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03:06
06:00Which of the following sugars are reducing sugars? Which ones would undergo mutarotation?
(a) methyl β-D-glucopyranoside
(b) 2,3,4,6-tetra-O-methyl-D-mannopyranose
(c) 1,3,6-tri-O-methyl-D-fructofuranose
(d) methyl 2,3,4,6-tetra-O-methyl-β-D-galactopyranoside
Which of the following sugars are reducing sugars? Which ones would undergo mutarotation?
(c) 6-O-(β-D-galactopyranosyl)-D-glucopyranose
Draw the structures (using chair conformations of pyranoses) of the following disaccharides.
(a) 4-O-(α-D-glucopyranosyl)-D-galactopyranose
(b) α-D-fructofuranosyl-β-D-mannopyranoside
(c) 6-O-(β-D-galactopyranosyl)-D-glucopyranose
Which of the following sugars are reducing sugars? Which ones would undergo mutarotation?
(b) α-D-fructofuranosyl-β-D-mannopyranoside
Erwin Chargaff’s discovery that DNA contains equimolar amounts of guanine and cytosine and also equimolar amounts of adenine and thymine has come to be known as Chargaff’s rule:
G = C and A = T
(a) Does Chargaff’s rule imply that equal amounts of guanine and adenine are present in DNA? That is, does G = A?
(b) Does Chargaff’s rule imply that the sum of the purine residues equals the sum of the pyrimidine residues? That is, does A + G = C + T?
(c) Does Chargaff’s rule apply only to double-stranded DNA, or would it also apply to each individual strand if the double helical strand were separated into its two complementary strands?
An unknown reducing disaccharide is found to be unaffected by invertase enzymes. Treatment with an α-galactosidase cleaves the disaccharide to give one molecule of D-fructose and one molecule of D-galactose. When the disaccharide is treated with excess iodomethane and silver oxide and then hydrolyzed in dilute acid, the products are 2,3,4,6-tetra-O-methylgalactose and 1,3,4-tri-O-methylfructose. Propose a structure for this disaccharide, and give its complete systematic name.
