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Unformatted text preview: BIology 1A Professor Doudna Spring 10 1 Pimentel 02/08/10 8am Lecture #9: Energe.cs • Reading: Chapter 9, pp. 162‐169 • Lecture outline: Cellular respira<on – Redox reac<ons – Electron transport chain – Glycolysis Overview: Life Is Work • Living cells require energy from outside sources • Some animals, such as the giant panda, obtain energy by ea<ng plants, and some animals feed on other organisms that eat plants Light energy • Energy ﬂows into an ecosystem as sunlight and leaves as heat • Photosynthesis generates O2 and organic molecules, which are used in cellular respira<on • Cells use chemical energy stored in organic molecules to regenerate ATP, which powers work ECOSYSTEM Photosynthesis in chloroplasts CO2 + H2O Cellular respira.on in mitochondria Organic + O molecules 2 ATP ATP powers most cellular work Heat energy Catabolic Pathways and Produc.on of ATP • The breakdown of organic molecules is exergonic • Fermenta.on is a par<al degrada<on of sugars that occurs without O2 • Aerobic respira.on consumes organic molecules and O2 and yields ATP • Anaerobic respira.on is similar to aerobic respira<on but consumes compounds other than O2 energy released breaking larger molecules to make smaller molecules Redox Reac.ons: Oxida.on and Reduc.on • The transfer of electrons during chemical reac<ons releases energy stored in organic molecules • This released energy is ul<mately used to synthesize ATP The Principle of Redox • Chemical reac<ons that transfer electrons between reactants are called oxida<on‐reduc<on reac<ons, or redox reac.ons • In oxida.on, a substance loses electrons, or is oxidized • In reduc.on, a substance gains electrons, or is reduced (the amount of posi<ve charge is reduced) these two rxns are always coupled Fig. 9‐UN1 reducing agent oxidizing agent becomes oxidized (loses electron) becomes reduced (gains electron) electron donor electron acceptor • The electron donor is called the reducing agent • The electron receptor is called the oxidizing agent • Some redox reac<ons do not transfer electrons but change the electron sharing in covalent bonds • An example is the reac<on between methane and O2 Fig. 9‐3 very electronegative and very strong oxidizing agent - exergonic reaction - delta G is negative Reactants becomes oxidized Products becomes reduced Methane (reducing agent) Oxygen (oxidizing agent) Carbon dioxide Water Oxida3on of Organic Fuel Molecules During Cellular Respira3on • During cellular respira<on, the fuel (such as glucose) is oxidized, and O2 is reduced: becomes oxidized becomes reduced broken into many steps in order to facilitate the cell in absorbing and harvesting the energy - delta G = -686 kcal/mol Stepwise Energy Harvest via NAD+ and the Electron Transport Chain • In cellular respira.on, glucose and other organic molecules are broken down in a series of steps • Electrons from organic compounds are usually ﬁrst transferred to NAD+, a coenzyme • As an electron acceptor, NAD+ func<ons as an oxidizing agent during cellular respira<on • Each NADH (the reduced form of NAD+) represents stored energy that is tapped to synthesize ATP Dehydrogenase Fig. 9‐4 2 e– + 2 H + Dehydrogenase NAD+ + 2[H] 2 e– + H + NADH H+ Reduc.on of NAD+ Oxida.on of NADH Nico.namide (reduced form) + H+ Nico.namide (oxidized form) most electrons are transferred to NAD+ • NADH passes the electrons to the electron transport chain • Unlike an uncontrolled reac<on, the electron transport chain passes electrons in a series of steps instead of one explosive reac<on • O2 pulls electrons down the chain in an energy‐ yielding tumble • The energy yielded is used to regenerate ATP allows cell to harvest energy Fig. 9‐5 H2 + 1/2 O2 2 H (from food via NADH) 2 H+ + 2 e– + 1/ O 2 2 Controlled release of energy for synthesis of ATP ATP ATP ATP 2 e– 2 H+ 1/ O 2 2 Elect Free energy, G Free energy, G ransp ron t ain ch Explosive release of heat and light energy ort H2O H2O (a) Uncontrolled reac.on (b) Cellular respira.on The Stages of Cellular Respira<on: A Preview • Cellular respira<on has three stages: 1st 2nd 3rd – Glycolysis (breaks down glucose into two molecules of pyruvate) – The citric acid cycle (completes the breakdown of glucose) – Oxida.ve phosphoryla.on (accounts for most of the ATP synthesis) glucose -> NADH -> electron transport chain -> H2O + CO2 Fig. 9‐6‐1 Electrons carried via NADH Glycolysis Glucose 2Pyruvate Cytosol ATP Substrate‐level phosphoryla.on mitochondria glycolysis occurs in the cytosol Fig. 9‐6‐2 Electrons carried via NADH Electrons carried via NADH and FADH2 Glycolysis Glucose Pyruvate Citric acid cycle Cytosol Mitochondrion ATP Substrate‐level phosphoryla.on ATP Substrate‐level phosphoryla.on - this is all in eukaroytic cell - for prokaryotes, this occurs in the plasma membrane
