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Key Themes Energy acquisition in photosynthesis: from sunlight to ATP & sugar production Lecture 8: Photosynthesis.

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Presentation on theme: "Key Themes Energy acquisition in photosynthesis: from sunlight to ATP & sugar production Lecture 8: Photosynthesis."— Presentation transcript:

1 Key Themes Energy acquisition in photosynthesis: from sunlight to ATP & sugar production Lecture 8: Photosynthesis

2 Yesterday’s Exit Ticket Glucose Process: Gycolysis Location: Cytosol # ATPs: Citric Acid Cycle Location: Mitochon. Matrix Products Released: CO2 Location: Mitoch. Inner Membrane Products Released: H20 # ATPs: Oxidative Phosphorylation 2 NADH NADH + FADH2 Pyruvate

3 Time to Photosynthesize!

4 Fig. 1.5 Sunlight Ecosystem Heat Cycling of chemical nutrients Producers (plants and other photosynthetic organisms) Chemical energy Consumers (such as animals) Photosynthesis Sun = ultimate energy source

5 Mint kept mouse alive, but not in the basement… "the injury which is continually done to the atmosphere by the respiration of such a large number of animals... is, in part at least, repaired by the vegetable creation" Joseph Priestly,

6 (a) Plants (c) Unicellular protist 10 µm 1.5 µm 40 µm (d) Cyanobacteria (e) Purple sulfur bacteria (b) Multicellular alga Photosynthetic Organisms Fig. 10.2

7 What is the goal of photosynthesis? Light  Chemical Energy Form C-H bonds for energy storage Harness the sun’s energy to do so Sugar [CH2O] + O2 Light + CO2 + H20 (energy) O2 + some ATPsugarsH2O H+ & e- CO2 Light dermalinstitute.com; gaia-health.com

8 O2 + some ATPH2O H+ & e- Light Step 1: Light-Dependent Reactions What is the goal of photosynthesis?

9 O2 + some ATPsugarsH2O H+ & e- CO2 Light Step 2: Light-Independent Reactions (Calvin Cycle) What is the goal of photosynthesis?

10 Overview of Photosynthesis solar energy Solar energy drives production of energy-rich ATP & NADPH ATP & NADPH drive conversion of CO2 to energy-rich sugar Fig O2 is a waste product O2

11 Because ATP is too unstable to serve as a storage form of energy, C-H bonds in sugars are instead used for energy storage. Fig. 8.8 ATP: Energy carrier

12 solar energy Fig Step 1: Light-Dependent Reactions Occur in: thylakoid membranes of chloroplasts Start with: H2O, NADP+, ADP, Pi Produce: NADPH, ATP, and O2 O2O2

13 Leaf cross section Vein Stomata CO2 O2 Mesophyll cell 5 µm Thylak oid space Thylak oid Gran um Stro ma 1 µm Fig Plant photosynthesis occurs in chloroplasts Chloroplast

14 Leaf cross section Vein Stomata CO2 O2 Chloroplast 5 µm Thylakoid space Thylakoid Granum Stroma 1 µm Fig Plant photosynthesis occurs in chloroplasts Inner membranes (thylakoids): Light reactions (light collection by chlorophyll & electron transport) Fluid space (stroma): Conversion of CO2 to sugars in Calvin cycle

15 Photosystems made up of chlorophylls absorb sunlight Photosystems use light energy to propel energized electrons into the photosynthetic electron transport chain Fig

16 e- Most chlorophylls absorb light energy & pass it on to a special chlorophyll that gives up an electron. Fig H2 O H+ + O2 water-splitting enzyme e-e- This special chlorophyll gets an electron back from a water molecule, leaving behind H+ (protons*) and O2. *H = 1 proton + 1 electron

17 e- The energized electron is propelled through the electron transport chain. Fig H2 O H+ + O2 e- Fig

18 Light ADP + i H+H+ ATP P synthase To Calvin Cycle STROMA (low H+ concentration) Thylakoid membrane THYLAKOID SPACE (high H+ concentration) STROMA (low H+ concentration) Photosystem II Photosystem I 4 H+ Light NADP+ + H+ NADPH +2 H+ H2 O O2 e–e– e–e– 1/ NADP+ reductase Now, let’s look at this whole process within the context of the thylakoid membranes Fig

19 Here’s an animation of photosynthetic electron transport. “When sunlight is absorbed into a plant, it triggers a chain reaction of electrons, which move from one molecule to the next… The Berkeley researchers borrowed this [chain reaction] for their artificial forest, but instead of relying on the pigment in chloroplast to trigger electron movement they used semiconductors.”

