Question: Does Lactate Production Occur in the Mitochondrion or the Sarcoplasm of the cell?
Answer: Sarcoplasm of the cell.
Question: What is the cause of acidosis or the 'burn?'
Answer: The production of H+ from the hydrolysis of ATP.
Question: What is the fate of the lactate formation? Answer: 50-75% of the lactate will be converted back to pyruvate (in the liver) and used for fuel in a process called the Cori cycle.
Lactate Formation Story Written in Paragraph Form
At the end of glycolysis 2 NADH+H+ and 2 pyruvate are two of the molecules of interest. During steady state conditions the NADH+H+ molecules go into the inner membrane of the mitchondrion and reduce FAD to FADH2 (NADH+H+ cannot get past the inner membrane). Pyruvate goes directly into the mitochondrion matrix to be oxidized. However, during strenuous exercise the energy demands exceed the oxygen supply in the ETC, causing a back-up in the ETC. NADH+H+ is inhibited and therefore donates its hydrogens to pyruvate, reducing pyruvate temporarily to lactate. NAD+ can then return to Step 6 of glycolysis to pick-up more hydrogens, and glycolysis can continue. Note that 50-75% of the lactate will be converted back to pyruvate and used for fuel in the Cori cycle.
Andrea Schoeny, 2011
Shuttle of NADH +H+ to FAD in the Mitochondrion in Steady State Conditions
Inhibited Shuttle of NADH +H+ to FAD in the Mitochondrion in Strenuous Exercise Conditions