Cellular Pathways that Harvest Chemical Energy : Respiration.
Ch06 lecture pathways that harvest and store chemical energy
-
Upload
tia-hohler -
Category
Education
-
view
79 -
download
2
Transcript of Ch06 lecture pathways that harvest and store chemical energy
![Page 1: Ch06 lecture pathways that harvest and store chemical energy](https://reader031.fdocuments.in/reader031/viewer/2022022415/5a64aa947f8b9a27568b88a3/html5/thumbnails/1.jpg)
Pathways that Harvest andStore Chemical Energy
6
![Page 2: Ch06 lecture pathways that harvest and store chemical energy](https://reader031.fdocuments.in/reader031/viewer/2022022415/5a64aa947f8b9a27568b88a3/html5/thumbnails/2.jpg)
Chapter 6 Pathways that Harvest and Store Chemical Energy
Key Concepts
• 6.1 ATP, Reduced Coenzymes, and Chemiosmosis Play Important Roles in Biological Energy Metabolism
• 6.2 Carbohydrate Catabolism in the Presence of Oxygen Releases a Large Amount of Energy
• 6.3 Carbohydrate Catabolism in the Absence of Oxygen Releases a Small Amount of Energy
![Page 3: Ch06 lecture pathways that harvest and store chemical energy](https://reader031.fdocuments.in/reader031/viewer/2022022415/5a64aa947f8b9a27568b88a3/html5/thumbnails/3.jpg)
Chapter 6 Pathways that Harvest and Store Chemical Energy
• 6.4 Catabolic and Anabolic Pathways Are Integrated
• 6.5 During Photosynthesis, Light Energy Is Converted to Chemical Energy
• 6.6 Photosynthetic Organisms Use Chemical Energy to Convert CO2 to Carbohydrates
![Page 4: Ch06 lecture pathways that harvest and store chemical energy](https://reader031.fdocuments.in/reader031/viewer/2022022415/5a64aa947f8b9a27568b88a3/html5/thumbnails/4.jpg)
Chapter 6 Opening Question
Why does fresh air inhibit the formation of alcohol by yeast cells?
![Page 5: Ch06 lecture pathways that harvest and store chemical energy](https://reader031.fdocuments.in/reader031/viewer/2022022415/5a64aa947f8b9a27568b88a3/html5/thumbnails/5.jpg)
Concept 6.1 ATP, Reduced Coenzymes, and Chemiosmosis Play Important Roles in Biological Energy Metabolism
Energy is stored in chemical bonds and can be released and transformed by metabolic pathways.
Chemical energy available to do work is termed free energy (G).
![Page 6: Ch06 lecture pathways that harvest and store chemical energy](https://reader031.fdocuments.in/reader031/viewer/2022022415/5a64aa947f8b9a27568b88a3/html5/thumbnails/6.jpg)
Concept 6.1 ATP, Reduced Coenzymes, and Chemiosmosis Play Important Roles in Biological Energy Metabolism
Five principles governing metabolic pathways:
1. Chemical transformations occur in a series of intermediate reactions that form a metabolic pathway.
2. Each reaction is catalyzed by a specific enzyme.
3. Most metabolic pathways are similar in all organisms.
![Page 7: Ch06 lecture pathways that harvest and store chemical energy](https://reader031.fdocuments.in/reader031/viewer/2022022415/5a64aa947f8b9a27568b88a3/html5/thumbnails/7.jpg)
Concept 6.1 ATP, Reduced Coenzymes, and Chemiosmosis Play Important Roles in Biological Energy Metabolism
4. In eukaryotes, many metabolic pathways occur inside specific organelles.
5. Each metabolic pathway is controlled by enzymes that can be inhibited or activated.
![Page 8: Ch06 lecture pathways that harvest and store chemical energy](https://reader031.fdocuments.in/reader031/viewer/2022022415/5a64aa947f8b9a27568b88a3/html5/thumbnails/8.jpg)
Concept 6.1 ATP, Reduced Coenzymes, and Chemiosmosis Play Important Roles in Biological Energy Metabolism
In cells, energy-transforming reactions are often coupled:
An energy-releasing (exergonic) reaction is coupled to an energy-requiring (endergonic) reaction.
![Page 9: Ch06 lecture pathways that harvest and store chemical energy](https://reader031.fdocuments.in/reader031/viewer/2022022415/5a64aa947f8b9a27568b88a3/html5/thumbnails/9.jpg)
Concept 6.1 ATP, Reduced Coenzymes, and Chemiosmosis Play Important Roles in Biological Energy Metabolism
Adenosine triphosphate (ATP) is a kind of “energy currency” in cells.
Energy released by exergonic reactions is stored in the bonds of ATP.
When ATP is hydrolyzed, free energy is released to drive endergonic reactions.
