Feedback for Multiple Choice Quiz 29 #2

  1. The other four reactions (on the "right side" of the TCA cycle) are all controlled by cycle intermediates and/or cofactors. Each of the four is also highly exergonic (see Table 19.2).

  2. The enzymes responsible are:
    a) Pyruvate dehydrogenase
    b) Pyruvate-aspartate transaminase (also produces OAA)
    c) Lactate dehydrogenase
    d) Pyruvate carboxylase
    e) Serine biosynthesis does not involve pyruvate

  3. Citrate synthese is highly exergonic (DG°' = -32 kJ/mol). The other four vary with DG°' = -4 to +6 kJ/mol.

  4. None of the TCA cycle metabolic intermediates are phosphorylated. Compare glycolysis where every metabolite between glucose and pyruvate is phosphorylated.

  5. Malate is transported to the cytosol where it can be converted to pyruvate, CO2, and NADPH; this transfers reducing equivalents indirectly to the cytosol. The dinucleotides NADH, NADPH, and FADH2 cannot cross the mitochondrial membrane (no carrier exists).
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