For each molecule of glucose entering into glycolysis, there is a resulting two molecules of pyruvate. Glucose is a 6-carbon molecule and pyruvate is a 3-carbon molecule. No carbon is gained or lost in this stage of energy production.

While four ATP are produced during glycolysis, two are also consumed in the process. This results in a net production of two molecules of ATP. Additionally two of the high energy intermediates NADH are produced for each molecule of glucose during glycolysis.

Glycolysis is the first step of aerobic respiration and takes place in the cytosol of the cell. The products of glycolysis (pyruvate and NADH) are transported into the mitochondria to continue the respiration processes. The Krebs cycle takes place in the mitochondrial matrix. The proteins of the electron transport chain are situated in the inner mitochondrial membrane, generating the proton gradient across this membrane by expelling protons into the intermembrane space.

Glycolysis is the first step of both aerobic and anaerobic cellular respiration. It results in the formation of two molecules of NADH, ATP, and pyruvate. FADH2 is not produced until the Krebs (citric acid) cycle.