Cellular Respiration: Harvesting Chemical Energy Chapter 9

Assemble polymers, pump substances across membranes, move and reproduce

The giant panda Obtains energy for its cells by eating plants which get their energy from the sun (sun in, heat out) Figure 9.1

Energy Flows into an ecosystem as sunlight and leaves as heat Light energy ECOSYSTEM CO 2 + H 2 O Photosynthesis in chloroplasts Cellular respiration in mitochondria Organic molecules + O 2 ATP powers most cellular work Figure 9.2 Heat energy

Catabolic pathways yield energy by oxidizing organic fuels The breakdown of organic molecules is exergonic Release of energy by the transfer of e-

Organic molecules possess PE due to atom arrangements Compounds participating in exergonic reactions act as fuels Enzymes help degrade molecules to release PE

One catabolic process, fermentation Is a partial degradation of sugars that occurs without oxygen

Cellular respiration Is the most prevalent and efficient catabolic pathway Consumes oxygen and organic molecules such as glucose Yields ATP Aerobic Anaerobic (bacteria)

To keep working Cells must regenerate ATP C 6 H 12 O 6 +6O 2 6CO 2 + 6H 2 O + Energy (ATP +heat)

Catabolic pathways yield energy Due to the transfer of electrons

Redox reactions Transfer electrons from one reactant to another by oxidation and reduction

In oxidation A substance loses electrons, or is oxidized In reduction A substance gains electrons, or is reduced

Examples of redox reactions becomes oxidized (loses electron) Na + Cl Na + + Cl becomes reduced (gains electron)

Some redox reactions Do not completely exchange electrons Change the degree of electron sharing in covalent bonds Reactants Products becomes oxidized CH 4 + 2O 2 CO 2 + Energy + 2 H 2 O H becomes reduced C O O O C O O H H H H H Figure 9.3 Methane (reducing agent) Oxygen (oxidizing agent) Carbon dioxide Water

Oxidation of Organic Fuel Molecules During Cellular Respiration During cellular respiration Glucose is oxidized and oxygen is reduced becomes oxidized C 6 H 12 O 6 + 6O 2 6CO 2 + 6H 2 O + Energy becomes reduced Reducing Agent is the electron donor (sugar) Oxidizing Agent is the electron acceptor (oxygen) Copyright 2005 Pearson Education, Inc. publishing as Benjamin Cummings

The Players Dehydrogenase removes a pair of H atoms (2 e-, 2 p) from glucose thus oxidizing it. Dehydrogenase delivers 2e- and 1 p to NAD+ and the other proton is releases as H+ ion. NAD+ is now NADH (stores energy for later use) Copyright 2005 Pearson Education, Inc. publishing as Benjamin Cummings

How do you get energy from NADH? ETC e- carry molecules in inner membrane of mitochondria e- move down from one carrier to another through REDOX reactions At the bottom, oxygen captures the e- with hydrogen to form water Copyright 2005 Pearson Education, Inc. publishing as Benjamin Cummings

Stepwise Energy Harvest via NAD + and the Electron Transport Chain Cellular respiration Oxidizes glucose in a series of steps Steps slow the reaction and allow the controlled release of energy that can be used instead of a massive loss Copyright 2005 Pearson Education, Inc. publishing as Benjamin Cummings

Electrons from organic compounds Are usually first transferred to NAD +, a coenzyme 2 e + 2 H + NAD + 2 e + H + NADH O O P O O O O P O CH 2 H O HO HO CH 2 H O H N + H OH N N O C NH 2 Nicotinamide (oxidized form) NH 2 N N H + 2[H] (from food) Dehydrogenase Reduction of NAD + Oxidation of NADH H N H O C + NH 2 Nicotinamide (reduced form) H HO H OH Figure 9.4

NADH, the reduced form of NAD + Passes the electrons to the electron transport chain

If electron transfer is not stepwise A large release of energy occurs As in the reaction of hydrogen and oxygen to form water H 2 + 1 / 2 O 2 Free energy, G Explosive release of heat and light energy (a) Uncontrolled reaction Figure 9.5 A H 2 O

The electron transport chain Passes electrons in a series of steps instead of in one explosive reaction Uses the energy from the electron transfer to form ATP

2 H + 1 / 2 O 2 (from food via NADH) Free energy, G 2 H + + 2 e Controlled release of energy for synthesis of ATP ATP ATP ATP 2 e 2 H + 1 / 2 O 2 H 2 O Figure 9.5 B (b) Cellular respiration

Respiration is a cumulative function of three metabolic stages Glycolysis The citric acid cycle Oxidative phosphorylation

