How do we release the energy in NADH and FAD Outline the process of oxidative phosphorylation Outline the process of Chemiosmosis Explain the Electron Transport Chain

Electron Transport. Now that most of the potential energy of glucose is stored in the high energy electron carriers NADH and FADH2, how does a cell extract that potential energy to make more ATP?

Just as we reduced these electron acceptors to add potential energy, we will oxidize these electron carriers to extract potential energy.

Oxidation and Reduction

Oxidation and Reduction Oxidation-reduction reactions always occur simultaneously because an electron gained by one molecule is donated by another molecule. The molecule or atom accepting the electrons are said to be reduced. The molecule or atom that loses an electron is oxidized Two electron carrier molecules that are often required in metabolic pathways are nicotinamide adenine dinucleotide (NAD+) and flavine adenine dinucleotide (FAD). Both NAD+ and FAD are considered the oxidized forms; NADH and FADH2

There are two requirements to oxidize NADH and FADH2: an electron acceptor and an electron transport chain. Electron Transport. Now that most of the potential energy of glucose is stored in the high energy electron carriers NADH and FADH2, how does a cell extract that potential energy to make more ATP? Just as we reduced these electron acceptors to add potential energy, we will oxidize these electron carriers to extract potential energy. There are two requirements to oxidize NADH and FADH2: an electron acceptor and an electron transport chain. The role of the final electron acceptor. NADH and FADH2 "like" electrons. The cell needs to find a way to get these molecules to release the high energy electrons. The cell requires a molecule that "likes" electrons even more than NADH and FADH2. One such molecule is molecular oxygen (O2). Molecular oxygen exerts a greater attraction for electrons than either of those electron carriers. Therefore, the cell will use O2 to remove the high energy electrons and release the potential energy stored in NADH and FADH2. How does a cell accomplish this electron transfer? Through electron transport chains. The role of electron transport chains. The electron transport chain is a series of membrane bound proteins found in the plasma membrane of prokaryotes that possess cofactors that are easily reduced/oxidized. These proteins undergo a series of redox reactions that passes electrons from one membrane-bound carrier to another and then to a final electron acceptor, in this case O2. By passing the electrons stepwise from NADH (and FADH2) to O2, the cell limits the loss of energy in the form of heat and stores the energy to drive ATP synthesis. Aerobes use oxygen atoms as final electron acceptors in the electron transport chain in a process known as aerobic respiration, whereas anaerobes use other inorganic molecules such as sulfate, nitrate, and carbonate as final electron acceptors in anaerobic respiration. Don't worry about learning the names of the cofactors like FMN, cyt b, etc. What I want you to take out of this figure is the fact that NADH (and FADH2) are oxidized in a series of steps, passing the electrons to a final acceptor (in this case oxygen), and releasing potential energy (notice the arrow on the left) into the cell that will be used to produce ATP.

Electron Transport chain Hydrogen has been attached to NAD and FAD during the Krebs cycle The NADH FADH2 are transferred down a chain of carriees at progressively lower energy levels As the hydrogen is passed from one carrier to the next energy is released to produce ATP Carriers include NAD, FAD, Coenzyme Q and cytochromes Cytochromes – iron containing proteins

Electron Transport chain Initially Hydrogen is passed along the chain. Hydrogen is then split into protons and electrons (only electrons are passed down the chain), At the end the protons and Electrons are recombined to form hydrogen, which then links with oxygen to form water Oxygen acts as the final acceptor of hydrogen atom The transfer of hydrogen to oxygen is catalysed by cytochrome oxidase Cyanide inhibits this enzyme – cyanide caused respiration to cease.

Chemiosmotic theory Mitochondria have a folded inner membrane which form cristae The cristae are lined with stalked particles This membrane appears to have a mechanism which actively transports protons (H+) from the space between the inner and outer membrane of organelles. This creates a electrochemical gradient of hydrogen ions across the inner membrane Was a theory put forward by Peter Mitchell in 1961 Energy of this charged membrane is synthesized to ATP

Chemiosmosis Is the movement of ions across a selectively-permeable membrane, down their electrochemical gradient. Generation of ATP by the movement of hydrogen ions across a membrane during cellular respiration. ATP synthase: the enzyme that makes ATP by chemiosmosis. It allows protons to pass through the membrane using the kinetic energy to phosphorylate ADP making ATP. The generation of ATP by chemiosmosis occurs in chloroplasts and mitochondria as well as in some bacteria.

Chemiosmosis Hydrogen atoms are picked up by NAD and later split to protons and electrons. Protons enter the space between the inner and outer membrane Electrons pass along cytochromes located within the inner membrane Protons flow back to the matrix via stalked granules to the higher concentration in the intermembranes space. This flow forces ADP with an inorganic phosphate to make ATP ATP-ase (associated with the stalked granules catalyses this reaction) The protons are recombined with the electrons and hydrogen atoms then they combine with oxygen to make water.

Animation of Electron Transport Chain http://highered.mcgraw-hill.com/sites/0072507470/student_view0/chapter25/animation__electron_transport_system_and_atp_synthesis__quiz_1_.html

Summary of Glycolysis 2 ATPs are used to start the process 4 ATPs are produced at the end – net gain of 2 ATPs 2 molecules of NADH are produced Involves substrate level phosphorylation, lysis, oxidation and ATP formation. Happens in cytoplasm of the cell Controlled by enzymes. If ATP levels are high, feedback inhibition occurs to control the process. 2 pyruvate molecules are present at the end of the process.

Summary of Link Reaction and Krebs Cycle For each Glucose molecule (2 cycles) 2 ATP molecules 6 molecules of NADH Two molecules of FADH2 4 molecules of carbon dioxide released

Summary of Electron Transport Chain Each molecule of FADH2 allows production of 2 ATPs Each molecule NADH allows production of 3ATPs.