Question

Do the NADH molecules produced from the pre-Krebs cycle (where pyruvate is converted into acetyl CoA) enter the electron transport chain? Why or why not?

Answer 1

The NADH produced during the conversion / oxidation of pyruvate into Acetyl CoA will enter into the ETS or it will be used in other pathways depends upon the organism type.

the microorganisms, anaerobic bacteria, there NADH is used for the reduction of acetyl CoA into some useful product like ethyl alcohol because TCA cycle and ETS is not found in bacteria as they lack mitochondria.

in eukaryotic Microorganism, TCA cycle and ETS both are found because they have mitochondria the power house, which use oxygen for complete oxidation of acetyl CoA into CO2 and H2O, so all the generated NADH along with FADH2 will enter into the ETS and produce ATP using the energy of protons.

so, as per the question NADH enter into ETS in eukaryotes but in bacteria since ETS is absent they do not enter rather used up in some other process/pathway