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Exchanges Across Membranes .docx

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Natural Science
NATS 1675
Ruthanna Dyer

th September 12 lecture Exchanges across Membranes 1. Active Transport - Movement of molecules from cell membrane across using energy, usually AGAINST a concentration gradients (not always) - sometimes accelerates downhill - Costs the cell metabolic energy to move substances - Used to not only move molecules, but fundamentally reserves active transport to move molecules the cell needs to sustain life (the cost for using energy) - In short supply, rare and important molecules - P. 90 diagram - summary of membrane associated process (look at lecture notes) - Almost every cell has a socium potassium exchange pump – 3Na for 2K  causes different concentration outside & inside the cell 2. Endocytosis/Exocytosis - Similar mechanism - Large particles/lumps moved into or out of cell. Endo=in, exo=out - Used for macromolecules too big to get through the cell membrane - The membrane wraps itself around these lumps – outer plasma lama wraps and engulfs the lump, then the ends punch together & pinch off the lump which is encapsulated in a portion of the membrane. - They are somewhat reverse process - Phagocytosis: for solid intake (ex RBC) “cell eating” - Pinocytosis: for liquid “cell drinking” - Receptor mediated endocytosis: membrane has intrinsic membrane proteins, which are receptors for certain kinds of molecules present in outside medium. When solute binds to receptor sites on proteins, initiates cascade of events that causes invagination of that portion of the membrane, internalizing that peice of membrane as a spherical vesicle (similar to endocytosis) - b/c this is a process that is only initiated when molecule binds to specific receptors in cell membrane, it’s called receptor mediated endocytosis. Requires binding of solute to the receptors to initiate confirmation changes in membrane that cause
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