Describe TCA cycle in detail. Give its energetics and features.
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A)In detail TCA:
Tricarboxylic acid cycle, (TCA cycle),also called Krebs cycle and citric acid cycle, the second stage of cellular respiration, the three-stage process by which living cells break down organic fuel molecules in the presence of oxygen to harvest the energy they need to grow and divide. This metabolic process occurs in most plants, animals, fungi, and many bacteria. In all organisms except bacteria the TCA cycle is carried out in the matrix of intracellular structures called mitochondria.
B)Energetics of the Kreb’s Cycle
Keeping in mind that 1 molecule of glucose would produce 2 molecules of pyruvate via glycolysis. Hence the net energy produced by the Kreb’s cycle for each molecule of pyruvate is doubled for each molecule of glucose. Thus net energy yield in Kreb’s cycle can be summarized as follows for each molecule of glucose:
Reaction
Number of ATP or reduced coenzyme formed*
Number of ATP ultimately formed
2 Pyruvate → 2 acetyl CoA
2 NADH
5
2 Isocitrate → 2 α- ketoglutarate
2 NADH
5
2 α- ketoglutarate → 2 succinyl CoA
2 NADH
5
2 Succinyl CoA → 2 succinate
2 ATP
2
2 Succinate → 2 fumarate
2 FADH2
3
2 Malate → 2 oxaloacetate
2 NADH
5
TOTAL
25 ATP
* Note- This is calculated as 2.5 ATP per NADH and 1.5 ATP per FADH2. This is because there are multiple electron transport shuttle pathways through which these can be broken to ATP.
C.Features
1.Acetyl group (2 carbon organic acid) from acetyl CoA transferred to 4 carbon molecule oxaloacetate 2.This forms a new C6 compound called tricarboxylic acid (TCA) or, citrate (citric acid) 3. Citrate then oxidized in a 7 step pathway to regenerate oxaloacetate and release 2 CO2 4. Oxaloacetate then combines with a new molecule of acetyl CoA to begin a new cycle.
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Tricarboxylic acid cycle, (TCA cycle),also called Krebs cycle and citric acid cycle, the second stage of cellular respiration, the three-stage process by which living cells break down organic fuel molecules in the presence of oxygen to harvest the energy they need to grow and divide. This metabolic process occurs in most plants, animals, fungi, and many bacteria. In all organisms except bacteria the TCA cycle is carried out in the matrix of intracellular structures called mitochondria.
B)Energetics of the Kreb’s Cycle
Keeping in mind that 1 molecule of glucose would produce 2 molecules of pyruvate via glycolysis. Hence the net energy produced by the Kreb’s cycle for each molecule of pyruvate is doubled for each molecule of glucose. Thus net energy yield in Kreb’s cycle can be summarized as follows for each molecule of glucose:
Reaction
Number of ATP or reduced coenzyme formed*
Number of ATP ultimately formed
2 Pyruvate → 2 acetyl CoA
2 NADH
5
2 Isocitrate → 2 α- ketoglutarate
2 NADH
5
2 α- ketoglutarate → 2 succinyl CoA
2 NADH
5
2 Succinyl CoA → 2 succinate
2 ATP
2
2 Succinate → 2 fumarate
2 FADH2
3
2 Malate → 2 oxaloacetate
2 NADH
5
TOTAL
25 ATP
* Note- This is calculated as 2.5 ATP per NADH and 1.5 ATP per FADH2. This is because there are multiple electron transport shuttle pathways through which these can be broken to ATP.
C.Features
1.Acetyl group (2 carbon organic acid) from acetyl CoA transferred to 4 carbon molecule oxaloacetate 2.This forms a new C6 compound called tricarboxylic acid (TCA) or, citrate (citric acid) 3. Citrate then oxidized in a 7 step pathway to regenerate oxaloacetate and release 2 CO2 4. Oxaloacetate then combines with a new molecule of acetyl CoA to begin a new cycle.
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