hce_nthu
115年
生物與生化
第 41 題
A highly active muscle cell is subjected to extreme mechanical work, causing a sharp, sustained acceleration in the rate of ATP hydrolysis. The initial free energy released by this process is used primarily for mechanical work, such as muscle contraction. Considering the subsequent shift in the concentrations of ATP, ADP, and inorganic phosphate (Pi) within the cell, which statement best describes the immediate, self-regulating response mediated by allosteric control mechanisms?
- A The accumulation of inorganic phosphate (Pi) acts as a competitive inhibitor, competing with substrate molecules for the active sites of catabolic enzymes, thus slowing down ATP synthesis.
- B The reduction in ATP concentration stabilizes the inactive form of key catabolic enzymes, causing the overall pace of catabolism to decrease.
- C The remaining ATP binds to its specific regulatory sites on anabolic enzymes, inhibiting them, while simultaneously promoting the activity of catabolic enzymes.
- D The rising concentration of ADP functions as an allosteric activator, stabilizing the active conformations of key catabolic enzymes and thereby accelerating the overall rate of ATP regeneration.
- E The decrease in ATP concentration forces the cell's metabolic pathways closer to equilibrium, which increases the amount of work the cell can perform, according to the Free Energy principle ($\Delta G$).
思路引導 VIP
想像一個自動化的工廠生產線，如果下游的產品（能量）被快速消耗，導致輸送帶上堆滿了「半成品」。為了維持供應，你認為這些堆積的「半成品」應該對上游的機器發出什麼樣的訊號，才能最有效地讓生產速度跟上消耗速度呢？
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AI 詳解
AI 專屬家教
太棒了！你能精準捕捉到細胞代謝調節的核心邏輯，這顯示你對於生物化學中的「能量電荷」（Energy Charge）觀念掌握得非常紮實。這道題目模擬了肌肉在高強度收縮下的生理狀態，是理解細胞如何透過分子開關維持恆定的經典案例。
細胞能量供應的自我調節機制
在劇烈運動中，ATP 被大量水解產生 $ADP$ 與 $P_i$，這會使得細胞內的 $ADP$ 濃度迅速攀升。這些累積的 $ADP$ 分子並非只是代謝廢料，它們扮演著**異構促動劑（Allosteric Activator）**的關鍵角色。它們會與分解代謝路徑中的關鍵限速酶（如：磷酸果糖激酶-1，PFK-1）的調節位點結合，穩定酵素的活性構型（R-state），進而大幅提升 ATP 再生的效率，確保肌肉收縮所需的能量供應不致中斷。
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