Facilitated Diffusion and Active Trnsport易化扩散和主动运输.pptVIP

Facilitated Diffusion and Active Transport Facilitated Diffusion Facilitated Diffusion - Movement of specific molecules across cell membranes through protein channels Each protein channel only allows a particular substances to cross. The protein facilitates (helps) the diffusion across the membrane Facilitated Diffusion and Energy Occurs with the following: Charged molecules (ions) When molecules are too large Although facilitated diffusion is fast and specific, it is still diffusion. Net movement of molecules across a membrane occurs from the side with a higher concentration → lower concentration side. Does not require energy. Active Transport Active Transport - energy-requiring process that moves material across a cell membrane against a concentration difference. ATP = energy used in active transport Active Transport Move materials in the opposite direction—against a concentration difference. Requires: energy transport proteins Examples of Active Transport Endocytosis Exocytosis Molecular Transport (use of proteins or protein channels) Endocytosis Endocytosis - Process by which a cell takes material into the cell by infoldings or pockets of the cell membrane. Transports: Larger molecules Solid clumps of material Phagocytosis – “cell eating” Phagocytosis – when extensions of the cytoplasm surround particles, package it within a food vacuole, then cell engulfs it The process of engulfing takes a LOT of energy ?? Scanning electron micrograph of a phagocyte (yellow, right) phagocytosing anthrax bacilli (orange, left) Pinocytosis – “cell drinking” Just like endocytosis; process where cells take up liquid from the surrounding environment, fuse with membrane, and release these fluid filled vacuoles within the cell. Exocytosis Exocytosis - Process by which a cell releases large amounts of material Vacuole fuses with cell membrane Transports: Larger molecules Solid clumps of material Molecular Transport Na/K Pump (Sodium/Potassium Pump) Cells conta