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Cellular Respiration CHAPTER 9 CELLULAR RESPIRATION Breathing In Mitochondria Oxygen, Glucose Digestion of food Carbondioxide, Water Breathing Out/ Urine C6H12O6 + O2 CO2 + H2O WHY?????+ 36 ATP Cell resp is so….. engaging even to canines….if Buddy gets it - oh … so will you! Cellular respiration and photosynthesis are opposite pathways (so .. ATP is made during cell resp and used during photosynthesis Fig. 9.1 Gasoline Combustion Cell Respiration Organic compounds + O2 -> CO2 + H2O + Energy Carbs, Protein, Lipids C6H12O6 + 6O2 -> 6CO2 + 6H2O + Energy (ATP + heat) ATP: Adenosine Triphosphate • Couples cell resp. to Anabolic reactions • Bonds between PO4 groups can be broken to release energy (ADP/AMP is made). ATP: Adenosine Triphosphate ATP: How it works…. review • PO 4 released from ATP is tagged to a substrate that will not normally react • Substrate is phosphorylated and now able to undergo the chemical reaction • *ATP can be regenerated * ATP Banks the Energy Released in Multiple Steps From Glucose CATABOLIC PATHWAY C6H12O6 + 6O2 -> 6CO2 + 6H2O Chemistry basics for cell respiration (NOT AGAIN!!) Food has electrons Electrons can be removed and moved This releases ENERGY! The loss of electrons is called oxidation (also addition of O) The addition of electrons is called reduction (also addition of H) Redox reaction – involves oxidation + reduction Na + Cl -> Na+ + Cl- • Na the electron donor, is the reducing agent and reduces Cl. • Cl the electron acceptor, is the oxidizing agent and oxidizes Na. Redox reactions require both a donor and acceptor An electron looses energy as it shifts from a less electronegative atom to a more electronegative one In the cell, electron moves from macromolecules (via a H reservoir) to oxygen Oxidized C6H12O6 + 6O2 -> 6CO2 + 6H2O + Energy (ATP + heat) Reduced A redox reaction that relocates electrons closer to oxygen releases chemical energy (ATP) Electrons from glucose/food are carried by NAD+ (high energy electron carrier) 1P - +2e 2H (food) + NAD+ -> NADH + H+ + Released in solution +2H + +2H - +2e - Nicotinamide Adenine Dinucleotide (NADH) – is the cells’ H reservoir - Dehydrogenase - enzyme Electrons “fall” from organic molecules to oxygen during cellular respiration in a stepwise manner Hydrogen atoms in Glucose give up these Electrons. Energy is released at each step ….. as ATP C6H12O6 Electron Transport Chain G = -53Kcal/mole of NADH Electrons are passed by increasingly electronegative molecules in the chain until they are caught by oxygen. Oxygen is the FINAL ELECTRON ACCEPTOR - why? Oxygen isFig. the 9.5 most electronegative acceptor in the Electron Transport Chain. It accepts the electrons (flowing from food) to make WATER The Process of Aerobic Cellular Respiration 1. Respiration involves Glycolysis, the Krebs cycle and Electron Transport Chain 2. Glycolysis - breaks glucose (6Carbon) into two pyruvates (3Carbon). Packages Hydrogen Electrons into NADH. Glycolysis Gain - 2 ATP + 2NADH 3. Shuttle - takes pyruvate from cytoplasm to mitochondria. Gain 2NADH. 4. Krebs cycle - takes the two 3 Carbon compounds from Glycolysis and extracts all Carbons and Oxygens as CO2 and Hydrogen electrons are transported by NADH/FADH2. Gain - 2 ATP + 6NADH + 2FADH2 5. Electron Transport Chain and Oxidative Phosphorylation: Move electrons through redox reactions, create a H+ (proton) gradient, and use the power of proton gradient to make ATP Gain - 10 NADH to 30 ATP and 2FADH2 to 4 ATP Aerobic Cellular respiration generates 38 ATP molecules for each sugar molecule it oxidizes. Shuttle may not be as efficient and produce less energy - so 36 ATP! C6H12O6 + 6O2 -> 6CO2 + 6H2O + 38ATP Energy flows from glucose -> NADH -> electron transport chain -> proton-motive force -> ATP Making ATP: Substrate level phosphorylation - (ATP made from substrates) & Oxidative ATP Phosphorylation - (ATP made via Electon transport Chain) 4 ATP in Substrate level phosphorylation Vs 34 ATP In Oxidative Phosphorylation Shuttle Fig. 9.6 2 2 34 1) Substrate-level phosphorylation (4/38 ATP) • Here an enzyme transfers a phosphate group from an organic molecule (the substrate) to ADP, forming ATP. Fig. 9.7 Remember that Electrons are REMOVED from HYDROGEN and they are PASSED DOWN the Electron Transport Chain along Redox Reactions What will be left if Electron is Removed from a Hydrogen Atom H+ (proton) 1P Coupling of the redox reactions of the electron transport chain to ATP synthesis is called chemiosmosis Electron Transport Chain (ETC) Does not make ATP!! Chemiosmosis couples ETC to Oxidative Phosphorylation Electrons from NADH are removed and H+ is released into 1P - intermembrane space during ETC +2e 2H (food) + NAD+ <- NADH + H+ + +2H + +2H - +2e - Nicotinamide Adenine Dinucleotide (NADH) – is the cells’ H reservoir - Dehydrogenase - enzyme 2) Oxidative Phosphorylation (90% ATP – 34/38): ATP synthase in the cristae makes ATP from ADP and Pi. • ATPsynthase used the energy of an existing proton gradient to power ATP synthesis. (H+ motive force) • This proton gradient develops between the intermembrane