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Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings PowerPoint Lectures for Biology, Seventh Edition Neil Campbell and Jane Reece.

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Presentation on theme: "Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings PowerPoint Lectures for Biology, Seventh Edition Neil Campbell and Jane Reece."— Presentation transcript:

1 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings PowerPoint Lectures for Biology, Seventh Edition Neil Campbell and Jane Reece Lectures by Chris Romero Chapter 9 Cellular Respiration: Harvesting Chemical Energy

2 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Overview: Life Is Work Living cells – Require transfusions of energy from outside sources to perform their many tasks Ex: The giant panda – Obtains (chemical, potential) energy for its cells by eating plants Figure 9.1

3 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 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 Heat energy Figure 9.2

4 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Review: 1st law- Energy cannot be created or destroyed. Energy can be converted from one form to another. The sum of the energy before the conversion is equal to the sum of the energy after the conversion. 2nd law- Some usable energy dissipates during transformations and is lost. During changes from one form of energy to another, some usable energy dissipates, usually as heat. The amount of usable energy therefore decreases.

5 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Cellular Respiration Glucose + O 2 energy (ATP) + CO 2 + H 2 O This is exergonic – G and converts one form of chemical energy (glucose) into another (ATP), with heat dissipates – Consumes oxygen and organic molecules (such as glucose) – Glucose Oxidation is the most prevalent and efficient catabolic pathway – Yields lots of ATP An alternate catabolic process, fermentation – Is a partial degradation of sugars that occurs without oxygen (in anaerobic conditions)

6 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings More on ATP ATP (adenosine triphosphate) ATP is a nucleotide. Nucleotides are the building blocks of nucleic acids such as DNA and RNA. They contain a nitrogen-containing base, a 5-carbon sugar, and phosphate groups. The energy in one glucose molecule is used to produce up to 38 ATP. ATP has approximately the right amount of energy for most cellular reactions.

7 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings ATP, ADP, AMP The bonds between the phosphate groups are high- energy bonds. Energy is required (and stored) to form the bonds and energy is released when the bonds are broken. (below)

8 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Phosphorylation When a phosphate group is transferred to another molecule, it is called PHOSPHORYLATION. ADP + P i + energy ----> ATP It takes about 7.3 kcals of energy to phosphorylate ADP into ATP Enzyme that catalyzes this reaction is ATP synthase ATP is produced and used continuously. The entire amount of ATP in an organism is recycled once per minute. Most cells maintain only a few seconds supply of ATP. To keep working, cells must regenerate ATP

9 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Phosphorylation Phosphate groups from ATP can also be transferred to other molecules. Enzymes that catalyze this reaction are called KINASES. In these phosphorylation reactions, energy is transferred from the phosphate group in ATP to the phosphorylated compound. This newly energized compound will participate in other reactions.

10 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Redox Reactions: Oxidation and Reduction Catabolic pathways also yield energy due to the transfer of electrons In oxidation – A substance loses electrons, or is oxidized In reduction – A substance gains electrons, or is reduced Redox reactions – Transfer electrons from one reactant to another by oxidation and reduction Na + Cl Na + + Cl – becomes oxidized (loses electron) becomes reduced (gains electron)

11 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Redox reactions Transfer of electrons from one reactant to another by oxidation and reduction When the electron moves to a lower energy level, energy is released.

12 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Redox contd Some redox reactions – Do not completely exchange electrons, instead they change the degree of electron sharing in covalent bonds CH 4 H H H H C OO O O O C HH Methane (reducing agent) Oxygen (oxidizing agent) Carbon dioxideWater + 2O 2 CO 2 + Energy + 2 H 2 O becomes oxidized becomes reduced Reactants Products Figure 9.3

13 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Oxidation of Organic Fuel Molecules During Cellular Respiration During cellular respiration – Glucose is oxidized and oxygen is reduced C 6 H 12 O 6 + 6O 2 6CO 2 + 6H 2 O + Energy becomes oxidized becomes reduced Glucose + Oxygen ----> Carbon dioxide + water + Energy Yields G = -686 Kcal/mole This energy is used to add phosphates to ADP + P ATP There is a need to convert glucose (sugar) which is stored chemical energy into ATP which is usable cell energy

14 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Electron carriers Some compounds can accept and donate electrons readily, and these are called electron carriers in organisms. There are a number of molecules that serve as electron carriers. – NAD (nicotinamide adenine dinucleotide) is used in respiration. Reduced to NADH. – NADP (nicotinamide adenine dinucleotide phosphate) is another used in photosynthesis. Reduced to NADPH – These molecules readily give up electrons (oxidized) and gain electrons (reduced). – FAD (flavin adenine dinucleotide) is reduced to FADH 2 – H often represents one electron, one proton.

