Developing Energy Pathways:  Aerobic Energy System

The oxidative system involves four methods to generate ATP:

ü      Slow glycolysis (aerobic glycolysis)

ü      Krebs cycle

ü      Electron transport chain

ü      Beta oxidation

The first method is slow glycolysis.  It comes into play when exercise is sustained for 1-3 minutes.  The break down of glucose consists of a series of enzymatic reactions.  The end result of the enzymatic reactions is ATP.  An individual glucose makes 2 pyruvate molecules and 2 ATP.  Pyruvate molecules enter into the Krebs cycle, but oxygen must be available for this to happen.  Click in this link for a clear understanding of the enzymatic reactions that convert proteins, fats, and carbohydrates into intermediate substances- How the Krebs Cycle Works.  In order for fats to enter the Krebs cycle they must go through a series of enzymatic reactions called beta oxidation.  The reactions condense free fatty acids to acetyl CoA and hydrogen. Acetyl CoA can now enter the Krebs cycle and from this state, fat metabolism continues the same course as carbohydrates.

The next and final step is for the electron transport chain to finish work started by the Krebs cycle.  The electron transport chain makes use of NADH and FADH 2 formed during glycolysis and the Krebs cycle to produce large amounts of ATP.  For a better understanding, click on this link about the Electron Transport Chain: The Movie.

In order for fat cells to enter the Kreb's cycle, the cells must go through a process called Beta oxidation.  The process starts with fatty acids or fat cells, in the form of Acyl-CoA molecules.  These molecules are broken down in mitochondria to make Acetyl-CoA, the entrance molecule for the Kreb's cycle.