8-19 Blackboard Questions.doc 3b1b4l

Timmy Ma Questions 1. In aqueous solutions there are three forms of glucose: the -form (36%), the -form (64%) and a trace amount of the open-chain form. At equilibrium, the alpha and beta cyclic forms are interconverted by way of the openchain structure. Explain (a) why the cyclic forms exist predominately in solutions, and (b) why the -form is more abundant than the -form. The acetyl is slightly more stable than the aldehyde so it exists in solutions. The beta conformation has all substituents in an equatorial conformation. 2. Name the monosaccharides and disaccharides in amylose and cellulose. Compare the structural and conformation differences between amylose and cellulose. A simple iodine test can be used to distinguish the two polysaccharides. Describe the iodine test and explain the observation. The repeating disaccharides in amylose and cellulose are -maltose and -cellobiose. Amylose and cellulose are both are polymers of D-glucose and differ only in the anomeric form used. Cellulose is formed by §-(1→4) glycosidic bonds, but alpha-amylose is formed by alpha-(1→4) glycosidic bonds. By adding iodine to an object that conatins starch like potatoes, starch will react with iodine producing a deep blue/ purple color this reaction is the result of the formation of polyiodide chains from the reaction of starch and iodine. 3. Write the reduction reaction of glucose to form sorbitol. List and explain the side effects caused by too much sorbitol consumption. Sorbitol is the reduced version of glucose; it is another type of monosaccharide known as sugar alcohol. Excessive consumption of sorbitol can cause bloating, diarrhea, gas, and cataracts. 4. Blood sugar levels can be detected by test strips, which are coated with glucose oxidase and an indicator. Write the oxidation reaction of glucose that happens in the testing process. The reagent strip includes a reactant system comprising an enzyme, such as glucose oxidase, capable of catalyzing the oxidation reaction of glucose to gluconic acid and hydrogen peroxide; an indicator or oxidizable dye, such as o-tolidine; and a substance having peroxidative activity capable of catalyzing the oxidation of the indicator. 5. Why are soluble fibers identified as prebiotics? Soluble fibers such as jams are nondigestible food ingredients that promotes the growth of beneficial microorganisms in the intestines.