Practice Questions

The iodine test requires a helix of sufficient length to stabilize the polyiodide chain. Glycogen's highly branched structure means its α-1,4 helical segments are very short. With iodine, it yields a reddish-brown color (not blue-black), which can be easily confused with a negative test if not careful.

Each monosaccharide has several polar -OH groups that can participate in hydrogen bonding with water molecules. This strong interaction (adhesion) overcomes the sugar-sugar interactions and allows the sugars to dissolve readily in water.

The D/L designation is fixed by the configuration of the highest-numbered chiral center (C-5 in hexoses). The α and β anomers are defined specifically by the orientation of the hydroxyl group on the newly formed chiral center, the anomeric carbon (C-1 in aldoses), relative to the ring.

Amylopectin is a homopolymer of D-glucose. Complete hydrolysis with strong acid will break all the α-1,4 and α-1,6 glycosidic bonds, yielding only D-glucose monomers as the final product.

Resistant starch is physically inaccessible or structurally resistant to pancreatic amylases. It passes to the colon, where it acts similarly to soluble fiber, being fermented by gut microbiota, producing beneficial short-chain fatty acids.

Agar melts at ~85°C and solidifies at ~32-40°C. Once gelled, it remains solid at typical incubation temperatures (e.g., 37°C) and is resistant to degradation by most microorganisms, making it an ideal, inert solidifying agent for culture media.

Both have the same molecular formula (C₆H₁₂O₆), but different functional groups—glucose is an aldehyde (aldose) and fructose is a ketone (ketose). This difference in the connectivity of atoms makes them structural (constitutional) isomers.

Branching enzyme is a transglycosylase. It cuts a short α-1,4-linked chain of 6-7 glucose units and transfers it to the 6-OH position of a glucose residue in the same or a nearby chain. This creates the α-1,6 branch points characteristic of amylopectin and glycogen.

Rumen microbes ferment cellulose and other carbohydrates to volatile fatty acids (VFAs) like acetate, propionate, and butyrate. These are absorbed through the rumen wall and serve as the primary energy source for the ruminant, not the glucose monomers of cellulose.

The Lobry de Bruyn–Alberta van Ekenstein transformation proceeds through the removal of a proton from C-2, forming an enediol (or enolate) intermediate. This intermediate can reprotonate to give either the original aldose (glucose), its C-2 epimer (mannose), or the ketose (fructose).