Overview: Life Is Work Living cells require energy from outside sources. Some animals, such as the giant panda, obtain energy by eating plants; others.

Overview: Life Is Work Living cells require energy from outside sources. Some animals, such as the giant panda, obtain energy by eating plants; others feed on organisms that eat plants Energy flows into an ecosystem as sunlight and leaves as heat Photosynthesis generates oxygen and organic molecules, which are used in cellular respiration Cells use chemical energy stored in organic molecules to regenerate ATP, which powers work

Overview LE 9-2 Light energy ECOSYSTEM Photosynthesis in chloroplasts
CO2 + H2O Organic molecules + O2 Cellular respiration in mitochondria ATP powers most cellular work Heat energy

Concept 9.1: Catabolic pathways yield energy by oxidizing organic fuels
Several processes are central to cellular respiration and related pathways

1.&2. Catabolic Pathways and Production of ATP
The breakdown of organic molecules is exergonic Fermentation is a partial degradation of sugars that occurs without oxygen Cellular respiration consumes oxygen and organic molecules and yields ATP Although carbohydrates, fats, and proteins are all consumed as fuel, it is helpful to trace cellular respiration with the sugar glucose: C6H12O6 + 6O2  6CO2 + 6H2O + Energy (ATP + heat)

3. – 4. Review of Redox The transfer of electrons during chemical reactions releases energy stored in organic molecules. This released energy is ultimately used to synthesize ATP Chemical reactions that transfer electrons between reactants are called oxidation-reduction reactions, or redox reactions

3., 4. , 5. Review of Redox In oxidation, a substance loses electrons, or is oxidized. In reduction, a substance gains electrons, or is reduced (the amount of positive charge is reduced) When compounds lose electrons, they release energy, when compounds gain electrons they gain energy. Xe Y X Ye- becomes oxidized (loses electron) becomes reduced (gains electron)

Oxidation of Organic Fuel Molecules During Cellular Respiration
During cellular respiration, the fuel (such as glucose) is oxidized and oxygen is reduced: C6H12O6 + 6O CO2 + 6H2O + Energy becomes oxidized becomes reduced

6. Stepwise Energy Harvest via NAD+ and the Electron Transport Chain
In cellular respiration, glucose and other organic molecules are broken down in a series of steps Electrons from organic compounds are usually first transferred to NAD+, a coenzyme As an electron acceptor, NAD+ functions as an oxidizing agent during cellular respiration Each NADH (the reduced form of NAD+) represents stored energy that is tapped to synthesize ATP

LE 9-4 NADH NAD+ 2 e– + 2 H+ 2 e– + H+ H+ Dehydrogenase + 2[H] + H+
(from food) + H+ Nicotinamide (reduced form) Nicotinamide (oxidized form)

7. NADH passes the electrons to the electron transport chain Unlike an uncontrolled reaction, the electron transport chain passes electrons in a series of steps instead of one explosive reaction Oxygen pulls electrons down the chain in an energy-yielding tumble The energy yielded is used to regenerate ATP

Electron transport chain
+ 1/2 O2 2 H + 1/2 O2 (from food via NADH) Controlled release of energy for synthesis of ATP 2 H+ + 2 e– ATP Explosive release of heat and light energy ATP Free energy, G Free energy, G Electron transport chain ATP 2 e– 1/2 O2 2 H+ H2O H2O Uncontrolled reaction Cellular respiration

8. An Accounting of ATP Production by Cellular Respiration
During cellular respiration, most energy flows in this sequence: glucose NADH electron transport chain oxygen About 40% of the energy in a glucose molecule is transferred to ATP during cellular respiration, making about 38 ATP

9. The Stages of Cellular Respiration: A Preview
Cellular respiration has three stages: Glycolysis (breaks down glucose into two molecules of pyruvate) The citric acid cycle (completes the breakdown of glucose) Electron Transport & Oxidative phosphorylation (accounts for most of the ATP synthesis) The process that generates most of the ATP is called oxidative phosphorylation because it is powered by redox reactions [Animation listed on slide following figure]

