28. Carbohydrates

Which class of carbohydrates is digested slowest in the human body?

An unknown disaccharide gives a positive Tollens' test. A glycosidase hydrolyzes it to d-galactose and d-mannose. When the disaccharide is treated with methyl iodide and Ag2O and then hydrolyzed with dilute HCl, the products are 2,3,4,6-tetra-O-methylgalactose and 2,3,4-tri-O-methylmannose. Propose a structure for the disaccharide.

Raffinose is a trisaccharide (C18H32O16) isolated from cottonseed meal. Raffinose does not reduce Tollens reagent, and it does not mutarotate. Complete hydrolysis of raffinose gives d-glucose, d-fructose, and d-galactose. When raffinose is treated with invertase, the products are d-fructose and a reducing disaccharide called melibiose. Raffinose is unaffected by treatment with a b-galactosidase, but an a-galactosidase hydrolyzes it to d-galactose and sucrose. When raffinose is treated with dimethyl sulfate and base followed by hydrolysis, the products are 2,3,4-tri-O-methylglucose, 1,3,4,6-tetraO-methylfructose, and 2,3,4,6-tetra-O-methylgalactose. Determine the complete structures of raffinose and melibiose, and give a systematic name for melibiose.

Which of the following foods is highest in polysaccharides?

Which of the following is a polysaccharide?

Which polysaccharide is primarily used for energy storage in animal cells?