Krebs Cycle MCQs

Mitochondria is involved in the synthesis of energy-rich compound ATP by oxidative phosphorylation Also called as "powerhouse of the cell" Reference: Ganong, 25th edition page no.36

Ans. is 'a' i.e., Pyruvate carboxylse [Ref Dinesh Puri 3`die p. 177] Conversion of pyruvate to malate by the cytoplasmic malic-enzyme. Malate can then enter the mitochondrion as a substrate for the TCA cycle. Pyruvate may react with aspartate or glutamate in transaminase reactions, producing the TCA cycle intermediates oxalocetate and a- ketogluarate, respectively. Several glycogenic amino acids may serve as source of TCA intermediates

Ans. is 'a' i.e., Both exergonic and endergonic reactions takes place [Ref : Harper 29th/e p. 151, 166] Citric acid cycle is called amphibolic pathway because it acts as a link between anabolic (endothermic) and catabolic (exothermic) pathways.

Ans. is 'a' i.e., alpha-Ketoglutarade - Succinyl CoA [Ref Harper's 28th/e p. 147, 154] Regulating steps in TCA Cycle are catalyzed by : a) Citrate Synthase : Catalyzes condensation of acetyl CoA & oxaloacetate to from citrate. Isocitrate dehydrogenase : Catalyzes the conversion of isocitrate to a-ketoglutarate by decarboxylation. a-ketoglutarate dehydrogenase : Catalyzes the conversion of a- ketoglutarate to succinyl CoA

Ans. is 'a' i.e., a-ketoglotarate synthase [Ref Harper 28th/e p. 147, 154]

In well fed state fatty acid (Palmitic acid) synthesis is active TCA cycle also takes place, Citrate and oxalosuccinate are intermediates in TCA Cycle Oxalosuccinate is an intermediate in the reaction of Isocitrate Dehydrogenase of TCA Cycle Acetoacetate, a primary ketone body is synthesized in fasting state. Reference: Harper's 32 nd edition, page 229

Ans. is 'b' i.e., ATP generation of pumping of proton [Ref Harper 29'die p. 125-127] Chemoiosmotic theory It states that "free energy of electron transport" is conserved by pumping protons from mitochondrial matrix to the intermembrane space, so as to create an electrochemical proton gradient across the inner mitochondrial membrane, with outer side of membrane is positively charged as compared to inside. Electrochemical potential of this gradient is used to synthesize ATP by ATP synthase

The enzymes of the citric acid cycle and β-oxidation, the respiratory chain complexes, and the machinery for oxidative phosphorylation are all found in mitochondria. Option A: Citric acid cycle breakdown acetyl CoA into CO2, H2O and reducing equivalents. Option B: Glycolysis breakdown glucose into pyruvate and producing reducing equivalents. Option D: Beta oxidation of fatty acids oxidizes fatty acid and producing reducing equivalents. Option C: Then the respiratory chain collects and transports all reducing equivalents, directing them to their final reaction with oxygen to form water, and oxidative phos phorylation is the process by which the liberated free energy is trapped as high-energy phosphate. Reference: Harper's illustrated biochemistry 32nd edition CH 13 PN 118