Welcome to My AP Biology Thoughts podcast, my name is Jacqueline Sun and I am your host for episode #5 called Unit 3 Cellular Energetics: OXIDATIVE PHOSPHORYLATION. Today we will be discussing the formation of ATP in the vital final step of cellular respiration. 

•  Oxidative Phosphorylation is the name for the entire final process in which ATP is created; it can be split into two parts which are the ETC and chemiosmosis. 
• Is an aerobic process which requires oxygen and follows the Krebs cycle.
• Uses 3 NADH and 1 FADH2 produced from the Krebs cycle, also requires oxygen as the final electron acceptor.
• The final product of Oxidative Phosphorylation is, of course, ATP. A byproduct is H2O.
• Takes place in the inner membrane of the mitochondria, involves 4 protein complexes labeled with roman numerals 1-4 from left to right and an ATP synthase that are all embedded within the membrane.

ETC

There are two electron carriers which will start the ETC: NADH and FADH2. I will first talk about NADH, because the process for FADH2 is slightly different. The electron carrier NADH is oxidized into NAD+, losing two electrons which are pumped into protein I. This energy transfer allows one H+ ion (lost from the NADH) to be actively transported into the intermembrane space. The H+ must be actively transported because there is a higher concentration of H+ in the intermembrane space than in the matrix. The electrons are then transferred by a transfer protein to protein III , and the energy that is lost in the transfer is again used to pump an H+ ion into the intermembrane space. Finally the lower-energy level electrons are transported once more to protein IV, and the energy lost in the transfer is used to pump another H+ over. At this point, the 2 electrons are much lower in energy level and must be removed to prevent a backup of electrons, so they will exit the last protein complex and bind with two free-flowing H+ ions and ½ of an O2 molecule to create H2O. This is how oxygen acts as the final electron acceptor and how it contributes to the creation of the byproduct of H2O. In summary, by the end of the process, NADH has pumped 3 total electrons. Now let's talk about FADH2. FADH2 is the other electron carrier and is oxidized at protein II, losing two electrons to be pumped into the ETC and turning into FAD and two H+ ions. It will then follow the same process as NADH. The key difference here is that FADH2 starts at protein II while NADH starts at protein I, meaning FADH2 will only pump two protons, making it slightly less efficient than NADH. 

Chemiosmosis (compared to previous process, considerably more straightforward)

Overall, ATP synthase, the central protein complex of chemiosmosis, will convert the potential energy of the proton gradient into chemical energy in ATP. Due to the ETC,