LE 9-6_1 Glycolysis Glucose Pyruvate Cytosol Mitochondrion ATP
Substrate-level phosphorylation

LE 9-6_2 Glycolysis Citric acid cycle Glucose Pyruvate Cytosol
Mitochondrion ATP ATP Substrate-level phosphorylation Substrate-level phosphorylation

LE 9-6_3 Electrons carried via NADH Electrons carried via NADH and
FADH2 Oxidative phosphorylation: electron transport and chemiosmosis Glycolysis Citric acid cycle Glucose Pyruvate Cytosol Mitochondrion ATP ATP ATP Substrate-level phosphorylation Substrate-level phosphorylation Oxidative phosphorylation

10. Oxidative phosphorylation accounts for almost 90% of the ATP generated by cellular respiration The electron transport chain accepts electrons from the break down of products from the first two steps and passes these electrons from one molecule to another. The synthesis of ATP is powered by the redox reactions of the electron transport chain

LE 9-7 11. A small amount of ATP is formed in glycolysis and the citric acid cycle by substrate-level phosphorylation Enzyme Enzyme ADP P Substrate + ATP Product

Animation: Glycolysis
12. & 13. Concept 9.2: Glycolysis harvests energy by oxidizing glucose to pyruvate Glycolysis (“splitting of sugar”) breaks down glucose into two molecules of pyruvate (a three carbon compound) Glycolysis occurs in the cytoplasm and has two major phases: Energy investment phase Energy payoff phase Animation: Glycolysis

14.& 15. LE 9-8 Energy investment phase Glucose 2 ADP + 2 P 2 ATP used
Glycolysis Citric acid cycle Oxidative phosphorylation Energy payoff phase ATP ATP ATP 4 ADP + 4 P 4 ATP formed 2 NAD+ + 4 e– + 4 H+ 2 NADH + 2 H+ 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+

14.& 15. LE 9-9a_1 Glucose ATP Hexokinase ADP Glucose-6-phosphate
Glycolysis Citric acid cycle phosphorylation Oxidation Glucose ATP ATP ATP ATP Hexokinase ADP Glucose-6-phosphate

LE 9-9a_2 Glucose ATP Hexokinase ADP Glucose-6-phosphate
Glycolysis Citric acid cycle Oxidation phosphorylation Glucose ATP ATP ATP ATP Hexokinase ADP Glucose-6-phosphate Phosphoglucoisomerase Fructose-6-phosphate ATP Phosphofructokinase ADP Fructose- 1, 6-bisphosphate Aldolase Isomerase Dihydroxyacetone phosphate Glyceraldehyde- 3-phosphate

LE 9-9b_1 2 NAD+ Triose phosphate dehydrogenase 2 NADH + 2 H+
1, 3-Bisphosphoglycerate 2 ADP Phosphoglycerokinase 2 ATP 3-Phosphoglycerate Phosphoglyceromutase 2-Phosphoglycerate

LE 9-9b_2 2 NAD+ Triose phosphate dehydrogenase 2 NADH + 2 H+
1, 3-Bisphosphoglycerate 2 ADP Phosphoglycerokinase 2 ATP 3-Phosphoglycerate Phosphoglyceromutase 2-Phosphoglycerate Enolase 2 H2O Phosphoenolpyruvate 2 ADP Pyruvate kinase 2 ATP Pyruvate

16. Net Energy Gains of Glycolysis
Glucose  2 Pyruvate + 2 H2O 4 ATP formed – 2 ATP used  2 ATP 2 NAD++ 4e H+  2NADH + 2 H+ 17. Glycolysis occurs in the cytosol and can occur without the presence of oxygen.

Concept 9.3: The citric acid cycle completes the energy-yielding oxidation of organic molecules
Before the citric acid cycle can begin, pyruvate must be converted to acetyl CoA, which links the cycle to glycolysis This is sometimes called the “preliminary step”

18. LE 9-10 CYTOSOL MITOCHONDRION NAD+ NADH + H+ Acetyl Co A Pyruvate
Coenzyme A Transport protein

18. Converting pyruvate to acetyl CoA
Pyruvates carboxyl is removed and given off as CO2 The remaining 2 carbon compound is oxidized forming acetate and transfers electrons to NAD+ to form NADH Coenzyme A is attached to acetate by an unstable bond (making it reactive) The acetyl group will be fed to the citric acid cycle to be further oxidized.

