Electron Transport Chain

or What about FADH?

Like NADH, FADH contains electons (and energy) from oxidation reactions. Remember that FADH, however, contains less energy than does NADH. Because of this, FADH is unable to donate its electrons to Complex I of the ETC. Instead, FADH donates its electons to Complex II (you were probably wondering why we skipped it before). Complex II eventually passes the electons on to Complex III via ubi. From then on, the electrons follow the same pathway as do those from NADH. Complex II, it turns out, does not move protons as the electons are transported! This means that every NADH that donates electrons to the ETC will cause more hydrogen ions to be transferred than does each FADH. Also, note that the electrons from FADH still end up on oxygen.

In summary

  1. Each NADH donates electrons to Complex I while each FADH donates electrons to Complex II. Complex I uses the energy of the electrons to transport hydrogen ions while Complex II does not.

  2. For each NADH and each FADH that donates electrons to the ETC, O2 is used and converted into one water molecule. Thus, to calculate the totall number of O2 used, add the number of NADH and FADH and divide by 2.

  3. The primary effect of the ETC is to pump hydrogen ions out of the mitochondrion so that there is a concentration gradient for hydrogen ions across the mitochondrial membrane. NADH causes more hydrogen ions to be pumped than does FADH.

I thought that we were going to make ATP


Go back to Contents