The Cellular Respiration Lecture 12

Outline Cellular Respiration Overview Glycolysis Citric Acid Cycle (Pyruvate Oxidation) Oxidative Phosphorylation

Cellular Respiration - Overview Life is work Cellular respiration provides the energy for cells to do work

Photosynthesis in chloroplasts Cellular respiration in mitochondria Light energy Figure 9.2 ECOSYSTEM Photosynthesis in chloroplasts  O2 Organic molecules CO2  H2O Cellular respiration in mitochondria Figure 9.2 Energy flow and chemical recycling in ecosystems. ATP powers most cellular work ATP Heat energy

Cellular Respiration – Redox reactions During cellular respiration – Glucose is oxidized and O2 is reduced OIL RIG (or for biology, reduced – gains hydrogens; oxidized loses hydrogens) becomes oxidized becomes reduced

Cellular Respiration – Overview- NAD+ Electrons move away from Carbon atoms in Glucose to NAD+ NAD+ is a carrier molecule that transfer helps transfer energy from Glucose to make ATP Oxidizing agent (accepts electrons and becomes reduced) NAD+, hydride ion and a proton

Cellular Respiration – Overview- NADH NADH then passes the electrons to the electron transport chain The chain moves the electrons in a series of steps O2 pulls the electrons down the chain The energy yielded is used to regenerate ATP

Cellular Respiration – The stages Three steps to get there: Glycolysis 2 ATPs Pyruvate Oxidation Citric Acid (Kreb’s) Cycle – 2 ATPs Oxidative phosphorylation (Electron Transport Chain and Chemiosmosis) - 26 – 28 ATPs

Electrons carried via NADH Electrons carried via NADH and FADH2 Figure 9.6-3 Electrons carried via NADH Electrons carried via NADH and FADH2 Oxidative phosphorylation: electron transport and chemiosmosis Pyruvate oxidation Glycolysis Citric acid cycle Glucose Pyruvate Acetyl CoA CYTOSOL MITOCHONDRION Figure 9.6 An overview of cellular respiration. ATP ATP ATP Substrate-level phosphorylation Substrate-level phosphorylation Oxidative phosphorylation

Cellular Respiration – Step 1 - Glycolysis Step one of cellular respiration - Oxidizing of glucose to pyruvate Splitting of sugar 1 molecule of glucose is broken into two molecules of pyruvate Occurs in the cytoplasm Has two major phases Energy investment phase Energy payoff phase Does not require O2

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+ Figure 9.8 Figure 9.8 The energy input and output of glycolysis. 2 Pyruvate  2 H2O Net Glucose 2 Pyruvate  2 H2O 4 ATP formed  2 ATP used 2 ATP 2 NAD+  4 e  4 H+ 2 NADH  2 H+

Glycolysis: Energy Investment Phase Figure 9.9-1 Glycolysis: Energy Investment Phase ATP Glucose Glucose 6-phosphate ADP Hexokinase 1 Figure 9.9 A closer look at glycolysis.

Phosphogluco- isomerase Figure 9.9-2 Glycolysis: Energy Investment Phase ATP Glucose Glucose 6-phosphate Fructose 6-phosphate ADP Hexokinase Phosphogluco- isomerase 1 2 Figure 9.9 A closer look at glycolysis.

Phosphogluco- isomerase Phospho- fructokinase Figure 9.9-3 Glycolysis: Energy Investment Phase ATP ATP Glucose Glucose 6-phosphate Fructose 6-phosphate Fructose 1,6-bisphosphate ADP ADP Hexokinase Phosphogluco- isomerase Phospho- fructokinase 1 2 3 Figure 9.9 A closer look at glycolysis.

Glycolysis: Energy Investment Phase Figure 9.9-4 Glycolysis: Energy Investment Phase ATP ATP Glucose Glucose 6-phosphate Fructose 6-phosphate Fructose 1,6-bisphosphate ADP ADP Hexokinase Phosphogluco- isomerase Phospho- fructokinase 1 2 3 Aldolase 4 Dihydroxyacetone phosphate Glyceraldehyde 3-phosphate Figure 9.9 A closer look at glycolysis. To step 6 Isomerase 5

Triose phosphate dehydrogenase 1,3-Bisphospho- glycerate Figure 9.9-5 Glycolysis: Energy Payoff Phase 2 NADH 2 NAD + 2 H Triose phosphate dehydrogenase 2 P i 1,3-Bisphospho- glycerate 6 Figure 9.9 A closer look at glycolysis.