Animation: Electron Transport
19. The citric acid cycle, also called the Krebs cycle, takes place within the mitochondrial matrix The cycle oxidizes organic fuel derived from pyruvate, generating one ATP, 3 NADH, and 1 FADH2 per turn It makes two turns for each glucose molecule. Animation: Electron Transport

20,21,22 LE 9-11 Pyruvate (from glycolysis, 2 molecules per glucose)
Citric acid cycle Oxidation phosphorylation NAD+ 20,21,22 CoA NADH ATP ATP ATP + H+ Acetyl CoA CoA CoA Citric acid cycle 2 CO2 FADH2 3 NAD+ FAD 3 NADH + 3 H+ ADP + P i ATP

The citric acid cycle has eight steps, each catalyzed by a specific enzyme
The acetyl group of acetyl CoA joins the cycle by combining with oxaloacetate, forming citrate The next seven steps decompose the citrate back to oxaloacetate, making the process a cycle The NADH and FADH2 produced by the cycle relay electrons extracted from food to the electron transport chain

LE 9-12_1 Acetyl CoA H2O Oxaloacetate Citrate Isocitrate Citric acid
Glycolysis Citric acid cycle Oxidation phosphorylation ATP ATP ATP Acetyl CoA H2O Oxaloacetate Citrate Isocitrate Citric acid cycle

LE 9-12_2 Acetyl CoA H2O Oxaloacetate Citrate Isocitrate CO2 Citric
Glycolysis Citric acid cycle Oxidation phosphorylation ATP ATP ATP Acetyl CoA H2O Oxaloacetate Citrate Isocitrate CO2 Citric acid cycle NAD+ NADH + H+ a-Ketoglutarate CO2 NAD+ NADH Succinyl CoA + H+

LE 9-12_3 Acetyl CoA H2O Oxaloacetate Citrate Isocitrate CO2 Citric
Glycolysis Citric acid cycle Oxidation phosphorylation ATP ATP ATP Acetyl CoA H2O Oxaloacetate Citrate Isocitrate CO2 Citric acid cycle NAD+ NADH Fumarate + H+ a-Ketoglutarate FADH2 CO2 NAD+ FAD Succinate P NADH i GTP GDP Succinyl CoA + H+ ADP ATP

23 LE 9-12_4 Acetyl CoA NADH + H+ H2O NAD+ Oxaloacetate Malate Citrate
Glycolysis Citric acid cycle Oxidation phosphorylation 23 ATP ATP ATP Acetyl CoA NADH + H+ H2O NAD+ Oxaloacetate Malate Citrate Isocitrate CO2 Citric acid cycle NAD+ H2O NADH Fumarate + H+ a-Ketoglutarate FADH2 CO2 NAD+ FAD Succinate P NADH i GTP GDP Succinyl CoA + H+ ADP ATP

24 & 25. The Pathway of Electron Transport
The electron transport chain is in the cristae of the mitochondrion Most of the chain’s components are proteins, which exist in multiprotein complexes. The carriers alternate reduced and oxidized states as they accept and donate electrons Electrons drop in free energy as they go down the chain and are finally passed to O2, which has the highest electronegativity. It then combines with H+ forming water

Concept 9.4: During oxidative phosphorylation, chemiosmosis couples electron transport to ATP synthesis Following glycolysis and the citric acid cycle, NADH and FADH2 account for most of the energy extracted from food These two electron carriers donate electrons to the electron transport chain, which powers ATP synthesis via oxidative phosphorylation

