1) Write the chemical equations for the three reactions in the citric acid cycle
ID: 101908 • Letter: 1
Question
1) Write the chemical equations for the three reactions in the citric acid cycle in which NADH is produced, including the enzymes involved. None of these reactions involves molecular oxygen (O2), but all three reactions are strongly inhibited by anaerobic conditions; explain why.
2) During electron transfer through the mitochondrial respiratory chain, the overall reaction is: NADH + 1/2 O2 + H+ -> NAD+ + H2O
3) The measured membrane potential across the inner membrane of a liver mitochondrion is approximately 0.168V. The pH of its matrix is 0.9 units higher than that of its intermembrane space.
a) Considering the number of proton ions transported through the mitochondrial inner membrane during oxidation of NADH, show how much energy of NADH oxidation is preserved in the form of electrochemical gradient?
b) What percentage of this energy is converted to produce ATP? ATP ® ADP + Pi DG'° = -31.4 kJ/mol
Assume that log ([ATP]/[ADP][Pi]) = - 1.13 and that 3 molecules of ATP are produced per pair of electrons transported by the respiratory chain.
d) Two transport processes across the inner membrane of the mitochondria reduce the proton motive force. Describe both process and briefly explain how they reduce the proton motive force.
Given the following reduction potentials, calculate the standard free-energy change, DG'°, for the reaction. (F = 96.48 kJ/V·mol): 1/2O2 + 2H+ + 2e- -> H2O E’0 = +0.816V
NAD+ + H+ + 2e- -> NADH E’0 = -0.320V
Note that RT= 2.478 kJ/mol
Explanation / Answer
Acetyl-CoA is formed from the breakdown of sugars by glycolysis which yield pyruvate that in turn is decarboxylated by the enzyme pyruvate dehydrogenase generating acetyl-CoA according to the following reaction scheme:
CH3C(=O)C(=O)Opyruvate + HSCoA + NAD+ CH3C(=O)SCoAacetyl-CoA + NADH + CO2
acetyl-coA is one important component of citric acid cycle.
Isocitrate + NAD+ Oxalo succinate + NADH +H+ (IN PRESENCE OF ISOCITRATE DEHYDROGENASE)
alpha ketoglutarate +NAD+ +CoA-SHSuccinyl Co-A+NADH + H+ +CO2 (IN PRESENCE OF ALPHA KETO GLUTARATE DEHYDROGENASE)
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