space and the matrix. Fig. 9.14 What’s happening in different locations of the Cytoplasm - Glycolysiscell? (End product is Pyruvate) Shuttle - Cytoplasm into Mitochondria Kreb’s Cycle - Matrix of Mitochondria (fluid inside mitochondria) Electron Transport Chain - Enzymes located all along the inner mitochondrial membrane; Electrons Inter ferried from NADH to Oxygen Membrane ATP Space H+ ions moved from Matrix to Space between Inner and Outer Membrane Oxidative phosphorylation: H+ ions move back into Matrix Fluid with Enzymes For Glycolysis ATP Synthase is in the Inner Mitochondial Membrane (Cristae - folds) ATP is made in the Matrix Glycolysis Krebs cycle Cytoplasm Mitochondrial Matrix No Oxygen Needed Needs Oxygen Glycolysis Krebs cycle S- COA C = O CH3 2CO2 Input = Glucose, 2ATP Input = Acetyl Co A Output = 2 Pyruvate, 4ATP, Output = 4CO2, 6NADH, 2NADH 2FADH2, 2ATP Glycolysis Fig. 9.8 Glycolysis Fig. 9.9a Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Glycolysis Fig. 9.9b Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Glycolysis Krebs cycle Shuttle CO2 ◊ The Krebs cycle consists of eight steps Fig. 9.11 ◊ The Krebs cycle Fig. 9.12 ELECTRON TRANSPORT CHAIN ◊ Electrons carried by NADH are transferred to the first molecule in the electron transport chain, flavoprotein (multiprotein I complex I). II • The electrons continue along the chain which III includes several cytochrome proteins and one lipid carrier - Ubiquinone • The final electron IV acceptor is: OXYGEN because it is MOST electronegative • The product is WATER and ……. (its not over) Fig. 9.13 ◊ Read this for Understanding: ◊ Electrons from NADH or FADH2 ultimately pass to oxygen. • one O2 molecule is reduced to two molecules of water. ◊ The electron transport chain generates no ATP directly. ◊ Its function is to break the large free energy drop from food to oxygen into a series of smaller steps that release energy in manageable amounts. ◊ The movement of electrons along the electron transport chain does contribute to chemiosmosis and ATP synthesis. ◊ A protein complex, ATP synthase, in the cristae actually makes ATP from ADP and Pi. ◊ ATP used the energy of an existing proton gradient to power ATP synthesis. • This proton gradient develops between the intermembrane space and the matrix. Fig. 9.14 Fig. 9.15 ◊ Chemiosmosis is an energy-coupling mechanism that uses energy stored in the form of an H+ gradient across a membrane to drive cellular work. • In the mitochondrion, chemiosmosis generates ATP. • Chemiosmosis in chloroplasts also generates ATP, but light drives the electron flow down an electron transport chain and H+ gradient formation. • Prokaryotes generate H+ gradients across their plasma membrane. ◊ They can use this proton-motive force not only to generate ATP but also to pump nutrients and waste products across the membrane and to rotate their flagella. Fig. 9.16 ◊ Fermentation: partial degradation of sugars in the absence of oxygen (Anaerobic) ◊ Cellular respiration: complete breakdwn of sugars in the presence of oxygen (Aerobic Respiration) Fermentation Cellular Respiration Anaerobic (No O) Aerobic (+ O) Input: Glucose, Output: ATP 1st Process: Glycolysis Electron Carrier: NAD+ Electron Acceptor: Electron Acceptor:Oxygen Pyruvate/Acetaldehyde (Complete oxidation of food) (incomplete oxidation of food) Cytoplasm Cytoplasm + Mitochondria End products: ATP = 2, Lactic Acid ATP =36, CO2 CH3CH2OHCOOH/Ethanol (C2H5OH) and H20 Fermentation enables some cells to produce ATP without the help of oxygen Anaerobic catabolism of sugars can occur by fermentation. In alcohol fermentation, pyruvate is converted to ethanol in two steps ◊ During lactic acid fermentation (muscle cells, bacteria) pyruvate is reduced directly by NADH to form lactate (ionized form of lactic acid). ◊ Some organisms (facultative anaerobes), including yeast and many bacteria, muscle cells can survive using either fermentation or respiration. ◊ Obligate anerobes = sorry, no choice have to be anerobic! ◊ Pure aerobes = neuron/brain cell! . Feedback mechanisms control cellular respiration ◊ Supply and demand regulates it ◊ Allosteric regulation of phosphofructokinase sets the pace of respiration. • This enzyme is inhibited by ATP and stimulated by AMP (derived from ADP). ◊ It responds to shifts in balance between production and degradation of ATP: ATP <-> ADP + Pi <-> AMP + Pi. • Thus, when ATP levels are high, inhibition of this enzyme slows glycolysis. • When ATP levels drop and ADP and AMP levels rise, the enzyme is active again and glycolysis speeds up. ◊ Citrate, the first product of the Krebs cycle, is also an inhibitor of phosphofructokinase. • This synchronizes the rate of glycolysis and the Krebs cycle. • Also, if intermediaries from the Krebs cycle are diverted to other uses (e.g., amino acid synthesis), glycolysis speeds up to replace these molecules. ◊ Metabolic balance is augmented by the control of other enzymes at other key locations in glycolysis and the Krebs cycle. ◊ Cells are thrifty, expedient, and responsive in their metabolism. .
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