BioChem

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Author:
smg71206
ID:
8861
Filename:
BioChem
Updated:
2010-03-02 18:27:12
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TCA Citric Acid Cycle
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Description:
TCA/Citric Acid Cycle
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  1. How is the TCA Cycle linked to glycolysis?
    The TCA Cycle begins with Citrate a C6 molecule. To get citrate, OAA (C4) is combined with Acetyl-CoA. Acetyl-CoA is produced from pyruvate reduction by pyruvate dehydrogenase complex.
  2. How is the TCA cycle linked to the ETC?
    During the TCA cycle 3 NADH, 1 FADH2 and 1 GTP is produce per rotation. Therefore, for every glucose molecule, which yeilds 2 pyruvate, 6 NADH, 2 FADH2 and 2 GTP are produced. These are then provide the "energy" to produce ATP in the ETC.
  3. How is the TCA cycle linked to gluconeogenesis?
    The end product of the TCA cycle, OAA can be used as the starting substrate for gluconeogenesis. Therefore, when glucose levels are low, instead of returning to the TCA cycle OAA can be converted to glucose.
  4. Where does the TCA cycle take place?
    The TCA cycle takes place within the mitochondrial matrix.
  5. Where do the chemical transformations occur in TCA cycle?
    • There are 8 chemical rxn that take place in the TCA cycle.
    • 1) OAA + Acetyl-CoA + Citrate synthase => Citrate
    • 2) Citrate + Aconitase => Isocitrate
    • 3) Isocitrate + isocitrate dehydrogenase + NAD+ => a-ketoglutarate + NADH + H+
    • 4) a-Ketoglutarate + a-Ketoglutarate dehydrogenase complex => Succinyl CoA + CO2 + NADH
    • 5) Succinyl CoA + Succinyl CoA synthetase + GDP => Succinate + CoA + GTP
    • 6) Siccinate + Succinate dehydrogenase + FAD => Fumarate + FADH2
    • 7) Fumarate + Fumarate dehydrogenase + H2O => Malate
    • 8) Malate + Malate dehydrogenase + NAD+ => OAA + NADH
  6. In which steps are GTP, FADH2 and NADH produced
    • GTP - in the oxidation of Succinate CoA to Succinate, in combination with a Pi and GDP.
    • FADH2 - in the oxidation of Succinate to Fumarate.
    • NADH - oxidation of a-Ketoglutarate to Succinyl Coa and oxidation of malate to OAA
  7. Describe the allosteric regulation of isocitrate dehydrogenase.
    Used to oxidize Isocitrate to a-Ketoglutarate, this step is inhibited by the presence of ATP and NADH. It is stimulated by ADP. Therefore, when ATP/NADH concentrations are hight, the rxn does not occure.
  8. Descibe the allosteric regulation of a-ketoglutarate dehydrogenase.
    Used to oxidize a-Ketoglutarate to Succinyl CoA buy adding CoA a S atom to yeild Succinyl CoA, CO2 and NADH. This step has NO stimulating factor, rather it only has inhibiting factors: ATP, succinyl CoA and NADH.
  9. Describe how citrate plays a role in regulatin the glycolytic and gluconeogenic pathways.
    For citrate to be produced, the break down of glucose to pyruvate is required. Citrate is required to perform the TCA cylce, which produces GTP, FADH2 and NADH need in the ETC. However, this decreases glucose levels. If there is no avaliable supply of glucose, it need to be produced. The final product of the TCA cycle is OAA with can be used to produce glucose via gluconeogenesis.
  10. Why can't Fatty Acids be QUANTITATIVELY converted to carbohydrates?
    Although FAs can enter the TCA cycle there is no way to monitor the C atom that the FA provide to the TCA cycle. In the cycle C atoms are lost and gained, however, there is no way to know which atom is lost and where it came from. Therefore, you cannot quantitatively convert FAs to carbohydrates. Most are removed as malate or go into the gluconeogenisis process or cleaved as CO2.

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