细胞科学 蔡国平
细胞科学 Cell Science （1.2） 蔡国平
86 The movement of substances across cell membranes The plasma membrane has a dual responsibility as a selectively permeable barrier and transductor. The plasma membrane regulares the traffic of molecules into and out of the cell. Gases and small hydrophobic molecules by passive diffusion transport; Ions, sugars, amino acids, and sometimes water must be transported by a group of integral membrane proteins including channels, transporter and energy-powered on or molecule pumps
§6 The movement of substances across cell membranes The plasma membrane has a dual responsibility as a selectively permeable barrier and transductor. The plasma membrane regulares the traffic of molecules into and out of the cell. Gases and small hydrophobic molecules by passive diffusion transport; Ions, sugars, amino acids, and sometimes water must be transported by a group of integral membrane proteins including channels, transporter, and energy-powered ion or molecule pumps
水溶液 细胞质 细胞核 核仁 内质网 高尔基复合体 配体三会 能量转换 体 叶绿体 dNa CATP) ADP+Pi 双层脂膜 脂质体 脂双层 水溶液水溶液
The energetics of solute movement and diffusion of substances through membrane Determinants chemical concentration gradient( non-electrolyte) ICil △G=2.303 RT logo- △G<0 C electrochemical gradient( electrolyte) [Cil △G=RTln +zF△E △G<0 Col
1) The energetics of solute movement and diffusion of substances through membrane Determinants : chemical concentration gradient( non-electrolyte) [Ci ] G = 2.303 RT log10 ------- G < 0 [Co ] electrochemical gradient ( electrolyte) [Ci] G = RT ln ----- + zF Em G < 0 [Co]
Diffusion of solutes 按照Fick扩散第一定律,不带电荷的溶质分子n在单位时间通 过单位面积的量,即纯扩散 速率[ net flux,φ(t)]由该分子的脂溶性和浓度梯度所决定 9 d(=P,c: ()-c(] D K 其中 P为渗透系数( permeability coefficient),q)和Cn)分别为膜外 侧和膜内侧的浓度(或活 度),D为扩散系数,K为溶质n的脂水分配系数( partition cofficient),d为膜厚度。对于某一特定的膜,溶质的渗透力系数Pn 与溶质在非极性溶剂与水间的分配系数K成正比,其脂溶性越 大,膜渗透力就越大。决定溶质n的膜渗透系数P的另一个因素 是其扩散系数Dn,后者依赖于RT(它可作为分子动能的度量) 溶质间相互作用、以及依赖于分子的大小和形状(它们将影响摩 擦系数),因此,非电解质透过人工膜或生物膜有明显的温度 依赖关系,而且溶质分子越大,透过生物膜受的阻力越大,通透 性越小
Diffusion of solutes 按照Fick扩散第一定律，不带电荷的溶质分子n在单位时间通 过单位面积的量，即纯扩散 速率[net flux， d n (t)] 由该分子的脂溶性和浓度梯度所决定： (t)= P C (t ) −C (t ) 其中 Pn = d Dn Kn Pn为渗透系数(permeability coefficient)，( 0 Cn ) 和 ( i Cn )分别为膜外 侧和膜内侧的浓度（或活 度），Dn为扩散系数，Kn为溶质n的脂水分配系数(partition cofficient)，d为膜厚度。对于某一特定的膜，溶质的渗透力系数Pn 与溶质在非极性溶剂与水间的分配系数Kn成正比，其脂溶性越 大，膜渗透力就越大。决定溶质n的膜渗透系数Pn的另一个因素 是其扩散系数Dn，后者依赖于RT（它可作为分子动能的度量）、 溶质间相互作用、以及依赖于分子的大小和形状（它们将影响摩 擦系数）， 因此，非电解质透过人工膜或生物膜有明显的温度 依赖关系，而且溶质分子越大，透过生物膜受的阻力越大，通透 性越小
Permeability of small molecules through lipid membrane hydrophobic fre Ons H,O,urea glt ucose sucrose H, Na, K, HCO3, CL benzene glycerol C O, membrane glycerol HO urea n CL KTNa 10 10-10 Permeability(cm/sec)
Permeability of small molecules through lipid membrane hydrophobic free-charge polar free-charge polar charged ions O2, N2 , H2O,urea, glucose sucrose H+ ,Na+ ,K+ , HCO3 - , CLbenzene glycerol C O2, _____ __________ _ membrane glycerol glucose H2O urea tryptophen CL- K+ Na+ 10-2 10-4 10-6 10-8 10-10 10-12 Permeability (cm/sec)
SMALL HYDROPHOBIC MOLECULES N2 benzene SMALL UNCHARGEDH20 POLAR glycerol ethanol MOLECULES UNCHARGED amino acids LARGER POLAR glucose nucleotides MOLECULES Na HCO K IONS Ca*, CI M synthetic lipid bila
2) Four basic mechanism by which solute molecules move across membrane actIve nonmediated carrier mediated B C d membrane D simple diffusion simple diffusion facilitated diffusion active transport through bilayer through channel
2） Four basic mechanism by which solute molecules move across membrane Passive active nonmediated carrier mediated A B C d membrane a b c D simple diffusion simple diffusion facilitated diffusion active transport through bilayer through channel
被动输运 主动输运 非载体介导 载体介导 A B C eeeee eeeeee C D
transported molecule channe carrier protein protein concentration bilayer gradient simple channel- carrier- diffusion mediated mediated PASSⅣ VE TRANSPORT ACTIVE TRANSPORT