20 What is the goal of photosynthesis? O2 + some ATPsugarsH2O H+ & e- (NADPH) CO 2 Light dermalinstitute.com; gaia-health.com Original electron donor in photosynthesis Electron acceptors from ETC: NADP+ Electron donors for Calvin cycle Electron acceptor from Calvin cycle

21 Protons are pumped into the inner thylakoid space and ATP is formed in the stroma Light ADP + i H+H+ ATP P synthase To Calvin Cycle STROMA (low H+ concentration) Thylakoid membrane THYLAKOID SPACE (high H+ concentration) STROMA (low H+ concentration) Photosystem II Photosystem I 4 H+ Light NADP+ + H+ NADPH +2 H+ H2 O O2 e–e– e–e– 1/ NADP+ reductase Fig

22 + P i H+ ADP ATP Fig Ligh t AD P i H+H+ AT P P synth ase STROMA (low H+ concentration) Thylako id membr ane THYLAKOID SPACE (high H+ concentration) STROMA (low H+ concentration) Photosystem II Photosyst em I 4 H+ Ligh t +2 H+ H2 O O2O2 e–e– e–e– 1/ 2 NADP+ reduct ase P i Inner thylakoid space stroma The ATP synthase “turbine”

23 Fig Same principle used for ATP formation in chloroplasts & mitochondria Fig.8.7

24 O2 + some ATPsugarsH2O H+ & e- CO 2 Light Step 1: Light-Dependent Reactions NADP+ NADPH What is the goal of photosynthesis?

25 O2 + some ATPsugarsH2O CO 2 Light Step 2: Light-Independent Reactions (Calvin Cycle) H+ & e- NADP + NADPH What is the goal of photosynthesis?

26 solar energy Fig Step 2: Calvin Cycle Occurs in: stroma (liquid space inside chloroplasts) Starts with: CO2, NADPH, ATP Produces: Sugar, NADP+, ADP, Pi O2O2

27 Light Reactions: Light collection & electron transport CO2 NADP + ADP P i + RuBP 3-Phosphoglycerate Calvi n Cycl e G3P ATP NADPH Starch (storage) Sucrose (export) Chloroplas t Light H2O O2 Fig O2O2

28 Light Reactions: Light collection & electron transport CO2 NADP + ADP P i + RuBP 3-Phosphoglycerate Calvi n Cycl e G3P ATP NADPH Starch (storage) Sucrose (export) Chloroplas t Light H2O O2 Fig Rubisco: combines RuBP with CO2 to form 3-PG

29 Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings. In this diagram of the Calvin cycle, compound X is the CO2 acceptor. If CO2 is cut off, then A.X and 3PG will both increase. B.X will increase, 3PG decrease. C.X will decrease, 3PG increase. D.X and 3PG will both decrease.

30 What is the goal of photosynthesis? Light  Chemical Energy Form C-H bonds for energy storage Harness the sun’s energy to do so Sugar [CH2O] + O2 Light + CO2 + H20 (energy) O2 + some ATPsugarsH2O H+ & e- CO 2 Light dermalinstitute.com; gaia-health.com

31 5 min break Wtfcontent.com

32 _k&feature=fvwrel Hank’s Crash Course in Photosynthesis

33 Plant adaptations to their environments Flickriver.com

34 What does a plant need? Light, CO2, H2O, (nutrients) Travelsfy.com

35 Light Reactions: Light collection & electron transport CO2 NADP + ADP P i + RuBP 3-Phosphoglycerate Calvi n Cycl e G3P ATP NADPH Starch (storage) Sucrose (export) Chloroplast Light H2O O2 Fig Acclimation to sun vs. shade? Sun Calvin Cycle enzymes Shade When LIGHT varies: Light, CO2, H2O, (nutrients)

36 When H2O varies: Light, CO2, H2O, (nutrients) Travelsfy.com Stomate Stomata CO2 H2O O2

37 When H2O varies: Light, CO2, H2O, (nutrients) Travelsfy.com; minnestota.publicradio.org; mccullagh.org CO2 H2O O2 In wet environments Stomata can stay wide open CO2 is relatively unlimited in plant cells In semi-arid environments Stomata are kept ajar to reduce water loss CO2 is acquired more slowly In dry environments Stomata are kept closed in the heat of the day Stomata are opened at night to acquire CO2

