How Cells Acquire Energy

1. How Cells Acquire Energy Chapter 7

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

3. Fig. 10-2 (a) Plants (c) Unicellular protist 10 µm (e) Purple sulfur bacteria 1.5 µm (b) Multicellular alga (d) Cyanobacteria 40 µm

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

5. Fig. 10-3 Leaf cross section Vein Mesophyll Stomata CO2 O2 Chloroplast Mesophyll cell Outer membrane Thylakoid Intermembrane space 5 µm Stroma Thylakoid space Granum Inner membrane 1 µm

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

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

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

9. 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

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

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

12. 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)

13. 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

14. Fig. 10-7 Light Reflected light Chloroplast Absorbed light Granum Transmitted light

15. Variety of Pigments Chlorophylls a and b Carotenoids Xanthophils

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. Fig. 10-12 STROMA Photosystem Photon Primary electron acceptor Light-harvesting complexes Reaction-center complex e– Thylakoid membrane Pigment molecules Special pair of chlorophyll a molecules Transfer of energy THYLAKOID SPACE (INTERIOR OF THYLAKOID)

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. Fig. 10-15 Primary acceptor Primary acceptor Fd Fd NADP+ + H+ Pq NADP+ reductase Cytochrome complex NADPH Pc Photosystem I ATP Photosystem II

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. Fig. 10-13-5 Electron transport chain Primary acceptor Primary acceptor 4 7 Electron transport chain Fd e– Pq 2 e– 8 e– e– NADP+ + H+ H2O Cytochrome complex 2 H+ NADP+ reductase + 3 NADPH O2 1/2 Pc e– e– P700 5 P680 Light Light 1 6 6 ATP Pigment molecules Photosystem I (PS I) Photosystem II (PS II)

30. 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

31. 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

32. 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

33. Fig. 10-17 STROMA (low H+ concentration) Cytochrome complex Photosystem I Photosystem II Light 4 H+ NADP+ reductase Light 3 Fd NADP+ + H+ NADPH Pq Pc e– 2 e– H2O O2 1/2 1 THYLAKOID SPACE (high H+ concentration) 4 H+ +2 H+ To Calvin Cycle Thylakoid membrane ATP synthase STROMA (low H+ concentration) ADP + ATP P i H+

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

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

36. 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

37. 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

38. 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

39. C3 and C4 plant structure compared

40. 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

41. 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

42. Fig. 10-5-4 CO2 H2O Light NADP+ ADP + P i Calvin Cycle Light Reactions ATP NADPH Chloroplast [CH2O] (sugar) O2

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