24. LE 9-13 NADH 50 FADH2 Multiprotein complexes 40 I FMN FAD Fe•S
II Q III Cyt b Oxidative phosphorylation: electron transport and chemiosmosis Glycolysis Citric acid cycle Fe•S 30 Cyt c1 Free energy (G) relative to O2 (kcal/mol) IV Cyt c Cyt a ATP ATP ATP Cyt a3 20 10 2 H+ + 1/2 O2 H2O

27 & 28 Chemiosmosis: The Energy-Coupling Mechanism
Electron transfer in the electron transport chain causes proteins to pump H+ from the mitochondrial matrix to the intermembrane space H+ then moves back across the membrane, passing through channels in ATP synthase ATP synthase uses the exergonic flow of H+ to drive phosphorylation of ATP This is an example of chemiosmosis, the use of energy in a H+ gradient to drive cellular work

27. LE 9-14 INTERMEMBRANE SPACE H+
A rotor within the membrane spins as shown when H+ flows past it down the H+ gradient. 27. H+ H+ H+ H+ H+ H+ A stator anchored in the membrane holds the knob stationary. A rod (or “stalk”) extending into the knob also spins, activating catalytic sites in the knob. H+ Three catalytic sites in the stationary knob join inorganic phosphate to ADP to make ATP. ADP + ATP P i MITOCHONDRAL MATRIX

Animation: Fermentation Overview
29. The energy stored in a H+ gradient across a membrane couples the redox reactions of the electron transport chain to ATP synthesis The H+ gradient is referred to as a proton-motive force, emphasizing its capacity to do work Animation: Fermentation Overview

30. LE 9-15 Inner mitochondrial membrane H+ H+ H+ H+ Protein complex
Citric acid cycle Oxidative phosphorylation: electron transport and chemiosmosis Glycolysis ATP ATP ATP H+ H+ H+ H+ Protein complex of electron carriers Cyt c Intermembrane space Q IV I III ATP synthase Inner mitochondrial membrane II 2H+ + 1/2 O2 H2O FADH2 FAD NADH + H+ NAD+ ADP + P ATP i (carrying electrons from food) H+ Mitochondrial matrix 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 Oxidative phosphorylation

31. An Accounting of ATP Production by Cellular Respiration
During cellular respiration, most energy flows in this sequence: glucose NADH electron transport chain proton-motive force ATP About 40% of the energy in a glucose molecule is transferred to ATP during cellular respiration, making about 38 ATP Each NADH generates ATP Each FADH2 generates 1.5 – 2 ATP

32. LE 9-16 CYTOSOL Electron shuttles span membrane MITOCHONDRION
2 NADH or 2 FADH2 2 NADH 2 NADH 6 NADH 2 FADH2 Glycolysis Oxidative phosphorylation: electron transport and chemiosmosis 2 Pyruvate 2 Acetyl CoA Citric acid cycle Glucose + 2 ATP + 2 ATP + about 32 or 34 ATP by substrate-level phosphorylation by substrate-level phosphorylation by oxidation phosphorylation, depending on which shuttle transports electrons form NADH in cytosol About 36 or 38 ATP Maximum per glucose:

33. Is it 36 or 38 ATP? Phosphorylation and redox reactions aren’t coupled Type of shuttle: NADH from glycolysis must be shuttled across the membrane as NAD+ of FAD. The amount of ATP formed depends on where the electrons are passed. Use of proton-motive force to drive other work

34. Concept 9.5: Fermentation enables some cells to produce ATP without the use of oxygen
Cellular respiration requires O2 to produce ATP Glycolysis can produce ATP with or without O2 (in aerobic or anaerobic conditions) In the absence of O2, glycolysis couples with fermentation to produce ATP Fermentation allows for the production of ATP without using either oxygen or any oxidative phosphorylation.