Glycolysis: Energy Payoff Phase Figure 9.9-6 Glycolysis: Energy Payoff Phase 2 ATP 2 NADH 2 NAD + 2 H 2 ADP 2 Triose phosphate dehydrogenase Phospho- glycerokinase 2 P i 1,3-Bisphospho- glycerate 7 3-Phospho- glycerate 6 Figure 9.9 A closer look at glycolysis.

Glycolysis: Energy Payoff Phase Figure 9.9-7 Glycolysis: Energy Payoff Phase 2 ATP 2 NADH 2 NAD + 2 H 2 ADP 2 2 Triose phosphate dehydrogenase Phospho- glycerokinase Phospho- glyceromutase 2 P i 1,3-Bisphospho- glycerate 7 3-Phospho- glycerate 8 2-Phospho- glycerate 6 Figure 9.9 A closer look at glycolysis.

Glycolysis: Energy Payoff Phase Figure 9.9-8 Glycolysis: Energy Payoff Phase 2 ATP 2 NADH 2 H2O 2 NAD + 2 H 2 ADP 2 2 2 Triose phosphate dehydrogenase Phospho- glycerokinase Phospho- glyceromutase Enolase 2 P i 9 1,3-Bisphospho- glycerate 7 3-Phospho- glycerate 8 2-Phospho- glycerate Phosphoenol- pyruvate (PEP) 6 Figure 9.9 A closer look at glycolysis.

Glycolysis: Energy Payoff Phase Figure 9.9-9 Glycolysis: Energy Payoff Phase 2 ATP 2 ATP 2 NADH 2 H2O 2 ADP 2 NAD + 2 H 2 ADP 2 2 2 Triose phosphate dehydrogenase Phospho- glycerokinase Phospho- glyceromutase Enolase Pyruvate kinase 2 P i 9 1,3-Bisphospho- glycerate 7 3-Phospho- glycerate 8 2-Phospho- glycerate Phosphoenol- pyruvate (PEP) 10 Pyruvate 6 Figure 9.9 A closer look at glycolysis.

Cellular Respiration – Step 2 – Citric Acid Cycle Pyruvate enters mitochondrion O2 dependent Oxidation of glucose is completed

Cellular Respiration – Step 2 – Citric Acid Cycle - Pyruvate Oxidation Pyruvate must be converted to Coenzyme A (acetyl CoA) This links glycolysis to the citric acid cycle Carried out by a multienzyme complex Complex catalyses three reactions

MITOCHONDRION CYTOSOL CO2 Coenzyme A NAD NADH + H Acetyl CoA Figure 9.10 MITOCHONDRION CYTOSOL CO2 Coenzyme A 1 3 2 NAD NADH + H Acetyl CoA Figure 9.10 Oxidation of pyruvate to acetyl CoA, the step before the citric acid cycle. Pyruvate Transport protein

Cellular Respiration – Step 2 - Pyruvate Oxidation – the Citric Acid Cycle Also called Krebs cycle Completes the breakdown of pyruvate to CO2 Generates 1 ATP, 3 NADH, and 1 FADH2

Pyruvate CO2 NAD CoA NADH + H Acetyl CoA CoA CoA Citric acid cycle Figure 9.11 CoA CoA Citric acid cycle 2 CO2 Figure 9.11 An overview of pyruvate oxidation and the citric acid cycle. FADH2 3 NAD FAD 3 NADH + 3 H ADP + P i ATP

Cellular Respiration – Step 2 - Pyruvate Oxidation – the Citric Acid Cycle 8 steps Each step catalyzed by a specific enzyme Acetyl group of acetyl CoA combines with oxaloacetate to form citrate Next 7 steps decompose citrate back to oxaloacetate Cycle NADH and FADH2 relay electrons to the electron transport chain

Citric acid cycle Acetyl CoA Oxaloacetate Citrate Figure 9.12-1 CoA-SH 1 Figure 9.12-1 Oxaloacetate Citrate Citric acid cycle Figure 9.12 A closer look at the citric acid cycle.

Citric acid cycle Acetyl CoA Oxaloacetate Citrate Isocitrate CoA-SH 1 H2O Figure 9.12-2 Oxaloacetate 2 Citrate Isocitrate Citric acid cycle Figure 9.12 A closer look at the citric acid cycle.

