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Cellular Respiration The process by which your cells transfer the energy in organic compounds (glucose, starch, carbohydrates) to ATP, the byproduct of this reaction is water and carbon dioxide. It occurs in the cells mitochondria, which are the energy producers for the cell. Cellular respiration occurs in three stages 1. Glycolysis 2. Krebs Cycle 3. Electron Transport Chain 1. Glycolysis occurs in the cytosol glucose (6 carbons) is broken down into two pyruvate molecules (3 carbons each) ATP consuming phase - 2 ATP are consumed ATP producing phase - 4 ATP are produced NET GAIN OF 2 ATP 2 NADH (Nicotinamide) are produced from two NAD+ (Nicotinamide adenine dinucleotide) which can be used to make more ATP in oxidative phosphorylation NET GAIN OF 2 NADH Animation of Glycolysis *If you remember one thing about glycolysis, remember that it yields 2 pyruvate, 2 ATP, and 2 NADH 2. Krebs Cycle (a.k.a. the CITRIC ACID CYCLE) occurs in the matrix of the mitochondria the breakdown of glucose is completed and CO2 is produced in the presence of oxygen, the two pyruvate molecules produced by glycolysis travel to mitochondria Krebs Cycle has 8 steps, each step is catalyzed by a different enzyme Each cycling requires the input of 2-carbon acetyl-CoA and two carbons are released as C02 glycolysis results in the production of 2 pyruvate molecules which are converted to acetyl-CoA, the Krebs cycle needs only ONE acetyl-coA, so it takes two complete turns of the krebs cycle before you get the products the NADH and FADH2 created in the Krebs cycle are used in the electron transport system to create large amounts of ATP Animation of Krebs Cycle *If you remember one thing about the Kreb's cycle, remember each pyruvate yields 4 NADH, 1 FADH2, and 1 ATP * Double this number, for each glucose that's dropped into the process, the Krebs cycle makes 2 turns, one for each pyruvate 3. The Electron Transport Chain (also known as oxidative phosphorylation) produces the energy that drives the synthesis of ATP in oxidative phosphorylation it consists of molecules (mostly proteins) that are embedded in the inner mitochondria Sitting atop these proteins are molecules that are alternately reduced and oxidized as they accept and donate electrons the initial electron acceptor in the chain is a flavoprotein (FMN) and it accepts an electron from NADH. The electron is then passed down a series of molecules to oxygen, which is the final electron acceptor. It is then combined with a couple of hydrogen atoms to form water. The process will not function in the absence of oxygen. FADH2 and NADH both donate electrons to the chain the electron transport chain doesn't make any ATP itself, instead these reactions are coupled to others to produce ATP, a process called CHEMIOSMOSIS Animation of Electron Transport Chain <--- View this! It will totally help you understand. The NET RESULTS of the Aerobic Respiration 1. Each NADH produces 3 ATP (remember 8 NADH were created in the Krebs Cycle and 2 in Glycolysis) 2. Each FADH2 produces 2 ATP (remember 2 FADH2 were created in the Kreb's Cycle) 3. Do the math, 34 ATP produced in the ETC + 2 from glycolysis + 2 from Krebs = 38 total ATP from each glucose 4. 2 ATP are used to move NADH to the mitochondria -- > for a grand total of 36 ATP produced from each glucose molecule Anaerobic Respiration In the absence of oxygen (remember that oxygen is the final electron acceptor) the cell goes through a process called FERMENTATION Fermentation takes place under anaerobic conditions (no oxygen present). Two types: Alcohol fermentation - occurs in yeasts, fungi and some bacteria. 2 Pyruvate --> 2 Acetaldehyde --> 2 ethanol Lactic acid fermentation - occurs in oxygen deprived human muscle cells where lactate is produced as a waste product. Muscle cramps are caused by increased acidity caused by the lactate build up. Anaerobic Respiration Steps 1. Glycolysis occurs, and pyruvate is produced, the pyruvate enters the Krebs cycle and produces NADH2 and FADH2, and some ATP 2. The problem occurs in the ETC, because there is no oxygen to be the final electron acceptor 3. NADH bulids up in the system, and NAD+ cannot be regenerated normally 4. Fermentation occurs to regenerate the NAD+ and create some ATP, but it is much less efficient than aerobic respiration