrary length by formation of additional phosphodiester bonds To form a nucleotide polymer, or polynucleotide.įor example, a free 3' hydroxyl of one nucleotide can form a phosphoester linkage with a phosphate group attached to the 5' hydroxyl group of another Nucleotides can be joined together in a series of phosphodiester linkages We'll look more carefully at the glycosidic bonds when we study carbohydrates later in the course. The attachment of the nitrogen-containing bases is through an N -glycosidic bond to the anomeric C1′of the sugar component. The sugar component provides hydroxyl groups to participate in phosphoester linkages with the phosphate groups that occur in nucleotides.įree nucleotides most commonly have at least one phosphate attached to the hydroxyl of the exocyclic carbon 5 (this is denoted as the 5′position, where the prime indicates an atom of the sugar component). Part of a nucleotide, making the latter a phosphate ester (or phosphoester) of a nucleoside. While DNA is composed of deoxyribonucleotides. Ribonucleotides are the monomeric units of RNA, Nucleotides are classed specifically as ribonucleotides orĭeoxyribonucleotides (depending on the identity of the sugar component). In the context of nucleotides, the bases are heterocyclic aromatic compounds of two general types: the purines, featuring a structure with two fused nitrogen-containing rings, and pyrimidines with a single ring. Nucleic acidsĪre typically long polymers built up of repeating units called nucleotides.īase with a sugar (usually ribose or deoxyribose) and phosphate. Of organisms, while RNA (ribonucleic acid) in most cases mediatesĮxpression of the genetic information stored in DNA. Is the physical realization of the genes and genomes Nucleic acids are one the major classes of biological macromolecules. Structural features of the DNA double helix. Tautomerism and base pairing Chargaff’s rules. Nucleotides: Nomenclature and chemical structure. ![]()
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