![Page 10: Ch06 lecture pathways that harvest and store chemical energy](https://reader031.fdocuments.in/reader031/viewer/2022022415/5a64aa947f8b9a27568b88a3/html5/thumbnails/10.jpg)
Figure 6.1 The Concept of Coupling Reactions
![Page 11: Ch06 lecture pathways that harvest and store chemical energy](https://reader031.fdocuments.in/reader031/viewer/2022022415/5a64aa947f8b9a27568b88a3/html5/thumbnails/11.jpg)
Figure 6.2 ATP
![Page 12: Ch06 lecture pathways that harvest and store chemical energy](https://reader031.fdocuments.in/reader031/viewer/2022022415/5a64aa947f8b9a27568b88a3/html5/thumbnails/12.jpg)
Concept 6.1 ATP, Reduced Coenzymes, and Chemiosmosis Play Important Roles in Biological Energy Metabolism
Hydrolysis of ATP is exergonic:
ΔG is about –7.3 kcal
energyfreePADPOHATP i ++→+ 2
![Page 13: Ch06 lecture pathways that harvest and store chemical energy](https://reader031.fdocuments.in/reader031/viewer/2022022415/5a64aa947f8b9a27568b88a3/html5/thumbnails/13.jpg)
Concept 6.1 ATP, Reduced Coenzymes, and Chemiosmosis Play Important Roles in Biological Energy Metabolism
Free energy of the bond between phosphate groups is much higher than the energy of the O—H bond that forms after hydrolysis.
text art pg 102 here(1st one, in left-hand column)
![Page 14: Ch06 lecture pathways that harvest and store chemical energy](https://reader031.fdocuments.in/reader031/viewer/2022022415/5a64aa947f8b9a27568b88a3/html5/thumbnails/14.jpg)
Concept 6.1 ATP, Reduced Coenzymes, and Chemiosmosis Play Important Roles in Biological Energy Metabolism
Phosphate groups are negatively charged, so energy is required to get them near enough to each other to make the covalent bonds in the ATP molecule.
ATP can be formed by substrate-level phosphorylation or oxidative phosphorylation.
![Page 15: Ch06 lecture pathways that harvest and store chemical energy](https://reader031.fdocuments.in/reader031/viewer/2022022415/5a64aa947f8b9a27568b88a3/html5/thumbnails/15.jpg)
Concept 6.1 ATP, Reduced Coenzymes, and Chemiosmosis Play Important Roles in Biological Energy Metabolism
Energy can also be transferred by the transfer of electrons in oxidation–reduction, or redox reactions.
• Reduction is the gain of one or more electrons.
• Oxidation is the loss of one or more electrons.
![Page 16: Ch06 lecture pathways that harvest and store chemical energy](https://reader031.fdocuments.in/reader031/viewer/2022022415/5a64aa947f8b9a27568b88a3/html5/thumbnails/16.jpg)
Concept 6.1 ATP, Reduced Coenzymes, and Chemiosmosis Play Important Roles in Biological Energy Metabolism
Oxidation and reduction always occur together.
![Page 17: Ch06 lecture pathways that harvest and store chemical energy](https://reader031.fdocuments.in/reader031/viewer/2022022415/5a64aa947f8b9a27568b88a3/html5/thumbnails/17.jpg)
Concept 6.1 ATP, Reduced Coenzymes, and Chemiosmosis Play Important Roles in Biological Energy Metabolism
Transfers of hydrogen atoms involve transfers of electrons (H = H+ + e–).
When a molecule loses a hydrogen atom, it becomes oxidized.
![Page 18: Ch06 lecture pathways that harvest and store chemical energy](https://reader031.fdocuments.in/reader031/viewer/2022022415/5a64aa947f8b9a27568b88a3/html5/thumbnails/18.jpg)
Concept 6.1 ATP, Reduced Coenzymes, and Chemiosmosis Play Important Roles in Biological Energy Metabolism
The more reduced a molecule is, the more energy is stored in its bonds.
Energy is transferred in a redox reaction.
Energy in the reducing agent is transferred to the reduced product.
![Page 19: Ch06 lecture pathways that harvest and store chemical energy](https://reader031.fdocuments.in/reader031/viewer/2022022415/5a64aa947f8b9a27568b88a3/html5/thumbnails/19.jpg)
Figure 6.3 Oxidation, Reduction, and Energy
![Page 20: Ch06 lecture pathways that harvest and store chemical energy](https://reader031.fdocuments.in/reader031/viewer/2022022415/5a64aa947f8b9a27568b88a3/html5/thumbnails/20.jpg)
Concept 6.1 ATP, Reduced Coenzymes, and Chemiosmosis Play Important Roles in Biological Energy Metabolism
Coenzyme NAD+ is a key electron carrier in redox reactions.
