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Biology 20 IB Cellular Respiration Notes 1. Cellular respiration – releases energy stored in glucose (and other fuel molecules) in a controlled step by step process that allows the production of ATP (adenosine triphosphate). C6H12O6 + 6O2 6CO2 + 6H2O - fuel molecules are oxidized to form CO2. - O2 is reduced to form water. - intermediate electron acceptors used to transfer electrons (in an electron transport chain) before they are finally grabbed by O2. - NAD+ is the is the main electron acceptor molecule in the ETC. 2. Steps of cellular respiration: 1) Glycolysis - glucose is split (in cytoplasm). 2) Kreb’s cycle - completes oxidation process - in mitochondrial matrix. 3) Electron transport chain - step by step energy release for ATP production. - includes chemiosmosis. - across mitochondrial inner membranes. 3. Energy yields: - occur in two ways: a. substrate level phosphorylation - ATP production results directly from breakdown of substrates (fuel molecules). b. oxidative phosphorylation – ATP production due to transfer of electrons from glucose to O2, via the electron transport chain and chemiosmosis. 4. Glycolysis: occurs in the cytoplasm - splitting glucose - done by ALL cells in some form or another. - no O2 req’d. - need glucose - yields ATP, NADH + H+, pyruvate Glycolysis glucose ATP ADP glucose phosphate ATP phosphorylation of glucose ADP fructose diphosphate lysis substrate level phosphorylation NAD+ TP NADH + H+ GP ADP ADP ATP ATP ADP ADP ATP ATP Pyruvate TP NAD+ NADH + H+ GP Pyruvate Glycolysis summary: - use 2 ATP, but gain 4 ATP back. - net yield per glucose: 2 ATP, 2 NADH + H+, 2 pyruvate (Note: the 2NADH and 2 pyruvate enter the mitochondria) 5. Kreb’s Cycle: occurs in the mitochondrial matrix: (draw a mitochondrion:show outer membrane, inner membrane, cristae, intermembrane space, matrix) a. the Link-reaction: -pyruvate is transported by a membrane protein into the mitochondrion, where it it converted to a 2-carbon acetyl coenzyme A. cytoplasm mitochondrion transport protein coenzyme A acetyl coenzyme A pyruvate CO2 NAD+ NADH + H+ step1: O2 removed (decarboxylation) step 2: remaining carbons oxidized (NAD+ reduced to NADH + H+) step 3: coenzyme A (CoA) is added to form acetyl CoA (acetyl CoA) The link reaction yields: 1 CO2 1 NADH + H+ 1 acetyl CoA b. Acetyl CoA enters Kreb’s Cycle: C3 (pyruvate) link reaction C2 C4 CO2 (acetyl CoA) Kreb’s Cycle C5 C6 CO2 One turn of the cycle yields: 2 CO2 3 NADH + H+ 1 FADH2 1 ATP (by substrate phosphorylation) Electron Transport Chains: all NADH + H+, and FADH2 are electron carriers. electrons are passed from these to other molecules embedded in the inner membrane of the mitochondria. coupled with the ETC is the pumping of H+ from the matrix across the membrane to the intermembrane space. the accumulated H+ diffuse back to the matrix through ATP synthase, causing ATP production. This is called oxidative phophorylation NADH + H+ ADP + P ATP FADH2 ADP + P ATP cytochromes ADP + P ATP H2O O2 **Each NADH + H+ yields 3 ATP **Each FADH2 yields 2 ATP *The terminal electron acceptor IS Arnold Schwarzenegger, I mean, OXYGEN. And, the final product formed from the ETC is water. 6. Calculation of total ATP yield during aerobic respiration: Glycolysis Link Reaction Kreb’s Cycle ETC Total ATP X3 X3 X 2** 18 6 4 X2 4 1 GLUCOSE: 2 pyruvate 2 pyruvate: 2 acetyl CoA 2 acetyl CoA: 6 NADH + H+ 2 NADH + H+ 2 NADH + H+ 2 FADH2 2 ATP (substrate level phosphorylation) 2 ATP (substrate level phosphorylation) 2 2 36 ATP Waste Gas 6 CO2 2 CO2 4 CO2 ** it takes two ATP to transfer the electrons from NADH produced by glycolysis (in the cytoplasm) through the mitochondrial membrane into the matrix. Consequently, the total ATP produced by the aerobic respiration of one glucose is 36. Even the total of 36 ATP per glucose is an average because the cell uses energy from the proton gradient in the mitochondria for other purposes such as the uptake of pyruvate from the cytoplasm. Further energy summary: Total yield for each molecule of glucose oxidized 36 ATP per glucose: 4 ATP from substrate level phosphorylation 32 ATP from oxidative phosphorylation-ETC 7. Anaerobic respiration: O2 not required energy yield much lower two types (for you to know): 1. Alcohol fermentation 2. Lactic acid production in muscles **both are modified forms of glycolysis 8. Alcoholic Fermentation: glucose ATP ADP glucose phosphate ATP phosphorylation of glucose ADP fructose diphosphate lysis substrate level phosphorylation TP NAD+ NADH + H+ GP ADP ADP ATP ATP ADP ADP ATP ATP Pyruvate TP NADH + H+ GP Pyruvate NADH + H+ NADH + H+ NAD+ Ethanol + CO2 NAD+ Ethanol + CO2 Summary: - uses 2 ATP, gains back 4 ATP - reducing pyruvate allows recycling of NAD+ - done by yeast and many bacteria do this. (wine and beer-making, food spoilage) Net Yield: - 2 ATP, 2 Ethanol + 2 CO2 NAD+ 9. Lactic Acid production by muscles: glucose ATP ADP glucose phosphate ATP phosphorylation of glucose ADP fructose diphosphate lysis substrate level phosphorylation TP NAD+ NADH + H+ GP ADP ADP ATP ATP ADP ADP ATP ATP Pyruvate TP NADH + H+ GP Pyruvate NADH + H+ NADH + H+ NAD+ Lactic Acid NAD+ NAD+ Lactic Acid Summary: - uses 2 ATP, gains back 4 ATP - reducing pyruvate allows recycling of NAD+ - done by muscles when an O2 debt exists. (Lactic acid is carried to liver by blood and converted back to pyruvate.) - also done by bacteria and yeast (cheese, yogurt) - results in a burning sensation in muscles Net Yield: - 2 ATP, 2 lactic acid NOTE: -aerobic respiration is 18X more efficient (2 ATP vs 36 ATP) anaerobic respiration yields about 5% of the aerobic respiration yield. 10. Other fuel molecules: Other food molecules can be used for ATP synthesis, but they may enter the cellular respiration pathways in different places: Proteins Carbohydrates Amino Acids Simple sugars Lipids Glycerol Fatty acids Glycolysis NH3 (pyruvate) Acetyl CoA Kreb’s Cycle Electron transport chain and oxidative phosphorylation Acetyl CoA plays a central role in food metabolism: it is an intermediate in sugar breakdown. fatty acids chains are broken into 2-carbon acetyl groups. When energy is in short supply an organism will metabolize: simple sugars stored complex sugars (glycogen) fats proteins (as a last resort) 10. Uses of ATP in the cell include energy for: chemical reactions (such as protein synthesis) nerve impulse transmission mechanical action (muscle contraction and the motion of flagella and cilia) active transport Ah yes, remember also that the energy conversions of cellular respiration are not 100%, some energy is lost as heat.