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Transcript
The Plasma Membrane - Gateway to the Cell 1 Types of Transport Across Cell Membranes 2 Simple Diffusion • Requires NO energy • Molecules move from area of HIGH to LOW concentration 3 DIFFUSION Diffusion is a PASSIVE process which means no energy is used to make the molecules move, they have a natural KINETIC ENERGY 4 Diffusion of Liquids 5 Diffusion through a Membrane Cell membrane Solute moves DOWN concentration gradient (HIGH to 6 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 7 Diffusion of H2O Across A Membrane High H2O potential Low solute concentration Low H2O potential 8 High solute concentration Aquaporins • Water Channels • Protein pores used during OSMOSIS WATER MOLECULES 9 Cell in Isotonic Solution 10% NaCL 90% H2O ENVIRONMENT CELL 10% NaCL 90% H2O NO NET MOVEMENT What is the direction of water movement? equilibrium The cell is at _______________. 10 Cell in Hypotonic Solution 10% NaCL 90% H2O CELL 20% NaCL 80% H2O What is the direction of water movement? 11 Cell in Hypertonic Solution 15% NaCL 85% H2O ENVIRONMENT CELL 5% NaCL 95% H2O What is the direction of water movement? 12 Cells in Solutions 13 Isotonic Solution NO NET MOVEMENT OF H2O (equal amounts entering & leaving) Hypotonic Solution CYTOLYSIS Hypertonic Solution PLASMOLYSIS 14 Cytolysis & Plasmolysis Cytolysis Plasmolysis 15 Osmosis in Red Blood Cells Isotonic Hypotonic Hypertonic 16 What Happens to Blood Cells? 17 hypotonic hypertonic isotonic hypertonic isotonic hypotonic 18 Three Forms of Transport Across the Membrane 19 Passive Transport Simple Diffusion Doesn’t require energy Moves high to low concentration Example: Oxygen or water diffusing into a cell and carbon dioxide diffusing out. 20 Passive Transport Facilitated diffusion Doesn’t require energy Uses transport proteins to move high to low concentration Examples: Glucose or amino acids moving from blood into a cell. 21 Proteins Are Critical to Membrane Function 22 Types of Transport Proteins • Channel proteins are embedded in the cell membrane & have a pore for materials to cross • Carrier proteins can change shape to move material from one side of the membrane to the other 23 Facilitated Diffusion Molecules will randomly move through the pores in Channel Proteins. 24 Facilitated Diffusion • Some Carrier proteins do not extend through the membrane. • They bond and drag molecules through the lipid bilayer and release them on the opposite side. 25 Carrier Proteins • Other carrier proteins change shape to move materials across the cell membrane 26 Active Transport Requires energy or ATP Moves materials from LOW to HIGH concentration AGAINST concentration gradient 27 Active transport Examples: Pumping Na+ (sodium ions) out and K+ (potassium ions) in against strong concentration gradients. Called Na+-K+ Pump 28 Sodium-Potassium Pump 3 Na+ pumped in for every 2 K+ pumped 29 out; creates a membrane potential Moving the “Big Stuff” Exocytosis - moving things out. Molecules are moved out of the cell by vesicles that fuse with the plasma membrane. This is how many hormones are secreted and how nerve 30 cells communicate with one another. Exocytosis Exocytic vesicle immediately after fusion with plasma membrane. 31 Moving the “Big Stuff” Large molecules move materials into the cell by one of three forms of endocytosis. 32 Pinocytosis Most common form of endocytosis. Takes in dissolved molecules as a vesicle 33 . Pinocytosis • Cell forms an invagination • Materials dissolve in water to be brought into cell • Called “Cell Drinking” 34 Example of Pinocytosis pinocytic vesicles forming mature transport vesicle Transport across a capillary cell (blue). 35 Receptor-Mediated Endocytosis Some integral proteins have receptors on their surface to recognize & take in hormones, cholesterol, etc. 36 Receptor-Mediated Endocytosis 37 38 Endocytosis – Phagocytosis Used to engulf large particles such as food, bacteria, etc. into vesicles Called “Cell Eating” 39 40 Phagocytosis About to Occur 41 Phagocytosis - Capture of a Yeast Cell (yellow) by Membrane Extensions of an Immune System Cell (blue) 42 Exocytosis The opposite of endocytosis is exocytosis. Large molecules that are manufactured in the cell are released through the cell membrane. Inside Cell Cell environment 43