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Cycle thylakoid membrane stroma concentragon

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Unformatted text preview: ded for 1 glucose? Regeneration of CO2 acceptor 3 CO2 (one at a time) Carbon fixation 6 × 3-C Calvin Cycle 5 × 3-C Reduction Fig. 10- UN2 1 glucose (C6H12O6) molecule produced from __ CO2, __ ATP & __ NADPH 1 G3P (3-C) Fig. 10-UN4 From Concept check 10.3 p. 199 8 Fig. 10- 18- 1 3 CO2 (Entering one at a Gme) Input: Phase 1: Carbon fixaJon Rubisco (enzyme) ← short- lived P intermediate P 3- PGA P P P 3 Ribulose bisphosphate (RuBP) •  CO2 incorporated into organic molecule RuBP •  Rubisco* (enzyme) agaches CO2 to a 5- C RuBP (ribulose bisphosphate), creates 6- C molecule; unstable- splits into two 3- C molecules [3PGA] Fig. 10- 18- 2 Phase 2: ReducJon- Energizes sugar •  ATP gives up P group (energy) and NADPH gives up H and e- ’s •  Intermediates lead to G3P, glucose P 3PGA 6 ATP 6 ADP P 6 G3P P P Fig. 10- 18- 3 CO2 3 P P 6 P 6 6 ADP Calvin Cycle 3 ATP NADPH 6 6 NADP+ 6 i P 3 P 3 ADP P Glucose and other organic compounds 1 P Output G3P (a sugar) •  One 3- C molecule exits; rest used to regenerate RuBP, 5- C molecule 3 •  ATP Ribulose bisphosphate (RuBP) consumed BPG 6 P ATP P 6 NADPH 6 NADP+ 6 P i Phase 3: RegeneraJon of the CO2 acceptor (RuBP) 5 P G3P 6 P G3P 1 G3P P Glucose and other organic (a sugar) compounds 9 ATP and NADPH transfer e- & H+ to the sugar intermediates (reduced) •  Product of Calvin cycle converted to many molecules: G3P→ glucose, starch & cellulose (carbs); also G3P → fagy acids or amino acids •  ADP and NADP+ are reused by light rxns. 10.4: AlternaGve pathways of CO2 fixaGon have evolved in hot, dry climates •  Hot & dry: plants close stomata to conserve H2O; this limits photosynthesis –  Why? Reduces CO2 entry –  Also prevents O2 exit (builds up), results in wasteful process: photorespiraJon 10 C3 , C4 & CAM: alternaGve photosyntheGc paths •  Most plants- C3 : fix CO2 via rubisco → forms 3- C cmpd. –  PhotorespiraJon: rubisco can agach both O2 & CO2 to RuBP (O2- - RuBP since O2>CO2 concentraGon) •  Wasteful: produces no G3P (…glucose, etc.) or ATP •  [ExplanaGon: C3 evolved when O2 scarce, not an issue] •  C4 and CAM: more efficient in hot, dry –  C4: diff. enzyme fixes CO2 into 4- C cmpd. & Calvin cycle occurs in separate plant cells –  CAM: opens stomata/fixes CO2 at night, enters Calvin cycle next day C3, C4 and CAM plants thrive under diff. condiGons •  C3: most plants (temperate) •  C4 and CAM: adaptaGons for photosyn. in hot, dry climates C4: Corn, Sugarcane CAM : CacG, Pineapple Sugarcane C4 Mesophyll cell Organic acid Bundlesheath cell CAM CO2 1 CO2 incorporated into four-carbon Organic acid organic acids (carbon fixation) CO2 Calvin Cycle Fig. 10- 20 Pineapple CO2 CO2 2 Organic acids release CO2 to Calvin cycle Sugar (a) SpaGal separaGon of steps Night Day Calvin Cycle Sugar (b) Temporal separaGon of steps 11...
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