CELLULAR RESPIRATION Chapter 1 Electron transport chain and chemiosmosis Mitochondrion Citric acid cycle Preparatory reaction 232 ADP or or ATP total net gain 2 ADP NADH NADH and FADH 2 Glycolysis NADH glucosepyruvate Cytoplasm e–e– e–e– e–e– e–e– e–e– e–e– e–e– 2 ADP 4 ADP ATP 2 ADP ATP

Outline  Cellular Respiration  Phases of Cellular Respiration  Glycolysis  Preparatory Reaction  Citric Acid Cycle  Electron Transport System  Fermentation

Overview  Living cells require energy from outside sources  Some animals, such as the giant panda, obtain energy by eating plants, and some animals feed on other organisms that eat plants

How do these leaves power the work of life for the giant panda?

Light energy ECOSYSTEM Photosynthesis in chloroplasts CO 2 + H 2 O Cellular respiration in mitochondria Organic molecules +O2+O2 ATP powers most cellular work Heat energy ATP

Cellular Respiration  A cellular process that breaks down carbohydrates and other metabolites with the connected buildup of ATP  Breakdown of organic molecules is exergonic Other metabolites? i.e.

ADP + P ATP intermembrane space cristae CO 2 H2OH2O g l u c o s e f r o m O 2 f r o m a i r O 2 and glucose enter cells, which release H 2 O and CO 2. Mitochondria use energy from glucose to form ATP from ADP + P.

Cellular Respiration: Processes  Several processes are central to cellular respiration and related pathways  Aerobic respiration consumes organic molecules and O 2 and yields ATP  Anaerobic respiration is similar to aerobic respiration but consumes compounds other than O 2  Fermentation is a partial degradation of sugars that occurs without necessary usage of O 2

Cellular Respiration: Processes  Most prevalent and efficient is aerobic process. C 6 H 12 O O 2  6 CO H 2 O + Energy (ATP + heat)  Energy extracted from glucose molecule:  Released step-wise  Allows ATP to be produced efficiently  Oxidation-reduction enzymes include NAD + and FAD as coenzymes

Redox Reactions: Oxidation and Reduction  The transfer of electrons during chemical reactions releases energy stored in organic molecules  This released energy is ultimately used to synthesize ATP becomes oxidized (loses electron) becomes reduced (gains electron)

Reactants becomes oxidized becomes reduced Products Methane (reducing agent) Oxygen (oxidizing agent) Carbon dioxideWater

Redox Reactions and Aerobic Cellular Respiration Electrons are removed from substrates and received by oxygen, which combines with H+ to become water. Glucose is oxidized and O 2 is reduced becomes oxidized becomes reduced

Step-wise Energy Harvest: NAD +  Step-wise reaction for energy harvest  Electrons from organic compounds are usually first transferred to NAD +, a coenzyme  As an electron acceptor, NAD + functions as an oxidizing agent during cellular respiration  Each NADH (the reduced form of NAD + ) represents stored energy that is tapped to synthesize ATP

Step-wise Energy Harvest: NAD +  NADH passes the electrons to the electron transport chain  Unlike an uncontrolled reaction, the electron transport chain passes electrons in a series of steps instead of one explosive reaction  O 2 pulls electrons down the chain in an energy-yielding tumble  The energy yielded is used to regenerate ATP

Free energy, G (a) Uncontrolled reaction H2OH2O H / 2 O 2 Explosive release of heat and light energy (b) Cellular respiration Controlled release of energy for synthesis of ATP 2 H e – 2 H + 1 / 2 O 2 (from food via NADH) ATP 1 / 2 O 2 2 H + 2 e – Electron transport chain H2OH2O

Stages of Cellular Respiration  Cellular respiration has four stages:  Glycolysis (breaks down glucose into two molecules of pyruvate)  Transition (preparatory) (pyruvates are oxidized and enter mitochondria)  The citric acid cycle (completes the breakdown of glucose)  Oxidative phosphorylation: Electron Transport Chain and chemiosis (accounts for most of the ATP synthesis)

Mitochondrion Substrate-level phosphorylation ATP Cytosol Glucose Pyruvate Glycolysis Electrons carried via NADH Substrate-level phosphorylation ATP Electrons carried via NADH and FADH 2 Oxidative phosphorylation ATP Citric acid cycle Oxidative phosphorylation: electron transport and chemiosmosis