NAD+ (oxidized form)
NADH (reduced form)
![Page 21: Ch06 lecture pathways that harvest and store chemical energy](https://reader031.fdocuments.in/reader031/viewer/2022022415/5a64aa947f8b9a27568b88a3/html5/thumbnails/21.jpg)
Figure 6.4 A NAD+/NADH Is an Electron Carrier in Redox Reactions
![Page 22: Ch06 lecture pathways that harvest and store chemical energy](https://reader031.fdocuments.in/reader031/viewer/2022022415/5a64aa947f8b9a27568b88a3/html5/thumbnails/22.jpg)
Concept 6.1 ATP, Reduced Coenzymes, and Chemiosmosis Play Important Roles in Biological Energy Metabolism
Reduction of NAD+ is highly endergonic:
Oxidation of NADH is highly exergonic:
NADHeHNAD →++ −++ 2
OHNADOHNADH 2221 +→++ ++
![Page 23: Ch06 lecture pathways that harvest and store chemical energy](https://reader031.fdocuments.in/reader031/viewer/2022022415/5a64aa947f8b9a27568b88a3/html5/thumbnails/23.jpg)
Figure 6.4 B NAD+/NADH Is an Electron Carrier in Redox Reactions
![Page 24: Ch06 lecture pathways that harvest and store chemical energy](https://reader031.fdocuments.in/reader031/viewer/2022022415/5a64aa947f8b9a27568b88a3/html5/thumbnails/24.jpg)
Concept 6.1 ATP, Reduced Coenzymes, and Chemiosmosis Play Important Roles in Biological Energy Metabolism
• In cells, energy is released in catabolism by oxidation and trapped by reduction of coenzymes such as NADH.
• Energy for anabolic processes is supplied by ATP.
Oxidative phosphorylation transfers energy from NADH to ATP.
![Page 25: Ch06 lecture pathways that harvest and store chemical energy](https://reader031.fdocuments.in/reader031/viewer/2022022415/5a64aa947f8b9a27568b88a3/html5/thumbnails/25.jpg)
Concept 6.1 ATP, Reduced Coenzymes, and Chemiosmosis Play Important Roles in Biological Energy Metabolism
Oxidative phosphorylation couples oxidation of NADH:
with production of ATP:
energyeHNADNADH +++→ −++ 2
ATPPADPenergy i →++
![Page 26: Ch06 lecture pathways that harvest and store chemical energy](https://reader031.fdocuments.in/reader031/viewer/2022022415/5a64aa947f8b9a27568b88a3/html5/thumbnails/26.jpg)
Concept 6.1 ATP, Reduced Coenzymes, and Chemiosmosis Play Important Roles in Biological Energy Metabolism
The coupling is chemiosmosis—diffusion of protons across a membrane, which drives the synthesis of ATP.
Chemiosmosis converts potential energy of a proton gradient across a membrane into the chemical energy in ATP.
![Page 27: Ch06 lecture pathways that harvest and store chemical energy](https://reader031.fdocuments.in/reader031/viewer/2022022415/5a64aa947f8b9a27568b88a3/html5/thumbnails/27.jpg)
Figure 6.5 A Chemiosmosis
![Page 28: Ch06 lecture pathways that harvest and store chemical energy](https://reader031.fdocuments.in/reader031/viewer/2022022415/5a64aa947f8b9a27568b88a3/html5/thumbnails/28.jpg)
Concept 6.1 ATP, Reduced Coenzymes, and Chemiosmosis Play Important Roles in Biological Energy Metabolism
ATP synthase—membrane protein with two subunits:
F0 is the H+ channel; potential energy of the proton gradient drives the H+ through.
F1 has active sites for ATP synthesis.
![Page 29: Ch06 lecture pathways that harvest and store chemical energy](https://reader031.fdocuments.in/reader031/viewer/2022022415/5a64aa947f8b9a27568b88a3/html5/thumbnails/29.jpg)
Figure 6.5 B Chemiosmosis
![Page 30: Ch06 lecture pathways that harvest and store chemical energy](https://reader031.fdocuments.in/reader031/viewer/2022022415/5a64aa947f8b9a27568b88a3/html5/thumbnails/30.jpg)
Concept 6.1 ATP, Reduced Coenzymes, and Chemiosmosis Play Important Roles in Biological Energy Metabolism
Chemiosmosis can be demonstrated experimentally.
A proton gradient can be introduced artificially in chloroplasts or mitochondria in a test tube.
ATP is synthesized if ATP synthase, ADP, and inorganic phosphate are present.
