Re: How many ATP are generated ?

Hi Olive,

Lactic Acid is the byproduct of glycolysis under anerobic conditions. It is made from Pyruvate in order to recycle NADH into NAD+ and permit additional rounds of glycolysis in skeletal muscle. I believe that Lactic Acid is converted back into Pyruvate in the liver, and that Pyruvate is then released from the liver into the blood stream where it is picked up by needy tissues.

In the process of converting of Lactic Acid back to Pyruvate, NAD+ is converted to NADH, so that there is no net loss of reducing equivalents. In the scenario that you described in your question, where 30 ATP equivalents are generated from Glucose, 2 ATP are generated in glycolysis (where 1 Glucose is converted to 2 Pyruvates), 3 are generated from the 2 NADH generated in glycloysis via oxidative phosphorylation, and the remaining 25 are generated as a result of the citric acid cycle and oxidative phosphorylation. Since these 25 ATP equivalents are generated for every 2 Pyruvate molecules that leave glycolysis, 12.5 ATP equivalents can be attributed to each Pyruvate.

However, since Pyruvate is generated from Lactic Acid in your question, we can add the 1.5 ATP generated from the NADH made when Lactic Acid was convereted to Pyruvate in Lactic Acid's favor, so that 14 ATP equivalents are generated for each Lactic Acid that is oxidized.

I hope that makes sense, Olive. If the numbers still don't seem right, or you want more information about the ATP equivalents generated in glycolysis and oxidative phosphorylation, I'm sure that you will find detailed explainations in the pertinent chapters of a college-level biochemistry text, such as Biochemistry by Lubert Stryer. You can also search our archives for answers containing the words glycolysis, lactic acid, skeletal muscle, and pyruvate.