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Human Physiology: Unit-1 Cell Membranes transport across cell and membrane BY DR BOOMINATHAN Ph.D. M.Sc.,(Med. Bio, JIPMER), M.Sc.,(FGSWI, Israel), Ph.D (NUS, SINGAPORE), PDF (USA) PONDICHERRY UNIVERSITY IV Lecture 9/August/2012 Source: Collected from various sources on the internet and modified by Dr Boominathan Ph.D. Regents Biology Cell Membranes & Movement Across Them Regents Biology 2006-2007 Cell (plasma) membrane Cells need an inside & an outside… separate cell from its environment cell membrane is the boundary IN OUT food - sugars - proteins - Lipids -salts -O2 -H2O waste - ammonia - salts - CO2 - H2O products - proteins Regents Biology cell needs materials in & products or waste out Building a membrane How do you build a barrier that keeps the watery contents of the cell separate from the watery environment? LIPIDS Remember: oil & water don’t mix!! What substance do you know that doesn’t mix with water? Regents Biology Lipids of cell membrane Membrane is made of special kind of lipid phospholipids “attracted to water” Membrane is a double layer phospholipid bilayer phosphate inside cell lipid outside cell Regents Biology “repelled by water” Semi-permeable membrane Cell membrane controls what gets in or out Need to allow some materials — but not all — to pass through the membrane semi-permeable only some material can get in or out So what needs to get across the membrane? sugar lipids Regents Biology aa O2 H 2O salt waste Crossing the cell membrane What molecules can get through the cell membrane directly? fats and oils can pass directly through inside cell waste outside cell Regents Biology lipid salt sugar aa H 2O but… what about other stuff? Cell membrane channels Need to make “doors” through membrane protein channels allow substances in & out specific channels allow specific material in & out H2O channel, salt channel, sugar channel, etc. inside cell salt wasteBiology Regents H 2O aa sugar outside cell How do you build a semi-permeable cell membrane? Channels are made of proteins proteins both “like” water & “like” lipids bi-lipid membrane Regents Biology protein channels in bi-lipid membrane Protein channels Proteins act as doors in the membrane channels to move specific molecules through cell membrane HIGH LOW Regents Biology Movement through the channel Why do molecules move through membrane if you give them a channel? HIGH ? LOW ? Regents Biology Molecules move from high to low Diffusion move from HIGH to LOW concentration Regents Biology Diffusion Move from HIGH to LOW concentration passive transport no energy needed Regents Biology diffusion diffusion of water osmosis Diffusion (without energy-simple) Move from HIGH to LOW inside cell Lipid Which way will Lipid substances move? Lipid LOW HIGH outside cell Lipid Lipid Regents Biology Lipid Lipid Lipid Lipid Facilitated Diffusion Move from HIGH to LOW through a channel sugar sugar sugar sugar inside cell sugar sugar LOW Which way will sugar move? HIGH outside cell sugar Regents Biologysugar sugar sugar sugar sugar sugar Diffusion Move from HIGH to LOW concentration directly through membrane simple diffusion no energy needed help through a protein channel facilitated diffusion (with help) no energy needed Regents Biology HIGH LOW Simple vs. facilitated diffusion simple diffusion inside cell lipid facilitated diffusion inside cell H 2O protein channel outside cell Regents Biology outside cell H 2O Active transport Cells may need molecules to move against concentration “hill” need to pump “uphill” from LOW to HIGH using energy protein pump requires energy ATP ATP Regents Biology Regents Biology Transport summary simple diffusion facilitated diffusion active transport Regents Biology ATP Osmosis Movement of Water Across Cell Membrane Regents Biology 2006-2007 Osmosis Water is very important, so we talk about water separately Osmosis diffusion of water from HIGH concentration of water to LOW concentration of water across a semi-permeable membrane Regents Biology Keeping water balance Cell survival depends on balancing water uptake & water loss freshwater Regents Biology balanced saltwater 1 Keeping right amount of water in cell Freshwater a cell in fresh water high concentration of water around cell Burst freshwater cell gains water example: Paramecium problem: cells gain water, swell & can burst water continually enters No problem, here Paramecium cell solution: contractile vacuole transports water out of cell Regents Biology 2 Keeping right amount of water in cell Saltwater I’m shrinking, I’m shrinking! a cell in salt water low concentration of water around cell cell loses water example: shellfish problem: cell loses water in plants: plasmolysis in animals: shrinking cell solution: take up water Regents Biology I will survive! saltwater 3 Keeping right amount of water in cell Balanced conditions That’s better! no difference in concentration of water between cell & environment cell in equilibrium example: blood problem: none water flows across membrane equally, in both directions volume of cell doesn’t change Regents Biology I could be better… balanced CELLS Regents Biology Chemical compositions of extracellular and intracellular fluids Downloaded from: StudentConsult (on 15 August 2012 04:30 AM) Regents Biology Na-K Channel: How it Works • • • • A type of active transport. 