15 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The electron transport chain 2 H 1 / 2 O 2 (from food via NADH) 2 H e – 2 H + 2 e – H2OH2O 1 / 2 O 2 Controlled release of energy for synthesis of ATP ATP Electron transport chain Free energy, G (b) Cellular respiration + Figure 9.5 B NADH, the reduced form of NAD + – Passes the electrons along an electron transport chain Electron are passed in a series of steps instead of in one explosive reaction If electron transfer is not stepwise – A large release of energy occurs = dangerous to living cells Uses the energy from the electron transfer to form ATP

16 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings ATP originates in cellular respiration What happens is that sugar is broken down into smaller molecules and energy is released. This energy is used to generate ATP from ADP and P. Sugar > smaller molecules >ADP + P i > ATP

17 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The Stages of Cellular Respiration: A Preview Respiration is a cumulative function of three metabolic stages Glycolysis – Breaks down glucose into two molecules of pyruvate The citric acid (Krebs) cycle – Completes the breakdown of glucose Oxidative phosphorylation – Is driven by the electron transport chain (ETC) – Generates ATP

18 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings An overview of cellular respiration Figure 9.6 Electrons carried via NADH Glycolsis Glucose Pyruvate ATP Substrate-level phosphorylation Electrons carried via NADH and FADH 2 Citric acid cycle Oxidative phosphorylation: electron transport and chemiosmosis ATP Substrate-level phosphorylation Oxidative phosphorylation Mitochondrion Cytosol

19 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Both glycolysis and the citric acid cycle – Can generate ATP by substrate-level phosphorylation Figure 9.7 Enzyme ATP ADP Product Substrate P +

20 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Concept 9.2: 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

21 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Glycolysis consists of two major phases – Energy investment phase – Energy payoff phase Glycolysis Citric acid cycle Oxidative phosphorylation ATP 2 ATP 4 ATP used formed Glucose 2 ATP + 2 P 4 ADP + 4 P 2 NAD e H + 2 NADH + 2 H + 2 Pyruvate + 2 H 2 O Energy investment phase Energy payoff phase Glucose 2 Pyruvate + 2 H 2 O 4 ATP formed – 2 ATP used 2 ATP 2 NAD e – + 4 H + 2 NADH + 2 H + Figure 9.8 exergonic, energy liberating - G endergonic, energy intake + G

22 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings A closer look at the energy investment phase: [Step 1] Energy input required Terminal P from an ATP (-->ADP) is bonded to the C6 of a glucose G = (enzyme: hexokinase) [Step 2] glucose phosphate------> fructose-6-phosphate atoms rearranged G = (enzyme: phosphoglucoisomerase) [Step 3] fructose-6-phosphate------> fructose 1,6 biphosphate Phosphate added to C1 G = (enzyme: phosphofructokinase) splits into two products [Step 4] fructose -1, 6 - biphosphate---> dihydroxyacetone phosphate AND glyceraldehyde phosphate* G = ( enzyme: aldolase) Our 6-carbon sugar is split into TWO 3-carbon products [Step 5] *Ultimately, all of the dihydroxyacetone phosphate will be converted into glyceraldehyde-3-phosphate, so each step is actually x 2 from here (because each of the two molecules will proceed through Steps 5- 9 ) dihydroxyacetone phosphate > glyceraldehyde-3-phosphate (enzyme: isomerase) Dihydroxyacetone phosphate Glyceraldehyde- 3-phosphate H H H H H OH HO CH 2 OH H H H H O H OH HO OH P CH 2 O P H O H HO H CH 2 OH P O CH 2 O O P HO H H OH O P CH 2 C O CH 2 OH H C CHOH CH 2 O O P ATP ADP Hexokinase Glucose Glucose-6-phosphate Fructose-6-phosphate ATP ADP Phosphoglucoisomerase Phosphofructokinase Fructose- 1, 6-bisphosphate Aldolase Isomerase Glycolysis CH 2 OH Oxidative phosphorylation Citric acid cycle Figure 9.9 A