Glycolysis Occurs in the cytosol Breaks down glucose into two molecules of pyruvate The citric acid cycle (Krebs) Occurs in the mitochondria Completes the breakdown of glucose Releases CO 2 Makes e- available for MASS production of ATP

Oxidative phosphorylation Occurs in the mitochondra Is driven by the electron transport chain Generates ATP

An overview of cellular respiration Electrons carried via NADH Electrons carried via NADH and FADH2 Glycolsis Glucose Pyruvate Citric acid cycle Oxidative phosphorylation: electron transport and chemiosmosis Cytosol Mitochondrion ATP ATP ATP Figure 9.6 Substrate-level phosphorylation Substrate-level phosphorylation Oxidative phosphorylation

Both glycolysis and the citric acid cycle Can generate ATP by substrate-level phosphorylation Enzyme Enzyme ADP Substrate P + ATP Figure 9.7 Product

Glycolysis harvests energy by oxidizing glucose to pyruvate Glycolysis Means splitting of sugar Breaks down glucose into pyruvate Occurs in the cytoplasm of the cell

Glycolysis consists of two major phases Energy investment phase Energy payoff phase Glycolysis Citric acid cycle Oxidative phosphorylation ATP ATP ATP Energy investment phase Glucose 2 ATP + 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 + 2 Pyruvate + 2 H 2 O Glucose 2 Pyruvate + 2 H 2 O 4 ATP formed 2 ATP used 2 ATP + 2 H + Figure 9.8 2 NAD + + 4 e + 4 H + 2 NADH

A closer look at the energy investment phase

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

A closer look at the energy payoff phase

2 NAD + 2 NADH + 2 H + 6 Triose phosphate dehydrogenase 2 P i 2 P O C O CHOH CH 2 O P 1, 3-Bisphosphoglycerate 2 ADP 7 Phosphoglycerokinase 2 ATP 2 O C CHOH CH 2 O P 3-Phosphoglycerate 8 Phosphoglyceromutase O 2 C O H C O P CH 2 OH 2-Phosphoglycerate 9 2 H 2 O Enolase 2 O C O C O P CH 2 Phosphoenolpyruvate 2 ADP 10 Pyruvate kinase 2 ATP Figure 9.8 B 2 O C O C O CH 3 Pyruvate

2 ATP 2NADH

The citric acid cycle completes the energy-yielding oxidation of organic molecules The citric acid cycle Takes place in the matrix of the mitochondrion Active transport takes pyruvate into the mitochondria

Before the citric acid cycle can begin Pyruvate must first be converted to acetyl CoA, which links the cycle to glycolysis CYTOSOL MITOCHONDRION O C C O O NAD + 2 NADH + H + S C CoA O 1 3 CH 3 CH 3 Acetyle CoA Pyruvate CO 2 Coenzyme A Transport protein Figure 9.10

C atom of carboxyl group removed and released as CO 2 Remaining 2 C compound is oxidized to form CYTOSOL acetate and NAD+=NADH O C C O O Coenzyme A attaches to acetate=acetyl coa which has a high PE NAD + 2 NAD H MITOCHONDRI ON + H + S C Co A O CH 3 Pyruvate 1 CO 2 Coenzyme A 3 CH 3 Acetyle CoA Figure 9.10 Transport protein

Generation of Acetyl coa makes: 1 NADH for each pyruvate 2 NADH have now been made

An overview of the citric acid cycle Pyruvate (from glycolysis, 2 molecules per glucose) Glycolysis Citric acid cycle Oxidative phosphorylatio n ATP ATP ATP CO 2 NADH + 3 H + Acetyle CoA CoA CoA CoA FADH 2 FAD Citric acid cycle ADP + P i 2 CO 2 3 NAD + 3 NADH + 3 H + Figure 9.11 ATP

A closer look at the citric acid cycle

Glycolysis Citric acid cycle Oxidative phosphorylation S C CoA O CH 3 Acetyl CoA CoA SH H 2 O NAD + HO FADH 2 NADH + H + CH 2 1 COO H 2 O COO CH CH 2 COO 7 COO CH HC COO Malate Oxaloacetate Fumarate FAD 8 6 Succinate O C COO COO CH 2 CH 2 COO ADP COO Figure 9.12 Citric acid cycle CoA SH 5 GTP GDP P i Citrate S CH 2 HO C COO CH 2 COO CH 2 COO CH 2 C O CoA Succinyl CoA 2 CoA SH 4 NAD + HO NADH + H + COO CH 2 HC COO CH COO Isocitrate 3 COO CH 2 CH 2 C O COO NAD + NADH α-ketoglutarate CO 2 CO 2 + H + Figure 9.12 ATP

