How Cells Release Stored Energy

 More than 100 mitochondrial disorders are known  Friedreich’s ataxia, caused by a mutant gene, results in loss of cordination, weak muscles, and visual problems  Animal, plants, fungus, and most protists depend on structurally sound mitochondria  Defective mitochondria can result in life threatening disorders

p.123 When Mitochondria Spin Their Wheels

 Descendents of African honeybees that were imported to Brazil in the 1950s  More aggressive, wider-ranging than other honeybees  Africanized bee’s muscle cells have large mitochondria

 Photosynthesizers get energy from the sun  Animals get energy second- or third-hand from plants or other organisms  Regardless, the energy is converted to the chemical bond energy of ATP

Anaerobic pathways  Evolved first  Don’t require oxygen  Start with glycolysis in cytoplasm  Completed in cytoplasm Aerobic pathways  Evolved later  Require oxygen  Start with glycolysis in cytoplasm  Completed in mitochondria

start (glycolysis) in cytoplasm completed in mitochondrion start (glycolysis) in cytoplasm completed in cytoplasm Aerobic Respiration Anaerobic Energy- Releasing Pathways Fig. 8-2, p.124 Main Types of Energy-Releasing Pathways

C 6 H O 2 6CO 2 + 6H 2 0 glucose oxygen carbon water dioxide

CYTOPLASM Glycolysis Electron Transfer Phosphorylation Krebs CYCLE ATP 2 CO 2 4 CO water 2 NADH 8 NADH 2 FADH 2 2 NADH 2 pyruvate e - + H + e - + oxygen (2 ATP net) glucose Typical Energy Yield: 36 ATP e-e- e - + H + ATP H+H+ e - + H + ATP 2 4 Fig. 8-3, p. 135

 NAD + and FAD accept electrons and hydrogen  Become NADH and FADH 2  Deliver electrons and hydrogen to the electron transfer chain

 A simple sugar (C 6 H 12 O 6 )  Atoms held together by covalent bonds In-text figure Page 126

 Energy-requiring steps ◦ ATP energy activates glucose and its six-carbon derivatives  Energy-releasing steps ◦ The products of the first part are split into three-carbon pyruvate molecules ◦ ATP and NADH form

GLUCOSE glucose GYCOLYSIS pyruvate to second stage of aerobic respiration or to a different energy-releasing pathway Fig. 8-4a, p.126 Glycolysis

ATP 2 ATP invested ENERGY-REQUIRING STEPS OF GLYCOLYSIS glucose ADP P P P P glucose–6–phosphate fructose–6–phosphate fructose–1,6–bisphosphate DHAP Fig. 8-4b, p.127 Glycolysis

ATP ADP ENERGY-RELEASING STEPS OF GLYCOLYSIS NAD + P PGAL 1,3–bisphosphoglycerate substrate-level phsphorylation PiPi 1,3–bisphosphoglycerate ATP NADH P PGAL NAD + PiPi PPPP 3–phosphoglycerate PP 2 ATP invested ADP Fig. 8-4c, p.127Glycolysis

2 ATP produced ATP ADP P substrate-level phsphorylation 2–phosphoglycerate ATP P pyruvate ADP PP 2–phosphoglycerate H2OH2OH2OH2O PEP Fig. 8-4d, p.127 Glycolysi s

2 ATP invested Energy-Requiring Steps of Glycolysis glucose PGAL P P ADP P ATP glucose-6-phosphate P fructose-6-phosphate ATP fructose1,6- bisphosphate PP ADP Figure 8- 4(2) Page 127

ADP ATP pyruvate ADP ATP pyruvate H2OH2O P PEP H2OH2O P P 2-phosphoglycerate P ADP ATP P 3-phosphoglycerate ADP ATP P 3-phosphoglycerate NAD + NADH PiPi 1,3-bisphosphoglycerate PP NAD + NADH PiPi 1,3-bisphosphoglycerate PP PGAL P P Figure 8-4 Page 127

Energy requiring steps: 2 ATP invested Energy releasing steps: 2 NADH formed 4 ATP formed Net yield is 2 ATP and 2 NADH

 Preparatory reactions ◦ Pyruvate is oxidized into two-carbon acetyl units and carbon dioxide ◦ NAD + is reduced  Krebs cycle ◦ The acetyl units are oxidized to carbon dioxide ◦ NAD + and FAD are reduced

Fig. 8-5a, p.128 mitochondrion

inner mitochondrial membrane outer mitochondrial membrane inner compartment outer compartment Fig. 8-6a, p.128 Second Stage Reactions Second Stage Reactions

Two pyruvates cross the inner mitochondrial membrane. outer mitochondrial compartment NADH FADH 2 ATP Krebs Cycle 6 CO 2 inner mitochondrial compartment Eight NADH, two FADH 2, and two ATP are the payoff from the complete break- down of two pyruvates in the second-stage reactions. The six carbon atoms from two pyruvates diffuse out of the mitochondrion, then out of the cell, in six CO Fig. 8-6b, p.128

pyruvate NAD + NADH coenzyme A (CoA) OO carbon dioxide CoA acetyl-CoA

Acetyl-CoA Formation acetyl-CoA (CO 2 ) pyruvate coenzyme A NAD + NADH CoA Krebs Cycle CoA NADH FADH 2 NADH ATP ADP + phosphate group NAD + FAD oxaloacetate citrate Fig. 8-7a, p.129 Preparatory Reactions

glucose GLYCOLYSIS pyruvate KREBS CYCLE ELECTRON TRANSFER PHOSPHORYLATION Fig. 8-7b, p.129 Preparatory Reactions