STAGE 1: Glycolysis Pathway: Splitting of Sugars  Glycolysis (“splitting of sugar”) breaks down glucose into two molecules of pyruvate  Occurs in the cytoplasm and has two major phases:  Energy investment phase  Energy payoff phase

Fig ATP ADP Hexokinase 1 ATP ADP Hexokinase 1 Glucose Glucose-6-phosphate Glucose Glucose-6-phosphate

Fig Hexokinase ATP ADP 1 Phosphoglucoisomerase 2 Phosphogluco- isomerase 2 Glucose Glucose-6-phosphate Fructose-6-phosphate Glucose-6-phosphate Fructose-6-phosphate

1 Fig Hexokinase ATP ADP Phosphoglucoisomerase Phosphofructokinase ATP ADP 2 3 ATP ADP Phosphofructo- kinase Fructose- 1, 6-bisphosphate Glucose Glucose-6-phosphate Fructose-6-phosphate Fructose- 1, 6-bisphosphate Fructose-6-phosphate 3

Fig Glucose ATP ADP Hexokinase Glucose-6-phosphate Phosphoglucoisomerase Fructose-6-phosphate ATP ADP Phosphofructokinase Fructose- 1, 6-bisphosphate Aldolase Isomerase Dihydroxyacetone phosphate Glyceraldehyde- 3-phosphate Aldolase Isomerase Fructose- 1, 6-bisphosphate Dihydroxyaceton e phosphate Glyceraldehyde - 3-phosphate 4 5

Fig NAD + NADH H + 2 2P i Triose phosphate dehydrogenase 1, 3-Bisphosphoglycerate 6 2 NAD + Glyceraldehyde- 3-phosphate Phosphoglyceraldehyde dehydrogenase NADH2 + 2 H + 2 P i 1, 3-Bisphosphoglycerate 6 2 2

Fig NAD + NADH 2 Triose phosphate dehydrogenase + 2 H + 2 P i 2 2 ADP 1, 3-Bisphosphoglycerate Phosphoglycerokinase 2 ATP 2 3-Phosphoglycerate ADP 2 ATP 1, 3-Bisphosphoglycerate 3-Phosphoglycerate Phosphoglycero- kinase 2 7

Fig Phosphoglycerate Triose phosphate dehydrogenase 2 NAD + 2 NADH + 2 H + 2 P i 2 2 ADP Phosphoglycerokinase 1, 3-Bisphosphoglycerate 2 ATP 3-Phosphoglycerate 2 Phosphoglyceromutase 2-Phosphoglycerate Phosphoglycero- mutase

Fig NAD + NADH H + Triose phosphate dehydrogenase 2 P i 1, 3-Bisphosphoglycerate Phosphoglycerokinase 2 ADP 2 ATP 3-Phosphoglycerate Phosphoglyceromutase Enolase 2-Phosphoglycerate 2 H 2 O Phosphoenolpyruvate Phosphoglycerate Enolase 2 2 H 2 O Phosphoenolpyruvate 9

Fig Triose phosphate dehydrogenase 2 NAD + NADH ADP 2 ATP Pyruvate Pyruvate kinase Phosphoenolpyruvate Enolase 2 H 2 O 2-Phosphoglycerate Phosphoglyceromutase 3-Phosphoglycerate Phosphoglycerokinase 2 ATP 2 ADP 1, 3-Bisphosphoglycerate + 2 H ADP 2 ATP Phosphoenolpyruvate Pyruvate kinase 2 Pyruvate 10 2 P i

Energy investment phase Glucose 2 ADP + 2 P 2 ATPused formed 4 ATP Energy payoff phase 4 ADP + 4 P 2 NAD e – + 4 H + 2 NADH + 2 H + 2 Pyruvate + 2 H 2 O Glucose Net 4 ATP formed – 2 ATP used2 ATP 2 NAD e – + 4 H + 2 NADH + 2 H + Glycolysis Pathway: Summary

29 Glycolysis: Inputs and Outputs Glycolysis inputs outputs 2 pyruvate 2 NADH 2 ADP 4 ATP total net gain glucose 2 NAD + 4 ADP + 4 P ATP 2 2

Pyruvate  is a pivotal metabolite in cellular respiration  If O 2 is not available to the cell, fermentation, an anaerobic process, occurs in the cytoplasm.  During fermentation, glucose is incompletely metabolized to lactate, or to CO 2 and alcohol (depending on the organism).  If O 2 is available to the cell, pyruvate enters mitochondria by aerobic process.

