细胞功能

  • Transmembrane transport
    • Passive transport
      • Simple diffusion
        • non-polar (lipid-soluble) molecules / small polar molecules without charges
        • high → low
        • 不消耗ATP
      • Facilitated diffusion
        • lipid-insoluble molecules
        • high → low
        • 不消耗ATP
        • channels
          • 4 type
              1. Voltage-gated ion channel
              1. Ligand-gated ion channel
              1. Mechanically-gated ion channel
              1. Water channel- aquaporin
          • 2 property
            • ion selectivity
            • gating
        • carriers
          • conformational change
          • saturation
    • Active transport
      • Primary active transport
        • Consume ATP directly
        • Na+-K+ pump transports 3Na+ out of and 2K+ into the cell against the ionic gradients, by converting ATP into ADP

          • Therefore, N+-K+ pump is also called N+-K+ ATPase
      • Secondary active transport
        • Consume energy stored in ionic gradients
    • Vesicular Transport
      • Exocytosis
        • constitutive exocytosis
        • regulated exocytosis
      • Endocytosis
        • Phagocytosis (solid)
        • Pinocytosis (liquid)
  • Signal transduction
    • Communication between/within cells via a series of molecules
    • Regulates cellular functions and maintain homeostasis
    • Receptors, ligands and effectors效应蛋白 are key components in the process of signal transduction
  • Bioelectricity
    • 外正内负，动作时钾出纳进
    • Resting Membrane Potential
      RMP
      • The higher the permeability of an ion is, the more it contributes to the resting membrane potential
      • K+ 的 permeability 更好
      • RMP close to the equilibrium potential of K+ ≈ -70mV
      • factor
        • ①Na+-K+ pump
        • ②[K+]o
        • ③K+/Na+ permeability
    • Action Potential
      AP
      • Only happens in excitable cells, namely muscle cells and neurons
      • 图例
        • 图例
        • abc: depolarization
        • cde: repolarization
        • ef: hyperpolarization
        • -55 threshold potential阈值
      • Na+ channel
        • 图
        • ①below or at-70mV: activation gate closes, inactivation gate opens; channel closes, no Na+ current, in resting state
        • ②at-55mV: activation gate suddenly opens, inactivation gate stays open; channel opens, inward Na+ current, in activated state.
        • ③-55→+30mV: activation gate opens, inactivation gate slowly closes; channel stays open, inward Na+ current, in activated state.
        • ④at +30mV: activation gate opens, inactivation gate completely closes and “locked”; channel closes, no Na+ current, in inactivated state.
        • ⑤+30→-70mV: activation gate opens, inactivation gate stays close and “locked”; channel closes, no Na+ current, in inactivated state.
      • K+ channel
        • 图
        • ①below -70mV: channel closes, no K+ current.
        • ②-70→+30mV: channel slowly opens, but still no K+ current.
        • ③+30→-70mV: channel fully opens, outward K+ current.
      • 过程
        • 图
        • 先Na+进导致动作电位，再K+出缓慢恢复
      • 特点
        • 电信号传输过程中propagation not decay 不会衰弱
        • Saltatory conduction 跳跃式传递
        • 可被激活性excitability在激活后一段时间为0(Absolute refractory period)然后缓慢恢复(Relative refractory period)
  • Muscle contraction
    • 3 kind of muscle
      • skeletal 骨骼肌
      • cardiac 心肌
      • smooth 平滑肌
      • Striated muscles横纹肌 = skeletal & cardiac muscles
      • Voluntary muscle随意肌 = skeletal muscle
    • 组成
      • 级别
        • 图
        • myofilaments排列构成sarcomere
        • 好多sarcomere连在一起构成myofibrils
        • sarcolemma肌膜包着myofibrils形成muscle fiber
        • muscle fiber构成muscle fascicle
      • sarcomere结构
        • 图
        • 一个z line到另一个z line之间是一个sarcomere
        • thick filaments(myosin)连着M line
        • thin filaments(actin,tropomyosin,troponin)连着Z line
      • muscle fiber / sarcotubular结构
        • 图
        • The sarcolemma肌膜 invaginates to form T tubules 横着的
        • The sarcoplasmic reticulum肌质网 surrounds each myofibril to form L tubules 竖着的，储存着Ca2+
        • L tubules become enlarged to form terminal cisterna when they meet T tubules
        • Two terminal cisternae flank a T tubule, and they become a triad 三位一体
    • Neuromuscular Junction
      • 图
        • electrical→chemical→electrical

          • 神经递质是乙酰胆碱ACh
    • Excitation-contraction Coupling
      • The process by which AP of the muscle fiber initiates contraction is called excitation-contraction coupling
      • 过程
        • 图
        • ④AP spreads over the plasma membrane of the muscle cell and continues via the T tubules.
        • ⑤L-type Ca2+ channels in membrane of T tubules change conformation.
        • ⑥At the triads, RyR is activated by the conformation change of L-type Ca2+ channel.
        • ⑦Ca2+is released from the sER.
        • ⑧Ca2+diffuses to the myofilaments, where it binds to TnC(troponin C).
        • ⑨The actomyosin cross-bridge cycle initiated.
        • ⑩Ca2+is recycled back to sER by Ca2+ pump.
    • Myofilament Sliding Theory
      • 图
      • 没有Ca2+的时候，tropomyosin盖住了myosin-binding site，防止myosin head bind to actin形成cross-bridge
      • 有Ca2+的时候，troponin C结合Ca2+，把tropomyosin扒拉开，让actin与myosin bind
      • cross-bridge cycle
      • The myosin head bind to actin to form the crossbridge
      • The cross-bridge keeps changing conformation while binding to different molecules, thus drags the thin filament along the thick filament.
      • Eventually, the muscle contracts
    • Performance of contraction
      • 两种contraction
        • Isotonic contraction
          • the muscle shortens with constant tension
          • In isotonic contraction, the contractile tension = afterload
          • The heavier the load is, the slower the muscle contracts
          • P = F * V
        • Isometric contraction
          • the muscle length doesn’t change with increased tension.
        • Usually, the isometric contraction comes first, then followed by the isotonic contraction
      • 最有力
        • Preload = initial length of muscle
        • Optimal initial length = resting length
        • 在resting length时候active tension最大，收缩更多就要有passive tension维持长度
        • The contraction reaches the maximum strength when the sarcomere is 2.0 ~ 2.2μM in length.
      • 影响因素
        • [Ca2+]i
        • The activity of the cross-bridge’s ATPase
        • The metabolism of the muscle cell
        • The expression of contraction-related proteins
      • motor unit
        • A motor unit consists of a motor neuron and the group of skeletal muscle fibers it innervates
        • Motor units have varied excitability
        • 图
      • multiple fiber summation
        • When a weak stimulus is sent, fewer motor units (the smaller ones) is stimulated and the contractile tension is small
        • As the stimuli grow stronger, more and more motor units (the smaller and the larger ones) are stimulated and the tension also grow stronger
        • 就是很小的刺激只能激活一部分motor unit，大的刺激能激活全部motor unit
      • frequency summation
        • 图
        • 刺激后过一段时间肌肉才收缩，连续的刺激会导致强直收缩tetanization
      • 不同肌肉
        • 图