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Transcript
Cell Membrane Gateway to the Cell Cell Membrane The cell membrane is flexible and allows a unicellular organism to move Structure of the Cell Membrane Cell Membrane The cell membrane is made of 2 layers of phospholipids called the phospholipid bilayer Phospholipids Contains 2 fatty acid tails (chains) that are nonpolar and one polar head Phospholipids • Polar heads are hydrophilic which means “water loving” • Non-polar tails are hydrophobic which means “water fearing” • Makes membrane selective in what crosses *Hydrophobic molecules pass easily; hydrophilic DO NOT* FLUID MOSAIC MODEL FLUID- because individual phospholipids and proteins can move around freely within the layer, like it’s a liquid. MOSAIC- because of the pattern produced by the scattered protein molecules when the membrane is viewed from above. Types of Transport Across Cell Membranes Diffusion • Requires NO energy (passive transport) • Molecules move from area of HIGH concentration to area of LOW concentration Diffusion of Liquids Diffusion through a Membrane Cell membrane Solute moves DOWN concentration gradient (HIGH to LOW) Osmosis • Diffusion of water across a membrane • Moves from HIGH water potential (low solute) to LOW water potential (high solute) Diffusion across a membrane Semipermeable membrane Three Forms of Transport Across the Membrane Passive Transport Simple Diffusion Facilitated diffusion •Doesn’t require energy •Doesn’t require energy •Moves from high to low concentration Example: Oxygen or water diffusing into a cell and carbon dioxide diffusing out. •Uses transport proteins to move from high to low concentration Examples: Glucose or amino acids moving from blood into a cell. Active Transport •Requires energy or ATP •Moves materials from LOW to HIGH concentration •Moves AGAINST a concentration gradient Isotonic Solution NO NET MOVEMENT OF H2O (equal amounts entering & leaving) Hypotonic Solution Hypertonic Solution CYTOLYSIS PLASMOLYSIS Cell in Isotonic Solution 10% NaCL 90% H2O ENVIRONMENT CELL 10% NaCL 90% H2O NO NET MOVEMENT Cell in Hypotonic Solution 10% NaCL 90% H2O ENVIRONMENT CELL ENVIRONMENT 20% NaCL 80% H2O Cell in Hypertonic Solution 15% NaCL 85% H2O ENVIRONMENT CELL 5% NaCL 95% H2O Osmosis in Red Blood Cells Isotonic Hypotonic Hypertonic Moving the “Big Stuff” Exocytosis moving things out Molecules are moved out of the cell by vesicles that fuse with the cell membrane. This is how many hormones are secreted and how nerve cells communicate with one another. Moving the “Big Stuff” Large molecules move materials into the cell by one of three forms of endocytosis. Pinocytosis Most common form of endocytosis. Takes in dissolved molecules as a vesicle. Receptor-Mediated Endocytosis Some integral proteins have receptors on their surface to recognize & take in hormones, cholesterol, etc. Phagocytosis Called “Cell Eating” Used to engulf large particles such as food, bacteria, etc. into vesicles