Cellular Respiration

Cellular Respiration Conversion of stored energy in biological molecules into ATP for cellular work - produces carbon dioxide and usually requires oxygen HOW: Gradual release of energy through a series of steps – slower release allows for a more efficient capture of the energy

(a) Uncontrolled reaction Free energy, G H2O Explosive release of heat and light energy H2 + 1/2 O2

Electron transport chain (b) Cellular respiration (from food via NADH) 2 H+ + 2 e– 2 H+ 2 e– H2O Controlled release of energy for synthesis of ATP ATP Electron transport chain Free energy, G (b) Cellular respiration + Figure 9.5 B

Overall Reaction C6H12O6 + 6 O2  6 CO2 + 6 H2O

Mechanisms of Cellular Respiration Transfer of electrons from a higher energy state (glucose) to a lower energy state (Water) through Oxidation-reduction reactions (REDOX) REDOX reactions: - transfer of electrons from one substance (reducing agent) to another (oxidzing agent) - result: reducing agent becomes more positive (Oxidized) and the oxidizing agent becomes more negative (REDUCED in charge)

NAD+ - nicotinamide adenine dinucleotide IMPORTANCE OF HYDROGEN ACCEPTORS chemicals that accept hydrogens from molecules and transfer them for other reactions NAD+ - nicotinamide adenine dinucleotide FAD - flavin adenine dinucleotide - allow for the gradual controlled release of energy

NAD+ H O O– + (from food) Dehydrogenase Reduction of NAD+ 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

TYPES of Cellular respiraton Aerobic - uses oxygen - most efficient - generates 36 - 38 ATP per glucose Anaerobic - (AKA fermentation) does not use oxygen - less efficient generates about 2 ATP

Aerobic cellular respiration occurs in the mitochondria Structure of the mitochondria Outer membrane Inner membrane Intermembranous space Matrix

Oxidative phosphorylation: electron transport and chemiosmosis 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 Cytosol

STEPS OF CELLULAR RESPIRATION 1. Glycolysis - splitting of sugar - in cytoplasm REACTANTS: Glucose (C6H12O6) ATP NAD+ (nicotinamide adenine dinucleotide) PRODUCTS: 2 Pyruvate (3 carbon sugars) 4 ATP (really 2 net ATP) NADH (reduced NAD+)

STEPS OF CELLULAR RESPIRATION 2. Kreb's Cycle - matrix of mitochondria PRODUCTS CO2 ATP NADH FADH2 REACTANTS: Pyruvate (sort of) ADP + P NAD+ FAD

STEPS OF CELLULAR RESPIRATION 3. Electron transport chain - innermembrane - intermembranous space REACTANTS: NADH FADH2 O2 ADP + P PRODUCTS: NAD+ FAD H2O ATP - lots

GLYCOLYSIS - splitting of sugar 6 carbon sugar split into 2, 3 carbon compounds to be made into PYRUVATE 10 steps in the cytosol of the cell broken into 2 parts: 1. Energy-Investment Phase: 2 ATP USED 2. Energy-Payoff Phase: 4 ATP and 2 NADH generated SUBSTRATE LEVEL PHOSPHORYLATION – transfer of phosphates from a molecule to ADP using an enzyme

Figure 9.7 Enzyme ATP ADP Product Substrate P +

Energy investment 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 +

Phosphoglucoisomerase 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

1, 3-Bisphosphoglycerate 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

ENERGY SUMMARY 2 ATP used 4 ATP and 2 NADH generated Yields 2 ATP and 2 NADH per glucose

Transport across Mitochondrial Membrane Prepping for Kreb’s: changing pyruvate to acetyl Co-A Pyruvate enters mitochondria and a carboxy group is removed producing CO2 - go from a 3 carbon to a 2 carbon 2 carbon compound loses a Hydrogen to NAD+ to make NADH and acetate NADH goes to ETC Acetate bonds with coenzyme A to make acetyl-CoA

