Citric Acid Cycle 1-3 Flashcards
Describe the functions of the Citric Acid Cycle.
The citric acid cycle is a common metabolic pathway for fuel molecules.
It is a crucial part of many catabolic processes.
The cycle serves as a gateway to the aerobic metabolism of any molecule that can be transformed into an acetyl group or component of the cycle.
Does not produce ATP directly.
Does not include O2 as a reactant.
Removes e-‘s (by oxidation) and passes them on to form NADH and FADH2.
State the ways in which the cycle is efficient.
Process is cyclical
A small number of citric acid molecules can make many NADH and FADH2.
Explain the importance of Acetyl CoA in the citric acid cycle.
Acetyl CoA comes from further oxidation of pyruvate from glycolysis and fatty acids (this happens in mitochondrial matrix).
Acetyl CoA sits in the centre of energy production for the cell as it allows different intermediates into the main energy producing pathway of the citric acid cycle.
Describe the synthesis/production of acetyl CoA
Pyruvate is the end product of glycolysis, and through the action of pyruvate dehydrogenase complex, the pyruvate molecule is decarboxylated, oxidised and then receives the CoA complex.
Describe the series of reactions associated with the different subunits of the pyruvate dehydrogenase complex.
E1 - catalyses the first decarboxylation of pyruvate.
E2 - transfers the acetyl group to coenzyme A.
E3 - recycles the lipoyllysine.
Explain how cells regulate the citric acid cycle when there is enough energy.
The regulation of production of pyruvate dehydrogenase is controlled by the needs of the cell.
If the cell has enough energy:
Then pyruvate is negatively inhibited to reduce the activity of pyruvate dehydrogenase and the production of Acetyl CoA, the excess energy is used as one of the 3 negative inhibitors.
Explain how cells regulate the citric acid cycle when the cell needs energy.
If the cell needs energy, the positive regulators, ADP and Pyruvate positively regulate pyruvate dehydrogenase and increase it’s activity, ultimately producing more Acetyl CoA and ATP.
Describe the oxidative decarboxylation of isocitrate to alpha-ketoglutarate.
Isocitrate is oxidised to alpha-ketoglutarate, which in turn reduced NAD to NADH. The COO- is removed from the isocitrate as carbon dioxide (CO2).
Describe the oxidative decarboxylation of alpha-ketoglutarate to succinyl CoA.
Alpha-ketoglutarate is oxidised to Succinyl CoA, coenzyme A binds to where COO- was bound and carbon dioxide is released, and CoA attaches on the molecule. NAD is reduced to NADH.
Describe the dehydrogenation of Succinate to Fumarate.
From Succinate, 2 hydrogens are taken from two neighbouring carbons, this causes a C=C double bond to form.
This results in the production of FADH2.
Describe the dehydrogenation of Malate to Oxaloacetate.
From Malate, 1 hydrogen is taken from the OH group creating a C=O bond. This produces NADH by the reduction of FAD.
Describe the links of the citric acid cycle to other biochemical processes.
The TCA cycle can provide the biosynthetic precursors of other biochemical processes.
The Acetyl CoA that combines with oxaloacetate to make citrate, comes from the further oxidation of pyruvate, after glycolysis.
This pyruvate can also convert to oxaloacetate by the enzyme pyruvate carboxylase (gluconeogenesis).
