Ch 21 part III 2 A 0993 B

生化Ch 21 part. III 重點整理 生科 2 A 0993 B 013許嘉珊 0993 B 035張以潔

心智圖 Rubisco regulation The fixation of carbon dioxide Dark reaction Photorespiration Hatch-Slack pathway C 4 plant Calvin-Benson cycle (Ch. 22) Pyruvate-Pi dikinase

The fixation of carbon dioxide • 5 C sugar + 1 C → 6 C intermediate • 6 C intermediate → 2* 3 C sugar 5 C sugar: Ribulose-1, 5 -bisphosphate 1 C : carbon dioxide 6 C sugar : 2 -carboxy-3 -ketoarabinitol 1, 5 -bisphosphate 3 C sugar: 3 -phosphoglycerate

The fixation of carbon dioxide http: //sandwalk. blogspot. com/2007/07/fixing-carbon-rubisco-reaction. html

Regulation of rubisco • 1. 將rubisco 變成active form: carbamylation + Mg 2+ *carbamylation: 碳酸根修飾於Lys上 • 2. Rubisco activase: 可以幫助Ru. BP從rubisco離開並進行 carbamylation使其活化 • 3. 光可以間接影響Rubisco的活性： a) 光會影響p. H值: 照光後電子傳遞鍊會推動proton pump將proton 打至P site， P site p. H值降低(變酸)，N site p. H升高(變鹼)。 【Rubisco activase, Rubisco, Calvin cycle enzymes在鹼性環境下， 活性會提高 】 b) 助於Mg 2+從lumen進入stroma中進行以催化反應 c) 助於還原作用，NADPH生成進入反應中，使BPG最終能還原成 G 3 P

Regulation of CO 2 fixation • 光調節的固碳作用促進cell respiration和hexose synthesis的基質循環

Pyruvate-Pi dikinase • 反應機構： 　　E-His + AMP-P-P +Pi → E-His-P + AMP + PPi 　　E-His-P + pyruvate → PEP + E-His 　Net : ATP + Pi + pyruvate AMP + PEP + PPi • 調控：Threonine phosphorylation→抑制

Question 1 • As discovered by Calvin, when algal cells are exposed to radioactive carbon dioxide in the light for only 1 second, the compound that is most quickly and most extensively labeled with radioactive C has how many carbon atoms? • A. 2 • B. 3 • C. 4 • D. 5 • E. 6

Answer • B

Question 2 Which statement about photosynthesis in C 4 plants is NOT true? • (A) the first product of carbon dioxide fixation is a compound with 4 carbon atoms. • (B) C 4 photosynthesis is an adaptation for plants living in hot, arid climates. • (C) carbon dioxide is initially fixed in mesophyll cells, but the Calvin cycle is active in bundle sheath cells in leaves of C 4 plants. • (D) less ATP is used overall for sugar biosynthesis in C 4 than in C 3 plants. C 4 photosynthesis is an adaptation for plants living in hot, arid climates like Tucson, Arizona. C 4 plants initially fix CO 2 in mesophyll cells as 4 -carbon compounds, and later release CO 2 in bundle sheath cells. There is an additional ATP requirement for each carbon dioxide utilized in this pathway. • (E) photorespiration is minimal in C 4 plants compared to C 3 plants.