Lecture 3- cell membranes


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Unformatted text preview: and Cl-, by shuttling them across the membrane. • Substances do not move across the barrier indiscriminately; membranes are selectively permeable. 10:25 Gardiner 2013 27 9 !permeability&depends&on&interaction&of&molecule&at&the& • Permeability of a molecule through a membrane depends on the interaction of that molecule with the hydrophobic core of the membrane. hydrophobic&core – Hydrophobic molecules, CO2, and O2, can dissolve in the lipid bilayer and cross easily. – Ions and polar molecules pass through with difficulty. – Proteins can assist and regulate the transport 10:25 Gardiner 2013 28 • Specific ions and polar molecules can cross the lipid bilayer by passing through transport proteins that span the membrane. – Some transport proteins have a hydrophilic channel that certain molecules or ions can use as a tunnel through the membrane. – Others bind to these molecules and carry their passengers across the membrane physically. !transport&proteins&are&necessary&to&get&things&across& the&membrane !a&simple&channel&allowing&things&to&move&in&and&out !Each&transport&protien&is&speci:ic&to&ONE&thing • Each transport protein is specific as to the substances that it will translocate (move). 10:25 Gardiner 2013 29 • For example, Paramecium, a protist, is hypertonic when compared to the pond water in which it lives. – In spite of a cell membrane water still continually enters the Paramecium cell. – Paramecium have a specialized organelle, the contractile vacuole, that functions as a bilge pump to force water out of the cell. 10 Specific proteins facilitate passive transport of water and selected solutes Facilitated*diffusion: !*create*a*channel*which*allows*something*to*cross*a* membrane • Many polar molecules and ions that are normally impeded by the lipid bilayer of the membrane diffuse passively with the help of transport proteins that span the membrane. • The passive movement of molecules down its concentration gradient via a transport protein is called facilitated diffusion. 10:25 Gardiner 2013 !N...
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