MAPK 三级级联为何能把渐变的输入转化为近乎全或无的输出？
Why can the three-tier MAPK cascade convert a graded input into a nearly all-or-none output?
级联中每一级激酶需要在两个位点被双磷酸化才充分活化，这种多位点需求产生了类似协同结合的超敏性，理论上单级的希尔系数可达 1.7 左右，三级串联后总体响应曲线变得很陡。当磷酸化酶与去磷酸化酶都接近饱和时还会出现零级超敏，进一步锐化阈值。若再叠加下游到上游的正反馈，如卵母细胞成熟中的 Mos-MEK-MAPK 环路，系统就获得双稳态并把渐变刺激转化为全或无的细胞命运决定。
Each kinase in the cascade must be phosphorylated at two sites for full activation, and this multisite requirement generates ultrasensitivity analogous to cooperative binding, with a single tier reaching an effective Hill coefficient near 1.7 and three tiers in series producing a much steeper overall curve. When kinase and phosphatase both operate near saturation, zero-order ultrasensitivity sharpens the threshold further. Adding feedback from downstream to upstream, as in the Mos-MEK-MAPK loop of oocyte maturation, confers bistability and turns a graded stimulus into an all-or-none fate decision.
难度 专业 · 适合 高中(15-18)
CC BY 4.0 · 已核验 · Verified 2026-10-04
来源 · Source
Huang CY, Ferrell JE Jr. Ultrasensitivity in the mitogen-activated protein kinase cascade. PNAS (1996) 93:10078-10083
Huang CY, Ferrell JE Jr. Ultrasensitivity in the mitogen-activated protein kinase cascade. PNAS (1996) 93:10078-10083
独立核验依据 · Independent verification: 核验依据 1 DOI 10.1073/pnas.93.19.10078
#MAPK级联 #超敏性 #双稳态 #正反馈
线粒体途径凋亡中，细胞色素 c 的释放如何被控制并触发 caspase 级联？
In mitochondrial apoptosis, how is cytochrome c release controlled and how does it trigger the caspase cascade?
凋亡刺激使 BH3-only 蛋白如 BID、BIM 上调，它们抑制 BCL-2 和 BCL-XL 等抗凋亡成员并直接活化 BAX 与 BAK。活化的 BAX 与 BAK 在线粒体外膜寡聚形成大孔道，导致外膜通透化，细胞色素 c 和 SMAC 释放到胞质。细胞色素 c 与 APAF-1 及 dATP 组装成凋亡体，招募并激活起始 caspase-9，后者切割激活 caspase-3 和 caspase-7 执行降解，SMAC 则解除 IAP 对 caspase 的抑制，使过程不可逆。
Apoptotic stimuli upregulate BH3-only proteins such as BID and BIM, which neutralize anti-apoptotic members like BCL-2 and BCL-XL and directly activate BAX and BAK. Activated BAX and BAK oligomerize in the outer mitochondrial membrane to form large pores, permeabilizing it so that cytochrome c and SMAC escape into the cytosol. Cytochrome c assembles with APAF-1 and dATP into the apoptosome, which recruits and activates initiator caspase-9; caspase-9 then cleaves caspase-3 and caspase-7, while SMAC relieves IAP inhibition of caspases and makes the process irreversible.
难度 专业 · 适合 大众
CC BY 4.0 · 已核验 · Verified 2026-08-23 · 2 条独立证据
来源 · Source
Urry 等,《Campbell Biology》第11版,Pearson,2017
L. A. Urry et al., Campbell Biology, 11th ed., Pearson, 2017
独立核验依据 · Independent verification: 核验依据 2 ISBN 978-0-13-409341-3 (11th ed., Pearson)
#线粒体凋亡 #细胞色素c #BAX/BAK #凋亡体
细胞周期的推进为何被设计成不可逆的单向过程，泛素化在其中起什么作用？
Why is cell-cycle progression built as an irreversible one-way process, and what role does ubiquitination play?
周期蛋白依赖性激酶的活性由周期蛋白丰度、CDK 抑制蛋白和磷酸化状态共同决定，而丰度控制的关键是两类泛素连接酶：SCF 复合体降解 CDK 抑制蛋白促进 S 期进入，APC/C 在中后期降解 securin 和 M 期周期蛋白以启动染色体分离与退出分裂。蛋白降解是热力学上不可逆的步骤，配合正反馈和双负反馈构成的开关，使细胞一旦跨过阈值就无法回退。这种设计避免了同一轮 DNA 复制被重复启动，保障基因组只复制一次。
Cyclin-dependent kinase activity is set by cyclin abundance, CDK inhibitor proteins and phosphorylation state, and abundance is governed largely by two ubiquitin ligases: the SCF complex degrades CDK inhibitors to allow S-phase entry, while APC/C destroys securin and mitotic cyclins to trigger chromosome separation and mitotic exit. Proteolysis is thermodynamically irreversible, and combined with positive and double-negative feedback it forms switches that prevent the cell from sliding backwards once a threshold is crossed. This design blocks re-initiation of replication so that the genome is copied exactly once per cycle.