CYTOSOL MITOCHONDRION Pyruvate Acetyle CoA NADH + H+ NAD+ 2 3 1 CO2 Coenzyme A Pyruvate Acetyle CoA S CoA C CH3 O Transport protein O–

KREB’S CYCLE EACH GLUCOSE TURNS THE CYCLE TWICE Where: Matrix of mitochondria 2 remaining Carbons go through the cycle producing 2 CO2 Process Generates Per acetyl - CoA: 3 NADH 1 FADH2 1 ATP X 2 = 6 NADH, 2 FADH2, 2 ATP per glucose EACH GLUCOSE TURNS THE CYCLE TWICE NADH and FADH2 go to ETC

Oxidative phosphorylation 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

Acetyl CoA Oxaloacetate Malate Citrate Isocitrate Citric acid cycle 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

ELECTRON TRANSPORT CHAIN - generates a proton gradient to drive oxidative phosphorylation (chemiosmosis) LOCATION: matrix: inner membrane: intermembranous space Inner membrane: Chain of proteins complexes that move electrons through membrane by redox reactions Each transfer from one complex to another lowers the energy of the electron Energy is used to pump H+ from the matrix to the intermembranous space BUILDS PROTON GRADIENT

Free energy (G) relative to O2 (kcl/mol) 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)

NADH breaks into NAD+ and H+ and electrons electrons go into electron transport chain – FADH2 deposits electrons further down chain At specific points H+ are pumped across the membrane - NAD+ is reused Each NADH gives enough energy for the production of 3 ATP Each FADH2 gives enough energy for the production of 2 ATP

Electron transport chain Oxidative phosphorylation 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

H+s pumping builds PROTON-MOTIVE FORCE or CHEMIOSMOTIC GRADIENT protons diffuse back across to other side through a protein (facilitated diffusion)  ATP synthase cylidrical rotor knob with a rod in the rotor

Electron transport chain Oxidative phosphorylation 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

CHEMIOSMOTIC PHOSPHORYLATION OXIDATIVE PHOSPHORYLATION as H+ pass through, the rotor turns the rod and the movement of the rod causes conformational changes in the knob which then phosphorulates ADP into ATP CHEMIOSMOTIC PHOSPHORYLATION or OXIDATIVE PHOSPHORYLATION

INTERMEMBRANE SPACE H+ P i + ADP ATP A rotor within the membrane spins clockwise when H+ flows past it down the H+ gradient. A stator anchored in the membrane holds the knob stationary. A rod (for “stalk”) extending into the knob also spins, activating catalytic sites in the knob. Three catalytic sites in the stationary knob join inorganic Phosphate to ADP to make ATP. MITOCHONDRIAL MATRIX

END OF ELECTRON TRANSPORT CHAIN Final electron acceptor is O2 for every 2 NADH or 1 FADH2 one O2 is reduced and forms water Electron Transport Chain Animation

CELLULAR RESPIRATION: AN OVERVIEW Overall Energy Yield = 36 – 38 ATP Glycolysis: 2 ATP, 2 NADH Kreb’s Cycle: 2 ATP, 8 NADH, 2 FADH2 ETC: ATP based on #’s of NADH and FADH2 # of NADH = 8 (Krebs) = 24 ATP # of FADH2 = 2 = 4 ATP Total ATP = 2 (Glyc) + 2 (Kreb’s) + 28 ATP = 32 ATP Remaining 4 – 6 from the 2 NADH from Glycolysis

Glycolysis NADH transfers Hydrogen across membrane of mitochondria membrane not permeable to NAD+ Transfers H’s to either NADH or FADH2 if to NADH = 3 ATP if to FADH2 = 2 ATP

TOTAL Yield: about 38 ATP per glucose ATP TOTALS: Glycolysis: 2 Kreb’s: 2 ETC: 32 - 34 TOTAL Yield: about 38 ATP per glucose efficiency of 40% compared to a car which is at best 25% Remaining energy lost as heat

