生化Ch21 partIII 重點整理 生科2A 0993B013許嘉珊 0993B035張以潔

心智圖 Rubisco regulation The fixation of carbon dioxide Hatch-Slack pathway Pyruvate-Pi dikinase Dark reaction Photorespiration C4 plant Calvin-Benson cycle (Ch.22)

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 + Mg2+ *carbamylation:碳酸根修飾於Lys上 2.Rubisco activase:可以幫助RuBP從rubisco離開並進行carbamylation使其活化 3.光可以間接影響Rubisco的活性： 光會影響pH值:照光後電子傳遞鍊會推動proton pump將proton打至P site， P site pH值降低(變酸)，N site pH升高(變鹼)。 【Rubisco activase, Rubisco, Calvin cycle enzymes在鹼性環境下，活性會提高 】 b) 助於Mg2+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G3P

Regulation of CO2 fixation 光調節的固碳作用促進cell respiration和hexose synthesis的基質循環

Regulation of CO2 fixation 照光後，pH值差很多 沒照光時，pH值沒差很多

Regulation of CO2 fixation 環境中之氧化還原狀態會影響蛋白質的結構進而影響活性。

Photorespiration 當氧氣過剩、二氧化碳不足時，植物行Photorespiration(光呼吸作用) Rubisco具兩種催化能力：carboxylase & oxygenase，當二氧化碳不足時oxygenase活性上升，分解RuBP RuBP + O2→ 3-PG + Phosphoglycerate 　3-PG可進入糖解作用，phosophoglycerate可被代謝成glycine，均能有效利用，但RuBP減少會降低光合作用的效率

Hatch-Slack pathway 目的：傳遞CO2至其他細胞 參與酵素：Pyruvate-Pi dikinase 　　　　　　(ATP→AMP+2Pi)

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

C4 plant C3植物行一般的固碳途徑 C4植物行Hatch-Slack pathway 　能夠有效的運用光能

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 C4 plants is NOT true? (A) the first product of carbon dioxide fixation is a compound with 4 carbon atoms. (B) C4 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 C4 plants. (D) less ATP is used overall for sugar biosynthesis in C4 than in C3 plantsC4 photosynthesis is an adaptation for plants living in hot, arid climates like Tucson, Arizona. C4 plants initially fix CO2 in mesophyll cells as 4-carbon compounds, and later release CO2 in bundle sheath cells. There is an additional ATP requirement for each carbon dioxide utilized in this pathway. (E) photorespiration is minimal in C4 plants compared to C3 plants.