Total number of dehydrogenases Krebs cycle -

Ans. is 'c' i.e., 4 o There are 4 dehydrogenase in TCA cycle(i) Isocitrate dehydrogenase, (ii) a-ketoglutarate dehydrogenase, (iii) Succinate dehydrogenase, (iv) Malate dehydrogenase.Important facts about TCA cycleo First product of the cycle is citrate Q synthesized by enzyme citrate synthase.o The final product is oxaloacetate which condenses with acetyl CoA to form the first product (citrate) of next cycle.o There are two irreversible steps : (i) oxaloacetate to citrate catalysed by citrate (synthase) Q, and (ii) a- ketoglutarate Q to succinyl CoA. catalyzed by a-ketoglutarate dehydrogenase,o Water (H2O) is lost at 3 reactions: (i) Conversion of citrate to cis-aconitate Q by aconitase, (ii) Conversion of cis-aconitate to isocitrate by aconitase, (iii) Conversion of fumarate to malate by fumarase.o NADH is produced and CO2 is liberated Q at 3 steps : (i) Conversion of isocitrate to a-ketoglutarate by isocitrate dehydrogenase Q, (ii) Conversion of a-ketoglutarate to succinyl CoA by a-ketoglutarate dehydrogenase, (iii) Conversion of L-malate to oxaloacetate by malate dehydrogenase,o FADH, is produced at 1 step i.e.. Conversion of succinate to fumarate by succinate dehydrogenase,o GTP is produced by substrate level phosphorylation by succinate thiokinase which is coverted ATP as GTP and ATP are interconvertible.oAs TCA cycle occurs in mitochondria, it is absent in cells which lack mitochondria, e.g., erythrocytes(r).