Concept explainers
The example of a silyl–Hilbert–Johnson nucleosidation reaction in Section 25.3 is presumed to involve an intermediate ribosyl cation that is stabilized by intramolecular interactions involving the C2 benzoyl group. This intermediate blocks attack by the heterocyclic base from the
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- During base excision repair, DNA glycosylase cleaves theN-glycosidic link between the altered base and the deoxyribose component of the nucleotide. Draw a typical nucleotideand indicate which bond is cleaved.arrow_forwardDraw the dinucleotide dApdG (shown above). Draw a dinucleotide that you would expect to hydrogen bond most stably to dApdG. Include every atom and every ring atom number, every charge, correct orientation of the base and the backbone linkages with respect to the ribose ring, the number of angstroms between N’s and O’s involved in the hydrogen bonds, and the number of angstroms between the riboses involved as support for each base in the hydrogen bonded pair.arrow_forwardThe enzyme that catalyzes the C-Cg bond cleavage reaction that converts serine to glycine removes the substituent (R) bonded to the a-carbon in the first step of the reaction. Starting with PLP bound to serine in an imine linkage, propose a mechanism for this reaction. (Hint: The first step involves removal of the proton from serine's OH group.)arrow_forward
- 5-Bromouracil (BU) resembles thymine sufficiently that BU base-pairs readily with adenine in a DNA helix, and it can readily substitute for thy- mine in DNA replication. However, its electron distribution allows it to resemble cytosine sufficiently that BU can pair with guanine. Show how a few rounds of replication in the presence of BU could convert an A-T base pair to G-C, and identify the products of each round of replication.arrow_forwardGive the major product that is formed when the primary hydroxyl group of the followingmonosaccharide reacts with propionic anhydride.arrow_forwardResearchers analysed a glycopeptide (a peptide carrying one or several oligosaccharide groups) and determined both the sequence of the peptide and the sequence of the sugar molecule. The latter was identified as a diholoside coupled to the peptide by an osidic bond. The systematic name of this sugar is: B-D-glucopyranosyl-(1→4)-ß-D-galactopyranose. : Represent the chemical formula of this diholoside in a way that all oses are Question 1 represented according to the Haworth convention. Apart from the furane and/or pyrane cycles all atoms of this molecule must be given.arrow_forward
- Under acidic conditions (catalytic amount of acid) in anhydrous methanol, D-galactose can be converted to the methyl galactopyranoside X on the right side of the reaction arrow. Write a detailed mechanism for the reaction. OH H+ HO HO `Me MeOH HO 'OH HO "OH OH OH Xarrow_forward5-Bromouracil, a highly mutagenic compound (that is, a compound that causes changes in DNA), is used in cancer chemotherapy. When administeredto a patient, it is converted to the triphosphate and incorporated into DNA in place of thymine, which it resembles sterically. Why does it causemutations?(Hint: The bromo substituent increases the stability of the enol tautomer.)arrow_forwardDraw a diagram of the linear and ring structures of ribose. Show the biochemical mechanism of cyclization of each and name the resultant ring – including the ring type & anomeric carbon designation. Draw and name an amine version, reduced version, and oxidized version, either in ring or Fisher projection.arrow_forward
- does structure E represent fructofuranose? explainarrow_forwardAn important technique for establishing relative configurations among isomeric aldoses and ketoses is to convert both terminal carbon atoms to the same functional group. This can be done either by selective oxidation or reduction. As a specific example, nitric acid oxidation of d-erythrose gives meso-tartaric acid . Similar oxidation of d-threose gives (2S,3S)-tartaric acid. Given this information and the fact that d-erythrose and d-threose are diastereomers, draw Fischer projections for d-erythrose and d-threose. Check your answers against Table 25.1.arrow_forwardWhat does the "alpha" indicate in "α-D-ribofuranose"? It is the first anomeric form. The sugar is "right-handed." It is the dominant form of the possible forms of D-ribofuranose. The position of the C1 -OH group relative to the plane of the ring. None of these.arrow_forward