ASD 3003 Human Physiology L3 Membrane Transport PDF

ASD 3003 Human Physiology L3 Membrane Transport 膜運輸 1  Membrane Transport Movement of substances into and out of the cell across the plasma membrane Two basic methods of transport Passive process No energy is...

ASD 3003 Human Physiology L3 Membrane Transport 膜運輸 1  Membrane Transport Movement of substances into and out of the cell across the plasma membrane Two basic methods of transport Passive process No energy is required Active process Cell must provide metabolic energy (usually ATP) Transport of Molecules Across Cell Membrane Passive Membrane Transport Diffusion擴散 (through phospholipid bilayer or ion channels) Facilitated diffusion促進擴散 Osmosis滲透 Active transport主動運輸 Primaryactive transport Secondary active transport 3  Diffusion Net movement is from high concentration to low concentration, or down a concentration gradient Particles tend to distribute themselves evenly within a solution  Factors Affecting Rate of Diffusion 1. Concentration gradient The greater the difference in concentration between two regions of a substance, the faster the rate of diffusion 2. Distance The shorter the distance between two regions of different concentrations, the faster the rate of diffusion 3. Surface area The greater the surface area, the faster the rate of diffusion Diffusion surfaces frequently have structures for increasing their surface area Factors Affecting Rate of Diffusion 4. Sizeand nature of the diffusion molecules Smaller molecules diffuse faster than larger ones Fat-soluble molecules diffuse more rapidly than water-soluble molecules 5. Temperature High temperature generally increases diffusion rate  Simple Diffusion 簡單擴散 Nonpolar and lipid- soluble substances Diffuse directly through the lipid bilayer Diffuse through channel proteins (for ions) Examples: ethanol, fatty acids, glycerol, steroids, etc & nonpolar gases like O2  Facilitated diffusion 促進擴散 For transporting large organic molecules e.g. glucose, amino acid Transport from high to low concentration without energy requirement Transport is helped by protein carriers蛋 白載體 within the membrane Solute binds to the specific binding site of the protein carrier Conformational change構象變化 of the carrier Solute dissociates分離 from the carrier 8  Osmosis The net movement of water molecules from a less concentrated solution (the region of high water potential 水勢) to a more concentrated solution (the region of lower water potential) through a selectively permeable membrane 選透性膜 Osmosis Diffusion and osmosis are both passive, i.e. energy from ATP is not used Osmosis usually results in a volume change http://skowalskibiology.weebly.com/enzymes-and-cellular- transport.html  6. Osmosis Cell membrane of animal cell is selectively permeable The water potential of the fluid surrounding the cells needs to be controlled carefully If the cell gains too much water, it will burst If it loses too much water, it will shrink Examples: Re-absorption of water by the proximal and distal convoluted tubules of the nephron Absorption of water by the intestinal canal — stomach, small intestine and the colon  7. Active Transport An energy-consuming transport of molecules or ions from a region of low concentration to a region of high concentration (against a concentration gradient) Special proteins within the cell membrane act as a specific protein ‘carriers’ The energy for active transport comes from ATP generated by respiration (in mitochondria) Active Transport Example: Na+/K+ ATPase Pumps Na+ to outside, K+ in Establishes and maintains concentration gradient of ions across cell membrane 13 Types of Active Transport Primary active transport Energy source: hydrolysis of ATP Example: Na+/K+ ATPase; Ca+ ATPase; H+ ATPase Secondary active transport (coupled transport) Energy source: use of ion concentration (often Na) difference across membrane Example: symport; antiport 14  Factors Affecting Rate of Active Transport 1. Concentration The greater the concentration difference, the more the energy needed (as greater concentration gradient should be overcome) 2. Energy availability The lack of energy decreases the rate of active transport Endocytosis and Exocytosis Endocytosis 內吞作用 Invagination內陷of plasma membrane becoming a vesicle囊泡 which is finally pinched off within the cytoplasm 16 Endocytosis and Exocytosis Exocytosis胞吐作用 Fusion融合 of a membrane-bound vesicle with the plasma membrane so that the lumen腔 of the vesicle is open to the extracellular細胞外 environment 17 Important words Simple Diffusion Facilitated diffusion Osmosis Active transport Concentration gradient Distance Surface area Temperature Water potential Carrier protein / protein carrier 18