Exercise Physiology: Theory and Application to Fitness and Performance 9th Edition by Scott Powers, Edward Howley

Exercise 10

Discuss the operation of the Krebs cycle and the electron transport chain in the aerobic production of ATP. What is the function of NAD+ and FAD in these pathways?

Step 1 of 2

Krebs cycle involves a series of redox reactions that is used to further oxidize the end products of glycolysis. The end product of glycolysis, the pyruvate (a three carbon molecule), is converted into acetyl Co-A (coenzyme A) (a two carbon molecule), with release of another carbon as carbon dioxide. Acetyl Co-A enters the krebs cycle, condenses with oxaloacetate (a four carbon molecule), to form citrate (six carbons). In a series of reactions in the pathway, oxaloacetate is regenerated, with liberation of two molecules of CO₂ and the pathway recycles with entry of another acetyl Co-A.

Much of the energy present in the intermediates of the reaction is harvested through redox reactions, in the form of NADH (reduced nicotinamide adenine dinucleotide) and FADH2 (reduced flavin adenine dinucleotide). One turn of Krebs cycle releases the following products:

• 2 molecules of CO₂

• 3 molecules of NADH

• 1 molecle of FADH₂

• 1 molecule of GTP (guanosine triphoshate)