3 sodium ions move out of cell 2 potassium ions move into cell. ATP is needed as each of these ions are moving against their conc. gradient. • Mostly used in cardiac muscle and nervous tissue. Maintains Na+K gradient concentration. • Huge amount of ATP goes into this NaK channel. Regents Biology Sodium –Potassium Channel Regents Biology Figure 3.11 Sodium-Potassium Channel A molecule of ATP is used with each “swap of Na/K ions Regents Biology Endocytosis (phagocytosis-Cell Eating) This is Vessicle transport during which the entire plasma membrane folds inward allowing large particles into the cell. Ex; the cell is ingesting microbes , perhaps? Regents Biology Cell Membrane Function Endocytosis The cell membrane can also engulf structures that are much too large to fit through the pores in the membrane proteins this process is known as endocytosis. In this process the membrane itself wraps around the particle and pinches off a vesicle inside the cell. In this animation an ameba engulfs a food particle. Regents Biology AS Biology, Cell membranes and 33 Regents Biology Exocytosis The opposite of ENDOcytosis. Large particles are leaving the cell. (digested microbes for example). Regents Biology Receptor-mediated Endocytosis Regents Biology This actually uses specific proteins to identify the substance to be taken into the cell. This is how your body gets rid of excess LDL (cholesterol)from your blood. Receptor- Mediated Endocytosis Viruses are species – specific , and receptor specific, transmitted via receptor-mediated endocytosis. Regents Biology Vesicle-mediated transport Vesicles and vacuoles that fuse with the cell membrane may be utilized to release or transport chemicals out of the cell or to allow them to enter a cell. Exocytosis is the term applied when transport is out of the cell. Regents Biology AS Biology, Cell 38 Cell Membrane (Transport) Notes Cell Membrane and Cell Wall: • ALL cells have a cell membrane made of proteins and lipids protein channel Layer 1 Cell Membrane Layer 2 lipid bilayer protein pump • SOME cells have cell membranes and cell walls – ex: plants, fungi and bacteria Cell Membrane Cell Wall Regents Biology • Plant cells have a cell wall made of cellulose – that cellulose is fiber in our diet • Bacteria and fungi also have cell walls, but they do not contain cellulose • Cell membranes and cell walls are porous allowing water, carbon dioxide, oxygen and nutrients to Regents Biology pass through easily Function of the Cell Membrane: • Cell membrane separates the components of a cell from its environment—surrounds the cell • “Gatekeeper” of the cell—regulates the flow of materials into and out of cell—selectively permeable • Cell membrane helps cells maintain homeostasis— stable internal balance Regents Biology Passive Transport A process that does not require energy to move molecules from a HIGH to LOW concentration Diffusion Facilitated Diffusion Osmosis Regents Biology • Diffusion is the movement of small particles across a selectively permeable membrane like the cell membrane until equilibrium is reached. These particles move from an area of high concentration to an area of low concentration. outside of cell inside of cell Regents Biology Regents Biology • Osmosis is the diffusion of water through a selectively permeable membrane like the cell membrane Water diffuses across a membrane from an area of high concentration to an area of low concentration. Semi-permeable membrane is permeable to water, but not to sugar Regents Biology Regents Biology Regents Biology • Facilitated Diffusion is the movement of larger molecules like glucose through the cell membrane – larger molecules must be “helped” Proteins in the cell membrane form channels for large molecules to pass through Proteins that form channels (pores) are called protein channels outside of cell inside of cell Regents Biology Glucose molecules Regents Biology Hypertonic Solutions: contain a high concentration of solute relative to another solution (e.g. the cell's cytoplasm). When a cell is placed in a hypertonic solution, the water diffuses out of the cell, causing the cell to shrivel. Hypotonic Solutions: contain a low concentration of solute relative to another solution (e.g. the cell's cytoplasm). When a cell is placed in a hypotonic solution, the water diffuses into the cell, causing the cell to swell and possibly explode. Isotonic Solutions: contain the same concentration of solute as another solution (e.g. the cell's cytoplasm). When a cell is placed in an isotonic solution, the water diffuses into and out of the cell at the same rate. The fluid that surrounds the body cells is isotonic. Regents Biology Regents Biology Regents Biology Active Transport Active transport is the movement of molecules from LOW to HIGH concentration. Energy is required as molecules must be pumped against the concentration gradient. Proteins that work as pumps are called protein pumps. Ex: Body cells must pump carbon dioxide out into the surrounding blood vessels to be carried to the lungs for exhale. Blood vessels are high in carbon dioxide compared to the cells, so energy is required to move the carbon dioxide across the cell membrane from LOW to HIGH concentration. outside of cell inside of cell Regents Biology Carbon Dioxide molecules Regents Biology ANALOGY: ENERGY NEEDED: Active Transport NO ENERGY NEEDED: Diffusion Osmosis Facilitated Diffusion Regents Biology Regents Biology • Endocytosis and Exocytosis is the mechanism by which very large molecules (such as food and wastes) get into and out of the cell Food is moved into the cell by Endocytosis Wastes are moved out of the cell by Exocytosis Regents Biology Regents Biology Ex: White Blood Cells, which are part of the immune system, surround and engulf bacteria by endocytosis. Regents Biology