![Page 31: Ch06 lecture pathways that harvest and store chemical energy](https://reader031.fdocuments.in/reader031/viewer/2022022415/5a64aa947f8b9a27568b88a3/html5/thumbnails/31.jpg)
Figure 6.6 An Experiment Demonstrates the Chemiosmotic Mechanism
![Page 32: Ch06 lecture pathways that harvest and store chemical energy](https://reader031.fdocuments.in/reader031/viewer/2022022415/5a64aa947f8b9a27568b88a3/html5/thumbnails/32.jpg)
Concept 6.1 ATP, Reduced Coenzymes, and Chemiosmosis Play Important Roles in Biological Energy Metabolism
Cellular respiration is a major catabolic pathway. Glucose is oxidized:
Photosynthesis is a major anabolic pathway. Light energy is converted to chemical energy:
tecarbohydraOenergylightOHCO +→++ 222 666
energychemicalOHCOOtecarbohydra ++→+ 222 666
![Page 33: Ch06 lecture pathways that harvest and store chemical energy](https://reader031.fdocuments.in/reader031/viewer/2022022415/5a64aa947f8b9a27568b88a3/html5/thumbnails/33.jpg)
Figure 6.7 ATP, Reduced Coenzymes, and Metabolism
![Page 34: Ch06 lecture pathways that harvest and store chemical energy](https://reader031.fdocuments.in/reader031/viewer/2022022415/5a64aa947f8b9a27568b88a3/html5/thumbnails/34.jpg)
Concept 6.2 Carbohydrate Catabolism in the Presence of Oxygen Releases a Large Amount of Energy
Cellular Respiration
A lot of energy is released when reduced molecules with many C—C and C—H bonds are fully oxidized to CO2.
Oxidation occurs in a series of small steps in three pathways:
1. glycolysis
2. pyruvate oxidation
3. citric acid cycle
![Page 35: Ch06 lecture pathways that harvest and store chemical energy](https://reader031.fdocuments.in/reader031/viewer/2022022415/5a64aa947f8b9a27568b88a3/html5/thumbnails/35.jpg)
Figure 6.8 Energy Metabolism Occurs in Small Steps
![Page 36: Ch06 lecture pathways that harvest and store chemical energy](https://reader031.fdocuments.in/reader031/viewer/2022022415/5a64aa947f8b9a27568b88a3/html5/thumbnails/36.jpg)
Figure 6.9 Energy-Releasing Metabolic Pathways
![Page 37: Ch06 lecture pathways that harvest and store chemical energy](https://reader031.fdocuments.in/reader031/viewer/2022022415/5a64aa947f8b9a27568b88a3/html5/thumbnails/37.jpg)
Concept 6.2 Carbohydrate Catabolism in the Presence of Oxygen Releases a Large Amount of Energy
Glycolysis: ten reactions.
Takes place in the cytosol.
Final products:
2 molecules of pyruvate (pyruvic acid)
2 molecules of ATP
2 molecules of NADH
![Page 38: Ch06 lecture pathways that harvest and store chemical energy](https://reader031.fdocuments.in/reader031/viewer/2022022415/5a64aa947f8b9a27568b88a3/html5/thumbnails/38.jpg)
Figure 6.10 Glycolysis Converts Glucose into Pyruvate (Part 1)
![Page 39: Ch06 lecture pathways that harvest and store chemical energy](https://reader031.fdocuments.in/reader031/viewer/2022022415/5a64aa947f8b9a27568b88a3/html5/thumbnails/39.jpg)
Figure 6.10 Glycolysis Converts Glucose into Pyruvate (Part 2)
![Page 40: Ch06 lecture pathways that harvest and store chemical energy](https://reader031.fdocuments.in/reader031/viewer/2022022415/5a64aa947f8b9a27568b88a3/html5/thumbnails/40.jpg)
Figure 6.10 Glycolysis Converts Glucose into Pyruvate (Part 3)
![Page 41: Ch06 lecture pathways that harvest and store chemical energy](https://reader031.fdocuments.in/reader031/viewer/2022022415/5a64aa947f8b9a27568b88a3/html5/thumbnails/41.jpg)
Concept 6.2 Carbohydrate Catabolism in the Presence of Oxygen Releases a Large Amount of Energy
Examples of reaction types common in metabolic pathways:
Step 6: Oxidation–reduction
Step 7: Substrate-level phosphorylation
text art pg 107 here
![Page 42: Ch06 lecture pathways that harvest and store chemical energy](https://reader031.fdocuments.in/reader031/viewer/2022022415/5a64aa947f8b9a27568b88a3/html5/thumbnails/42.jpg)
Concept 6.2 Carbohydrate Catabolism in the Presence of Oxygen Releases a Large Amount of Energy
Pyruvate Oxidation:
Products: CO2 and acetate; acetate is then bound to coenzyme A (CoA)
![Page 43: Ch06 lecture pathways that harvest and store chemical energy](https://reader031.fdocuments.in/reader031/viewer/2022022415/5a64aa947f8b9a27568b88a3/html5/thumbnails/43.jpg)
Concept 6.2 Carbohydrate Catabolism in the Presence of Oxygen Releases a Large Amount of Energy
Citric Acid Cycle: 8 reactions, operates twice for every glucose molecule that enters glycolysis.
Starts with Acetyl CoA; acetyl group is oxidized to two CO2.
