Practice Questions

Sugars are polar and partition between an organic mobile phase and a water stationary phase held by the paper. Slight differences in structure (e.g., number of -OH groups) cause them to partition differently and thus migrate at different rates, allowing for separation and identification.

The enzyme glucose (xylose) isomerase catalyzes the reversible isomerization of glucose to the sweeter fructose. This process is used to convert a portion of the glucose from corn starch into fructose, creating high-fructose corn syrup (HFCS).

Pancreatic α-amylase, like salivary amylase, is an endoglycosidase that hydrolyzes internal α-1,4 bonds. It cannot cleave α-1,6 bonds at branch points. Therefore, the products are the disaccharide maltose, the trisaccharide maltotriose, and oligosaccharides containing branch points called α-limit dextrins.

Chitin is the primary structural polysaccharide in the cell walls of fungi, the exoskeletons of arthropods, and the beaks of cephalopods. It provides rigidity and strength, analogous to the role of cellulose in plants.

The D/L nomenclature is a convention based on glyceraldehyde. A sugar is D if the -OH group on the chiral carbon farthest from the carbonyl group (the highest numbered chiral center) is drawn on the right side in a standard Fischer projection.

The vitrification (glass formation) hypothesis suggests that trehalose forms a stable glassy matrix. Its many -OH groups replace the hydrogen bonds normally provided by water to the polar head groups of membrane phospholipids and to the protein surface, maintaining their native conformation during dry periods.

Branching frequency is measured by the ratio of α-1,6 branch points to α-1,4 linkages in the linear chain. Glycogen has a higher ratio than amylopectin, with branches occurring roughly every 8-12 glucose units compared to every 24-30 in amylopectin.

The α-1,4 linkage in starch produces a helical chain that is flexible and digestible. The β-1,4 linkage in cellulose produces a straight, rigid chain that can form strong inter-chain hydrogen bonds, making it structural and indigestible to organisms lacking cellulase.

A five-membered ring (furanose) forms when the keto group on C-2 of a ketose reacts with the hydroxyl group on C-5. This is the predominant ring form for fructose in solution, creating a fructofuranose structure.

Inulin is a polysaccharide of D-fructose linked by β-2,1 glycosidic bonds. It is not metabolized and is freely filtered at the glomerulus without being reabsorbed or secreted, making it an ideal marker for measuring the glomerular filtration rate (GFR).