One cycle produces 3 NADH, 1 FADH 2 and 1 ATP GO AROUND TWICE!!!! So that is a total of: 6 NADH, 2 FADH 2 and 2 ATP

Made of two parts: ETC Chemiosmosis

Collection of molecules embedded in inner membrane of mitocondria In the electron transport chain Electrons from NADH and FADH 2 lose energy in several steps

At the end of the chain Electrons are passed to oxygen, forming water NO ATP is made but e- energy becomes manageable 50 NADH FADH2 Free energy (G) relative to O 2 (kcl/mol) 40 30 20 10 FMN I Fe S FAD Fe S II O III Cyt b Fe S Multiprotein complexes Cyt c 1 Cyt c IV Cyt a Cyt a 3 0 2 H + + 1 2 O 2 Figure 9.13 H 2 O

Energy coupling mechanism Energy is stored in H+ gradient across a membrane It is used to drive the production of ATP ATPase is needed

ATP synthase Is the enzyme that actually makes ATP INTERMEMBRANE SPACE H + H + H + H + H + H + H + 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. H + A rod (for stalk ) extending into the knob also spins, activating catalytic sites in the knob. Figure 9.14 ADP + P i MITOCHONDRIAL MATRIX ATP Three catalytic sites in the stationary knob join inorganic Phosphate to ADP to make ATP.

At certain steps along the electron transport chain Electron transfer causes protein complexes to pump H + from the mitochondrial matrix to the intermembrane space

The resulting H + gradient Stores energy Drives chemiosmosis in ATP synthase Is referred to as a proton-motive force

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

Net production of 36-38 ATP

An Accounting of ATP Production by Cellular Respiration During respiration, most energy flows in this sequence Glucose to NADH to electron transport chain to proton-motive force to ATP Copyright 2005 Pearson Education, Inc. publishing as Benjamin Cummings

There are three main processes in this metabolic enterprise CYTOSOL Electron shuttles span membrane 2 NADH or MITOCHONDRION 2 FADH 2 2 NADH 2 NADH 6 NADH 2 FADH 2 Glycolysis 2 Glucose Pyruvate 2 Acetyl CoA Citric acid cycle Oxidative phosphorylation: electron transport and chemiosmosis + 2 ATP + 2 ATP + about 32 or 34 ATP by substrate-level phosphorylation 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 Figure 9.16

Fermentation enables some cells to produce ATP without the use of oxygen Cellular respiration Relies on oxygen to produce ATP In the absence of oxygen Cells can still produce a small amount of ATP through fermentation

Glycolysis Can produce ATP with or without oxygen, in aerobic or anaerobic conditions It is the ETC that requires oxygen (without it the e- are not pulled down the series of proteins and chemiosmosis fails) Glycolysis can couple with fermentation to produce ATP

Fermentation consists of: Glycolysis plus reactions that regenerate NAD +, which can be reused by glyocolysis

During lactic acid fermentation Pyruvate is reduced directly to NADH to form lactate as a waste product NAD+ is now free to accept e- and make 2 ATP from remaining sugar molecule (s) Lactate accumulates in muscles=sore and fatigued

In alcohol fermentation Pyruvate is converted to ethanol in two steps, one of which releases CO 2

2 ADP + 2 P 1 2 ATP Glucose Glycolysis 2 NAD + 2 NADH O O C C O CH 3 2 Pyruvate 2 CO 2 H H C OH H C O CH 3 2 Ethanol (a) Alcohol fermentation CH 3 2 Acetaldehyde 2 ADP + 2 P 1 2 ATP Glucose Glycolysis O 2 NAD + 2 NADH C O H C OH O C O C O CH 3 Figure 9.17 CH 3 2 Lactate (b) Lactic acid fermentation

Both fermentation and cellular respiration Use glycolysis to oxidize glucose and other organic fuels to pyruvate Fermentation and cellular respiration Differ in their final electron acceptor Cellular respiration Produces more ATP

Pyruvate is a key juncture in catabolism Glucose CYTOSOL Pyruvate No O 2 present Fermentation O 2 present Cellular respiration Ethanol or lactate Acetyl CoA MITOCHONDRION Citric acid cycle Figure 9.18

Catabolic pathways Funnel electrons from many kinds of organic molecules into cellular respiration

The catabolism of various molecules from food

Food isn t just for energy Biosynthesis-making of cellular molecules for repair and growth Consumption of ATP