Oxaloacetate is regenerated in the last step.
![Page 44: Ch06 lecture pathways that harvest and store chemical energy](https://reader031.fdocuments.in/reader031/viewer/2022022415/5a64aa947f8b9a27568b88a3/html5/thumbnails/44.jpg)
Figure 6.11 The Citric Acid Cycle
![Page 45: Ch06 lecture pathways that harvest and store chemical energy](https://reader031.fdocuments.in/reader031/viewer/2022022415/5a64aa947f8b9a27568b88a3/html5/thumbnails/45.jpg)
Concept 6.2 Carbohydrate Catabolism in the Presence of Oxygen Releases a Large Amount of Energy
Final reaction of citric acid cycle:
![Page 46: Ch06 lecture pathways that harvest and store chemical energy](https://reader031.fdocuments.in/reader031/viewer/2022022415/5a64aa947f8b9a27568b88a3/html5/thumbnails/46.jpg)
Concept 6.2 Carbohydrate Catabolism in the Presence of Oxygen Releases a Large Amount of Energy
Electron transport/ATP Synthesis:
NADH is reoxidized to NAD+ and O2 is reduced to H2O in a series of steps.
Respiratory chain—series of redox carrier proteins embedded in the inner mitochondrial membrane.
Electron transport—electrons from the oxidation of NADH and FADH2 pass from one carrier to the next in the chain.
![Page 47: Ch06 lecture pathways that harvest and store chemical energy](https://reader031.fdocuments.in/reader031/viewer/2022022415/5a64aa947f8b9a27568b88a3/html5/thumbnails/47.jpg)
Figure 6.12 Electron Transport and ATP Synthesis in Mitochondria
![Page 48: Ch06 lecture pathways that harvest and store chemical energy](https://reader031.fdocuments.in/reader031/viewer/2022022415/5a64aa947f8b9a27568b88a3/html5/thumbnails/48.jpg)
Concept 6.2 Carbohydrate Catabolism in the Presence of Oxygen Releases a Large Amount of Energy
The oxidation reactions are exergonic; the energy is used to actively transport H+ ions out of the mitochondrial matrix, setting up a proton gradient.
ATP synthase in the membrane uses the H+ gradient to synthesize ATP by chemiosmosis.
![Page 49: Ch06 lecture pathways that harvest and store chemical energy](https://reader031.fdocuments.in/reader031/viewer/2022022415/5a64aa947f8b9a27568b88a3/html5/thumbnails/49.jpg)
Concept 6.2 Carbohydrate Catabolism in the Presence of Oxygen Releases a Large Amount of Energy
About 32 molecules of ATP are produced for each fully oxidized glucose.
The role of O2: most of the ATP produced is formed by oxidative phosphorylation, which is due to the reoxidation of NADH.
![Page 50: Ch06 lecture pathways that harvest and store chemical energy](https://reader031.fdocuments.in/reader031/viewer/2022022415/5a64aa947f8b9a27568b88a3/html5/thumbnails/50.jpg)
Concept 6.3 Carbohydrate Catabolism in the Absence of Oxygen Releases a Small Amount of Energy
Under anaerobic conditions, NADH is reoxidized by fermentation.
There are many different types of fermentation, but all operate to regenerate NAD+.
The overall yield of ATP is only two—the ATP made in glycolysis.
![Page 51: Ch06 lecture pathways that harvest and store chemical energy](https://reader031.fdocuments.in/reader031/viewer/2022022415/5a64aa947f8b9a27568b88a3/html5/thumbnails/51.jpg)
Concept 6.3 Carbohydrate Catabolism in the Absence of Oxygen Releases a Small Amount of Energy
Lactic acid fermentation:
End product is lactic acid (lactate).
NADH is used to reduce pyruvate to lactic acid, thus regenerating NAD+.
![Page 52: Ch06 lecture pathways that harvest and store chemical energy](https://reader031.fdocuments.in/reader031/viewer/2022022415/5a64aa947f8b9a27568b88a3/html5/thumbnails/52.jpg)
Figure 6.13 A Fermentation
![Page 53: Ch06 lecture pathways that harvest and store chemical energy](https://reader031.fdocuments.in/reader031/viewer/2022022415/5a64aa947f8b9a27568b88a3/html5/thumbnails/53.jpg)
Concept 6.3 Carbohydrate Catabolism in the Absence of Oxygen Releases a Small Amount of Energy
Alcoholic fermentation:
End product is ethyl alcohol (ethanol).
Pyruvate is converted to acetaldehyde, and CO2 is released. NADH is used to reduce acetaldehyde to ethanol, regenerating NAD+ for glycolysis.