STAGE 2: Transition (Preparatory) Stage  Connects glycolysis to the citric acid cycle  End product of glycolysis, pyruvate, enters the mitochondrial matrix  Pyruvate converted to 2-carbon acetyl CoA  Attached to Coenzyme A to form acetyl-CoA  Electron picked up (as hydrogen atom) by NAD +  CO 2 released, and transported out of mitochondria into the cytoplasm

CYTOSOLMITOCHONDRION NAD + NADH+ H Pyruvate Transport protein CO 2 Coenzyme A Acetyl CoA

STAGE 3: Citric Acid Cycle/ Krebs Cycle Pyruvate NAD + NADH + H + Acetyl CoA CO 2 CoA Citric acid cycle FADH 2 FAD CO NAD H + ADP +P i ATP NADH  Occurs in the mitochondria

Fig Acetyl CoA Oxaloacetate Citrate CoA—SH Citric acid cycle 1 2 H2OH2O Isocitrate

Fig Acetyl CoA CoA—SH Oxaloacetate Citrate H2OH2O Citric acid cycle Isocitrate NAD + NADH + H +  -Keto- glutarate CO2CO2

Fig Acetyl CoA CoA—SH Oxaloacetate Citrate H2OH2O Isocitrate NAD + NADH + H + Citric acid cycle  -Keto- glutarate CoA—SH NAD + NADH + H + Succinyl CoA CO2CO2 CO2CO2

Fig Acetyl CoA CoA—SH Oxaloacetate Citrate H2OH2O Isocitrate NAD + NADH + H + CO2CO2 Citric acid cycle CoA—SH  -Keto- glutarate CO2CO2 NAD + NADH + H + Succinyl CoA CoA—SH GTP GDP ADP P i Succinate ATP

Fig Acetyl CoA CoA—SH Oxaloacetate H2OH2O Citrate Isocitrate NAD + NADH + H + CO2CO2 Citric acid cycle CoA—SH  -Keto- glutarate CO2CO2 NAD + NADH + H + CoA—SH P Succinyl CoA i GTP GDP ADP ATP Succinate FAD FADH 2 Fumarate

Fig Acetyl CoA CoA—SH Oxaloacetate Citrate H2OH2O Isocitrate NAD + NADH + H + CO2CO2  -Keto- glutarate CoA—SH NAD + NADH Succinyl CoA CoA—SH PP GDP GTP ADP ATP Succinate FAD FADH 2 Fumarate Citric acid cycle H2OH2O Malate i CO2CO2 + H + 3 4

Fig Acetyl CoA CoA—SH Citrate H2OH2O Isocitrate NAD + NADH + H + CO2CO2  -Keto- glutarate CoA—SH CO2CO2 NAD + NADH + H + Succinyl CoA CoA—SH P i GTP GDP ADP ATP Succinate FAD FADH 2 Fumarate Citric acid cycle H2OH2O Malate Oxaloacetate NADH +H + NAD

41 Citric Acid Cycle: Balance Sheet inputsoutputs 4 CO 2 6 NADH 2 FADH 2 2 acetyl groups 6 NAD + 2 FAD 2 ADP + 2 P ATP 2 Citric acid cycle

STAGE 4: The Electron Transport Chain  Occurs in the cristae of mitrochondrion  Most of the chain’s components are proteins, which exist in multiprotein complexes  The carriers alternate reduced and oxidized states as they accept and donate electrons  Electrons drop in free energy as they go down the chain and are finally passed to O 2, forming H 2 O

STAGE 4: The Electron Transport Chain  Series of carrier molecules:  Pass energy rich electrons successively from one to another  Complex arrays of protein and cytochromes Cytochromes are respiratory molecules Complex carbon rings with metal atoms in center  Receives electrons from NADH & FADH 2  Produce ATP by chemiosis (proton pumps and ATP Synthase)  Oxygen serves as a final electron acceptor  Oxygen ion combines with hydrogen ions to form water

Protein complex of electron carriers H+H+ H+H+ H+H+ Cyt c Q    VV FADH 2 FAD NAD + NADH (carrying electrons from food) Electron transport chain 2 H / 2 O 2 H2OH2O ADP + P i Chemiosmosis Oxidative phosphorylation H+H+ H+H+ ATP synthase ATP 21

Cellular Respiration: Summary

Cellular Respiration Energy Summary: Aerobic  In general the flow would be as such for ATP production:  glucose  NADH  electron transport chain  proton-motive force  ATP  About 40% of the energy in a glucose molecule is transferred to ATP during cellular respiration, making about 38 ATP  HIGH!