难度 专业 · 适合 高中(15-18)
CC BY 4.0 · 已核验 · Verified 2026-08-23 · 2 条独立证据
来源 · Source
Urry 等,《Campbell Biology》第11版,Pearson,2017
L. A. Urry et al., Campbell Biology, 11th ed., Pearson, 2017
独立核验依据 · Independent verification: 核验依据 2 ISBN 978-0-13-409341-3 (11th ed., Pearson)
#CDK-周期蛋白 #APC/C #泛素化降解 #不可逆开关
细胞周期的检验点分别监控什么，缺失后会带来什么后果？
What does each cell-cycle checkpoint monitor, and what happens when checkpoints fail?
G1/S 检验点评估营养、生长信号和 DNA 损伤，决定细胞是否越过限制点进入不可逆的复制程序；G2/M 检验点确认 DNA 复制完成且损伤已修复才允许进入分裂；纺锤体组装检验点在所有着丝点被正确附着前抑制 APC/C，阻止染色体分离。检验点失效会让带有损伤或未完成复制的基因组进入分裂，产生突变累积、染色体错分与非整倍体，这是肿瘤发生中的常见早期事件。
The G1/S checkpoint weighs nutrients, growth signals and DNA damage before the cell passes the restriction point into an irreversible commitment to replicate; the G2/M checkpoint confirms that replication is complete and damage repaired before mitosis; the spindle assembly checkpoint holds APC/C inactive until every kinetochore is properly attached, blocking chromosome segregation. When checkpoints fail, damaged or under-replicated genomes enter division, producing accumulated mutations, missegregation and aneuploidy, a frequent early event in tumorigenesis.
难度 进阶 · 适合 大众
CC BY 4.0 · 已核验 · Verified 2026-10-04
来源 · Source
Nurse P. A long twentieth century of the cell cycle and beyond. Cell (2000) 100:71-78
Nurse P. A long twentieth century of the cell cycle and beyond. Cell (2000) 100:71-78
独立核验依据 · Independent verification: 核验依据 1 DOI 10.1016/s0092-8674(00)81684-0
#细胞周期 #检验点 #纺锤体组装检验点 #非整倍体
细胞凋亡与细胞坏死在过程和后果上有什么区别？
How do apoptosis and necrosis differ in process and consequence?
凋亡是耗能的程序性死亡：细胞皱缩、染色质凝聚、DNA 被核酸酶切成片段，细胞膜保持完整并把磷脂酰丝氨酸外翻作为吞噬信号，最终形成凋亡小泡被邻近细胞清除，几乎不引发炎症。坏死多由缺氧、毒素或机械损伤造成，细胞肿胀、膜破裂，胞内容物包括损伤相关分子模式外泄，引起明显炎症反应。近年还发现程序性坏死和焦亡等受调控的溶解性死亡形式，说明二者的界限并非绝对。
Apoptosis is an energy-dependent programmed death in which the cell shrinks, chromatin condenses, DNA is cut into fragments, the membrane stays intact and exposes phosphatidylserine as an eat-me signal, and the resulting bodies are cleared by neighbours with little inflammation. Necrosis typically follows hypoxia, toxins or mechanical injury: the cell swells, the membrane ruptures and contents including damage-associated molecular patterns leak out, provoking marked inflammation. Regulated lytic forms such as necroptosis and pyroptosis show that the boundary between the two is not absolute.
难度 进阶 · 适合 大众
CC BY 4.0 · 来源待核验 · Source pending review
来源 · Source
出处备注：此条未指向带版次的可引用著作（通识性内容、机构文件或未展开的英文书名），本库不提供独立书目出处；如需精确引用，需由编辑补全具体篇目与版次。
Galluzzi L 等. Molecular mechanisms of cell death: recommendations of the Nomenclature Committee on Cell Death 2018. Cell Death & Differentiation (2018) 25:486-541
Galluzzi L et al. Molecular mechanisms of cell death: recommendations of the Nomenclature Committee on Cell Death 2018. Cell Death & Differentiation (2018) 25:486-541
#凋亡 #坏死 #程序性死亡 #炎症反应
受体酪氨酸激酶接到配体后如何把信号传向细胞内部？
How does a receptor tyrosine kinase relay a signal inward after binding its ligand?
生长因子结合胞外域后促使受体二聚化或聚簇，两条链的胞内激酶域相互交叉磷酸化特定酪氨酸残基。这些磷酸酪氨酸成为含 SH2 或 PTB 结构域的接头蛋白的停靠位点，招募 GRB2-SOS 启动 RAS-MAPK 通路，或招募 PI3K 启动 AKT 通路，也可通过 PLCγ 产生钙与 DAG 信号。信号强度由受体内吞降解、蛋白酪氨酸磷酸酯酶去磷酸化和负反馈基因产物共同限定，其失调是许多癌症的驱动事件。
Ligand binding to the extracellular domain promotes receptor dimerization or clustering so that the intracellular kinase domains cross-phosphorylate specific tyrosine residues. These phosphotyrosines become docking sites for adaptors bearing SH2 or PTB domains, recruiting GRB2-SOS to launch the RAS-MAPK pathway, PI3K to launch AKT signalling, or PLC-gamma to generate calcium and DAG signals. Output is limited by receptor endocytosis and degradation, protein tyrosine phosphatases and feedback inhibitors, and loss of this restraint drives many cancers.
难度 进阶 · 适合 初中(12-15)
CC BY 4.0 · 已核验 · Verified 2026-10-04
来源 · Source
Lemmon MA, Schlessinger J. Cell signaling by receptor tyrosine kinases. Cell (2010) 141:1117-1134
Lemmon MA, Schlessinger J. Cell signaling by receptor tyrosine kinases. Cell (2010) 141:1117-1134
独立核验依据 · Independent verification: 核验依据 1 DOI 10.1016/j.cell.2010.06.011
#受体酪氨酸激酶 #自磷酸化 #接头蛋白 #RAS-MAPK
cAMP 作为第二信使是如何产生并把细胞外信号放大的？
How is the second messenger cAMP generated, and how does it amplify an extracellular signal?
激动剂结合 G 蛋白偶联受体后使受体构象改变，激活 Gs 蛋白的 α 亚基并使其与 GTP 结合，进而激活腺苷酸环化酶把 ATP 转化为 cAMP。cAMP 结合蛋白激酶 A 的调节亚基，释放催化亚基去磷酸化多种底物酶和转录因子。由于一个受体可激活多个 G 蛋白、一个环化酶能生成大量 cAMP、一个激酶可磷酸化众多底物，信号在每一步都被级联放大；磷酸二酯酶水解 cAMP 则负责终止信号。
Agonist binding changes the conformation of a G-protein-coupled receptor, which activates the alpha subunit of Gs and loads it with GTP, in turn switching on adenylyl cyclase to convert ATP into cAMP. cAMP binds the regulatory subunits of protein kinase A, freeing catalytic subunits to phosphorylate many target enzymes and transcription factors. Because one receptor activates several G proteins, one cyclase makes many cAMP molecules and one kinase phosphorylates many substrates, gain accumulates at every step, while phosphodiesterases hydrolyse cAMP to terminate the signal.
难度 进阶 · 适合 初中(12-15)
CC BY 4.0 · 已核验 · Verified 2026-10-04
来源 · Source
Rosenbaum DM, Rasmussen SGF, Kobilka BK. The structure and function of G-protein-coupled receptors. Nature (2009) 459:356-363
Rosenbaum DM, Rasmussen SGF, Kobilka BK. The structure and function of G-protein-coupled receptors. Nature (2009) 459:356-363
独立核验依据 · Independent verification: 核验依据 1 DOI 10.1038/nature08144
#cAMP #GPCR #蛋白激酶A #信号放大
为什么细胞要把胞质游离钙浓度维持在极低水平，这与钙信号有什么关系？
Why do cells keep cytosolic free calcium extremely low, and how does that relate to calcium signalling?
静息细胞的胞质游离钙约为 100 纳摩尔，而细胞外和内质网腔内可达毫摩尔级，跨膜差异达一万倍以上，这靠质膜钙泵、钠钙交换体和内质网上的 SERCA 泵持续耗能维持。正因为本底极低，少量通道开放即可使局部浓度骤升数十倍，形成快速、高信噪比的信号。持续高钙会激活蛋白酶和磷脂酶并促进线粒体通透性转变导致细胞死亡，所以钙信号必须以短暂脉冲或振荡形式出现。
Resting cytosolic free calcium is around 100 nanomolar while extracellular fluid and the endoplasmic reticulum lumen reach millimolar levels, a gradient of more than ten thousand-fold maintained at energetic cost by plasma-membrane calcium pumps, sodium-calcium exchangers and SERCA pumps. Because the baseline is so low, opening a few channels raises local concentration tens of fold, giving fast signals with a high signal-to-noise ratio. Sustained high calcium activates proteases and phospholipases and promotes mitochondrial permeability transition and death, so calcium signals must appear as brief spikes or oscillations.
难度 进阶 · 适合 初中(12-15)
CC BY 4.0 · 已核验 · Verified 2026-08-23 · 2 条独立证据
来源 · Source
Urry 等,《Campbell Biology》第11版,Pearson,2017
L. A. Urry et al., Campbell Biology, 11th ed., Pearson, 2017
独立核验依据 · Independent verification: 核验依据 2 ISBN 978-0-13-409341-3 (11th ed., Pearson)
#钙信号 #钙泵 #浓度梯度 #钙振荡