Download presentation
Presentation is loading. Please wait.
1
8 Photosynthesis
2
Concept 8.3: The Calvin cycle uses the chemical energy of ATP and NADPH to reduce CO2 to sugar
The Calvin cycle, like the citric acid cycle, regenerates its starting material after molecules enter and leave the cycle Unlike the citric acid cycle, the Calvin cycle is anabolic It builds sugar from smaller molecules by using ATP and the reducing power of electrons carried by NADPH © 2016 Pearson Education, Inc. 2
3
The Calvin cycle has three phases
Carbon enters the cycle as CO2 and leaves as a sugar named glyceraldehyde 3-phospate (G3P) For net synthesis of one G3P, the cycle must take place three times, fixing three molecules of CO2 The Calvin cycle has three phases Carbon fixation Reduction Regeneration of the CO2 acceptor © 2016 Pearson Education, Inc. 3
4
CALVIN CYCLE LIGHT REACTIONS
Figure 8.UN03 H2O CO2 Light NADP+ ADP CALVIN CYCLE LIGHT REACTIONS ATP Figure 8.UN03 In-text figure, Calvin cycle schematic, p. 174 NADPH O2 [CH2O] (sugar) © 2016 Pearson Education, Inc.
5
The product is 3-phosphoglycerate
Phase 1, carbon fixation, involves the incorporation of the CO2 molecules into ribulose bisphosphate (RuBP) using the enzyme rubisco The product is 3-phosphoglycerate © 2016 Pearson Education, Inc. 5
6
3 CO2, entering one per cycle
Figure 8.17-s1 Input: 3 CO2, entering one per cycle Phase 1: Carbon fixation Rubisco 3 P P 3 P P 6 P RuBP 3-Phosphoglycerate Calvin Cycle Figure 8.17-s1 The Calvin cycle (step 1) © 2016 Pearson Education, Inc.
7
Phase 2, reduction, involves the reduction and phosphorylation of 3-phosphoglycerate to G3P
Six ATP and six NADPH are required to produce six molecules of G3P, but only one exits the cycle for use by the cell © 2016 Pearson Education, Inc. 7
8
3 CO2, entering one per cycle
Figure 8.17-s2 Input: 3 CO2, entering one per cycle Phase 1: Carbon fixation Rubisco 3 P P 3 P P 6 P RuBP 3-Phosphoglycerate 6 ATP 6 ADP Calvin Cycle 6 P P 1,3-Bisphosphoglycerate 6 NADPH 6 NADP+ 6 P Figure 8.17-s2 The Calvin cycle (step 2) i 6 P G3P Phase 2: Reduction Glucose and other organic compounds Output: 1 P G3P © 2016 Pearson Education, Inc.
9
Three additional ATP are required to power this step
Phase 3, regeneration, involves the rearrangement of the five remaining molecules of G3P to regenerate the initial CO2 receptor, RuBP Three additional ATP are required to power this step © 2016 Pearson Education, Inc. 9
10
3 CO2, entering one per cycle
Figure 8.17-s3 Input: 3 CO2, entering one per cycle Phase 1: Carbon fixation Rubisco 3 P P 3 P P 6 P RuBP 3-Phosphoglycerate 6 ATP 6 ADP 3 ADP Calvin Cycle 6 P P 3 ATP 1,3-Bisphosphoglycerate 6 NADPH Phase 3: Regeneration of RuBP 6 NADP+ 6 P Figure 8.17-s3 The Calvin cycle (step 3) i 5 P G3P 6 P G3P Phase 2: Reduction Glucose and other organic compounds Output: 1 P G3P © 2016 Pearson Education, Inc.