23 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings A closer look at the energy payoff phase [Step 6] 2 Glyceraldehyde-3-phosphate molecules are then oxidized 2 hydrogens (with e - ) are removed, and NAD + is reduced to NADH and H + Also, a free phosphate attaches to each of the glyceraldehyde-3-phosphates 2 Glyceraldehyde-3-phosphate > 1, 3 biphosphoglycerate (x2) NAD + is reduced to NADH and H + P i = free phosphates, not taken from another molecule such as ATP NAD = nicotinamide adenine dinucleotide (niacin derivative) G = (enzyme: triose phosphate dehydrogenase) [Step 7] a P is released from each 1,3 biphosphoglycerate molecule and is used to "recharge" 2 ADPs----> 2 ATPs thus, converting the 1,3 biphosphoglycerate to 3-phosphoglycerate (highly exergonic= large G to pull preceding reactions forward) (x2) 1,3 Diphosphoglycerate > 3-phosphoglycerate ADP---> ATP G = -4.5 (enzyme: phosphoglycerokinase) (x 2) [Step 8] The remaining P group is enzymatically transferred from the 3C to the 2C 3- phosphoglycerate > 2 - phosphoglycerate G = (enzyme: phosphoglyceromutase) (x 2) [Step 9] A molecule of H 2 O removed 2 - phosphoglycerate > phosphoenolpyruvate - H 2 O G = (enzyme: enolase) (x 2) [Step 10] Another phosphate P is transferred to ADP ( highly exergonic, pulls 2 preceding rxns!!!) phosphoenolpyruvate > pyruvate (pyruvic acid) G = ( enzyme: pyruvate kinase) ADP---> ATP 2 NAD + NADH H + Triose phosphate dehydrogenase 2 P i 2 P C CHOH O P O CH 2 O 2 O–O– 1, 3-Bisphosphoglycerate 2 ADP 2 ATP Phosphoglycerokinase CH 2 OP 2 C CHOH 3-Phosphoglycerate Phosphoglyceromutase O–O– C C CH 2 OH H O P 2-Phosphoglycerate 2 H 2 O 2 O–O– Enolase C C O P O CH 2 Phosphoenolpyruvate 2 ADP 2 ATP Pyruvate kinase O–O– C C O O CH Pyruvate O

24 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Mitochondria Review The mitochondrion is surrounded by two membranes. The outer is smooth and the inner folds inwards. The inner folds are called cristae. Within the inner compartment of the mitochondrion, surrounding the cristae, there is a dense solution known as the matrix. The matrix contains enzymes, co-enzymes, water, phosphates, and other molecules needed in respiration. The outer membrane is permeable to most small molecules, but the inner one permits the passage of only certain molecules, such as pyruvic acid and ATP. Proteins are built into the membrane of the cristae. These proteins are involved with the Electron Transport Chain. The inner membrane is about 80% protein and 20% lipids. 95% of the ATP generated by the heterotrophic cell is produced by the mitochondrion.

25 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The Fate of the Pyruvate The pyruvate passes from the cytoplasm (where its produced thru glycolysis) and crosses the outer & inner membranes of the mitochondria Before entering the Krebs Cycle, the 3-C pyruvate molecule is oxidized: the carbon and oxygen atoms of the carboxyl group are removed (into CO 2 ) and a 2-C acetyl group is left (CH 3 CO) In the course of this rxn, the carboxyl hydrogen reduces a molecule of NAD + to NADH The acetyl is momentarily accepted by a "coenzyme A" molecule (a large, complex molecule formed from pantothenic acid (vitamin B)), forming Acetyl-CoA From here the Acetyl CoA can enter the Krebs (aka, Citric Acid) Cycle. Acetyl CoA moves into the mitochondria and is completely dismantled by the enzymes in the mitochondria.

26 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Before the citric acid cycle can begin – Pyruvate must first be converted to acetyl CoA, which links the cycle to glycolysis CYTOSOLMITOCHONDRION NADH + H + NAD CO 2 Coenzyme A Pyruvate Acetyle CoA S CoA C CH 3 O Transport protein O–O– O O C C CH 3 Figure 9.10

27 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings An overview of the citric acid cycle ATP 2 CO 2 3 NAD + 3 NADH + 3 H + ADP + P i FAD FADH 2 Citric acid cycle CoA Acetyle CoA NADH + 3 H + CoA CO 2 Pyruvate (from glycolysis, 2 molecules per glucose) ATP Glycolysis Citric acid cycle Oxidative phosphorylatio n Figure 9.11 Discovered 1937 by British biochemist Sir Hans Adolf Krebs CO 2 is produced. Acetyls are dismantled and reconfigured. The electrons are what's important. The Krebs's cycle only gives us two molecules of ATP. Added with the two molecules of ATP made in Glycolysis, the total is now a meager four molecules of ATP. The remainder of the ATPs come from the Electron Transport System, which takes the electrons produced in the Krebs's cycle and makes ATP.