![Page 54: Ch06 lecture pathways that harvest and store chemical energy](https://reader031.fdocuments.in/reader031/viewer/2022022415/5a64aa947f8b9a27568b88a3/html5/thumbnails/54.jpg)
Figure 6.13 B Fermentation
![Page 55: Ch06 lecture pathways that harvest and store chemical energy](https://reader031.fdocuments.in/reader031/viewer/2022022415/5a64aa947f8b9a27568b88a3/html5/thumbnails/55.jpg)
Concept 6.4 Catabolic and Anabolic Pathways Are Integrated
Metabolic pathways are linked.
Carbon skeletons (molecules with covalently linked carbon atoms) can enter catabolic or anabolic pathways.
![Page 56: Ch06 lecture pathways that harvest and store chemical energy](https://reader031.fdocuments.in/reader031/viewer/2022022415/5a64aa947f8b9a27568b88a3/html5/thumbnails/56.jpg)
Figure 6.14 Relationships among the Major Metabolic Pathways of the Cell
![Page 57: Ch06 lecture pathways that harvest and store chemical energy](https://reader031.fdocuments.in/reader031/viewer/2022022415/5a64aa947f8b9a27568b88a3/html5/thumbnails/57.jpg)
Concept 6.4 Catabolic and Anabolic Pathways Are Integrated
Catabolism:
Polysaccharides are hydrolyzed to glucose, which enter glycolysis.
Lipids break down to fatty acids and glycerol. Fatty acids can be converted to acetyl CoA.
Proteins are hydrolyzed to amino acids that can feed into glycolysis or the citric acid cycle.
![Page 58: Ch06 lecture pathways that harvest and store chemical energy](https://reader031.fdocuments.in/reader031/viewer/2022022415/5a64aa947f8b9a27568b88a3/html5/thumbnails/58.jpg)
Concept 6.4 Catabolic and Anabolic Pathways Are Integrated
Anabolism:
Many catabolic pathways can operate in reverse.
Gluconeogenesis—citric acid cycle and glycolysis intermediates can be reduced to form glucose.
Acetyl CoA can be used to form fatty acids.
Some citric acid intermediates can form nucleic acids.
![Page 59: Ch06 lecture pathways that harvest and store chemical energy](https://reader031.fdocuments.in/reader031/viewer/2022022415/5a64aa947f8b9a27568b88a3/html5/thumbnails/59.jpg)
Concept 6.4 Catabolic and Anabolic Pathways Are Integrated
Amounts of different molecules are maintained at fairly constant levels—the metabolic pools.
This is accomplished by regulation of enzymes—allosteric regulation, feedback inhibition.
Enzymes can also be regulated by altering the transcription of genes that encode the enzymes.
![Page 60: Ch06 lecture pathways that harvest and store chemical energy](https://reader031.fdocuments.in/reader031/viewer/2022022415/5a64aa947f8b9a27568b88a3/html5/thumbnails/60.jpg)
Concept 6.5 During Photosynthesis, Light Energy Is Converted to Chemical Energy
Photosynthesis involves two pathways:
Light reactions convert light energy into chemical energy (in ATP and the reduced electron carrier NADPH).
Carbon-fixation reactions use the ATP and NADPH, along with CO2, to produce carbohydrates.
![Page 61: Ch06 lecture pathways that harvest and store chemical energy](https://reader031.fdocuments.in/reader031/viewer/2022022415/5a64aa947f8b9a27568b88a3/html5/thumbnails/61.jpg)
Figure 6.15 An Overview of Photosynthesis
![Page 62: Ch06 lecture pathways that harvest and store chemical energy](https://reader031.fdocuments.in/reader031/viewer/2022022415/5a64aa947f8b9a27568b88a3/html5/thumbnails/62.jpg)
Concept 6.5 During Photosynthesis, Light Energy Is Converted to Chemical Energy
Light is a form of electromagnetic radiation, which travels as a wave but also behaves as particles (photons).
Photons can be absorbed by a molecule, adding energy to the molecule—it moves to an excited state.
![Page 63: Ch06 lecture pathways that harvest and store chemical energy](https://reader031.fdocuments.in/reader031/viewer/2022022415/5a64aa947f8b9a27568b88a3/html5/thumbnails/63.jpg)
Figure 6.16 The Electromagnetic Spectrum
![Page 64: Ch06 lecture pathways that harvest and store chemical energy](https://reader031.fdocuments.in/reader031/viewer/2022022415/5a64aa947f8b9a27568b88a3/html5/thumbnails/64.jpg)
Concept 6.5 During Photosynthesis, Light Energy Is Converted to Chemical Energy
Pigments: molecules that absorb wavelengths in the visible spectrum.
Chlorophyll absorbs blue and red light; the remaining light is mostly green.
Absorption spectrum—plot of light energy absorbed against wavelength.
