Today I am just briefly going to discuss the fate of pyruvate.
SO, THE BIG QUESTION IS WHAT HAPPENS TO PYRUVATE AFTER IT IS MADE FROM GLYCOLYSIS.
Well, the fate of pyruvate depend on two factor whether oxygen is present or not.
In the presence of oxygen (aerobic condition) pyruvate is converted to acetyl-CoA by the enzyme pyruvate dehydrogenase which enters the TCA or Kerb cycle where large (most) of ATP molecules is generated.
In the absence of oxygen (anaerobic conditions) pyruvate undergoes fermentation either lactic acid fermentation or alcohol fermentation. In this fermentation reaction NO ATP molecules is generated, however reduced NAD+ is generated from fermentation. The NAD+ regenerated is used in the glycolysis process to make ATP. Therefore these cells only get energy (2 ATP) from glycolysis and not from the TCA cycle. Example of such cell are red blood cells.
LACTATE FERMENTATION: occurs in muscle, erythrocytes, and some other cells. The pyruvate made in red blood cells is converted to lactate by the enzyme lactate dehydrogenase. This mite be confusing since there are a lot of oxygen in red blood so why pyruvate isn’t converted to acetyl CoA and enter the TCA cycle. Pyruvate made from glycolysis does not enter the TCA cycle because the red blood cells do not have mitochondria which is the site for the TCA cycle (the TCA cycle occurs in the matrix of the mitochondria). Since NAD+ concentration is low the main purpose of fermentation in red blood cell is to regenerate NAD+ to enter the glycolysis pathway to yield ATP, since glycolysis the main manufacture of energy (ATP) for red blood cells.
Moreover lactate is made in muscles. This occurs when the muscles are under vigorous muscle contraction due to exercise activities, when this occurs lactic acid builds up in the muscles causing cramps and pain. This is one way the brain is telling the body to STOP!!! When oxygen become present in the muscle the pyruvate is convert to acetyl CoA which may enter the TCA cycle to generate ATP.
ETHANOL FERMENTATION: is a two step reaction which uses 2 enzymes; pyruvate decarboxylase and alcohol dehydrogenase. TPP is an co-factor for both of these enzymes.
REMINDER: 2 molecules of pyruvate made from one molecules of glucose therefore two molecules of NAD+ is regenerated.
NOTE: The net gain of ATP molecules made from one glucose molecule which enters the glycolysis pathway is two (2).
THE IMAGES USED ABOVE WAS TAKEN FROM THE SITES: