How Cells Acquire Energy

1. How Cells Acquire Energy Chapter 7

2. Carbon and Energy Sources • Photoautotrophs • Carbon source is carbon dioxide • Energy source is sunlight • Heterotrophs • Get carbon and energy by eating autotrophs or one another

3. Photoautotrophs • Capture sunlight energy and use it to carry out photosynthesis • Plants • Some bacteria • Many protistans

4. T.E. Englemann’s Experiment Background • Certain bacterial cells will move toward places where oxygen concentration is high • Photosynthesis produces oxygen

5. T.E. Englemann’s Experiment Figure 7.1Page 111

6. Photosynthesis Energy-storing pathway Releases oxygen Requires carbon dioxide Aerobic Respiration Energy-releasing pathway Requires oxygen Releases carbon dioxide Linked Processes

7. Chloroplast Structure two outer membranes stroma inner membrane system (thylakoids connected by channels) Figure 7.3d, Page 116

8. Photosynthesis Equation LIGHT ENERGY 12H2O + 6CO2 6O2 + C2H12O6 + 6H2O Water Carbon Dioxide Oxygen Glucose Water In-text figurePage 115

9. Reactants 12H2O 6CO2 Products 6O2 C6H12O6 6H2O Where Atoms End Up In-text figurePage 116

10. Two Stages of Photosynthesis sunlight water uptake carbon dioxide uptake ATP ADP + Pi LIGHT-DEPENDENT REACTIONS LIGHT-INDEPENDENT REACTIONS NADPH NADP+ glucose P oxygen release new water In-text figurePage 117

11. Electromagnetic Spectrum Shortest Gamma rays wavelength X-rays UV radiation Visible light Infrared radiation Microwaves Longest Radio waves wavelength

12. Visible Light • Wavelengths humans perceive as different colors • Violet (380 nm) to red (750 nm) • Longer wavelengths, lower energy Figure 7.5aPage 118

13. Photons • Packets of light energy • Each type of photon has fixed amount of energy • Photons having most energy travel as shortest wavelength (blue-violet light)

14. Pigments • Color you see is the wavelengths not absorbed • Light-catching part of molecule often has alternating single and double bonds • These bonds contain electrons that are capable of being moved to higher energy levels by absorbing light

15. Variety of Pigments Chlorophylls a and b Carotenoids Anthocyanins Phycobilins

16. Chlorophylls Main pigments in most photoautotrophs chlorophyll a Wavelength absorption (%) chlorophyll b Wavelength (nanometers) Figure 7.6a Page 119 Figure 7.7Page 120

17. Accessory Pigments Carotenoids, Phycobilins, Anthocyanins beta-carotene phycoerythrin (a phycobilin) percent of wavelengths absorbed wavelengths (nanometers)

18. Pigments in Photosynthesis • Bacteria • Pigments in plasma membranes • Plants • Pigments and proteins organized into photosystems that are embedded in thylakoid membrane system

19. Arrangement of Photosystems water-splitting complex thylakoid compartment H2O 2H + 1/2O2 P680 P700 acceptor acceptor pool of electron carriers PHOTOSYSTEM II stroma PHOTOSYSTEM I Figure 7.10Page 121

20. Light-Dependent Reactions • Pigments absorb light energy, give up e-, which enter electron transfer chains • Water molecules split, ATP and NADH form, and oxygen is released • Pigments that gave up electrons get replacements

21. Photosystem Function: Harvester Pigments • Most pigments in photosystem are harvester pigments • When excited by light energy, these pigments transfer energy to adjacent pigment molecules • Each transfer involves energy loss

22. Photosystem Function: Reaction Center • Energy is reduced to level that can be captured by molecule of chlorophyll a • This molecule (P700 or P680) is the reaction center of a photosystem • Reaction center accepts energy and donates electron to acceptor molecule

23. Pigments in a Photosystem reaction center Figure 7.11Page 122

24. Electron Transfer Chain • Adjacent to photosystem • Acceptor molecule donates electrons from reaction center • As electrons pass along chain, energy they release is used to produce ATP

25. Cyclic Electron Flow • Electrons • are donated by P700 in photosystem I to acceptor molecule • flow through electron transfer chain and back to P700 • Electron flow drives ATP formation • No NADPH is formed

26. Cyclic Electron Flow e– electron acceptor Electron flow through transfer chain sets up conditions for ATP formation at other membrane sites. electron transfer chain e– e– ATP e– Figure 7.12Page 122

27. Noncyclic Electron Flow • Two-step pathway for light absorption and electron excitation • Uses two photosystems: type I and type II • Produces ATP and NADPH • Involves photolysis - splitting of water

28. Machinery of Noncyclic Electron Flow H2O second electron transfer chain photolysis e– e– ATP SYNTHASE first electron transfer chain NADPH NADP+ ATP ADP + Pi PHOTOSYSTEM II PHOTOSYSTEM I Figure 7.13aPage 123

29. Energy Changes second transfer chain e– NADPH e– first transfer chain Potential to transfer energy (volts) e– e– (Photosystem I) (Photosystem II) 1/2O2 + 2H+ H2O Figure 7.13bPage 123

30. Chemiosmotic Model of ATP Formation • Electrical and H+ concentration gradients are created between thylakoid compartment and stroma • H+ flows down gradients into stroma through ATP synthesis • Flow of ions drives formation of ATP

31. Chemiosmotic Model for ATP Formation H+ is shunted across membrane by some components of the first electron transfer chain Gradients propel H+ through ATP synthases; ATP forms by phosphate-group transfer Photolysis in the thylakoid compartment splits water H2O e– acceptor ATP SYNTHASE ATP ADP + Pi PHOTOSYSTEM II Figure 7.15Page 124

32. Light-Independent Reactions • Synthesis part of photosynthesis • Can proceed in the dark • Take place in the stroma • Calvin-Benson cycle

33. Overall reactants Carbon dioxide ATP NADPH Overall products Glucose ADP NADP+ Calvin-Benson Cycle Reaction pathway is cyclic and RuBP (ribulose bisphosphate) is regenerated

34. 6 CO2 (from the air) Calvin- Benson Cycle CARBON FIXATION 6 6 RuBP unstable intermediate 12 PGA 6 ADP 12 ATP 6 ATP 12 NADPH 4 Pi 12 ADP 12 Pi 12 NADP+ 10 PGAL 12 PGAL 2 PGAL Pi P Figure 7.16Page 125 glucose

35. The C3 Pathway • In Calvin-Benson cycle, the first stable intermediate is a three-carbon PGA • Because the first intermediate has three carbons, the pathway is called the C3 pathway

36. Photorespiration in C3 Plants • On hot, dry days stomata close • Inside leaf • Oxygen levels rise • Carbon dioxide levels drop • Rubisco attaches RuBP to oxygen instead of carbon dioxide • Only one PGAL forms instead of two

37. C4 Plants • Carbon dioxide is fixed twice • In mesophyll cells, carbon dioxide is fixed to form four-carbon oxaloacetate • Oxaloacetate is transferred to bundle-sheath cells • Carbon dioxide is released and fixed again in Calvin-Benson cycle

38. CAM Plants • Carbon is fixed twice (in same cells) • Night • Carbon dioxide is fixed to form organic acids • Day • Carbon dioxide is released and fixed in Calvin-Benson cycle

39. light LIGHT-DEPENDENT REACTIONS 6O2 12H2O ATP NADP+ NADPH ADP + Pi PGA CALVIN-BENSON CYCLE PGAL 6H2O 6CO2 RuBP P C6H12O6 (phosphorylated glucose) end product (e.g., sucrose, starch, cellulose) Summary of Photosynthesis LIGHT-INDEPENDENT REACTIONS Figure 7.21Page 129

40. Satellite Images Show Photosynthesis Atlantic Ocean  Photosynthetic activity in spring Figure 7.20Page 128