Cell Transport Mechanisms and Homeostasis

1. Cell Transport Mechanisms and Homeostasis If the Balance is wrong, your blood cells will not survive or function. Pre-Made! Precisely Balanced! 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% Cells! 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.

2. 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! Contains a Precisely Balanced Solution of all of the RIGHT STUFF! This is Homeostasis! Must be able to Transport the RIGHT STUFF IN! The Cell NEEDS Specific Things: The right Ions, as many Amino Acids as Possible, Glucose, “Its” Proteins, etc… Other things are Kicked OUT.

3. R R R R r 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! But then the Chain? ? ? ? But Remember!! Hydrophobic Core Inside Membrane! Hydrophilic Edges Outside Membrane! VARIABLE in SHAPE!! Opening COULD BE: OR OTHERS!

4. 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.

5. If there is no Restriction to the Movement of the Solutes (Remember – Water will move by itself!), they will form a SOLUTION! Solutes Stick Together!! Water IS the SOLVENT and breaks-up the SOLUTES from each other. Once the SOLUTES are separate, they WILL SCATTER until completely distributed as a Solution. BUT! Solvents Stick to Solutes!

6. Cells DO NOT Really WANT This! Must have the RIGHT STUFF in the RIGHT Place! DIFFUSION leads to Equal Concentrations Everywhere! NORMAL CONDITION! 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

7. 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. Once Diffusion has proceeded, the solutes have been disrupted and scattered as much as possible within their space. Diffusion makes substances spread out completely and is GOING TO HAPPEN UNLESS IT IS STOPPED!! Diffusion WILL MAKE ALL SOLUTIONS THE SAME!! End with randomly separated Solutes = Lowest Concentration = SOLUTION!! Always Moving! Begin with packed Solutes = High Concentration

8. 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! Most Substances CANNOT pass through the membrane – would need to be Polar AND NonPolar -so the Bilayer is a real boundary! 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. But they CAN Pass through “their” Transport Protein IF IT IS OPEN!

9. 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. It is NOT, so there have to be ways to restrict movement of various molecules. AND THERE ARE!! Concentration Gradient High to low. Low Concentration Inside.

10. 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!! Naturally moving H  L, No Energy required! Can Move Anything IF IT FITS!! Naturally moving L H, No Energy required!

11. ATP ADP 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?! This is how the Cell “Get’s” what it NEEDS!! Diffusion makes everything the same, but Active Transport can Force High Concentrations to Happen!! Wants Out! Why?! But?! The substance will bind with “its” Transport Protein, but waits for? But, The Cell NEEDS these molecules and must “Pump” them IN! That is “Work”! Work requires? Once “Energized”, the substance is “pumped” against the Concentration Gradient to make one side MORE Concentrated! Anti-Diffusion!

12. 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!! Low Conc. Outside, but it cannot penetrate the Membrane. Not Equal. 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! High Conc. of the RIGHT STUFF Inside! Wants OUT (!), But cannot exit. It was moved inside by the cell. This can be a Problem because? In Osmosis, water moves to make both sides Equal!

13. 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. In Animals, this is a captured Food Vacuole. FOOD Transported on to be Digested/Used!

14. 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.

15. 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. Some substances are Blocked = Kept Out! Some Substances are let/carried In = Selective! Cytoplasm Selective Permeability Extracellular Fluid Many Substances are Kept/Trapped Inside! Waste/Used Substances are expelled = Exocytosis!

16. 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?!