<prompt> Net gain of ATP in glycolysis571520  <response>: During the anaerobic oxygen deficient condition, when one molecule of glucose is conveed into 2 molecules of lactate, there is a net yield of 2 molecules of ATP. 4 molecules of ATP are synthesized by the 2 substrate level phosphorylations steps 6 and 9. But 2 molecules of ATP are used in the steps 1 and 3, hence the net yield is only 2 ATP Table 9.4. The whole reaction is summarized as Glucose 2 Pi 2 ADP -- 2 Lactate 2 ATP iv.But when oxygen is in plenty, the two NADH molecules, generated in the glyceraldehyde3-phosphate dehydrogenase reaction step 5, can enter the mitochondrial electron transpo chain for complete oxidation. As each NADH provides 2.5 ATPs, this reaction generates 2.5 x 2 5 ATPs. Thus when oxygen is available, the net gain of energy from the glycolysis pathway is 7 ATPs Table 9.5.Hence the ATP yield from glycolysis is different in anaerobic and aerobic conditions.Ref: DM Vasudevan, 7th edition, page no: 112 