Energy and Metabolism

ID #2209

I'm trying to sort out the differences in respiration for eukaryotes/prokaryotes/anaerobic conditions. So eukaryotes and prokaryotes both do glycolysis/krebs/ETC. but the difference is that this all takes place in the cytoplasm for prokaryotes. In anaerobic conditions, the only yields come from glycolysis? Is that correct? Why is it that the NADH from glycolysis only produces 4 ATP in eukaryotes instead of 6?

Both eukaryotes and prokaryotes that undergo aerobic respiration can perform glycolysis, pyruvate oxidation, the Krebs Cycle, and the ETC+oxidative phosphorylation. Glycolysis always occurs in the cytoplasm of all living cells. The Krebs Cycle occurs in the cytoplasm of prokaryotes and in the mitochondrial matrix in eukaryotes. The ETC occurs in the plasma membrane of prokaryotes and the inner mitochondrial membrane of eukaryotes. 

Under anaerobic conditions, ATP is only made from glycolysis since the Krebs Cycle and the ETC only occur in the presence of oxygen (as the terminal electron acceptor). 

For your third question, NADH that are produced by eukaryotic cells during glycolysis need to be imported from the cytoplasm into the mitochondrial matrix for the ETC. The NADH molecules can easily pass through porins found in the outer mitochondrial membrane, but they need to be actively transported through the inner mitochondrial membrane. This active transport costs one ATP per NADH, so the net ATP produced from each NADH reduced during glycolysis is 2.

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