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3. Facilitated Diffusion (Assisted diffusion) Facilitated diffusion: diffusion of specific particles through ______transport proteins_________ found in the membrane from _high____ to __low____ concentration Involves transport proteins called ___carrier proteins ____________ which are _____specific_____________ for one type of molecule How do carrier proteins work? 1. carrier protein binds to molecule to be transported 2. protein changes shape – shields molecule from interior of cell membrane 3. molecule moves through protein and is released 4. protein returns to original shape and is reusable 4. Diffusion Through Ion Channels Diffusion through ion channels: diffusion of __ions____ from _high____ to __low_____ concentration Involves transport proteins called __ion channels_________ or __channel proteins________ which are usually __specific _____ for one type of ion ions are _charged__________ so… o they’re __insoluble_____ in lipids o they can’t get through the __nonpolar interior ______________ of membrane some ion channels are always open; others open and close (gated channels) o opening/closing may be controlled by 1. membrane stretching 2. electrical signals 3. chemical signals examples of some common ions: Examples of molecules that move through carrier proteins: Na+, K+, Ca+2, Mg+, Cl-, PO4-, HCO3******* GLUCOSE !!!! – it’s needed quickly in the cell but is too large to diffuse quickly on its own Why are these ions important? other small polar molecules (like some amino acids) heartbeat, nerve conduction, fluid balance, O2 delivery, acid-base balance Facilitated diffusion is similar to another process that we talked about earlier this year. What process is that? How are the two processes similar?