MCQs

The internal cavity of the amylose helix is hydrophobic and of a specific diameter that perfectly accommodates a linear chain of polyiodide ions (I₃⁻ or I₅⁻). This precise structural complementarity is the molecular basis for the specific and sensitive iodine-starch color reaction.

The non-reducing nature means sucrose's carbonyl groups are protected in the glycosidic bond. Therefore, it cannot participate in the Maillard reaction (non-enzymatic glycation) with amino groups. This prevents the formation of Schiff bases and advanced glycation end-products that could damage proteins and nucleic acids in the phloem sap.

The length of the polyiodide chain within the helix dictates the absorption wavelength. Amylopectin's branched structure limits the length of the continuous helical segments available, resulting in the inclusion of shorter polyiodide chains, which absorb light differently and produce a red-violet color.

Galactose and glucose are C-4 epimers. The conversion of galactose to glucose in the liver involves a series of enzyme-catalyzed reactions (the Leloir pathway), but the net result is a change in the configuration of the hydroxyl group at the C-4 position. The UDP-hexose 4-epimerase enzyme directly catalyzes this epimerization.

The regular, extensive inter-chain hydrogen bonds create a crystalline, paracrystalline array. This structure is what gives cotton, wood, and other cellulosic materials their remarkable tensile strength and rigidity, making cellulose an ideal structural molecule.

Fructose in its free, furanose form is the sweetest of all natural sugars. In HFCS-55 (55% fructose, 45% glucose), the free fructose is immediately available to bind to the sweet receptor, whereas in sucrose, fructose is glycosidically linked and must first be hydrolyzed.

The gel matrix of agarose acts as a molecular sieve. During electrophoresis, charged macromolecules (like DNA) move through the pores. Smaller molecules move faster and farther, while larger molecules are retarded. This sieving separates the molecules by size.