Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 7 How Cells Make ATP: Energy-Releasing Pathways Chapter 8: Cellular Respiration

Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 7 How Cells Make ATP: Energy-Releasing Pathways The net equation for glucose breakdown is : C 6 H 12 O O 2 = 6 CO H 2 O + energy Glucose is a high ‑ energy molecule; CO 2 and H 2 O are low ‑ energy molecules; cellular respiration is thus exergonic because it releases energy. Cellular Respiration

Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 7 How Cells Make ATP: Energy-Releasing Pathways Cellular Respiration The breakdown of glucose yields synthesis of 36 or 38 ATP (depending on certain conditions); this preserves about 39% of the energy available in glucose. This is relatively efficient compared to, for example, the 25% efficiency of a car burning gasoline.

Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 7 How Cells Make ATP: Energy-Releasing Pathways Cellular respiration Aerobic respiration –Requires molecular oxygen –Includes redox reactions Anaerobic –Anaerobic respiration –Fermentation –Do not require oxygen All exergonic (releases energy… spontaneous…downhill reaction)

Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 7 How Cells Make ATP: Energy-Releasing Pathways Phases of Cellular Respiration 4 phases: 1.Glycolysis is the breakdown of glucose in the cytoplasm into two molecules of pyruvate. Enough energy is released for an immediate yield of two ATP. Glycolysis takes place outside the mitochondria and does not utilize oxygen; it is therefore an anaerobic process.

Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 7 How Cells Make ATP: Energy-Releasing Pathways In the preparatory (prep) reaction Pyruvate enters a mitochondrion and is oxidized to a two-carbon acetyl group and CO 2 is removed; this reaction occurs twice per glucose molecule.

Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 7 How Cells Make ATP: Energy-Releasing Pathways The citric acid cycle 1)occurs in the matrix of the mitochondrion and produces NADH and FADH 2 ; 2)is a series of reactions that gives off CO 2 and produces one ATP; 3)turns twice because two acetyl-CoA molecules enter the cycle per glucose molecule; 4)produces two immediate ATP molecules per glucose molecule.

Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 7 How Cells Make ATP: Energy-Releasing Pathways The electron transport chain 1)is a series of carriers in the inner mitochondrial membrane that accept electrons from glucose--electrons are passed from carrier to carrier until received by oxygen; 2)passes electrons from higher to lower energy states, allowing energy to be released and stored for ATP production;

Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 7 How Cells Make ATP: Energy-Releasing Pathways What Type of Process is Cellular Respiration? An Oxidation-Reduction Process or REDOX Reaction Oxidation of GLUCOSE --> CO 2 + H 2 O (e - removed from C 6 H 12 O 6 ) Reduction O 2 to H 2 O (e - passed to O 2 )

Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 7 How Cells Make ATP: Energy-Releasing Pathways What Carries the Electrons? NAD + (nicotinadenine dinucleotide) acts as the energy carrier NAD + (nicotinadenine dinucleotide) acts as the energy carrier NAD + is a coenzyme NAD + is a coenzyme It’s Reduced to NADH when it picks up two electrons and one hydrogen ion It’s Reduced to NADH when it picks up two electrons and one hydrogen ion

Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 7 How Cells Make ATP: Energy-Releasing Pathways Are There Any Other Electron Carriers? YES! Another Coenzyme! YES! Another Coenzyme! FAD+ (Flavin adenine dinucleotide) FAD+ (Flavin adenine dinucleotide) Reduced to FADH 2 Reduced to FADH 2

Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 7 How Cells Make ATP: Energy-Releasing Pathways Other Cellular Respiration Facts Metabolic Pathway that breaks down carbohydrates Metabolic Pathway that breaks down carbohydrates Process is Exergonic as High- energy Glucose is broken into CO 2 and H 2 O Process is Exergonic as High- energy Glucose is broken into CO 2 and H 2 O Process is also Catabolic because larger Glucose breaks into smaller molecules Process is also Catabolic because larger Glucose breaks into smaller molecules

Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 7 How Cells Make ATP: Energy-Releasing Pathways Review of Mitochondria Structure Smooth outer Membrane Folded inner membrane Folds called Cristae Space inside cristae called the Matrix

Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 7 How Cells Make ATP: Energy-Releasing Pathways What are the Stages of Cellular Respiration? GlycolysisGlycolysis Formation of acetyl Co-AFormation of acetyl Co-A The Krebs CycleThe Krebs Cycle The Electron Transport ChainThe Electron Transport Chain Copyright Cmassengale

Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 7 How Cells Make ATP: Energy-Releasing Pathways Four stages of aerobic respiration Takes place in the cytosol –Glycolysis Takes place in the mitochondrion –Formation of acetyl CoA –Citric acid cycle –Electron transport chain/chemiosmosis

Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 7 How Cells Make ATP: Energy-Releasing Pathways Four stages of aerobic respiration

Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 7 How Cells Make ATP: Energy-Releasing Pathways Summary of aerobic respiration

Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 7 How Cells Make ATP: Energy-Releasing Pathways Glycolysis “Sugar splitting” Occurs in the cytosol Does not require oxygen (anaerobic) Divided into two major phases –Energy investment phase –Energy capture phase 1 glucose molecule produces net yield of two NADH molecules and two ATP molecules

Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 7 How Cells Make ATP: Energy-Releasing Pathways Glycolysis Energy investment Phosphorylation occurs- 2 ATP molecules transfer a phosphate to a G3P sugar Energy Capture 4 ATP molecules and 2 NADH

Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 7 How Cells Make ATP: Energy-Releasing Pathways Formation of acetyl CoA Catalyzed by enzyme pyruvate dehydrogenase –First carboxyl group is split off as carbon dioxide –Then remaining two-carbon fragment is oxidized and electrons transferred to NAD + –Finally, oxidized two-carbon group is attached to coenzyme A

Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 7 How Cells Make ATP: Energy-Releasing Pathways Formation of acetyl CoA Catalyzed by the multienzyme complex pyruvate dehydrogenase

Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 7 How Cells Make ATP: Energy-Releasing Pathways Citric acid cycle (Krebs Cycle) For 1 glucose, two acetyl groups enter the citric acid cycle Each two-carbon acetyl group combines with a four-carbon compound Two CO 2 molecules are removed Energy captured as one ATP, three NADH, and one FADH 2 per acetyl group (These will act as energy carriers for the electron transport chain) **So… 2 acetyl groups yields 4 CO 2, 6 NADH, 2 FADH 2, 2 ATP

Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 7 How Cells Make ATP: Energy-Releasing Pathways Citric acid cycle Also known as the Krebs Cycle or the tricarboxylic acid (TCA) cycle Because 1 glucose produces 2 acetyl CoA molecules two cycles are required per glucose After 2 turns the original glucose can be said to have been completely consumed **So… 2 acetyl groups yields 4 CO2, 6 NADH, 2 FADH2, 2 ATP

Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 7 How Cells Make ATP: Energy-Releasing Pathways Detail of citric acid cycle

Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 7 How Cells Make ATP: Energy-Releasing Pathways A Little Krebs Cycle History Discovered by Hans Krebs in 1937 Discovered by Hans Krebs in 1937 He received the Nobel Prize in physiology or medicine in 1953 for his discovery He received the Nobel Prize in physiology or medicine in 1953 for his discovery Forced to leave Germany prior to WWII because he was Jewish Forced to leave Germany prior to WWII because he was Jewish

Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 7 How Cells Make ATP: Energy-Releasing Pathways Electron transport chain Series of electron carriers Each carrier exists in oxidized or reduced form Electrons pass down the electron transport chain in series of redox reactions Lose energy as pass along the chain Released energy is used to pump protons across the inner membrane space (Hydrogen ions=protons) Oxygen is the final electron acceptor

Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 7 How Cells Make ATP: Energy-Releasing Pathways Electron Transport Chain Summary 34 ATP Produced34 ATP Produced Oxygen is the final electron acceptorOxygen is the final electron acceptor H 2 O ProducedH 2 O Produced Occurs Across Inner Mitochondrial membraneOccurs Across Inner Mitochondrial membrane Uses coenzymes NAD+ and FAD+ to accept e- from glucoseUses coenzymes NAD+ and FAD+ to accept e- from glucose NADH = 3 ATP’sNADH = 3 ATP’s FADH 2 = 2 ATP’sFADH 2 = 2 ATP’s Copyright Cmassengale

Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 7 How Cells Make ATP: Energy-Releasing Pathways Electron transport chain

Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 7 How Cells Make ATP: Energy-Releasing Pathways Accumulation of protons within the inter-membrane space

Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 7 How Cells Make ATP: Energy-Releasing Pathways Electron transport and chemiosmosis Energy from the energy carriers is used to move the H+ ions

Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 7 How Cells Make ATP: Energy-Releasing Pathways Electron Transport Chain Animation Electron Transport Chain Animation Copyright Cmassengale

Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 7 How Cells Make ATP: Energy-Releasing Pathways Energy yield from complete oxidation of glucose by aerobic respiration

Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 7 How Cells Make ATP: Energy-Releasing Pathways What if Oxygen is not Available Anaerobic respiration takes place Not as efficient as aerobic respiration

Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 7 How Cells Make ATP: Energy-Releasing Pathways Fermentation  Occurs when O 2 NOT present (anaerobic)  Called Lactic Acid fermentation in muscle cells (makes muscles tired)  Temporary and 80% of the lactate will be exported to liver and regenerated into more glucose for muscle cells  Called Alcohol fermentation in yeast (produces ethanol)  Basis for production of beer, wine, and makes bread dough rise  Nets only 2 ATP Copyright Cmassengale

Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 7 How Cells Make ATP: Energy-Releasing Pathways Many organisms depend on nutrients other than glucose Products of protein and lipid catabolism enter same metabolic pathways as glucose Amino acids are deaminated

Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 7 How Cells Make ATP: Energy-Releasing Pathways Energy from carbohydrates, proteins, and fats Amino acids can have an amine group removed by demamination and converted to urea…leaving the carbon chain to be metabolized Lipids will generate 44 ATP

Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 7 How Cells Make ATP: Energy-Releasing Pathways Anaerobic respiration versus fermentation Anaerobic respiration –Electrons transferred from fuel molecules to electron transport chain –Final electron acceptor is inorganic substance Fermentation –Anaerobic process that does not use electron transport chain