28. Carbohydrates

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 β-galactosidase, but an α-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-tetra-O-methylfructose, and 2,3,4,6-tetra-O-methylgalactose. Determine the complete structures of raffinose and melibiose, and give a systematic name for melibiose.

What is the main structural difference between a. amylose and cellulose?

What is the main structural difference between c. amylopectin and glycogen?

Hyaluronic acid, a component of connective tissue, is the fluid that lubricates joints. It is a polymer of alternating N-acetyl-D-glucosamine and D-glucuronic acid subunits joined by β-1,3′-glycosidic linkages. Draw a short segment of hyaluronic acid.

What is the main structural difference between b. amylose and amylopectin?

What is the main structural difference between d. cellulose and chitin?

A derivative of chitin, called chitosan, is sometimes incorporated into bandages to aid healing. Propose a reaction to convert the chitin dimer into a chitosan dimer. [Note: The glycoside linkage is unstable in acid.]

Draw the structures of the following nucleotides.

(a) guanosine triphosphate (GTP)

Draw the structures of the following nucleotides.

(b) deoxycytidine monophosphate (dCMP)

Draw the structures of the following nucleotides.

(c) cyclic guanosine monophosphate (cGMP)

Refer to Figure 20.5 to answer the following questions: a. People with type O blood can donate blood to anyone, but they cannot receive blood from everyone. From whom can they not receive blood?

Refer to Figure 20.5 to answer the following questions: b. People with type AB blood can receive blood from anyone, but they cannot give blood to everyone. To whom can they not give blood?