Action spectrum—plot of the biological activity of an organism against the wavelengths to which it is exposed
![Page 65: Ch06 lecture pathways that harvest and store chemical energy](https://reader031.fdocuments.in/reader031/viewer/2022022415/5a64aa947f8b9a27568b88a3/html5/thumbnails/65.jpg)
Figure 6.17 Absorption and Action Spectra
![Page 66: Ch06 lecture pathways that harvest and store chemical energy](https://reader031.fdocuments.in/reader031/viewer/2022022415/5a64aa947f8b9a27568b88a3/html5/thumbnails/66.jpg)
Concept 6.5 During Photosynthesis, Light Energy Is Converted to Chemical Energy
In plants, two chlorophylls absorb light energy chlorophyll a and chlorophyll b.
Accessory pigments—absorb wavelengths between red and blue and transfer some of that energy to the chlorophylls.
![Page 67: Ch06 lecture pathways that harvest and store chemical energy](https://reader031.fdocuments.in/reader031/viewer/2022022415/5a64aa947f8b9a27568b88a3/html5/thumbnails/67.jpg)
Figure 6.18 The Molecular Structure of Chlorophyll (Part 1)
![Page 68: Ch06 lecture pathways that harvest and store chemical energy](https://reader031.fdocuments.in/reader031/viewer/2022022415/5a64aa947f8b9a27568b88a3/html5/thumbnails/68.jpg)
Figure 6.18 The Molecular Structure of Chlorophyll (Part 2)
![Page 69: Ch06 lecture pathways that harvest and store chemical energy](https://reader031.fdocuments.in/reader031/viewer/2022022415/5a64aa947f8b9a27568b88a3/html5/thumbnails/69.jpg)
Concept 6.5 During Photosynthesis, Light Energy Is Converted to Chemical Energy
The pigments are arranged into light-harvesting complexes, or antenna systems.
A photosystem spans the thylakoid membrane in the chloroplast; it consists of antenna systems and a reaction center.
![Page 70: Ch06 lecture pathways that harvest and store chemical energy](https://reader031.fdocuments.in/reader031/viewer/2022022415/5a64aa947f8b9a27568b88a3/html5/thumbnails/70.jpg)
Concept 6.5 During Photosynthesis, Light Energy Is Converted to Chemical Energy
When chlorophyll (Chl) absorbs light, it enters an excited state (Chl*), then rapidly returns to ground state, releasing an excited electron.
Chl* gives the excited electron to an acceptor and becomes oxidized to Chl+.
The acceptor molecule is reduced.
−+ +→+ acceptorChlacceptorChl *
![Page 71: Ch06 lecture pathways that harvest and store chemical energy](https://reader031.fdocuments.in/reader031/viewer/2022022415/5a64aa947f8b9a27568b88a3/html5/thumbnails/71.jpg)
Concept 6.5 During Photosynthesis, Light Energy Is Converted to Chemical Energy
The electron acceptor is first in an electron transport system in the thylakoid membrane.
Final electron acceptor is NADP+, which gets reduced:
ATP is produced chemiosmotically during electron transport (photophosphorylation).
NADPHeHNADP →++ −++ 2
![Page 72: Ch06 lecture pathways that harvest and store chemical energy](https://reader031.fdocuments.in/reader031/viewer/2022022415/5a64aa947f8b9a27568b88a3/html5/thumbnails/72.jpg)
Figure 6.19 Noncyclic Electron Transport Uses Two Photosystems
![Page 73: Ch06 lecture pathways that harvest and store chemical energy](https://reader031.fdocuments.in/reader031/viewer/2022022415/5a64aa947f8b9a27568b88a3/html5/thumbnails/73.jpg)
Concept 6.5 During Photosynthesis, Light Energy Is Converted to Chemical Energy
Two photosystems:
• Photosystem I absorbs light energy at 700 nm, passes an excited electron to NADP+, reducing it to NADPH.
• Photosystem II absorbs light energy at 680 nm, produces ATP, and oxidizes water molecules.
![Page 74: Ch06 lecture pathways that harvest and store chemical energy](https://reader031.fdocuments.in/reader031/viewer/2022022415/5a64aa947f8b9a27568b88a3/html5/thumbnails/74.jpg)
Concept 6.5 During Photosynthesis, Light Energy Is Converted to Chemical Energy
Photosystem II
When Chl* gives up an electron, it is unstable and grabs an electron from another molecule, H2O, which splits the H—O—H bonds.
221
2 2*2 OHChlOHChl ++→+ +
![Page 75: Ch06 lecture pathways that harvest and store chemical energy](https://reader031.fdocuments.in/reader031/viewer/2022022415/5a64aa947f8b9a27568b88a3/html5/thumbnails/75.jpg)
Concept 6.5 During Photosynthesis, Light Energy Is Converted to Chemical Energy
Photosystem I
When Chl* gives up an electron, it grabs another electron from the end of the transport system of Photosystem II. This electron ends up reducing NADP+ to NADPH.
