清华大学：《生物化学》课程PPT教学课件（英文版）Biological Membranes and Transport（2/2）

Biological membranes and transport part I Dunging pei, Ph D 裴端卿 Tsinghua University Cell phone:1368301-7108 peixx003oumn edu

Biological Membranes and Transport part II • Duanqing Pei, Ph.D. • 裴 端 卿 • Tsinghua University • Cell phone: 136-8301-7108 • peixx003@umn.edu

Biological Membranes and transport part II Passive transport: with the gradient Water transport--aquaporins Glucose transporters Co-transport of chloride and bicarbonate Active transport: against the gradient Transport ATPases Ion channels

Biological Membranes and Transport part II • Passive transport: with the gradient – Water transport—aquaporins – Glucose transporters – Co-transport of chloride and bicarbonate • Active transport: against the gradient – Transport ATPases – Ion channels

Simple diffusion across permeable membranes ●● @● 。g 1 Before equilibrium At equilibrium Net flux No net flux

Simple diffusion across permeable membranes

Electrochemical Potentials: chemical gradient/electric potential G G ⊙ ⊙ ⊙ ⊙ V>0 V=0 Before equilibrium At equilibrium (b)

Electrochemical Potentials: chemical gradient/electric potential

Selectively permeable barriers Hydrated of living organisms: all solute membranes- intracellular and pl dasma Simple diffusion--virtuall Simple diffusion without transport impermeable to polar and charged species (too slow to be Diffusion meaningful); permeable for with transporter usIon certain gases- molecular oxygen, nitrogen, methane and △ Transport water(huge concentration) Passive transport(facilitated diffusion)-passage of polar compounds and ions aided by membrane proteins that lowers Transporter the activation energy Transporter or permeases

Selectively permeable barriers of living organisms: all membranes—intracellular and plasma Simple diffusion—virtually impermeable to polar and charged species (too slow to be meaningful); permeable for certain gases- molecular oxygen, nitrogen, methane and water (huge concentration) Passive transport (facilitated diffusion)—passage of polar compounds and ions aided by membrane proteins that lowers the activation energy Transporter or permeases

Aquaporins: transmembrane channels that allow rapid movement of water across plasma membrane in various cells--erythrocytes proximal renal tubule cells table 12-3 Aquaporins Aquaporin Roles and location AQP-1 Fluid reabsorption in proximal renal tubule secretion of aqueous humor in eye and cerebrospinal fluid in central nervous system; water homeostasis in lung AQP-2 Water permeability in renal collecting duct (mutations produce nephrogenic diabetes insipidus) AQP-3 Water retention in renal collecting duct AQP-4 Reabsorption of cerebrospinal fluid in central nervous system regulation of brain edema AQP-5 Fluid secretion in salivary glands, lachrymal glands, and alveolar epithelium of lung TIP Water uptake by plant vacuole, regulating turgor pressure Source: King, L.S.& Agre, P(1996)Pathophysiology of the aquaporin water channels Annu. Rev. Physio/ 58, 619-648

Aquaporins: transmembrane channels that allow rapid movement of water across plasma membrane in various cells—erythrocytes, proximal renal tubule cells

Transmembrane topology of an aquaporin, AQP ype Outside 回的9 00000o收p图000 Inside HSN 4 cOo- a tetramer Flow rate: 5x10/sec, better than the best enzyme catalyse(4x10 /s) AG<15kJ/mol: continuous stream, not much interruption

Transmembrane topology of an aquaporin, AQP-1 Type III A tetramer Flow rate: 5x108 /sec, better than the best enzyme catalyase (4x107 /s) DG<15kJ/mol: continuous stream, not much interruption

Glucose transporter of erythrocytes(GluT1): plasma conc=5 mM transporter-50,000 more efficient than simple diffusion O Hydrophobic O Polar O Charged Outside Inside tNHa COO

Glucose transporter of erythrocytes (GluT1): plasma conc=5 mM; transporter—50,000 more efficient than simple diffusion

-Ser-Leu-Val-Thr-Asn-Phe-Ile eu 5 Helical Wheel diagram 6 Asn Phe Distribution of polar Vs nonpolar residues hydrophobic amphipathic helix(one 1 Ser side hydrophobic, the other hydrophilic) hydrophilic Thr Ile 4 (b)

Helical Wheel Diagram: Distribution of polar vs nonpolar residues— amphipathic helix (one side hydrophobic, the other hydrophilic) hydrophobic hydrophilic

Formation of a channel by side-by-side association of 5 or 6 amphipathic helices Hydrogen bonds

Formation of a channel by side-by-side association of 5 or 6 amphipathic helices Hydrogen bonds