28 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Figure 9.12 Acetyl CoA NADH Oxaloacetate Citrate Malate Fumarate Succinate Succinyl CoA -Ketoglutarate Isocitrate Citric acid cycle SCoA SH NADH FADH 2 FAD GTP GDP NAD + ADP P i NAD + CO 2 CoA SH CoA SH CoA S H2OH2O + H + H2OH2O C CH 3 O OCCOO – CH 2 COO – CH 2 HO C COO – CH 2 COO – CH 2 HCCOO – HOCH COO – CH CH 2 COO – HO COO – CH HC COO – CH 2 COO – CH 2 CO COO – CH 2 CO COO – Glycolysis Oxidative phosphorylation NAD + + H + ATP Citric acid cycle Figure 9.12 A closer look at the citric acid cycle In general: 2-C acetyl combines with 4-C oxaloacetic acid to form a 6-C citric acid. Two carbons (per cycle) are oxidized to CO 2 which regenerates a molecule of oxaloacetic acid Each turn of the cycle uses up one acetyl group and regenerates a oxaloacetic acid, then begins the cycle again. Energy is released by breaking C-H and C-C bonds and is stored by transforming ADP to ATP (1 molecule per turn of the cycle) and to convert NAD + to NADH and H + (3x per cycle) Also, FAD (flavin adenine dinucleotide) is converted to FADH 2 (one molecule per cycle) 1. No oxygen is required in Krebs Cycle 2. All e - and p + are accepted by either NAD + or FAD There are 8 steps in the cycle and the aim is to totally dismantle the Acetyl CoA, using only its electrons. We have totally taken apart the glucose molecule. Only four ATPs have resulted, 2 from glycolysis and 2 from the CAC. But we still have a lot of ELECTRONS captured in the form of NADH and FADH 2 = potential energy

29 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Oxidative phosphorylation Concept 9.4: During oxidative phosphorylation, chemiosmosis couples electron transport to ATP synthesis NADH and FADH 2 – Donate electrons to the electron transport chain, which powers ATP synthesis via oxidative phosphorylation

30 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The Pathway of Electron Transport 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 Transport Chain carriers are called CYTOCHROMES (consist of protein and a heme group = atom of iron enclosed in a porphyrin ring (note the similarity to hemoglobin!) electrons are "passed down" a "staircase" of cytochromes and the energy released in lowering the energy level is stored in additional ATP molecules...called Oxidative Phosphorylation remember, the energy from lowering electrons can do this: ADP + P = ATP ---> for every e - passed down the chain from NADH, 3 ATPs are formed ---> for every 2e - from FADH 2, 2 ATP's are formed H2OH2O O2O2 NADH FADH2 FMN FeS O FAD Cyt b Cyt c 1 Cyt c Cyt a Cyt a 3 2 H I II III IV Multiprotein complexes Free energy (G) relative to O 2 (kcl/mol) Figure 9.13

31 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Chemiosmosis: The Energy-Coupling Mechanism ATP synthase – Is the enzyme that actually makes ATP INTERMEMBRANE SPACE H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+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 Figure 9.14

32 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Chemiosmosis Is an energy-coupling mechanism that uses energy in the form of a H + gradient across a membrane to drive cellular work 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

33 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Chemiosmosis and the electron transport chain Oxidative phosphorylation. electron transport and chemiosmosis Glycolysis ATP Inner Mitochondrial membrane H+H+ H+H+ H+H+ H+H+ H+H+ ATP P i Protein complex of electron carners Cyt c I II III IV (Carrying electrons from, food) NADH + FADH 2 NAD + FAD + 2 H / 2 O 2 H2OH2O 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 ATP synthase Q Oxidative phosphorylation Intermembrane space Inner mitochondrial membrane Mitochondrial matrix Figure 9.15

