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Transcript
Cellular Transport Notes Plasma (Cell) Membrane Functions: a. Controls what enters and exits the cell to maintain an internal balance called homeostasis b. It is selectively permeable c. Provides protection and support (maintains integrity of cell) d. Allows cell to receive and respond to incoming messages (signal transduction) Structure of cell membrane Phospholipid Bilayer – 2 layers of phospholipids a.Phosphate head is polar (water loving)= hydrophilic b.Fatty acid tails non-polar (water fearing)= hydrophobic Fluid Mosaic Model The phospholipids are not attached. They float next to each other Phospholipid Lipid Bilayer Cell membranes have pores (holes) in it Selectively permeable: Allows some molecules in and keeps other molecules out Some materials can go straight through the phospholipids= lipid soluble This includes small, non-polar molecules Others are larger or lipid insoluble and have to use a transport protein to get through Lipid insoluble Pores Lipid soluble Structure of the Plasma Membrane 4 parts of plasma membrane: 1. phospholipids 2. proteins 3. cholesterol 4. carbohydrates Types of Membrane Proteins 1. Integral- into or all the way through membrane 2. Peripheral- attached to the outside of membrane Cellular Adhesion Molecules (CAMs) Enable cells to stick to each other • • • • CAMs direct WBC’s to the site of injury Help cells of embryos attach to other cells and form the placenta Help establish connections between nerve cells In cancers- CAMs aren’t working properly and cancer cells don’t get slowed as they spread around the body • Arthritis may occur because WBC’s are captured by the wrong CAMs Cellular Adhesion Molecules (CAMs) direct white blood cells (WBC’s) to site of injury 1. CAMs called selectins coat the WBC, slowing it down as it passes through the blood vessel and binds to a carbohydrate on the inner wall 2. CAMs called adhesion receptor proteins on the lining of the blood vessel bind to CAMs called integrins on the WBC 3. The WBC is directed through a pore space between the endothelial cells of the wall of the blood vessel Types of Cell Transport Types of Cellular Transport •Animations of Active Transport & Passive Transport • Weeee!! ! Passive Transport cell doesn’t use energy 1. Diffusion 2. Facilitated Diffusion 3. Osmosis 4. Filtration • Goes down the concentration gradient high low Active Transport cell does use energy 1. Solute (protein) Pumps 2. Endocytosis 3. Exocytosis 4. Transcytosis This is gonna be hard work!! Goes against the concentration gradient high low Passive Transport • • • cell uses no energy molecules move randomly Molecules spread out from an area of high concentration to an area of low concentration. • (HighLow) Goes down the concentration gradient, like skating downhill Weeee!!! high low 3 Types of Passive Transport 1. Simple Diffusion – molecules go through the phospholipid bilayer 2. Facilitative Diffusion – diffusion with the help of transport proteins 3. Osmosis – diffusion of water 4. Filtration- the process that forces molecules through a membrane by exerting pressure Diffusion Animation of diffusion random movement of particles from an area of high concentration to an area of low concentration. • Diffusion continues until all molecules are evenly spaced (equilibrium is reached)- • Movement is caused from random collisions of particles http://bio.winona.edu/berg/Free.htm Dissolving sugar cube. The cube slowly disappears as the sugar dissolves and then diffuses to regions where there is less sugar (H->L) Eventually the sugar molecules are evenly distributed. Diffusion of Oxygen and Carbon Dioxide O2 diffuses in , CO2 diffuses out An equilibrium in never reached. Intracellular O2 is always low because it is constantly used up in metabolic reactions. Extracellular o O2 is high because of the actions of the respiratory and cardiovascular systems. The concentration gradient always allows O2 to diffuse into the cells The level of the CO2 created as a waste product is always higher inside the cell than outside, so CO2 always diffuses out. Molecules (both solvent and solute) will move across a permeable membrane until an equilibrium is reached. Diffusional equilibrium does not normally occur in organisms. Instead, they tend to reach a physiological steady state, where concentration s of diffusing substances are unequal, but stable Factors that influence rate of diffusion 1. Concentration gradient- the higher the concentration, the faster it diffuses. • But, if the concentration gradient is too high, because of the momentum, the movement may not be able to stop and the cell will burst. 