Citric acid cycle Acetyl CoA Oxaloacetate Citrate Isocitrate CoA-SH 1 H2O Figure 9.12-3 Oxaloacetate 2 Citrate Isocitrate NAD Citric acid cycle NADH 3 + H CO2 -Ketoglutarate Figure 9.12 A closer look at the citric acid cycle.

Citric acid cycle Acetyl CoA Oxaloacetate Citrate Isocitrate CoA-SH 1 H2O Figure 9.12-4 Oxaloacetate 2 Citrate Isocitrate NAD Citric acid cycle NADH 3 + H CO2 CoA-SH -Ketoglutarate 4 Figure 9.12 A closer look at the citric acid cycle. CO2 NAD NADH Succinyl CoA + H

Citric acid cycle Acetyl CoA Oxaloacetate Citrate Isocitrate CoA-SH 1 H2O Figure 9.12-5 Oxaloacetate 2 Citrate Isocitrate NAD Citric acid cycle NADH 3 + H CO2 CoA-SH -Ketoglutarate 4 Figure 9.12 A closer look at the citric acid cycle. CoA-SH 5 CO2 NAD Succinate P i NADH GTP GDP Succinyl CoA + H ADP ATP

Citric acid cycle Acetyl CoA Oxaloacetate Citrate Isocitrate CoA-SH 1 H2O Figure 9.12-6 Oxaloacetate 2 Citrate Isocitrate NAD Citric acid cycle NADH 3 + H CO2 Fumarate CoA-SH -Ketoglutarate 4 Figure 9.12 A closer look at the citric acid cycle. 6 CoA-SH 5 FADH2 CO2 NAD FAD Succinate P i NADH GTP GDP Succinyl CoA + H ADP ATP

Citric acid cycle Acetyl CoA Oxaloacetate Malate Citrate Isocitrate CoA-SH 1 H2O Figure 9.12-7 Oxaloacetate 2 Malate Citrate Isocitrate NAD Citric acid cycle NADH 3 7 + H H2O CO2 Fumarate CoA-SH -Ketoglutarate 4 Figure 9.12 A closer look at the citric acid cycle. 6 CoA-SH 5 FADH2 CO2 NAD FAD Succinate P i NADH GTP GDP Succinyl CoA + H ADP ATP

Citric acid cycle Acetyl CoA Oxaloacetate Malate Citrate Isocitrate CoA-SH NADH 1 H2O + H Figure 9.12-8 NAD Oxaloacetate 8 2 Malate Citrate Isocitrate NAD Citric acid cycle NADH 3 7 + H H2O CO2 Fumarate CoA-SH -Ketoglutarate 4 Figure 9.12 A closer look at the citric acid cycle. 6 CoA-SH 5 FADH2 CO2 NAD FAD Succinate P i NADH GTP GDP Succinyl CoA + H ADP ATP

Cellular Respiration – Step 3 – Oxidative Phosphorylation In oxidative phosphorylation chemiosmosis couples electron transport to ATP synthesis NADH & FADH2 are electron carriers They donate electrons to the electron transport chain The electron transport chain powers ATP synthesis via oxidative phosphorylation

Cellular Respiration – Step 3 – Oxidative Phosphorylation – Electron transport chain In the inner membrane (cristae) of the mitochondrion Most components are membrane bound proteins Most exist in complexes The free energy of the electrons is dropping as they move down the chain Each time they are moving to a more stable state Ultimately they are passed to O2 to from H2O

Multiprotein complexes I 40 II NADH 50 2 e NAD FADH2 2 e FAD Multiprotein complexes I 40 FMN II FeS FeS Figure 9.13 Q III Cyt b 30 FeS Cyt c1 IV Free energy (G) relative to O2 (kcal/mol) Cyt c Cyt a Cyt a3 20 Figure 9.13 Free-energy change during electron transport. 10 2 e (originally from NADH or FADH2) 2 H + 1/2 O2 H2O

Cellular Respiration – Step 3 – Oxidative Phosphorylation – Electron transport chain Electrons are transferred from NADH or FADH2 to the ETC They are passed through several proteins Cytochromes contain an iron atom The ETC doesn’t generate ATP directly It breaks the free-energy drop into smaller, manageable steps

