Biochemistry - MCQ Practice Questions

Ribose is a pentose sugar (5-carbon sugar) that is a component of RNA. Deoxyribose is found in DNA, while glucose and fructose are hexose sugars.

Glycogen, the storage polysaccharide in animals, is primarily stored in the liver (100-120g) and skeletal muscles (400-500g). The liver glycogen maintains blood glucose, while muscle glycogen is used locally.

Maltose consists of two glucose units linked by an α(1→4) glycosidic bond. This is a reducing disaccharide formed during starch digestion.

Phosphoglucose isomerase (PGI) catalyzes the reversible conversion of glucose-6-phosphate to fructose-6-phosphate in glycolysis, step 2.

Sucrose (table sugar) is a disaccharide composed of one glucose and one fructose unit linked by an α(1→2) glycosidic bond. It is a non-reducing sugar.

Simple carbohydrates include monosaccharides (glucose, fructose, galactose) and oligosaccharides (2-10 units like sucrose, maltose, lactose). Complex carbohydrates are polysaccharides with >10 units (starch, glycogen, cellulose).

Phosphoglucose isomerase catalyzes the reversible isomerization of glucose-6-phosphate to fructose-6-phosphate, the second step of glycolysis.

Complete oxidation of glucose yields approximately 30-32 ATP molecules when accounting for the cost of transporting NADH across the mitochondrial membrane (P/O ratio of 2.5 for NADH and 1.5 for FADH2).

Sucrose (α-glucose + β-fructose) is a non-reducing sugar because both anomeric carbons are involved in the 1,2-glycosidic linkage, making it unable to reduce Benedict's reagent.

Fructokinase phosphorylates fructose to fructose-1-phosphate in the liver. This bypasses the rate-limiting phosphofructokinase step, making fructose metabolism less regulated.

Sedoheptulose is a seven-carbon ketose (heptose) that participates in the non-oxidative phase of the pentose phosphate pathway.

Glycogen synthase catalyzes the transfer of glucose from UDP-glucose to the C4-OH group of the terminal glucose in glycogen, forming α-1,4-glycosidic bonds.

Mannose differs from glucose only at the C2 position (the configuration of the -OH group and -H). Therefore, mannose is the C2 epimer of glucose.

Fructose is a ketohexose (6-carbon ketone sugar) with the molecular formula C₆H₁₂O₆, making it a structural isomer of glucose. Galactose and mannose are aldohexoses (epimers of glucose), while ribose is a pentose.

Maltose consists of two glucose units linked by an α-1,4-glycosidic bond. Sucrose contains glucose and fructose, lactose contains glucose and galactose, and trehalose has an α-1,1-glycosidic linkage.

Sucrose is a non-reducing disaccharide formed by α-1,2-glycosidic linkage between C1 of glucose and C2 of fructose, blocking both anomeric carbons. It cannot mutarotate or act as a reducing sugar. Other options are reducing sugars with free anomeric carbons.

Ribose is a 5-carbon (pentose) sugar, while glucose, galactose, and fructose are hexoses (6-carbon sugars).

Phosphoglucose isomerase catalyzes the isomerization of glucose-6-phosphate to fructose-6-phosphate in the second step of glycolysis.

Phosphofructokinase-1 (PFK-1) catalyzes the phosphorylation of fructose-6-phosphate to fructose-1,6-bisphosphate and is subject to allosteric inhibition by ATP and citrate.

Anaerobic glycolysis produces 4 ATP molecules but consumes 2 ATP, resulting in a net gain of 2 ATP per glucose molecule.