Fig. 9‐6‐3 Electrons carried via NADH Electrons carried via NADH and FADH2 Glycolysis Glucose Pyruvate Citric acid cycle Oxida.ve phosphoryla.on: electron transport and chemiosmosis Cytosol Mitochondrion vast majority of ATP is made here ATP Substrate‐level phosphoryla.on ATP Substrate‐level phosphoryla.on ATP Oxida.ve phosphoryla.on • The process that generates most of the ATP is called oxida.ve phosphoryla.on because it is powered by redox reac<ons • Oxida<ve phosphoryla<on accounts for almost 90% of the ATP generated by cellular respira<on • A smaller amount of ATP is formed in glycolysis and the citric acid cycle by substrate‐level phosphoryla.on Fig. 9‐7 Enzyme ADP P Substrate Enzyme + Product enzyme transfers phosphate group from substrate to ADP to form ATP and dephosphorylated product ATP Glycolysis harvests chemical energy by oxidizing glucose to pyruvate • Glycolysis (“spli`ng of sugar”) breaks down glucose into two molecules of pyruvate • Glycolysis occurs in the cytoplasm and has two major phases: – Energy investment phase – Energy payoﬀ phase input 2 molecules of ATP net production of pyruvate, ATP, and NADH Fig. 9‐8 Energy investment phase Glucose 2 ADP + 2 P 2 ATP used Energy payoﬀ phase 4 ADP + 4 P 4 ATP formed 2 NAD+ + 4 e– + 4 H+ 2 NADH + 2 H+ 2 Pyruvate + 2 H2O Net Glucose 2 Pyruvate + 2 H2O 2 ATP 2 NADH + 2 H+ 4 ATP formed – 2 ATP used 2 NAD+ + 4 e– + 4 H+ Fig. 9‐9‐1 Glucose ATP 1 Hexokinase ADP Glucose Glucose‐6‐phosphate ATP 1 Hexokinase ADP closes around the glucose and phosphorylates glucose unable to cross cell membrane because phosphate is very charged; phosphate also makes glucose more reactive Glucose‐6‐phosphate Fig. 9‐9‐2 Glucose ATP 1 Hexokinase ADP used to isomerize glucose-6-phosphate Glucose‐6‐phosphate 2 Phosphoglucoisomerase Glucose‐6‐phosphate 2 Phosphogluco‐ isomerase Fructose‐6‐phosphate Fructose‐6‐phosphate Fig. 9‐9‐3 Glucose ATP 1 Hexokinase ADP Fructose‐6‐phosphate Glucose‐6‐phosphate 2 Phosphoglucoisomerase Adds another phosphate to the sugar, making it a lot more reactive ATP 3 Fructose‐6‐phosphate ATP 3 Phosphofructokinase ADP ADP Phosphofructo‐ kinase PFK Fructose‐ 1, 6‐bisphosphate Highly subjective to feedback inhibition; if there is a lot of product, it will bind to PFK to inhibit Fructose‐ 1, 6‐bisphosphate Fig. 9‐9‐4 Glucose ATP 1 Hexokinase ADP Glucose‐6‐phosphate 2 Phosphoglucoisomerase Fructose‐6‐phosphate ATP Fructose‐ 1, 6‐bisphosphate 4 Aldolase 3 Phosphofructokinase ADP Isomerase Fructose‐ 1, 6‐bisphosphate 4 Aldolase 5 5 Isomerase Dihydroxyacetone phosphate Glyceraldehyde‐ 3‐phosphate Glyceraldehyde‐ Dihydroxyacetone catalyzes interconversion of 3‐phosphate phosphate the two; never really is an equilibrium
only this continues into the citric acid cycle Fig. 9‐9‐5 2 NAD+ 6 Triose phosphate dehydrogenase 2 P
i Energy Payoff Stages 2 NADH + 2 H+ 2 1, 3‐Bisphosphoglycerate Glyceraldehyde‐ 3‐phosphate 2 NAD+ 6 Triose phosphate dehydrogenase 2 P i 2 NADH + 2 H+ 2 1, 3‐Bisphosphoglycerate Fig. 9‐9‐6 2 NAD+ 6 Triose phosphate dehydrogenase 2 P
i 2 NADH + 2 H+ 2 1, 3‐Bisphosphoglycerate 2 ADP Phosphoglycerokinase 2 ATP 7 2 1, 3‐Bisphosphoglycerate 2 ADP 2 3‐Phosphoglycerate 2 ATP 7 Phosphoglycero‐ kinase 2 3‐Phosphoglycerate Fig. 9‐9‐7 2 NAD+ 6 Triose phosphate dehydrogenase 2 P i 2 NADH + 2 H+ 2 1, 3‐Bisphosphoglycerate 2 ADP 7 Phosphoglycerokinase 2 ATP 2 3‐Phosphoglycerate 8 Phosphoglyceromutase 2 3‐Phosphoglycerate 8 Phosphoglycero‐ mutase relocates phosphate 2 2‐Phosphoglycerate 2 2‐Phosphoglycerate Fig. 9‐9‐8 2 NAD+ 6 Triose phosphate dehydrogenase 2 P
i 2 NADH + 2 H+ 2 1, 3‐Bisphosphoglycerate 2 ADP 7 Phosphoglycerokinase 2 ATP 2 3‐Phosphoglycerate 2 2‐Phosphoglycerate
9 8 Phosphoglyceromutase 2 2‐Phosphoglycerate 2 H2O Enolase removes H2O 9 2 H2O Enolase 2 Phosphoenolpyruvate 2 Phosphoenolpyruvate Fig. 9‐9‐9 2 NAD+ 6 Triose phosphate dehydrogenase 2 P
i 2 NADH + 2 H+ 2 1, 3‐Bisphosphoglycerate 2 ADP 7 Phosphoglycerokinase 2 ATP 2 2 3‐Phosphoglycerate Phosphoenolpyruvate 2 ADP 8 Phosphoglyceromutase 10 Pyruvate kinase 2 ATP 2 2‐Phosphoglycerate 9 2 H2O Enolase Removes phosphate 2 Phosphoenolpyruvate 2 ADP 10 Pyruvate kinase 2 ATP 2 Pyruvate 2 Pyruvate ...
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