Chapter 9 Cellular Respiration

Energy Transformations

Metabolism Respiration Link The giant panda obtains energy for its cells by eating plants

E Transformations, Thermodynamics, Ecosystems Energy flows into ecosystem as sunlight, and out as heat Light energy ECOSYSTEM CO2 + H2O Photosynthesis in chloroplasts Cellular respiration in mitochondria Organic molecules + O2 ATP powers most cellular work Heat energy Figure 9.2

Metabolism Respiration Link Catabolic pathways yield Energy by oxidizing organic fuels

Oxidation, Reduction (No way to make this fun) Reducing agents lose electrons and are oxidized, and the oxidizing agents gains electrons and is reduced. The oxidizing agent removes electrons from another substance, and is thus itself reduced. Because it "accepts" electrons, the oxidizing agent is also called an electron acceptor. Oxygen is the quintessential oxidizer.

Catabolic Pathways and Production of ATP Breakdown of organic molecules is exergonic Energy Released

Metabolism Respiration Link Cellular respiration Most prevalent and efficient catabolic pathway Consumes O2 and organic molecules e.g. glucose Yields ATP

Metabolism Respiration Link The Big Idea Why We Eat and Breathe Glucose is oxidized oxygen is reduced

Stepwise Energy Harvest Glucose oxidized in a series of steps

Electrons from Glyceraldehyde-3-Phosphate Electrons from organic compounds Usually first transferred to NAD+, a coenzyme NAD+ H O O– P CH2 HO OH N+ C NH2 N Nicotinamide (oxidized form) + 2[H] (from food) Dehydrogenase Reduction of NAD+ Oxidation of NADH 2 e– + 2 H+ 2 e– + H+ NADH Nicotinamide (reduced form) Figure 9.4

NADH (reduced form of NAD+) Electrons from NADH NADH (reduced form of NAD+) Passes electrons to the e- transport chain

Follow the Bouncing Electrons e- transport chain Passes e- in a series of steps instead of explosive reaction Uses E from the e- transfer to form ATP

Oxidative phosphorylation Driven by e- transport chain Generates ATP

The 3 Stages of Cellular Respiration Glycolysis Citric acid cycle (Kreb’s cycle) Oxidative phosphorylation (Electron Transport/ Chemiosmosis)

Step by Step Glycolsis Glucose Pyruvate ATP Substrate-level phosphorylation Mitochondrion

Step by Step Citric acid cycle Mitochondrion ATP Substrate-level phosphorylation Mitochondrion Glycolsis Glucose Pyruvate Citric acid cycle

Oxidative phosphorylation: electron transport and chemiosmosis Step by Step Electrons carried via NADH Glycolsis Glucose Pyruvate ATP Substrate-level phosphorylation Electrons carried via NADH and FADH2 Citric acid cycle Oxidative phosphorylation: electron transport and chemiosmosis Oxidative Mitochondrion

Glycolysis Glycolysis harvests E by oxidizing glucose to pyruvate Means “splitting sugar” Glucose  pyruvate Occurs in cytoplasm

Glycolysis Glycolysis: Breaks down glucose into two molecules of pyruvate Citric acid (Kreb’s)cycle: Completes breakdown of glucose

Energy investment phase Glycolysis 2 major phases E investment phase E payoff phase Glycolysis Citric acid cycle Oxidative phosphorylation ATP 2 ATP 4 ATP used formed Glucose 2 ATP + 2 P 4 ADP + 4 2 NAD+ + 4 e- + 4 H + 2 NADH + 2 H+ 2 Pyruvate + 2 H2O Energy investment phase Energy payoff phase 4 ATP formed – 2 ATP used 2 NAD+ + 4 e– + 4 H + Figure 9.8

Phosphoglucoisomerase Glycolysis: Energy Investment Dihydroxyacetone phosphate Glyceraldehyde- 3-phosphate H OH HO CH2OH O P CH2O CH2 C CHOH ATP ADP Hexokinase Glucose Glucose-6-phosphate Fructose-6-phosphate Phosphoglucoisomerase Phosphofructokinase Fructose- 1, 6-bisphosphate Aldolase Isomerase Glycolysis 1 2 3 4 5 Oxidative phosphorylation Citric acid cycle Figure 9.9 A

1, 3-Bisphosphoglycerate Glycolysis: Energy Pay Off 2 NAD+ NADH 2 + 2 H+ Triose phosphate dehydrogenase P i P C CHOH O CH2 O– 1, 3-Bisphosphoglycerate 2 ADP 2 ATP Phosphoglycerokinase 3-Phosphoglycerate Phosphoglyceromutase CH2OH H 2-Phosphoglycerate 2 H2O Enolase Phosphoenolpyruvate Pyruvate kinase CH3 6 8 7 9 10 Pyruvate Figure 9.8 B

Kreb’s Cycle Citric acid (or Kreb’s, or TCA) cycle completes the E-yielding oxidation of organic molecules Takes place in matrix of mitochondrion

Pyruvate first converted to acetyl CoA, links cycle to glycolysis Kreb’s Cycle Pyruvate first converted to acetyl CoA, links cycle to glycolysis CYTOSOL MITOCHONDRION NADH + H+ NAD+ 2 3 1 CO2 Coenzyme A Pyruvate Acetyle CoA S CoA C CH3 O Transport protein O–

Oxidative phosphorylation Kreb’s Cycle Overview of citric acid cycle ATP 2 CO2 3 NAD+ 3 NADH + 3 H+ ADP + P i FAD FADH2 Citric acid cycle CoA Acetyle CoA NADH CO2 Pyruvate (from glycolysis, 2 molecules per glucose) Glycolysis Oxidative phosphorylation Figure 9.11