Cellular Respiration: Anaerobic and Fermentative Glycolysis can produce ATP with or without O 2 (in aerobic or anaerobic conditions)  In the absence of O 2, glycolysis couples with fermentation or anaerobic respiration to produce ATP  Anaerobic respiration uses an electron transport chain with an electron acceptor other than O 2, for example sulfate  Fermentation uses phosphorylation instead of an electron transport chain to generate ATP

Fig. 9-18a 2 ADP + 2 P i 2 ATP GlucoseGlycolysis 2 Pyruvate 2 NADH2 NAD H + CO 2 2 Acetaldehyde 2 Ethanol (a) Alcohol fermentation 2

Fig. 9-18b Glucose 2 ADP + 2 P i 2 ATP Glycolysis 2 NAD + 2 NADH + 2 H + 2 Pyruvate 2 Lactate (b) Lactic acid fermentation

Fermentation and Aerobic Respiration Compared  Both processes use glycolysis to oxidize glucose and other organic fuels to pyruvate  The processes have different final electron acceptors: an organic molecule (such as pyruvate or acetaldehyde) in fermentation and O 2 in cellular respiration  Cellular respiration produces 38 ATP per glucose molecule; fermentation produces 2 ATP per glucose molecule

52 Efficiency of Fermentation Fermentation inputs outputs 2 lactate or 2 alcohol and 2 CO 2 glucose 2 ADP + 2 P net gain ATP 2

 Obligate anaerobes carry out fermentation or anaerobic respiration and cannot survive in the presence of O 2  Yeast and many bacteria are facultative anaerobes, meaning that they can survive using either fermentation or cellular respiration  In a facultative anaerobe, pyruvate is a fork in the metabolic road that leads to two alternative catabolic routes Fermentation and Aerobic Respiration Compared

Fig Glucose Glycolysis Pyruvate CYTOSOL No O 2 present: Fermentation O 2 present: Aerobic cellular respiration MITOCHONDRION Acetyl CoA Ethanol or lactate Citric acid cycle

Fermentation: Pros and Cons  Advantages  Provides a quick burst of ATP energy for muscular activity.  Disadvantages  Lactate is toxic to cells.  Lactate changes pH and causes muscles to fatigue.  Oxygen debt and cramping

56 Products of Fermentation Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. © The McGraw Hill Companies, Inc./Bruce M. Johnson, photographer

Products of Fermentation 57 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. © The McGraw Hill Companies, Inc./Bruce M. Johnson, photographer

Products of Fermentation 58 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. © The McGraw Hill Companies, Inc./Bruce M. Johnson, photographer

Review 1. Name the four stages of cellular respiration; for each, state the region of the eukaryotic cell where it occurs and the products that result 2. In general terms, explain the role of the electron transport chain in cellular respiration 4. Explain where and how the respiratory electron transport chain creates a proton gradient for 3 ATP production 5. Distinguish between fermentation and anaerobic respiration 6. Distinguish between obligate and facultative anaerobes

Mitochondria and Alternative Energy Sources Petite mutants of yeast have defective mitochondria incapable of oxidative phosphorylation. What carbon sources can these mutants use to grow? a. Glucose b. fatty acids c. Pyruvate d. all of the above e. none of the above

Glycolysis To sustain high rates of glycolysis under anaerobic conditions, cells require a. functioning mitochondria. b. Oxygen. c. oxidative phosphorylation of ATP. d. NAD+. e. All of the above are correct.

Electron Transport Chain and Respiration 1 Rotenone inhibits complex I (NADH dehydrogenase). When complex I is completely inhibited, cells will a. neither consume oxygen nor make ATP. b. not consume oxygen and will make ATP through glycolysis and fermentation. c. not consume oxygen and will make ATP only through substrate-level phosphorylation. d. consume less oxygen but still make some ATP through both glycolysis and respiration.

Catabolism and Anaerobiosis During intense exercise, as muscles go into anaerobiosis, the body will increase its consumption of a. fats. b. proteins. c. carbohydrates. d. all of the above

Evolution of Metabolic Pathways Glycolysis is found in all domains of life and is therefore believed to be ancient in origin. What can be said about the origin of the citric acid cycle, the electron transport chain, and the F1 ATPase? a. They evolved after photosynthesis generated free oxygen. b. They evolved before photosynthesis and used electron acceptors other than oxygen. c. Individual enzymes were present before photosynthesis but served other functions, such as amino acid metabolism. d. They evolved when the ancestral eukaryotes acquired mitochondria.