1.4 Membrantransport

Transport durch Membranen Passiver Transport: OHNE ATP-Energie, MIT dem Konzentrationsgradienten

Transport durch Membranen - passiver Transport Diffusion: Die passive Bewegung von Partikeln von einer Region hoher Konzentration in eine Region niedriger Konzentration

Diffusion: Die passive Bewegung von Partikeln von einer Region hoher Konzentration in eine Region niedriger Konzentration. Wasser Tropfen von Farbe Figure :4-2 Title: Diffusion of a dye in water Caption:

Transport durch Membranen - passiver Transport Einfache Diffusion: Substanzen (kein Wasser) bewegen sich durch Phospholipide. Erleichterte Diffusion: Durch Kanäle oder Membran-Proteine. Diese ändern ihre Struktur, um Substanzen (kein Wasser) durchzulassen.

Ionen, z.B. Ka+ Kanalprotein Aminosäuren, Zucker, Kleine Proteine Einfache Diffusion Erleichterte Diffusion durch einen Kanal kleine Moleküle (O2, CO2, H2O) Ionen, z.B. Ka+ Kanalprotein Erleichterte Diffusion durch Transportprotein Aminosäuren, Zucker, Kleine Proteine Figure :4-3 Title: Diffusion through the plasma membrane Caption: (a) Simple diffusion: gases such as oxygen and carbon dioxide and lipid-soluble molecules can diffuse directly through the phospholipids. (b) Facilitated diffusion through a channel: protein channels (pores) allow passage of some water-soluble molecules, principally ions, that cannot diffuse directly through the bilayer. (c) Facilitated diffusion through a carrier. Exercise Imagine an experiment that measures the initial rate of diffusion into cells placed in sucrose solutions of various different concentrations. Sketch a graph (initial diffusion rate versus solution concentration) that shows the result expected if diffusion is simple, and a graph that shows the result expected for facilitated diffusion. Transportprotein

Transport durch Membranen passiver Transport Osmose: ist die passive Bewegung von Wassermolekülen durch eine semipermeable Membran, von einem Bereich von gelöster Substanz in niedriger Konzentration zu einem Bereich von gelöster Substanz in höherer Konzentration.

Osmose: ist die passive Bewegung von Wassermolekülen durch eine semipermeable Membran, von einem Bereich von gelöster Substanz in niedriger Konzentration zu einem Bereich von gelöster Substanz in höherer Konzentration. Semipermeable Membran Zuckermolekül Wasser Figure :4-4 part b Title: Osmosis part b Caption: (b) A bag is made of a membrane selectively permeable to free water molecules (white dots) but not to larger molecules, such as sugar (yellow hexagons) or water molecules held to the sugars by hydrogen bonds. If the bag is filled with a sugar solution and suspended in pure water, free water molecules will diffuse down their concentration gradient from the high concentration of water outside the bag to the lower concentration of water inside the bag. The bag will swell and may burst as water enters. Question Imagine a container of glucose solution, divided into two compartments (A and B) by a membrane that is permeable to water and glucose but not to sucrose. If some sucrose is added to compartment A, how will the contents of compartment B change?

Transport durch Membranen Aktiver Transport: MIT ATP-Energie, GEGEN dem Konzentrationsgradienten

Transport durch Membranen Aktiver Transport Proteinpumpen, z.B. Ka+-Na+-Pumpe Mit ATP werden Ionen gegen den Konzentrationsgradienten durch die Membran gepumpt.

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Transport durch Membranen Aktiver Transport Endozytose/ Exozytose: Vesikel fusionieren mit der Membran und transportieren so Substanzen in die Zelle und heraus.

Endozytose 0.1 micrometer Figure :4-8 Title: Receptor-mediated endocytosis Caption: These electron micrographs illustrate the sequence of events in receptor-mediated endocytosis. (a) The shallow depression in the plasma membrane is coated on the inside with a protein (dark, fuzzy substance in the micrographs) and bears receptor proteins on the outside (not visible). (b, c) The pit deepens and (d) eventually pinches off as a coated vesicle. The protein coating is recycled back to the plasma membrane.

extrazellulär Zyto- plasma Plasmamembran Figure :4-8 part a Title: Receptor-mediated endocytosis part a Caption: These electron micrographs illustrate the sequence of events in receptor-mediated endocytosis. (a) The shallow depression in the plasma membrane is coated on the inside with a protein (dark, fuzzy substance in the micrographs) and bears receptor proteins on the outside (not visible). (b, c) The pit deepens and (d) eventually pinches off as a coated vesicle. The protein coating is recycled back to the plasma membrane. Plasmamembran

Figure :4-8 part b Title: Receptor-mediated endocytosis part b Caption: These electron micrographs illustrate the sequence of events in receptor-mediated endocytosis. (a) The shallow depression in the plasma membrane is coated on the inside with a protein (dark, fuzzy substance in the micrographs) and bears receptor proteins on the outside (not visible). (b, c) The pit deepens and (d) eventually pinches off as a coated vesicle. The protein coating is recycled back to the plasma membrane.

Figure :4-8 part c Title: Receptor-mediated endocytosis part c Caption: These electron micrographs illustrate the sequence of events in receptor-mediated endocytosis. (a) The shallow depression in the plasma membrane is coated on the inside with a protein (dark, fuzzy substance in the micrographs) and bears receptor proteins on the outside (not visible). (b, c) The pit deepens and (d) eventually pinches off as a coated vesicle. The protein coating is recycled back to the plasma membrane.

Vesikel 0.1 mikrometer Figure :4-8 part d Title: Receptor-mediated endocytosis part d Caption: These electron micrographs illustrate the sequence of events in receptor-mediated endocytosis. (a) The shallow depression in the plasma membrane is coated on the inside with a protein (dark, fuzzy substance in the micrographs) and bears receptor proteins on the outside (not visible). (b, c) The pit deepens and (d) eventually pinches off as a coated vesicle. The protein coating is recycled back to the plasma membrane. 0.1 mikrometer

Exozytose Zytoplasma 0.2 micrometer Figure :4-9 Title: Exocytosis Caption: Exocytosis is functionally the reverse of endocytosis. Question How does exocytosis differ from diffusion of materials out of a cell? Zytoplasma 0.2 micrometer