Biochemistry - MCQ Practice Questions

Denaturation is disruption of non-covalent interactions (hydrogen bonds, hydrophobic interactions, ionic bonds) that maintain higher-order structures. Peptide bonds (primary structure) remain intact. Some proteins can refold (renature) if conditions permit, as demonstrated by Anfinsen's ribonuclease experiments.

Leucine is a nonpolar, hydrophobic amino acid with an isobutyl side chain. Serine and threonine are polar uncharged, while aspartate is acidic and polar.

Collagen triple helix is stabilized by hydrogen bonds between the three polypeptide chains and covalent cross-links (lysine and hydroxylysine residues) between molecules, providing mechanical strength.

LDH catalyzes the interconversion of lactate and pyruvate using NAD+ as an electron acceptor and NADH as an electron donor in the coupled redox reaction.

ER chaperones like BiP (heat shock protein 70) assist in protein folding, prevent aggregation, and aid in proper disulfide bond formation during synthesis.

Peptide bonds form through a condensation reaction between the carboxyl group (-COOH) of one amino acid and the amino group (-NH2) of another, releasing H2O. They are covalent and stable.

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.