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Overview of oxidative phosphorylation:
- Catabolism of carbohydrate, lipid, amino acids converge on Cellular Respiration.
- Involves reduction.
- Electrons donated by NADH and FADH2.
- Happens in mitochondria
Overview of photophosphorylation:
- The process by which sunlight is captured and used to drive ATP synthesis - Absolutely requires light.
- Involves oxidation of H2O to O2
- NADP+ is the final electron acceptor
- Happens in chloroplasts
NAD+ and NADP+
FAD and FMN
Universal electron carriers:
- Ubiquinone (Coenzyme Q)
- Iron-Sulfur Proteins
Ubiquinone (coenzyme Q):
- long isoprenoid side-chain
- vary mobile
- shuttles electrons between various carriers.
- Accepts one electron (semiquinone radical) or two (ubiquinol)
- Contain iron-heme groups.
- Tightly, but non-covalently, associated with the protein.
- Most are integral proteins of the inner mitochondrial membrane.
- Three classes.
What are the three classes of cytochromes:
- Iron protoporphyrin IX (in b-type cytochromes).
- Heme C (in c-type cytochormes).
- Heme A (in a-type cytochromes).
- Iron is associated with inorganic sulfur or Cys sulfur (not heme sulfur).
- Participate in one-electron transfers.
- Rieske iron- sulfur protein iron coordinates with 2 His instead of 2 Cys.
Sequence of electron transport in the respiratory chain:
- electrons move from NADH, succinate, or other donors to..
- iron-sulfur proteins
- Ubiquinone (coenzyme Q)
- cytochromes (and copper centers)
- molecular oxygen (final electron acceptor)
ECT complex names:
- Complex I = NADH dehydrogenase
- Complex II = succinate dehydrogenase
- Complex III = cytochrome bc1
- Complex IV = cytochrome oxidase
Phosphates transferred (P) to oxygens oxidized (O).
2.5 [10 protons pumped out per pair of electrons transferred/ 4 - number of protons required to drive the synthesis of 1 ATP
Succinate P/O ratio:
1.5 [ 6 protons pumped – electrons entering the second complex don’t pump 4 protons across like complex one does].
Name some enzymes in mitochondria that can use the products of oxidative phosphorylation as a reactant
- Enzymes in the mitochondria that can use it as a reactant are isocitrate dehydrogenase,
- alpha-ketoglutarate dehydrogenase complex, and malate dehydrogenase.
Proton Motive Force:
- provides energy to
- drive ATP synthesis. ATP synthesis results from coupling proton flux to phosphorylation. Pumping out H+ generates an electrochemical gradient and the
- energy is stored as a proton motive force.
- Two components:
- Chemical energy potential – due to a H+ chemical gradient across the membrane,
- and an electrical potential energy – due to a separation of charge (H+).
the Chemiosmotic Hypothesis
- 1. H+ are pumped to the intermembrane space using the electron transport chain
- 2. An electrochemical gradient is generated that serves as a proton motive force
- 3. H+ move down their gradient to generate the force for ATP synthesis