35. Types of Fermentation Fermentation consists of glycolysis plus reactions that regenerate NAD+, which can be reused by glycolysis and is the electron acceptor of the process Two common types are alcohol fermentation and lactic acid fermentation

36. In alcohol fermentation, pyruvate is converted to ethanol in two steps, with the first releasing CO2 Alcohol fermentation by yeast is used in brewing, winemaking, and baking Play

36. Alcohol fermentation 2 ADP + 2 P 2 ATP Glucose Glycolysis
LE 9-17a 36. 2 ADP + 2 P 2 ATP i Glucose Glycolysis 2 Pyruvate 2 NAD+ 2 NADH 2 CO2 + 2 H+ 2 Acetaldehyde 2 Ethanol Alcohol fermentation

37. In lactic acid fermentation, pyruvate is reduced to NADH, forming lactate as an end product, with no release of CO2 Lactic acid fermentation by some fungi and bacteria is used to make cheese and yogurt Human muscle cells use lactic acid fermentation to generate ATP when O2 is scarce

37. Lactic acid fermentation 2 ADP + 2 P 2 ATP Glucose Glycolysis
LE 9-17b 37. 2 ADP + 2 P 2 ATP i Glucose Glycolysis 2 NAD+ 2 NADH 2 CO2 + 2 H+ 2 Pyruvate 2 Lactate Lactic acid fermentation

Fermentation and Cellular Respiration Compared
Both processes use glycolysis to oxidize glucose and other organic fuels to pyruvate The processes have different final electron acceptors: an organic molecule (such as pyruvate) in fermentation and O2 in cellular respiration Cellular respiration produces much more ATP

38. Yeast and many bacteria are facultative anaerobes, meaning that they can survive using either fermentation or cellular respiration In a facultative anaerobe, pyruvate is a fork in the metabolic road that leads to two alternative catabolic routes

LE 9-18 Glucose CYTOSOL Pyruvate No O2 present Fermentation O2 present Cellular respiration MITOCHONDRION Ethanol or lactate Acetyl CoA Citric acid cycle

Concept 9.6: Glycolysis and the citric acid cycle connect to many other metabolic pathways
Gycolysis and the citric acid cycle are major intersections to various catabolic and anabolic pathways

39. The Versatility of Catabolism
Catabolic pathways funnel electrons from many kinds of organic molecules into cellular respiration Glycolysis accepts a wide range of carbohydrates Proteins must be digested to amino acids; amino groups can feed glycolysis or the citric acid cycle Fats are digested to glycerol (used in glycolysis) and fatty acids (used in generating acetyl CoA) An oxidized gram of fat produces more than twice as much ATP as an oxidized gram of carbohydrate

LE 9-19 Carbohydrates Fats Amino acids Sugars Glycerol Fatty acids
Proteins Carbohydrates Fats Amino acids Sugars Glycerol Fatty acids Glycolysis Glucose Glyceraldehyde-3- P NH3 Pyruvate Acetyl CoA Citric acid cycle Oxidative phosphorylation

40. Biosynthesis (Anabolic Pathways)
The body uses small molecules to build other substances by using food as the carbon skeletons to make the cells own molecules. These small molecules may come directly from food, from glycolysis, or from the citric acid cycle Biosynthesis is an anabolic pathway that consumes energy Step 5 of glycolysis produces droxyacetate phosphate which can be converted into the precursor of fats. This is why we store fat if we eat too much.

Regulation of Cellular Respiration via Feedback Mechanisms
Feedback inhibition is the most common mechanism for control If ATP concentration begins to drop, respiration speeds up; when there is plenty of ATP, respiration slows down Control of catabolism is based mainly on regulating the activity of enzymes at strategic points in the catabolic pathway

Fructose-1,6-bisphosphate
LE 9-20 Glucose 41. AMP Glycolysis Fructose-6-phosphate Stimulates + Phosphofructokinase – – Fructose-1,6-bisphosphate Inhibits Inhibits Pyruvate ATP Citrate Acetyl CoA Citric acid cycle Oxidative phosphorylation

Overview: Life Is Work Living cells require energy from outside sources. Some animals, such as the giant panda, obtain energy by eating plants; others.

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Overview: Life Is Work Living cells require energy from outside sources. Some animals, such as the giant panda, obtain energy by eating plants; others.

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Presentation on theme: "Overview: Life Is Work Living cells require energy from outside sources. Some animals, such as the giant panda, obtain energy by eating plants; others."— Presentation transcript:

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