38 When H2O varies: Light, CO2, H2O, (nutrients) Travelsfy.com; minnestota.publicradio.org; mccullagh.org In wet environments Stomata can stay wide open CO2 is relatively unlimited in plant cells In semi-arid environments Stomata are kept ajar to reduce water loss CO2 is acquired more slowly In dry environments Stomata are kept closed in the heat of the day Stomata are opened at night to acquire CO2 “C3” Most plants More “C4” plants Many grasses More “CAM” plants Cacti, many other desert succulents

39 Most plants (C3 plants) use only Calvin cycle: First product has 3 carbons (phosphoglycerate). Light Reactions: Light collection & electron transport CO2 NADP + AD P P i + RuB P 3- Phosphoglycerat e Calv in Cycl e G3 P AT P NADP H Starch (storag e) Sucrose (export) Chloropla st Ligh t H2O O2 Fig

40 Most plants (C3 plants) use only Calvin cycle: First product has 3 carbons (phosphoglycerate). The C4 pathway CO2 PEP carboxylase Oxaloacetate (4C) Malate (4C) PEP (3C) AD P AT P Pyruvate (3C) CO2 Calvi n Cycle Suga r Vascula r tissue Fig Some plants (C4 plants) use an additional CO2 fixation cycle before the Calvin cycle: The enzyme PEP carboxylase “fixes” CO2 into a sugar with 4 carbons Once enough new CO2 has been stored in the 4-C sugar, it moves into the Calvin Cycle Leaf surface Inside of leaf

41 C4 plants: This process allows the Calvin Cycle to run smoothly despite low CO2 conditions The C4 pathway Mesophy ll cell CO2 PEP carboxylase Oxaloacetate (4C) Malate (4C) PEP (3C) AD P AT P Pyruvate (3C) CO2 Bundle - sheath cell Calvi n Cycle Suga r Vascula r tissue Fig

42 CAM plants: Take the C4 process one step further The C4 pathway Mesophy ll cell CO2 PEP carboxylase Oxaloacetate (4C) Malate (4C) PEP (3C) AD P AT P Pyruvate (3C) CO2 Bundle - sheath cell Calvi n Cycle Suga r Vascula r tissue CO2 is collected and converted to 4-carbon sugar at night Sugar is stored in vacuoles In the morning, stomata close and malic acid is broken down to enter the Calvin Cycle

43 Light Reactions: Light harvesting and photosynthetic electron transport CO2 NADP + ADP P i + RuB P 3-Phosphoglycerate Cal vin Cyc le G3P ATP NADPH Starc h (stora ge) Sucrose (export) Chloroplast Ligh t H2O O2 Fig

44 Why isn’t every plant a C4 plant? Advantage of C3 plants C3 plants need less energy since they don’t run two cycles Advantage in less sunny, moist, cool, CO2-rich climates. Typically more cold-tolerant. Mountainphotographer.com

45 Since ATP is too unstable, C-H bonds in sugars are used for energy storage.

46 In both mitochondria and chloroplasts: Carbon conversion cycles in fluid space: Calvin cycle vs. citric acid cycle (Krebs cycle) (CO2  sugar)(sugar  CO2) Electron transport chain & ATP synthase on inner membranes (thylakoid or mitochondrial)

47 Light Reactions: Light collection & electron transport CO2 NAD P+ AD P P i + RuB P 3- Phosphoglycerat e Calv in Cycl e G3 P AT P NADP H Starch (storag e) Sucrose (export) Chloropla st Ligh t H2O O2 Fig Photosynthesis Carbon source: Carbon product: CO2 Sugar (C-H bonds) Ultimate energy source: Final energy-rich product: Sunlight Sugar (C-H bonds) H (electron + H+) source: Water (H-O-H)

48 Electron transport and ATP synthase Mitochondrion ATP Electrons carried off by NADH & FADH2 Citric acid cycle ATP GlucosePyruvate Glycolysis Electrons carried off by NADH Fig. 9.6 Some ATP Lots of Cytosol Respiration Carbon source: Carbon product: Organic molecules with C-H bonds CO2 Final energy-rich product:ATP Energy source: C-H bonds H (electron + H+) source: C-H bonds

49 Fig Same principle used for ATP formation in mitochondria & chloroplasts Fig.8.7

50 Fig Citric acid cycleCalvin cycle

51 In both mitochondria and chloroplasts: Carbon conversion cycles in fluid space Electron transport chain & ATP synthase on inner membranes

52 Today’s Exit Ticket Process: Location: CO2 + H2O O2 Fig Process: Location:


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