11
Evolution of Alternative Mechanisms of Carbon Fixation in Hot, Arid Climates
Adaptation to dehydration is a problem for land plants, sometimes requiring trade-offs with other metabolic processes, especially photosynthesis On hot, dry days, plants close stomata, which conserves H2O but also limits photosynthesis The closing of stomata reduces access to CO2 and causes O2 to build up These conditions favor an apparently wasteful process called photorespiration © 2016 Pearson Education, Inc. 11
12
In most plants (C3 plants), initial fixation of CO2, via rubisco, forms a three-carbon compound (3-phosphoglycerate) In photorespiration, rubisco adds O2 instead of CO2 in the Calvin cycle, producing a two-carbon compound Photorespiration decreases photosynthetic output by consuming ATP, O2, and organic fuel and releasing CO2 without producing any ATP or sugar © 2016 Pearson Education, Inc. 12
13
Photorespiration may be an evolutionary relic because rubisco first evolved at a time when the atmosphere had far less O2 and more CO2 Photorespiration limits damaging products of light reactions that build up in the absence of the Calvin cycle © 2016 Pearson Education, Inc. 13
14
C4 Plants C4 plants minimize the cost of photorespiration by incorporating CO2 into a four-carbon compound An enzyme in the mesophyll cells has a high affinity for CO2 and can fix carbon even when CO2 concentrations are low These four-carbon compounds are exported to bundle-sheath cells, where they release CO2 that is then used in the Calvin cycle © 2016 Pearson Education, Inc. 14
15
Sugarcane CO2 C4 Mesophyll Organic cell acid CO2 Bundle- sheath cell
Figure 8.18a Sugarcane CO2 C4 Mesophyll cell Organic acid CO2 Figure 8.18a C4 and CAM photosynthesis compared Bundle- sheath cell Calvin Cycle Sugar (a) Spatial separation of steps © 2016 Pearson Education, Inc.
16
Figure Figure C4 and CAM photosynthesis compared (part 1: C4, sugarcane) Sugarcane © 2016 Pearson Education, Inc.
17
CAM Plants Some plants, including pineapples and many cacti and succulents, use crassulacean acid metabolism (CAM) to fix carbon CAM plants open their stomata at night, incorporating CO2 into organic acids Stomata close during the day, and CO2 is released from organic acids and used in the Calvin cycle © 2016 Pearson Education, Inc. 17
18
Pineapple CO2 CAM Organic acid Night CO2 Day Calvin Cycle Sugar
Figure 8.18b Pineapple CO2 CAM Organic acid Night CO2 Figure 8.18b C4 and CAM photosynthesis compared Day Calvin Cycle Sugar (b) Temporal separation of steps © 2016 Pearson Education, Inc.
19
Figure Figure C4 and CAM photosynthesis compared (part 2: CAM, pineapple) Pineapple © 2016 Pearson Education, Inc.
20
The C4 and CAM pathways are similar in that they both incorporate carbon dioxide into organic intermediates before entering the Calvin cycle In C4 plants, carbon fixation and the Calvin cycle occur in different cells In CAM plants, these processes occur in the same cells, but at different times of the day © 2016 Pearson Education, Inc. 20
21
Calvin Cycle Calvin Cycle
Figure 8.18 Sugarcane Pineapple CO2 CO2 C4 CAM Mesophyll cell Organic acid Organic acid Night CO2 CO2 Figure 8.18 C4 and CAM photosynthesis compared Bundle- sheath cell Day Calvin Cycle Calvin Cycle Sugar Sugar (a) Spatial separation of steps (b) Temporal separation of steps © 2016 Pearson Education, Inc.
22
The Importance of Photosynthesis: A Review
The energy entering chloroplasts as sunlight gets stored as chemical energy in organic compounds Sugar made in the chloroplasts supplies chemical energy and carbon skeletons to synthesize the organic molecules of cells Plants store excess sugar as starch in the chloroplasts and in structures such as roots, tubers, seeds, and fruits In addition to food production, photosynthesis produces the O2 in our atmosphere © 2016 Pearson Education, Inc. 22
23
Electron transport chain
Figure 8.19 O2 CO2 Mesophyll cell Sucrose (export) Chloroplast H2O H2O CO2 Light NADP+ ADP 3-Phosphoglycerate LIGHT REACTIONS: Photosystem II Electron transport chain Photosystem I + P i CALVIN CYCLE RuBP ATP G3P NADPH Starch (storage) Figure 8.19 A review of photosynthesis O2 Sucrose (export) LIGHT REACTIONS CALVIN CYCLE REACTIONS Are carried out by molecules in the thylakoid membranes Convert light energy to the chemical energy of ATP and NADPH Split H2O and release O2 Take place in the stroma Use ATP and NADPH to convert CO2 to the sugar G3P Return ADP, inorganic phosphate, and NADP+ to the light reactions H2O © 2016 Pearson Education, Inc.
24
Electron transport chain
Figure H2O CO2 Light NADP+ ADP 3-Phosphoglycerate LIGHT REACTIONS: Photosystem II Electron transport chain Photosystem I + P i CALVIN CYCLE RuBP ATP G3P Figure A review of photosynthesis (part 1: chloroplast) Starch (storage) NADPH O2 Sucrose (export) © 2016 Pearson Education, Inc.
