MCQs

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).

The synthesis of sucrose involves UDP-glucose as the glucosyl donor. The reaction is: UDP-glucose + Fructose-6-phosphate → Sucrose-6-phosphate + UDP. ADP-glucose is the activated monomer for starch synthesis.

Starch and glycogen are composed of α-D-glucose units, where the -OH on the anomeric carbon (C1) is below the plane of the ring. Cellulose consists of β-D-glucose, where the anomeric -OH is above the plane of the ring. This simple difference makes starch digestible and cellulose indigestible to humans.

The number of possible stereoisomers for a molecule with 'n' chiral centers is 2ⁿ. A sugar with 4 chiral centers has 2⁴ = 16 possible stereoisomers. These are divided into 8 D-sugars and their 8 L-enantiomeric counterparts.

Endoglycosidases cleave glycosidic bonds internally within a polysaccharide chain, producing shorter oligosaccharides (dextrins). In contrast, exoglycosidases cleave sugar residues one at a time from the non-reducing end of the chain.

Hyaluronic acid is a linear, unbranched polymer with repeating disaccharide units containing glucuronic acid (negatively charged). The polymer chains are long and rigid, and they trap a large volume of water, forming a viscous solution that acts as an excellent shock absorber and lubricant.

The anomeric carbon is derived from the carbonyl carbon of the open-chain form. In glucose, this is C-1. The nucleophilic attack by the C-5 hydroxyl group on this planar carbonyl carbon can occur from either face, creating the two possible anomeric configurations: α (-OH down) or β (-OH up).

The enzyme lactase (a β-galactosidase) is specific for the β-configuration of the galactose residue and the 1,4 linkage to glucose. Sucrase acts on the α,β-1,2 linkage of sucrose, and maltase acts on the α-1,4 linkage of maltose.

The "sweetness" is a function of binding affinity to the receptor. Fructose exists in solution in several forms, including a significant proportion of a sweet furanose form, which interacts more optimally with the receptor's binding site than the pyranose forms of glucose.

Peptidoglycan (murein) is unique to bacteria. Its carbohydrate backbone is a linear chain of alternating N-acetylglucosamine (NAG) and N-acetylmuramic acid (NAM) linked by β-1,4 glycosidic bonds. Lysozyme hydrolyzes this specific bond.

Fructose is phosphorylated to fructose-1-phosphate, which is cleaved to glyceraldehyde and dihydroxyacetone phosphate, entering glycolysis downstream of PFK-1. This bypasses a critical regulatory checkpoint, allowing a rapid, unregulated influx of carbon that can overload the TCA cycle and lead to increased de novo lipogenesis.

A non-reducing sugar lacks a free carbonyl group, so it cannot participate in non-enzymatic glycation (Maillard reaction) with amino groups. This stability is crucial in the hemolymph, where high concentrations of trehalose could otherwise react with and damage circulating proteins.

Starch is synthesized in plastids. Transitory starch is synthesized in chloroplasts during photosynthesis and broken down at night. Storage starch is synthesized and stored in amyloplasts (non-pigmented plastids) in tissues like tubers, seeds, and roots.

Dextran is a branched bacterial polysaccharide of D-glucose, with a backbone of α-1,6 glycosidic linkages and α-1,3 branch points. Its high molecular weight and colloidal osmotic properties make it useful for drawing fluid into the circulatory system.

Cellulose's linear, unbranched chains allow them to lie parallel and form extremely stable, regular intermolecular hydrogen bonds. These strong lateral interactions create crystalline microfibrils that exclude water and are highly resistant to hydrolysis.

The osazone formation involves C-1 and C-2 of a reducing sugar. Glucose and fructose differ only in the configuration at C-1 and C-2 (glucose is an aldose, fructose is a ketose). The reaction eliminates these differences, forming an identical phenylosazone. The rest of the carbon skeleton is identical.