Question

Describe how ATP synthase makes ATP. Include in your answer what type of energy is being converted in this process?

Explain why oxidation of FADH2 in the electron transport chain produces fewer molecules of ATP and NADH?

Answer 1

ATP synthesis:

ATP synthase is an inner mitochondrial membrane-bound enzyme. It consists also known as the F0-F1 complex. F0 complex is a membrane-bound proton pore. It allows protons to move from mitochondrial intermembrane space into the mitochondrial matrix. It is connected to F1 complex by ? subunit of the F1 complex. The F1 complex is the ATP synthase with catalytic sites. F1 complex synthesizes ATP by stabilizing ATP more than the ADP, thus converting it into a spontaneous reaction. However, due to strong binding to ATP, F1 complex needs the energy to release it from the site which is provided by proton motive force. At any given time, three catalytic sites exist in three different conformations- empty, ADP-bound and ATP-bound state. The empty catalytic site is in contact with the connecting ?-subunit. Protons flowing from intermembrane space to matrix along concentration gradient rotates F0 complex. This, in turn, rotates ?-subunit, changing its contact to the nearby catalytic site (with bound ATP). ATP containing catalytic site upon contact with ?-subunit releases the ATP into the matrix. The site now attains empty conformation.

FADH vs NADH energy yield:

Four protons are required for each ATP synthesis. Electron transport chain is driven by electron carrier molecules, NADH and FADH2. NADH and FADH2 transfer ten and six protons, respectively, to the mitochondrial intermembrane space. NADH transfers its electrons to complex1 which serves dual function of electron transport and proton pump. It transfers four extra protons before transferring electrons to complex 3. FADH2 transfers its electrons to complex 3 via complex 2. Complex 2 has no proton pumping properties