Overall Reactants  Acetyl-CoA  3 NAD +  FAD  ADP and P i Overall Products  Coenzyme A  2 CO 2  3 NADH  FADH 2  ATP

NAD + NADH =CoA acetyl-CoA oxaloacetatecitrate CoA H2OH2O malateisocitrate H2OH2O H2OH2O FAD FADH 2 fumarate succinate ADP + phosphate group ATP succinyl-CoA OO CoA NAD + NADH OO NAD + NADH  -ketoglutarate Figure 8-6 Page 129

 All of the carbon molecules in pyruvate end up in carbon dioxide  Coenzymes are reduced (they pick up electrons and hydrogen)  One molecule of ATP forms  Four-carbon oxaloacetate regenerates

 Glycolysis2 NADH  Preparatory reactions 2 NADH  Krebs cycle 2 FADH NADH  Total 2 FADH NADH

 Occurs in the mitochondria  Coenzymes deliver electrons to electron transfer chains  Electron transfer sets up H + ion gradients  Flow of H + down gradients powers ATP formation

glucose GLYCOLYSIS pyruvate KREBS CYCLE ELECTRON TRANSFER PHOSPHORYLATION Fig. 8-8a, p.130 Phosphorylation

Fig. 8-8b, p.130 OUTER COMPARTMENT INNER COMPARTMENT Electron Transfer Chain ATP Synthase ATP H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ NADH + H + NAD + + 2H + FAD + 2H + FADH 2 2H + + 1/2 0 2 H2OH2O ADP + P i e-e- e-e- e-e- Phosphorylation

glucose glycolysis e–e– KREBS CYCLE electron transfer phosphorylation 2 PGAL 2 pyruvate 2 NADH 2 CO 2 ATP 2 FADH 2 H+H+ 2 NADH 6 NADH 2 FADH 2 2 acetyl-CoA ATP 2 Krebs Cycle 4 CO 2 ATP 36 ADP + P i H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ Fig. 8-9, p.131Phosphorylation

NADH OUTER COMPARTMENT INNER COMPARTMENT

ATP ADP + P i INNER COMPARTMENT

 Electron transport phosphorylation requires the presence of oxygen  Oxygen withdraws spent electrons from the electron transfer chain, then combines with H + to form water

 Glycolysis ◦ 2 ATP formed by substrate-level phosphorylation  Krebs cycle and preparatory reactions ◦ 2 ATP formed by substrate-level phosphorylation  Electron transport phosphorylation ◦ 32 ATP formed

 NADH formed in cytoplasm cannot enter mitochondrion  It delivers electrons to mitochondrial membrane  Membrane proteins shuttle electrons to NAD + or FAD inside mitochondrion  Electrons given to FAD yield less ATP than those given to NAD +

 686 kcal of energy are released  7.5 kcal are conserved in each ATP  When 36 ATP form, 270 kcal (36 X 7.5) are captured in ATP  Efficiency is 270 / 686 X 100 = 39 percent  Most energy is lost as heat

 Do not use oxygen  Produce less ATP than aerobic pathways  Two types ◦ Fermentation pathways ◦ Anaerobic electron transport

 Begin with glycolysis  Do not break glucose down completely to carbon dioxide and water  Yield only the 2 ATP from glycolysis  Steps that follow glycolysis serve only to regenerate NAD +

C 6 H 12 O 6 ATP NADH 2 acetaldehyde electrons, hydrogen from NADH 2 NAD ADP 2 pyruvate 2 4 energy output energy input glycolysis ethanol formation 2 ATP net 2 ethanol 2 H 2 O 2 CO 2 Fig. 8-10d, p.132 Alcoholic Fermentatio n

C 6 H 12 O 6 ATP NADH 2 lactate electrons, hydrogen from NADH 2 NAD ADP 2 pyruvate 2 4 energy output energy input glycolysis lactate fermentation 2 ATP net Fig. 8-11, p.133 Lactate Fermentation

Fig. 8-12, p.133 Lactate Fermentation

 Carried out by certain bacteria  Electron transfer chain is in bacterial plasma membrane  Final electron acceptor is compound from environment (such as nitrate), not oxygen  ATP yield is low

FOOD complex carbohydrates simple sugars pyruvate acetyl-CoA glycogenfats proteins amino acids carbon backbones fatty acids glycerol NH 3 PGAL glucose-6-phosphate GLYCOLYSIS KREBS CYCLE urea

FOOD fatsglycogen complex carbohydrates proteins simple sugars (e.g., glucose) amino acids glucose-6- phosphate carbon backbones NH 3 urea ATP (2 ATP net) PGAL glycolysis ATP 2 glycerol fatty acids NADHpyruvate acetyl-CoA NADHCO 2 Krebs Cycle NADH, FADH 2 CO 2 ATP many ATP water H+H+ e – + oxygen e–e– 4 ATP 2 Fig. 8-13b, p.135 electron transfer phosphorylation Alternativ e Energy Sources

 When life originated, atmosphere had little oxygen  Earliest organisms used anaerobic pathways  Later, noncyclic pathway of photosynthesis increased atmospheric oxygen  Cells arose that used oxygen as final acceptor in electron transport

p.136b Processes Are Linked