Cellular Respiration – Step 3 – Oxidative Phosphorylation – ETC – Energy-coupling Mechanism The transfer of electrons causes proteins to pump H+ from mitochondrial matrix to the intermembrane space H+ moves back across the membrane Movement drives ATP synthase ATP synthase uses the exergonic flow of H+ to drive phosphorylation of ATP Chemiosmosis – the use of a H+ gradient to drive cellular work

INTERMEMBRANE SPACE H Stator Rotor Internal rod Catalytic knob ADP + Figure 9.14 Internal rod Catalytic knob Figure 9.14 ATP synthase, a molecular mill. ADP + P i ATP MITOCHONDRIAL MATRIX

Protein complex of electron carriers H H H Protein complex of electron carriers Figure 9.15 H Cyt c IV Q III I ATP synth- ase II 2 H + 1/2O2 H2O FADH2 FAD Figure 9.15 Chemiosmosis couples the electron transport chain to ATP synthesis. NAD NADH ADP  P i ATP (carrying electrons from food) H 1 Electron transport chain 2 Chemiosmosis Oxidative phosphorylation

Cellular Respiration – Step 3 – Oxidative Phosphorylation – ETC – Energy-coupling Mechanism Energy from the redox reaction of the ETC is stored in the proton (H+) gradient Proton gradient is reffered to as a proton-motive force The flow of protons back down the gradient provides the energy to drive ATP synthesis.

Cellular Respiration – Summary Energy Flow: glucose  NADH  electron transport chain  proton-motive force  ATP ~ 34% of the energy in a glucose molecule is transferred to ATP during cellular respiration Makes about 32 ATP (not exactly known)

Oxidative phosphorylation: electron transport and chemiosmosis Figure 9.16 Electron shuttles span membrane MITOCHONDRION 2 NADH or 2 FADH2 2 NADH 2 NADH 6 NADH 2 FADH2 Oxidative phosphorylation: electron transport and chemiosmosis Glycolysis Pyruvate oxidation Citric acid cycle Glucose 2 Pyruvate 2 Acetyl CoA Figure 9.16 ATP yield per molecule of glucose at each stage of cellular respiration.  2 ATP  2 ATP  about 26 or 28 ATP About 30 or 32 ATP Maximum per glucose: CYTOSOL

Cellular Respiration – Fermentation and anaerobic respiration Allows cells to produce ATP without oxygen The electron transport chain will not operate without O2 In instances of oxygen debt, glycolysis couples with fermentation or anaerobic respiration

Cellular Respiration – Fermentation Fermentation uses substrate-level (direct transfer of phosphoryl group) phosphorylation instead of an electron transport chain to generate ATP Consists of glycolysis plus reactions that regenerate NAD+ NAD+ can be reused by glycolysis Two common types Alcohol fermentation Lactic acid fermentation

Cellular Respiration – Fermentation – alcohol fermentation Pyruvate is converted to ethanol in 2 steps First step releases CO2 Yeast – used in brewing, winemaking and baking

  2 ADP  2 P i 2 ATP Glucose Glycolysis 2 Pyruvate 2 NAD 2 NADH Figure 9.17a Glucose Glycolysis 2 Pyruvate 2 NAD  2 NADH 2 CO2  2 H  Figure 9.17 Fermentation. 2 Acetaldehyde 2 Ethanol (a) Alcohol fermentation

Cellular Respiration – Fermentation – Lactic Acid Pyruvate is reduced by NADH forming lactate No CO2 is released Lactic Acid fermentation by some fungi and bacteria is used to make yogurt and cheese Human muscle cells use lactic acid fermentation to generate ATP during oxygen debt.

  2 ADP  2 P i 2 ATP Glucose Glycolysis 2 NAD 2 NADH  2 H Figure 9.17b Glucose Glycolysis 2 NAD  2 NADH  2 H  2 Pyruvate Figure 9.17 Fermentation. 2 Lactate (b) Lactic acid fermentation

Cellular Respiration – Anaerobic Respiration Anaerobic respiration uses an electron transport chain with a different final electron acceptor NO3-, SO42+, or CO32-

Cellular Respiration – Anaerobic Respiration Obligate anaerobes – carry out fermentation or anaerobic respiration only Cannot survive in the presence of O2 Facultative anaerobes – can survive with or without O2 Several types of yeast and bacteria

Cellular Respiration – Comparisons