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Lecture 2

Lecture 2 - Across the Membrane.pdf

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Jane Mitchell

Lecture 2 – Crossing the Membrane Permeability of the Membrane  Very permeable to Hydrophobic Molecules  Semi-permeable to small uncharged polar molecules  Impermeable to large uncharged polar molecules or Ions Proteins for transport  All are multipass transmembrane proteins  Proteins are selective to either a class or maybe an individual molecule  Different cell membranes have different transport proteins Proteins of Passive Transport  Channel Mediated Facilitated Diffusion o The ion or large uncharged polar molecule enters/exits the cell via a (gated) channel o When the gate is opened, a lot of the molecule can cross at the same time  Transporter Mediated Facilitated Diffusion o A proteins undergoes conformational shifts to allow a few molecules to move in or out Channel Proteins  Create a hydrophilic “pore” across the membrane  May be highly selective  Much faster transportation than a transporter; like a “highway” o May be gated or non-gated o Non-gated = always open o Gated = opening & closing is regulated via electrical, mechanical, or chemical signals  Electrical: When receiving an electrical charge, the gate opens  Mechanical: A force (eg. Stretching) occurs on the membrane, the gate opens  Chemical: A ligand binds on the outside/inside of membrane, and channel opens Uniporters  Glut Uniporter o One molecule attaches to the porter o The porter bring the molecule through the membrane into the area of low concentration o Occurs by conformational change o Goes along the concentration gradient Prote
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