34 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Summary There are three main processes in this metabolic enterprise Electron shuttles span membrane CYTOSOL 2 NADH 2 FADH 2 2 NADH 6 NADH 2 FADH 2 2 NADH Glycolysis Glucose 2 Pyruvate 2 Acetyl CoA Citric acid cycle Oxidative phosphorylation: electron transport and chemiosmosis MITOCHONDRION 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 + 2 ATP + about 32 or 34 ATP or Figure 9.16

35 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The energy tally sheet Glycolysis:2 ATP=2 ATP 2 NADH ets 6 ATP=6 ATP Oxidation: pyruvate acetyl CoA 1 NADH ets 3 ATP (x2)= 6 ATP CAC/Krebs1 ATP x2 turns 2 ATP 3 NADH ets 9 ATP x2 turns 18 ATP 1 FADH 2 ets 2 ATP x2 turns 4 ATP= 24 ATP TOTAL = 38 ATP

36 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings efficiency Less than 40% of the energy in a glucose molecule is transferred to ATP during cellular respiration, making approximately 38 ATP G = ADP + P i --> ATP = about 7 kcal/mole X 38 = 266 kcal/mole (captured in P bonds) G = -686 kcal/mole (free energy change during glycolysis and oxidation for glucose) = about 39% efficiency

37 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings FERMENTATION Concept 9.5: Fermentation enables some cells to produce ATP without the use of oxygen Oxidative cellular respiration – Relies on oxygen to produce ATP – Involves Krebs cycle and ETS In the absence of oxygen – Cells can still produce a little bit of ATP through fermentation

38 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Without oxygen: Glycolysis – Can produce ATP with or without oxygen, in either aerobic or anaerobic conditions – Pyruvate is produced, some ATP is made In anaerobic respiration (fermentation) pyruvate must be processed in the absence of oxygen The breakdown of the sugar still takes place through a series of chemical reactions, but with a different outcome.

39 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The Evolutionary Significance of Glycolysis Glycolysis – Occurs in the cytoplasm of nearly all organisms – Probably evolved in ancient prokaryotes before there was oxygen in the atmosphere

40 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 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

41 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Fermentation Living organisms have developed numerous and different fermentation pathways; however, most organisms use the following Embden-Meyerhoff pathway, named for the two discoverers. The pyruvate can take two pathways in anaerobic respiration: – a. Pyruvate will be converted to ethyl alcohol (ethanol) and carbon dioxide. This is called alcoholic fermentation and is the basis of our wine, beer and liquor industry. – b. The pyruvate will be converted to lactic acid. This is called lactic acid fermentation. Lactic acid is what makes your muscles burn during prolonged exercise, this process is also used to make yogurt.

42 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Types of Fermentation Fermentation consists of – Glycolysis plus reactions that regenerate NAD +, which can be reused by glyocolysis In alcohol fermentation – Pyruvate is converted to ethanol in two steps, one of which releases CO 2 During lactic acid fermentation – Pyruvate is reduced directly to NADH to form lactate as a waste product

43 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 2 ADP + 2 P1P1 2 ATP Glycolysis Glucose 2 NAD + 2 NADH 2 Pyruvate 2 Acetaldehyde 2 Ethanol (a) Alcohol fermentation 2 ADP + 2 P1P1 2 ATP Glycolysis Glucose 2 NAD + 2 NADH 2 Lactate (b) Lactic acid fermentation H H OH CH 3 C O – O C CO CH 3 H CO O–O– CO CO O CO C OHH CH 3 CO 2 2 Figure 9.17

44 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Fermentation and Cellular Respiration Compared 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 Oxidative cellular respiration – Produces more ATP

45 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The Versatility of Catabolism Concept 9.6: Glycolysis and the citric acid cycle connect to many other metabolic pathways Catabolic pathways – Funnel electrons from many kinds of organic molecules into cellular respiration

46 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The catabolism of various molecules from food Amino acids Sugars Glycerol Fatty acids Glycolysis Glucose Glyceraldehyde-3- P Pyruvate Acetyl CoA NH 3 Citric acid cycle Oxidative phosphorylation Fats Proteins Carbohydrates Figure 9.19

47 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Regulation of Cellular Respiration via Feedback Mechanisms Cellular respiration – Is controlled by allosteric enzymes at key points in glycolysis and the citric acid cycle Enzyme 1Enzyme 2Enzyme 3 A B C D Reaction 1Reaction 2Reaction 3 Starting molecule Product

48 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Feedback Control Regulates Biological Processes 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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