Electron Transport System & Chemiosmosis Oxidative Phosphorylation

Phases of aerobic cellular respiration Glycolysis Transition / Link or Acetyl-CoA reaction Krebs cycle Electron transport system These phases are nothing more than metabolic reactions involving the conversion of glucose & other molecules into carbon dioxide & water The resulting energy released from this conversion will be used to produce ATP

Cellular Respiration: Last Step Electron transport System (ETS) Occurs in within the inner mitochondrial membrane Reactants = 10 NADH, 2 FADH2, 6 O2, ADP + Pi Products = approximately 36 – 38 ATPs, 4 H2O

Electron Transport System The ETS is a series of electron carriers embedded in the inner membrane of the mitochondrion. Each electron carrier in the system is slightly more electronegative than the one before it. Electrons enter ETS from NADH & FADH2 As the electrons are passed from carrier to carrier, they give off energy because they’re being passed to more and more electronegative carriers.

Electron Transport System That energy given off by the electrons as they travel is used to pump H+ from the matrix into the intermembrane space, This action creates a huge concentration gradient of H+ between the matrix and intermembrane space. The H + can only flow back into the matrix through the protein ATP synthase, which uses the kinetic energy of H+ flow to create ATP from ADP & Pi Finally, at the end of the chain the electrons “jump off” the last carrier & combine with O2 to form H2O

Chemiosmosis & Oxidative Phosphorylation Chemiosmosis can be described as the coupling of the redox reactions of the electron transport chain to ATP synthesis by setting up a concentration gradient of H+ ions across a membrane. Chemiosmosis provides the energy for ATP synthesis via the flow of H+ ions across a membrane. This method of producing ATP is called oxidative phosphorylation. The process of oxidative phosphorylation is different from the direct transfer of a Pi from one molecule to ADP – called substrate level phosphorylation - which we saw in glycolysis and Kreb’s cycle.

Cellular Respiration

Cellular Respiration View Animation!

Cellular Respiration: Final Totals Energy yield from glucose metabolism ATP produced via substrate level phosphorylation Glycolysis – 2 ATP Krebs Cycle – 2 ATP ATP produced via chemiosmosis 2 NADH from glycolysis – 4-6 ATP 2 NADH from transition step – 6 ATP 6 NADH from Krebs Cycle – 18 ATP 2 FADH2 from Krebs Cycle – 4 ATP TOTAL 36-38 ATP Efficiency 36 ATP = 263 kcal 1 glucose = 686 kcal 39% of the energy in glucose is converted to ATP, the rest is lost as HEAT

Cellular Respiration

A FEW PRACTICE QUESTIONS What are the 4 steps of aerobic cellular respiration & where do they specifically occur in the cell or mitochondria? Describe the structure of a mitochondrion What goes in & comes out of glycolysis, the transition reaction, & Krebs? What is NADH? Describe how ATP is synthesized in the ETS. How does this synthesis compare with ATP synthesized in glycolysis?