Kreb’s Cycle: A closer Look Acetyl CoA NADH Oxaloacetate Citrate Malate Fumarate Succinate Succinyl CoA a-Ketoglutarate Isocitrate Citric acid cycle S SH FADH2 FAD GTP GDP NAD+ ADP P i CO2 H2O + H+ C CH3 O COO– CH2 HO HC CH 1 2 3 4 5 6 7 8 Glycolysis Oxidative phosphorylation ATP Figure 9.12

Oxidative phosphorylation: 3 Big Ideas NADH and FADH2Donate e- to e- transport chain, which powers ATP synthesis via oxidative phosphorylation Chemiosmosis couples e- transport to ATP synthesis e- from NADH and FADH2 lose E in steps

Oxidative Phosphorylation At end of the chain e- passed to O2, forming water H2O O2 NADH FADH2 FMN Fe•S O FAD Cyt b Cyt c1 Cyt c Cyt a Cyt a3 2 H + + 12 I II III IV Multiprotein complexes 10 20 30 40 50 Free energy (G) relative to O2 (kcl/mol)

Chemiosmosis: The Energy-Coupling Mechanism ATP synthase Enzyme that actually makes ATP Energy from e- drives formation of hydrogen concentration gradient. Potential Energy !!!! INTERMEMBRANE SPACE H+ P i + ADP ATP MITOCHONDRIAL MATRIX

e- transfer pumps H+ f/ mitochondrial matrix to intermembrane space Chemiosmosis e- transfer pumps H+ f/ mitochondrial matrix to intermembrane space INTERMEMBRANE SPACE H+ P i + ADP ATP MITOCHONDRIAL MATRIX

Chemiosmosis Resulting H+ gradient Stores E Drives chemiosmosis Referred to as a proton-motive force E-coupling mechanism, drives cellular work INTERMEMBRANE SPACE H+ P i + ADP ATP MITOCHONDRIAL MATRIX

Electron transport chain Oxidative phosphorylation Chemiosmosis and the e- transport chain Oxidative phosphorylation. electron transport and chemiosmosis Glycolysis ATP Inner Mitochondrial membrane H+ P i Protein complex of electron carners Cyt c I II III IV (Carrying electrons from, food) NADH+ FADH2 NAD+ FAD+ 2 H+ + 1/2 O2 H2O ADP + Electron transport chain Electron transport and pumping of protons (H+), which create an H+ gradient across the membrane Chemiosmosis ATP synthesis powered by the flow Of H+ back across the membrane synthase Q Oxidative phosphorylation Intermembrane space mitochondrial matrix Figure 9.15

An Accounting of ATP Production by Cellular Respiration 3 main processes in metabolism Electron shuttles span membrane CYTOSOL 2 NADH 2 FADH2 6 NADH Glycolysis Glucose 2 Pyruvate Acetyl CoA Citric acid cycle Oxidative phosphorylation: electron transport and chemiosmosis MITOCHONDRION by substrate-level phosphorylation by oxidative phosphorylation, depending on which shuttle transports electrons from NADH in cytosol Maximum per glucose: About 36 or 38 ATP + 2 ATP + about 32 or 34 ATP or Figure 9.16

~ 40% of E in a glucose molecule Energy Transfer not 100% ~ 40% of E in a glucose molecule Transferred to ATP during cellular respiration, making ~ 36 ATP

Fermentation Glycolysis Produces ATP w/ or w/o oxygen, aerobic or anaerobic conditions Glycolysis + reactions that regenerate NAD+, which can be reused by glyocolysis Two types alcohol and lactic acid

Fermentation Glycolysis + reactions that regenerate NAD+, which can be reused by glyocolysis

Fermentation Alcohol fermentation Pyruvate  ethanol in two steps, one of which releases CO2

Lactic acid Fermentation Pyruvate reduced by NADH to form lactate as a waste product (Pyruvate oxidizes NADH) OUCH !

Fermentation - Cellular Respiration Compared Both use glycolysis to oxidize glucose to pyruvate Differ in final e- acceptor Aldehyde transition step in alcohol fermentation Pyruvate in lactic acid fermentation Cellular respiration produces more ATP Tiny Bubble

You never knew how exciting PYRUVATE was Pyruvate is key juncture in catabolism Glucose CYTOSOL Pyruvate No O2 present Fermentation O2 present Cellular respiration Ethanol or lactate Acetyl CoA MITOCHONDRION Citric acid cycle Figure 9.18

Evolutionary Significance of Glycolysis Glycolysis occurs in nearly all organisms Probably evolved before O2 in the atmosphere

Catabolism of various molecules from food Amino acids Sugars Glycerol Fatty Glycolysis Glucose Glyceraldehyde-3- P Pyruvate Acetyl CoA NH3 Citric acid cycle Oxidative phosphorylation Fats Proteins Carbohydrates Figure 9.19 Beta Oxidation 2X more ATP

Biosynthesis (Anabolic Pathways) The body uses small molecules to build other substances Some Intermediates of glycoysis and the Kreb’s Cycle can be used to form amino acids

The control of cellular respiration Glucose Glycolysis Fructose-6-phosphate Phosphofructokinase Fructose-1,6-bisphosphate Inhibits Pyruvate ATP Acetyl CoA Citric acid cycle Citrate Oxidative phosphorylation Stimulates AMP + – Figure 9.20

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