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Biology II – Chapter 8: Cellular Respiration The metabolic process that harnesses the energy in organic compounds and turns them into usable energy called ATP. The primary fuel for cellular respiration is glucose. Oxygen is required for ATP production. Carbon dioxide is released as a by-product. The conversion of glucose and oxygen into carbon dioxide, water, and energy in the form of ATP Occurs in the mitochondria of the cell. o Matrix – fluid contained in the inner compartment – Krebs cycle occurs here o Cristae – Intermembrane compartment (between the inner and outer membrane) – electron transport occurs here C6H12O6 + 6O2 glucose + oxygen gas enzymes = 6CO2 + 6H2O + energy carbon dioxide + water + ATP energy Cellular Respiration occurs in 2 stages: o Glycolysis – glucose is broken down. o Presence of oxygen determines the 2nd stage: Aerobic – oxygen present – Cellular Respiration – large amount of ATP is made Anaerobic – oxygen absent – Fermentation – alcohol or lactic acid is made Glycolysis (1st Stage of Cellular Respiration) o Takes place in the cytoplasm – does not require oxygen o Not necessary for aerobic cellular respiration, even though it plays a role in it. o Glucose (beginning product) is broken down and converted into 2 pyruvate (end product) – producing small amounts of ATP and NADH that enters the mitochondria o Each Pyruvate is then split into CO2 (by-product) and two-carbon acetyl group Krebs Cycle (2nd Stage of Cellular Respiration) o Begins and ends with citric acid o Occurs in the matrix o If Oxygen is present: Aerobic Cellular Respiration occurs: Pyruvate and NADH are used to make a large amount of ATP. o Occurs in the mitochondria of Eukaryotic cells. o Occurs in the cell membrane of Prokaryotic cells. o If Oxygen is not present: Fermentation occurs: Pyruvate is converted into lactate or ethanol (alcohol) and carbon dioxide (CO2); additional ATP is not generated. o Lactate – (lactate fermentation) – animal cells – cells deprived of oxygen produce lactic acid instead of pyruvate; once oxygen is available lactic acid turns back into pyruvate o Ethanol (alcohol) and CO2 – (alcoholic fermentation) – yeast cells – produces/gives off CO2 and alcohol is evaporated Advantages Animal Muscle cells are able to cells produce ATP when oxygen is limited due to vigorous work Yeast Yeast cells are capable of cells growing and dividing when oxygen is limited Disadvantages Lactate will begin to build up and cause muscle fatigue where they no longer contract The alcohol they produce eventually kills them if the initial glucose levels are high Electron Transport Chain o Occurs in the inner compartment (the cristae) of the mitochondria. o Hydrogen ions are pumped out of the inner compartment of the mitochondria. o Hydrogen accumulates in the outer compartment – producing the concentration gradient. o Chemiosmosis takes place and a large amount of ATP is produced as hydrogen diffuses into the inner compartment through a channel protein. o At the end of the transport system, hydrogen combines with oxygen to form water (H2O). Oxygen is the final electron acceptor. Glycolysis ATP Produced per Glucose Molecule Direct By Way of Electron Transport System 2 ATP 2 NADH2 = 6 ATP Transition Reaction Krebs Cycle Subtotals Grand Total 2 ATP 2 NADH2 = 6 ATP 6 NADH2 = 18 ATP 2 FADH2 = 4 ATP 34 ATP 4 ATP 38 ATP Harvesting Energy – Glycolysis and Cellular Respiration/Fermentation: Glucose Stage 1 – Glucose is broken down to pyruvate. NAD ADP NADH2 ATP Stage 1 Pyruvate Anaerobic (without O2) Fermentation Ethanol (alcohol) and CO2 or lactate Stage 2 Aerobic (with O2) Respiration Mitochondrion Stage 2 – The presence of O2 determines whether aerobic respiration or fermentation will occur. ATP H2O Aerobic Cellular Respiration versus Photosynthesis Aerobic Cellular Photosynthesis Respiration Mitochondrion Chloroplast Releases energy Requires energy Requires O2 Releases O2 Releases CO2 Requires CO2 Comparison of Aerobic Respiration & Photosynthesis o Both use a hydrogen carrier Aerobic cellular respiration – NAD Photosynthesis – NADP o Both use an electron transport system located in membranes to generate ATP o Both occur in daylight hours Only aerobic cellular respiration occurs at night o Plant and animal cells carry on aerobic cellular respiration Only plant cells carry on photosynthesis o Photosynthesis is the build up of glucose o Aerobic cellular respiration is the break down of glucose o The overall equation for both are opposite each other: photosynthesis energy + 6 CO2 + 6 H2O C6H12O6 + 6 O2 aerobic cellular respiration