BIOC 212 Lecture Notes - Lecture 56: Lipid Bilayer, Malate-Aspartate Shuttle, Hemoglobin
29 May 2018
School
Department
Course
Professor
Metabolism XVIII
Complex II & Protons
• Complex II integrates citric acid cycle reactions directly into the ETC
• Have succinate and its product fumarate
o Citric acid cycle products that get dehydrogenated (removal of H, oxidation)
o As go through citric acid cycle, are oxidizing carbons and releasing CO2
• Harvest that energy
• Complex II does not pump protons
• By feeding directly into ubiquinone, these electrons skip complex I
o This is an example of how harvest energy from citric acid cycle directly and
feed it into the ETC
• Harvest the H from succinate by binding it to FADH
o Generate FADH2
o FADH2 then directly adds these electrons into an Fe-S cluster or go through
a chain of Fe-S pores and another set of heme molecules
o Then donated directly to ubiquinone
• In citric acid cycle, take hydrides off of carbon --allowing water from the matrix to
replace that binding site in the carbon
o Handing electrons into this chain in the membrane
• Electron donated by FADH2 thus do not pump as many protons out of the
matrix as electrons donated by NADH
o This is because FADH2 is not a strong enough electron donor to feed
complex I
• It cannot add as much energy to the proton gradient
Heme Groups Also Used by ETC
• Hemes are another one of these metal binding electron handling centers
o Redox center
o Found throughout the ETC; not really in complex I so much since hemes are
relative good binders of electrons
• Bind them tightly
o Have higher affinity for electrons; harder to remove electrons from hemes
• So once bind the heme, already have lost a lot of the energy that you
had when started the chain
• Show up later, and are readily involved in the last steps of ETC, before hand
electrons directly to molecular oxygen
