1. Balance Sheet for the Citric Acid Cycle The citric acid cycle has eight enzym
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Question
1. Balance Sheet for the Citric Acid Cycle The citric acid cycle has eight enzymes: citrate synthase, aconitase, isoci trate dehydrogenase, ?-ketoglutarate dehydrogenase, succinyl CoA synthetase, succinate dehydrogenase, fumarase, and malate dehydrogenase (a) Write a balanced equation for the reaction catalyzed by each enzyme (b) Name the cofactor(s) required by each enzyme reaction. (c) For each enzyme determine which of the following describes the type of reaction(s) catalyzed: condensation (carbon-carbon bond formation); dehydration (loss of wa ter); hydration (addition of water); decarboxylation (loss of CO2); oxidation-reduction; substrate-level phosphorylation; isomerization. (d) Write a balanced net equation for the catabolism of acetyl-CoA to CO2Explanation / Answer
1. Citric Acid Cycle is otherwise also known as "KREB'S CYCLE".
(A)
Below are the reaction equations catalysed by each enzyme:-
Citrate synthase :
Oxaloacetate + Acteyl-CoA --> Citryl-CoA + H2O -->Citrate + CoA (type- Aldol condensation)
Aconitase : This is actually a 2 step mechanism.
Citrate <-(forward rxn removes water)-> cis-Aconitate <-(forward react with water)-> Isocitrate
(type- Hydration and dehydration)
Isocitrate dehydrogenase :
Isocitatrate + NAD+ --> Oxalosuccinate + NADH + H+ (oxidation)
Oxalosuccinate + H+ --> CO2 + ?-ketoglutarate (decarboxylation)
Overall reaction is ------ Isocitrate + NAD+ --> ?-ketoglutarate +CO2 + NADH
?-Ketoglutarate dehydrogenase :
?-ketoglutarate+ CoA + NAD+ -(?-ketoglutarate dehydrogenase complex)-> succinyl-CoA + CO2A +NADH
(Oxidativedecarboxylation)
Succinyl-CoA synthetase :
Succinyl CoA + Pi + GDP --> succinate + CoA + GTP (substrate-level phosphorylation)
Succinate dehydrogenase :
His-FAD + succinate <--> His- FADH2 + fumarate (oxidation)
Fumarase :
Fumarate + H2O --> L-Malate (hydration)
Malate dehydrogenase :
Malate + NAD+ <--> oxaloacetate + NADH + H+ (oxidation)
(B) The cofactors required in Kreb's cycle by each enzyme reaction is given below.
ENZYME COFACTORS
isocitrate dehydrogenase NADP+
a-ketoglutarate dehydrogenase NAD+, FAD, LIPOATE
succinic thiokinase ATP
succinate dehydrogenase FAD, FeS GROUP
malate dehydrogenase NAD+
(C)
Plz refer to my answer 1.(A) where I have given the type of reaction in bracket in bold italic.
(D)
The Net Equation: Acetyl-S-CoA + 4 oxidized coenzymes[3 NAD+ + 1 FAD] + ADP + Phosphate --> 2 CO2 + 1 ATP + CoA-SH + 4 reduced coenzymes[3 NADH + 1 FADH2]
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