Glycolysis Citric acid cycle 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

RELATED METABOLIC PROPERTIES Glycolysis uses NAD+ to Oxidize Glucose for glucose to continue to be used for the generation of energy the cell must recycle the NADH to NAD+ NEED A FINAL ELECTRON ACCEPTOR - usually Oxygen WHAT HAPPENS WHEN THERE IS NO OXYGEN? NADH has no place to put its hydrogens - glucose can’t be broken down NEED ANOTHER ELECTRON ACCEPTOR: with oxygen  aerobic without Oxygen  anaerobic

Anaerobic Metabolic Pathways = Fermentation Alcohol Fermentation: Irreversible 2 steps: pyruvate is converted to acetylaldehyde by the removal of a carbon - forms CO2 - the bubbles in alcoholic beverages acetalyaldehyde is reduced by NADH - forms ethanol and frees up NAD+ for glycolysis Generates NO ENERGY WHERE: bacteria and fungus cells

Pyruvate is reduced to lactate - frees up NAD+ for glycolysis Lactic Acid Fermentation: Reversible Pyruvate is reduced to lactate - frees up NAD+ for glycolysis PRODUCES NO ENERGY and NO CO2 - burning and pain in cells Lactate can be converted back to pyruvate when removed from cells and processed in liver

(a) Alcohol fermentation (b) Lactic acid fermentation 2 ADP + 2 P1 2 ATP Glycolysis Glucose 2 NAD+ 2 NADH 2 Pyruvate 2 Acetaldehyde 2 Ethanol (a) Alcohol fermentation 2 Lactate (b) Lactic acid fermentation H OH CH3 C O – O O– CO2 2

COMPARISON OF AEROBIC AND ANAEROBIC ATP Generated per glucose Aerobic: about 38 Anaerobic: 2 FINAL ELECTRON ACCEPTOR CR - oxygen Ferm - organic molecule

METABOLISM OF OTHER BIOLOGICAL MOLECULES GLUCOSE: break down of starch or glycogen feeds directly into the process Other Monosaccharides and Dissacharides - easily incorporated early in glycolysis

METABOLISM OF OTHER BIOLOGICAL MOLECULES Proteins: broken down into amino acids most used to build proteins in cells - extra are processed by deaminification - removal of amine group nitrogen group  urine remaining portions enter into respiration dependent on structure

METABOLISM OF OTHER BIOLOGICAL MOLECULES FATS: glycerol and fatty acids glycerol  glyceraldehyde phosphate fatty acids: broken down into 2 carbon molecules  acetyl CoA provide tremendous amounts of energy because of numerous carbon bonds FATS GIVE TWICE AS MUCH ENERGY

METABOLISM OF OTHER BIOLOGICAL MOLECULES HOWEVER: NOT ALL BIOMOLECULES OR INTERMEDIATES OF CELLULAR RESPIRATION ARE USED FOR PRODUCTION OF ENERGY some are used to build other molecules

Glucose NH3 Pyruvate Amino acids Sugars Glycerol Fatty Glycolysis Glyceraldehyde-3- P Pyruvate Acetyl CoA NH3 Citric acid cycle Oxidative phosphorylation Fats Proteins Carbohydrates

CONTROL OF METABOLISM Feedback inhibition: too much ATP inhibits phosphofructokinase (first irreversible step in process) stops generation of Pyruvate and thus the production of ATP When ATP stores are low, AMP is formed and binds to phosphofructokinase to stimulate production of energy Phosphofructokinase also sensitive to citrate - too much citrate - moves out of mitochondria and inhibits enzyme - slows glycolysis until citrate is consumed - PREVENTS THE CELL FROM WASTING RESOURCES

Fructose-1,6-bisphosphate Glucose Glycolysis Fructose-6-phosphate Phosphofructokinase Fructose-1,6-bisphosphate Inhibits Pyruvate ATP Acetyl CoA Citric acid cycle Citrate Oxidative phosphorylation Stimulates AMP + –