![Page 76: Ch06 lecture pathways that harvest and store chemical energy](https://reader031.fdocuments.in/reader031/viewer/2022022415/5a64aa947f8b9a27568b88a3/html5/thumbnails/76.jpg)
Concept 6.5 During Photosynthesis, Light Energy Is Converted to Chemical Energy
ATP is needed for carbon-fixation pathways.
Cyclic electron transport uses only photosystem I and produces ATP; an electron is passed from an excited chlorophyll and recycles back to the same chlorophyll.
![Page 77: Ch06 lecture pathways that harvest and store chemical energy](https://reader031.fdocuments.in/reader031/viewer/2022022415/5a64aa947f8b9a27568b88a3/html5/thumbnails/77.jpg)
Figure 6.20 Cyclic Electron Transport Traps Light Energy as ATP
![Page 78: Ch06 lecture pathways that harvest and store chemical energy](https://reader031.fdocuments.in/reader031/viewer/2022022415/5a64aa947f8b9a27568b88a3/html5/thumbnails/78.jpg)
Concept 6.6 Photosynthetic Organisms Use Chemical Energy to Convert CO2 to Carbohydrates
The Calvin cycle: CO2 fixation. It occurs in the stroma of the chloroplast.
Each reaction is catalyzed by a specific enzyme.
![Page 79: Ch06 lecture pathways that harvest and store chemical energy](https://reader031.fdocuments.in/reader031/viewer/2022022415/5a64aa947f8b9a27568b88a3/html5/thumbnails/79.jpg)
Figure 6.21 The Calvin Cycle
![Page 80: Ch06 lecture pathways that harvest and store chemical energy](https://reader031.fdocuments.in/reader031/viewer/2022022415/5a64aa947f8b9a27568b88a3/html5/thumbnails/80.jpg)
Concept 6.6 Photosynthetic Organisms Use Chemical Energy to Convert CO2 to Carbohydrates
1. Fixation of CO2:
CO2 is added to ribulose 1,5-bisphosphate (RuBP).
Ribulose bisphosphate carboxylase/oxygenase (rubisco) catalyzes the reaction.
A 6-carbon molecule results, which quickly breaks into two 3-carbon molecules: 3-phosphoglycerate (3PG).
![Page 81: Ch06 lecture pathways that harvest and store chemical energy](https://reader031.fdocuments.in/reader031/viewer/2022022415/5a64aa947f8b9a27568b88a3/html5/thumbnails/81.jpg)
Figure 6.22 RuBP Is the Carbon Dioxide Acceptor
![Page 82: Ch06 lecture pathways that harvest and store chemical energy](https://reader031.fdocuments.in/reader031/viewer/2022022415/5a64aa947f8b9a27568b88a3/html5/thumbnails/82.jpg)
Concept 6.6 Photosynthetic Organisms Use Chemical Energy to Convert CO2 to Carbohydrates
2. 3PG is reduced to form glyceraldehyde 3-phosphate (G3P).
![Page 83: Ch06 lecture pathways that harvest and store chemical energy](https://reader031.fdocuments.in/reader031/viewer/2022022415/5a64aa947f8b9a27568b88a3/html5/thumbnails/83.jpg)
Concept 6.6 Photosynthetic Organisms Use Chemical Energy to Convert CO2 to Carbohydrates
3. The CO2 acceptor, RuBP, is regenerated from G3P.
Some of the extra G3P is exported to the cytosol and is converted to hexoses (glucose and fructose).
When glucose accumulates, it is linked to form starch, a storage carbohydrate.
![Page 84: Ch06 lecture pathways that harvest and store chemical energy](https://reader031.fdocuments.in/reader031/viewer/2022022415/5a64aa947f8b9a27568b88a3/html5/thumbnails/84.jpg)
Concept 6.6 Photosynthetic Organisms Use Chemical Energy to Convert CO2 to Carbohydrates
The C—H bonds generated by the Calvin cycle provide almost all the energy for life on Earth.
Photosynthetic organisms (autotrophs) use most of this energy to support their own growth and reproduction.
Heterotrophs cannot photosynthesize and depend on autotrophs for chemical energy.
![Page 85: Ch06 lecture pathways that harvest and store chemical energy](https://reader031.fdocuments.in/reader031/viewer/2022022415/5a64aa947f8b9a27568b88a3/html5/thumbnails/85.jpg)
Answer to Opening Question
Pasteur’s findings:
Catabolism of the beet sugar is a cellular process, so living yeast cells must be present.
With air (O2) yeasts used aerobic metabolism to fully oxidize glucose to CO2.
Without air, yeasts used alcoholic fermentation, producing ethanol, less CO2, and less energy (slower growth).
![Page 86: Ch06 lecture pathways that harvest and store chemical energy](https://reader031.fdocuments.in/reader031/viewer/2022022415/5a64aa947f8b9a27568b88a3/html5/thumbnails/86.jpg)
Figure 6.23 Products of Glucose Metabolism