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Transcript
Cell Transport • Moving things into and out of the cell through the cell membrane to maintain balance (homeostasis) • Passive: – Doesn’t take any energy from the cell – Just happens (kinetic energy of molecules) • Active: – Uses the cell’s energy, from mitochondria – ATP (Adenosine TriPhosphate) Cell Memebrane • Phospholipid Bilayer – 2 layers, back to back, of molecules of fat called phospholipids • Fluid Mosaic – Other molecules, too, like proteins, but they don’t just sit there, they move around • Selectively permeable – Not just anything can pass through Cell membrane Diffusion • Molecules simply move from an area of higher concentration to lower (with concentration gradient) • Because of the molecules’ kinetic energy (passive) • Will stop when reach equilibrium (equal concentration) • Molecules still move, but for each one that moves in to the cell, one moves out (no net movement) Diffusion across cell membrane • Happens only for very small particles (salt, etc.) • Move between phospholipid molecules of the bilayer • Or for molecules that are nonpolar (hydrophobic) and dissolve into the space between the two layers of the cell membrane, but not in water Facilitated diffusion • For molecules that are too big to get in (e.g. sugar), or have charges (ions) • Proteins in the cell membrane will chemically bind to the molecule. (specific…only 1 molecule per protein…like a lock and key) • The protein will then change shape and the molecule will move in or out of the cell. • Takes no energy (passive) Facilitated diffusion •Note: each protein is specific for one molecule, but there are many different proteins in each cell membrane Osmosis • Special kind of diffusion (passive) • Only for water across the membrane • Water can move against its concentration gradient, that is water can move from low water to high water concentration • Water moves to “water down” whatever is most concentrated. Osmosis • If the cell has more “stuff” dissolved outside than inside, it is in a hypertonic environment • It will try to “water down” the environment to make it less harsh • Water leaves the cell, the cell shrinks (plasmolysis) • http://www.youtube.com/watch? v=gWkcFU-hHUk&feature=related Osmosis • If the cell has more “stuff” dissolved inside than outside, it is in a hypotonic environment • It will try to “water down” the inside to make it less harsh • Water enters the cell, the cell grows • If it gets too big, it explodes (cytolysis) • http://vimeo.com/2726364 Osmosis • If the cell has equal amounts of “stuff” dissolved inside and out, it is in an isotonic environment • Water molecules will move both in and out of the cell equally, so there is no net movement of water • Notes: water still moves in and out in hypertonic and hypotonic solutions, but the net movement is in one direction Equilibrium • Passive transport will continue until equal concentrations are reached in and out of the cell (equilibrium). • Molecules still move back and forth across the membrane, but do so at equal rates • No net (total) movement of molecules, though Active Transport • Sometimes cell wants higher or lower concentrations (not equilibrium) • Have to use the cell’s energy (ATP adenosine triphosphate) • Moves against concentration, i.e. from low to high concentration • Moves large molecules or large amounts of molecules Protein Pumps • Energy changes shape of the protein to move things in/out of the cell • Is specific…each protein can only chemically bind with one molecule, but there are many different proteins in the cell membrane (like a lock and key) • Na+ K + pump Protein pumps • 3 sodiums are taken out of the cell and 2 potassiums brought in using ATP. Transport by vesicle • Moves large molecules or large quantities of something into and out of the cell • Into the cell is called endocytosis – Pinocytosis: water/liquid moves – Phagocytosis: solids move • Out of the cell is called exocytosis (e.g. products from Golgi Apparatus) Endocytosis •Note part of cell membrane makes the vesicle and is now inside the cell! •http://www.youtube.com/watch?v=W6rnhiMxt KU Exocytosis •Note the vesicle fuses with the cell membrane and is now part of it! •http://www.youtube.com/watch?v=U9pvm_4bHg ATP •Adenosine Triphosphate •Adenosine Diphosphate •ATP •ADP + P + energy