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Transcript
Cell Transport Mechanisms and Homeostasis Cell Cytoplasm is full of many different Substances. Mostly WATER as the Solvent making movement and reactivity of the various molecules possible. ≈ 80% Water! Lots of dissolved Ions – but different concentrations than in the Blood. Sugars and Proteins and other molecules. 5% If the Balance is wrong, your blood cells will not survive or function. Pre-Made! Cells! Precisely Balanced! An IV represents Balance with the Cells of your Blood. Not the same Stuff, but equal amounts! 5% Sugar (Dextrose or Ringer’s Lactate) or 0.9% Salt = Cell. Cell Transport Mechanisms and Homeostasis OUTSIDE = Extracellular Fluid. Contains all sorts of things that cells need and that the Organism Provides. Your Digestive Tract is Choosy, but not perfectly Picky! Selective Permeability allows Cells to Choose and Move the RIGHT STUFF – CONTROLLED!! INSIDE = Cytoplasm. THE RIGHT STUFF! The Cell NEEDS Specific Things: The right Ions, as many Amino Acids as Possible, Glucose, “Its” Proteins, etc… Other things are Kicked OUT. Contains a Precisely Balanced Solution of all of the RIGHT STUFF! This is Homeostasis! Must be able to Transport the RIGHT STUFF IN! Cell Transport Mechanisms and Homeostasis Transport Proteins can do their job because they are specific in SHAPE! Only Proteins can do this because they are so Variable! R R ? R R ? r But then the Chain? ? But Remember!! Hydrophobic Core Hydrophilic Edges Inside Membrane! Outside Membrane! VARIABLE in SHAPE!! Opening COULD BE: OR OTHERS! Water is the Solvent! Water diffuses into the Solute (High to low conc.) and dissolves it! H20 H20 H20 Dry Solutes cannot move – they are bound together as a Solid. If there is no Restriction to the Movement of the Solutes (Remember – Water will move by itself!), they will form a SOLUTION! Water IS the SOLVENT and breaksup the SOLUTES from each other. Once the SOLUTES are separate, they WILL SCATTER until completely distributed as a Solution. Solutes Stick Together!! BUT! Solvents Stick to Solutes! DIFFUSION leads to Equal Concentrations Everywhere! NORMAL CONDITION! Cells DO NOT Really WANT This! Must have the RIGHT STUFF in the RIGHT Place! Cells will HAVE TO Choose and Separate what is in the Cytoplasm. This Membrane is NOT doing that here, but Cell’s Membrane will be SELECTIVELY PERMEABLE! INSIDE ≠ OUTSIDE Cell Transport Mechanisms and Homeostasis DIFFUSION is the most basic form of molecular movement. In Diffusion, substances scatter as much as possible. As they collide and scatter, they will spread out. Diffusion WILL MAKE ALL SOLUTIONS THE SAME!! Begin with packed Solutes = High Concentration End with randomly separated Solutes = Lowest Concentration = SOLUTION!! Always Moving! Cell Transport Mechanisms and Homeostasis BUT REMEMBER! The Cell is surrounded by a Plasma Membrane that IS NOT just Open to Anything/Everything. The Plasma Membrane Controls Access to the Cell! Polar “Heads” line-up with Aqueous Surface Inside and Outside. Hydrophilic = Loves Water! Fatty Acid “Tails” are Non-Polar and avoid Water Inside the Membrane = Fat Sandwich! Hydrophobic = Fears Water. Most Substances CANNOT pass through the membrane – would need to be Polar AND NonPolar -so the Bilayer is a real boundary! But they CAN Pass through “their” Transport Protein IF IT IS OPEN! Cell Transport Mechanisms and Homeostasis SIMPLE DIFFUSION The simplest process of molecular Transport. Always High conc. To low conc. Always moves to make balance on both sides. Diffusion is trying to force everything to be a Solution. That is NOT always what the Cell wants! High Concentration Outside IF THIS Happened ALL of the TIME: Cytoplasm would be the SAME as the Outside of the Cell. Low Concentration Inside. It is NOT, so there have to be ways to restrict movement of various molecules. AND THERE ARE!! Cell Transport Mechanisms and Homeostasis Facilitated Diffusion: Passive Transport through a Selectively Permeable Membrane. Only a few substances can move through a Plasma Membrane through Simple Diffusion. Everything else will require a Transport Protein that forms an openable and closeable Hole through the Lipids. The Transport Protein must have an opening that “suits” the substance. Shape, Charge, Size, etc… all must be Right! Since each substance requires a different Transport Protein – There are LOTS in the membrane of every Cell!! Can Move Anything IF IT FITS!! Cell Transport Mechanisms and Homeostasis Active Transport Cells have very Specific Needs and sometimes need to “Pack” molecules in and out of the membrane. That would be moving AGAINST the Concentration Gradient and is impossible in Diffusion. To move things from low to High concentration requires Energy = ATP! Wants In?! Why Not?! Wants Out! The substance will bind with “its” Transport Protein, but waits for? Why?! But?! But, The Cell NEEDS these molecules and must “Pump” them IN! That is “Work”! Work requires? ATP ADP Once “Energized”, the substance is “pumped” against the Concentration Gradient to make one side MORE Concentrated! AntiDiffusion! Cell Transport Mechanisms and Homeostasis OSMOSIS: The reality of molecular Transport. Everything is Aqueous!! Most Molecules CANNOT pass through the Cell Membrane directly. However, Water is a small molecule and can “leak” through the various Transport Proteins and CANNOT be completely Stopped! Water is Always Moving!! But Water is everywhere as a solvent. It is always sticking to the various Solutes of the Environment. They have to Polar if they are Dissolved!! The Solutes (Hearts) cannot move (NOW!), but Water can always penetrate the Membrane! This can be a Problem because? Low Conc. Outside, but it cannot penetrate the Membrane. Not Equal. High Conc. of the RIGHT STUFF Inside! Wants OUT (!), But cannot exit. It was moved inside by the cell. In Osmosis, water moves to make both sides Equal! Cell Transport Mechanisms and Homeostasis Endocytosis The previous forms of Membrane Transport moved one molecule at a time. Sometimes Cells want to engulf Large Amounts of a substance – often Food Particles. Endo = Inside, Cyto = Cell. This is often referred to as Bulk Transport. Phopholipid Bilayers will merge and separate if the Cytoskeleton attaches and pulls on them. Membrane and Food pinched into Cell. F O O D In Animals, this is a captured Food Vacuole. Transported on to be Digested/Used! Cell Transport Mechanisms and Homeostasis ExoCytosis What goes in – Must come Out! After it has been used and Processed by the Cell! Or Made for Export! Exo = Outside, Cyto = Cell. This form of Bulk Transport removes materials from the Cell. After the Food Vacuole has been “used”, the waste that is still in the “container” can be expelled. Cell Transport Mechanisms and Homeostasis Cells HAVE to be in “Balance” because of Osmosis. The Water molecules cannot be completely stopped, so the Cytoplasm WILL BE in equal concentration with the Extracellular Fluid in Animal Cells. However, the inside and Outside will be VERY DIFFERENT because of Membrane Transport. Cytoplasm Extracellular Fluid Many Substances are Kept/Trapped Inside! Cell Transport Mechanisms and Homeostasis Animal Cells are Delicate and require very precise Transport Processes to stay in Homeostasis. No Extra Support. Other Cells Possess a external Cell Wall that helps allow them to survive changing external conditions. WATER! But this is OK because the Vacuole holds the water and keeps it separate from the Cytoplasm! Why is it Important to keep the Water OUT of the Cytoplasm?!