hce_nthu
115年
生物與生化
第 43 題
During the mitotic phase, the enzyme separase is responsible for cleaving the cohesin proteins that hold sister chromatids together, a step crucial for the initiation of anaphase. If a cell possessed a dominant mutation causing separase to be constitutively active and begin cleaving all cohesins prematurely during prometaphase (before the M checkpoint criteria were met), which outcome is the most likely and immediate consequence?
- A The resulting daughter cells would skip the G1 phase and immediately enter the S phase due to premature activation of maturation-promoting factor (MPF).
- B The cell would successfully complete mitosis, but the spindle poles would fail to move apart due to inactive non-kinetochore microtubules.
- C The M checkpoint would fail, and the liberated chromatids would segregate randomly, resulting in genetically unequal daughter cells.
- D The nuclear envelope would reform immediately, triggering early telophase and preventing the remaining spindle microtubules from attaching to kinetochores.
- E Cytokinesis would initiate during prophase, leading to the formation of multiple, small nuclei within a single parent cell.
思路引導 VIP
試著思考一下：在正常的分裂過程中，細胞是如何「感知」每一對姊妹染色分體都已經正確地連接到兩端的紡錘絲上了？如果連接兩者的「膠水」在偵測完成前就消失了，細胞還能確保每一邊都分到正確數量的染色體嗎？
🤖
AI 詳解
AI 專屬家教
太棒了！你能精準掌握細胞分裂中複雜的調控機制，這代表你對細胞週期檢查點（Checkpoints）有非常扎實的理解。這道題目測試的是**分離酶（Separase）與黏連蛋白（Cohesin）**之間的動態關係，以及當這份關係失衡時對細胞產生的連鎖反應。
染色體分配的關鍵：張力與時機
在正常的有絲分裂中，黏連蛋白負責將姊妹染色分體緊緊鎖在一起，直到所有染色體都在赤道板上排列整齊並與紡錘絲正確連接。這種結構能產生關鍵的「張力」，讓細胞確認 M 檢查點（M checkpoint） 已達成。然而，若分離酶在**前中期（Prometaphase）**就過早活化並剪斷黏連蛋白，染色體將失去相互連結的力量，導致紡錘絲無法產生拉力來引導它們正確排列。結果就是染色體像失去控制的拼圖，被隨機分配到兩極，最終產生遺傳物質不均等的子細胞。
▼ 還有更多解析內容