Chapter 7

(Integrates with Chapters 5 and 6 .) Human hemoglobin can react with sugars in the blood (usually glucose) to form covalent adducts. The \(a\) -amino groups of N-terminal valine in the Hb \(\beta\) -subunits react with the \(C-1\) (aldehyde) carbons of monosaccharides to form aldimine adducts, which rearrange to form very stable ketoamine products. Quantitation of this "glycated hemoglobin" is important clinically, especially for diabetic individuals. Suggest at least three methods by which glycated Hb could be separated from normal Hb and quantitated.

A 0.2 -g sample of amylopectin was analyzed to determine the fraction of the total glucose residues that are branch points in the structure. The sample was exhaustively methylated and then digested, yielding \(50 \mu \mathrm{mol}\) of 2,3 -dimethylglucose and \(0.4 \mu \mathrm{mol}\) of 1,2,3,6 tetramethylglucose. a. What fraction of the total residues are branch points? b. How many reducing ends does this sample of amylopectin have?

(Integrates with Chapters \(4,5, \text { and } 23 .)\) The caloric content of protein and carbohydrate are quite similar, at approximately 16 to \(17 \mathrm{kJ} / \mathrm{g},\) whereas that of fat is much higher, at \(38 \mathrm{kJ} / \mathrm{g}\). Discuss the chemical basis for the similarity of the values for carbohydrate and for protein.

Treatment with chondroitin and glucosamine is offered as one popular remedy for arthritis pain. Suggest an argument for the efficacy of this treatment, and then comment on its validity, based on what you know of polysaccharide chemistry.

Certain foods, particularly beans and legumes, contain substances that are indigestible (at least in part) by the human stomach, but which are metabolized readily by intestinal microorganisms, producing flatulence. One of the components of such foods is stachyose. Beano is a commercial product that can prevent flatulence. Describe the likely breakdown of stachyose in the human stomach and intestines and how Beano could contribute to this process. What would be an appropriate name for the active ingredient in Beano?

Give the systematic name for stachyose.

Prolonged exposure of amylopectin to starch phosphorylase yields a substance called a limit dextrin. Describe the chemical composition of limit dextrins, and draw a mechanism for the enzymecatalyzed reaction that can begin the breakdown of a limit dextrin.

What properties of hyaluronate, chondroitin sulfate, and keratan sulfate make them ideal components of cartilage?