25
CALVIN CYCLE REACTIONS
Figure LIGHT REACTIONS CALVIN CYCLE REACTIONS Are carried out by molecules in the thylakoid membranes Convert light energy to the chemical energy of ATP and NADPH Split H2O and release O2 Take place in the stroma Use ATP and NADPH to convert CO2 to the sugar G3P Return ADP, inorganic phosphate, and NADP+ to the light reactions Figure A review of photosynthesis (part 2: light reactions vs calvin cycle) © 2016 Pearson Education, Inc.
26
Photosynthesis is one of many important processes conducted by a working plant cell
© 2016 Pearson Education, Inc. 26
27
MAKE CONNECTIONS: The Working Cell
Figure 8.20 MAKE CONNECTIONS: The Working Cell Movement Across Cell Membranes (Chapter 5) DNA Nucleus mRNA Nuclear pore Energy Transformations in the Cell: Photosynthesis and Cellular Respiration (Chapters 6-8) Rough endoplasmic reticulum (ER) Protein Protein in vesicle mRNA Vacuole Ribosome Vesicle forming Photosynthesis in chloroplast CO2 Golgi apparatus H2O Protein ATP Organic molecules Transport pump Plasma membrane ATP O2 Cellular respiration in mitochondrion ATP Figure 8.20 Make connections: the working cell ATP Flow of Genetic Information in the Cell: DNA → RNA → Protein (Chapters 3–5) Cell wall O2 CO2 H2O © 2016 Pearson Education, Inc.
28
Flow of Genetic Information in the Cell:
Figure DNA Nucleus mRNA Nuclear pore Rough endoplasmic reticulum (ER) Protein Protein in vesicle Figure Make connections: the working cell (part 1) mRNA Ribosome Flow of Genetic Information in the Cell: DNA → RNA → Protein (Chapters 3-5) © 2016 Pearson Education, Inc.
29
Flow of Genetic Information in the Cell:
Figure Vesicle forming Golgi apparatus Protein Plasma membrane Figure Make connections: the working cell (part 2) Cell wall Flow of Genetic Information in the Cell: DNA → RNA → Protein (Chapters 3-5) © 2016 Pearson Education, Inc.
30
Energy Transformations in the Cell: Photosynthesis
Figure Photosynthesis in chloroplast CO2 H2O ATP Transport pump Organic molecules ATP O2 Cellular respiration in mitochondrion ATP ATP Movement Across Cell Membranes (Chapter 5) Figure Make connections: the working cell (part 3) Energy Transformations in the Cell: Photosynthesis and Cellular Respiration (Chapters 6-8) O2 CO2 H2O © 2016 Pearson Education, Inc.
31
Figure 8.UN04-1 Figure 8.UN04-1 Skills exercise: making scatter plots with regression lines (part 1) © 2016 Pearson Education, Inc.
32
by invasive velvetleaf plants
Figure 8.UN04-2 Corn plant surrounded by invasive velvetleaf plants Figure 8.UN04-2 Skills exercise: making scatter plots with regression lines (part 2) © 2016 Pearson Education, Inc.
33
Electron transport chain Primary acceptor Electron transport Fd chain
Figure 8.UN05 Electron transport chain Primary acceptor Electron transport chain Fd Primary acceptor NADP+ NADP+ reductase + H+ H2O Pq NADPH O2 Cytochrome complex Pc Figure 8.UN05 Summary of key concepts: linear electron flow Photosystem I ATP Photosystem II © 2016 Pearson Education, Inc.
34
Calvin Cycle Regeneration of CO2 acceptor
Figure 8.UN06 3 CO2 Carbon fixation 3 x 5C 6 x 3C Calvin Cycle Regeneration of CO2 acceptor Figure 8.UN06 Summary of key concepts: the Calvin cycle 5 x 3C Reduction 1 G3P (3C) © 2016 Pearson Education, Inc.
35
Figure 8.UN07 pH 4 pH 7 pH 4 pH 8 Figure 8.UN07 Test your understanding, question 9 (thylakoids and pH) ATP © 2016 Pearson Education, Inc.
36
Figure 8.UN08 Test your understanding, question 14 (“watermelon snow”)
© 2016 Pearson Education, Inc.
Similar presentations