2. Distance- more rapid diffusion over shorter distances 3. Temperature- higher temps, faster diffusion Simple Diffusion Lipid (fat) soluble molecules pass directly through the cell membrane, between the phospholipid molecules = small, non-polar molecules Ex.: fats, CO2, O2, steroids, urea, ethanol, general anesthetics Facilitated diffusion Diffusion of specific particles through transport proteins found in the membrane a. Transport Proteins are specific – they “select” only certain molecules to cross the membrane b. Transports larger or charged molecules Examples: H2O, amino acids, glucose, ions such as H+, Na+, Cl-, Ca2+ Channel Protein Small ions Carrier Protein Glucose, amino acids Facilitated diffusion Larger molecules like glucose and amino acids Small ions Ion channels can be gated or non-gated Channel Proteins animations Types of gates Ligands= molecules that bind specifically to receptors Osmosis diffusion of water through a selectively permeable membrane • Water moves from high to low concentrations • “Water follows salt” Cell membranes are generally permeable to water. So ,water may pass directly through the membrane or use protein channels called aquaporins Osmosis animation Osmosis and Cells The concentrations in cells: 0.9% NaCl 5% sugar • Isotonic Solution Osmosis Animations for isotonic, hypertonic, and hypotonic solutions Isotonic: The concentration of solutes in the solution is equal to the concentration of solutes inside the cell. Result: Water moves equally in both directions and the cell remains same size= Dynamic Equilibrium • Hypotonic Solution Osmosis Animations for isotonic, hypertonic, and hypotonic solutions Hypotonic: The solution has a lower concentration of solutes and a higher concentration of water than inside the cell. (Low solute; High water) hemolysis Result: Water moves from the solution to inside the cell Cell Swells and bursts open = cytolysis Hypertonic Solution • Osmosis Animations for isotonic, hypertonic, and hypotonic solutions Hypertonic: The solution has a higher concentration of solutes and a lower concentration of water than inside the cell. (High solute; Low water) shrivels Result: Water moves from inside the cell into the solution: Cell shrinks =Plasmolysis/ Crenates What type of solution are these red blood cells in? Isotonic Hypertonic Hypotonic Filtration • Forces molecules through a membrane by exerting pressure High Low pressure Hydrostatic pressure- will force water molecules through to the other side of a membrane while large solid particles are left behind Example: water in blood forced out through capillaries , but blood cells and large particles in the plasma remain inside. -------------------------------------------------------------------------Example: Kidneys- pressure forces solute from the blood across a membrane and into the nephron Filtration is commonly used to separate solids from liquids Blood pressure can force liquid and small particles through the pore spaces in the walls of capillaries. Larger particles remain in the blood. Active Transport •cell uses energy Against the concentration gradient •actively moves molecules to where they are needed •Movement from an area of low concentration to an area of high concentration This is gonna be hard work!! high •(Low High) •Three Types: low High Low Active Transport 1. Protein or Solute Pumps Sodium Potassium Pumps (Active Transport using proteins) require energy to transport in and out of the cell Example: Sodium / Potassium Pumps are important in nerve impulses Protein changes shape to move molecules: this requires energy! 2. Endocytosis: taking bulky material into a cell • • • • Uses energy Cell membrane in-folds around a particle Forms a vesicle (a phagosome) Solid particles are digested as the vesicle merges with a lysosome • This is how white blood cells eat bacteria! a. phagocytosis- solids – “cell eating” b. Pinocytosis- liquids c. Receptor-mediated endocytosis pinocytosis phagocytosis Receptormediated endocytosis Moves very specific types of particles into the cell 3. Exocytosis: Forces material out of cell in bulk • membrane surrounding the material fuses with cell membrane • Cell changes shape – requires energy ex: - hormones -wastes released from cell -neurotransmitters - manufactured proteins secreted by cell Endocytosis & Exocytosis animations 4. Transcytosis combines endo- and exocytosis to selectively and rapidly transport a substance or particle from one end of the cell to the other This process occurs in normal physiology and disease HIV uses transcytosis to cross epithelial cells into the anus, mouth, and female reproductive organs.