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.

The higher density of non-reducing ends in glycogen allows more glycogen phosphorylase molecules to work simultaneously on a single molecule, dramatically increasing the rate of glucose-1-phosphate release during sudden demands for energy.

Glycogenesis is the anabolic process of converting excess glucose into glycogen for storage, primarily in the liver and muscle. Glycogenolysis is its catabolic counterpart. Gluconeogenesis is the synthesis of new glucose from non-sugar sources.

Benedict's reagent is an alkaline solution of copper(II) sulfate and sodium carbonate. In a hot alkaline environment, glucose's carbonyl group reduces Cu²⁺ to Cu⁺, forming a colored precipitate. The alkalinity is crucial for the reaction to proceed.

Epimers are a subclass of diastereomers that differ in configuration at exactly one chiral center. For example, D-glucose and D-galactose are C-4 epimers, and D-glucose and D-mannose are C-2 epimers. Anomers are epimers specifically at the hemiacetal/hemiketal carbon.

The debranching enzyme's α-1,6-glucosidase activity specifically hydrolyzes the α-1,6 bond at a branch point, releasing a free glucose molecule. This action is essential for the complete degradation of glycogen and amylopectin, as phosphorylase cannot act on or near these bonds.

Reduction of the carbonyl group of glucose (by agents like NaBH₄ or H₂ over catalyst) converts it to the sugar alcohol sorbitol (glucitol). The aldehyde (-CHO) is reduced to a primary alcohol (-CH₂OH). Oxidation would yield an acid, not an alcohol.

Lysozyme (muramidase) cleaves the β-1,4 glycosidic bond between the C1 of N-acetylmuramic acid (NAM) and the C4 of N-acetylglucosamine (NAG) in the peptidoglycan layer, causing cell wall weakening and bacterial lysis.