Introduction to Biology Notes: Chapter 7- Membrane Structure and Function
Introduction to Biology Notes: Chapter 7- Membrane Structure and Function Biology 1107
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This 3 page Class Notes was uploaded by Cheyenne prather on Tuesday March 1, 2016. The Class Notes belongs to Biology 1107 at East Georgia State College taught by Dr. Silva in Winter 2016. Since its upload, it has received 28 views. For similar materials see General Biology in Biological Sciences at East Georgia State College.
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Date Created: 03/01/16
Introduction to Biology Notes: Chapter 7 Membrane Structure and Function Plasma Membrane: boundary that separates the living cell from its surroundings - It is selective permeable Selective Permeable: allows some substances to cross it more easily than others Cellular Membranes: fluid mosaics of lipids and proteins Amphipathic: contains hydrophobic and hydrophilic regions Fluid Mosaic Model: states that a membrane is a fluid structure with a “mosaic” of various proteins embedded in it Factors that Affect Membrane Fluidity - Temperature - Cholesterol Membrane Protein: - Peripheral Proteins: bound to the surface of the membrane - Integral Proteins: penetrate the hydrophobic core Transmembrane Proteins: integral proteins that span the membrane 6 Major Functions of Membrane Proteins: a. Transport b. Enzymatic activity c. Signal transduction d. Cellcell recognition e. Intercellular joining f. Attachment to the cytoskeleton and extracellular matrix Role of Membrane Carbohydrates - Cell recognition Aquaporins: facilitate the passage of water Transport Across Plasma Membrane - Passive transport o Diffusion o Osmosis o Facilitated diffusion - Active transport o Cotransport - Bulk transport o Exocytosis o Endocytosis Passive Transport: substances diffuse down their concentration gradient with no energy investment Dynamic Equilibrium: many molecules cross the membrane in one direction as in the other Osmosis: diffusion of water across a selectively permeable membrane Water Balance of Cells Without Cell Walls Tonicity: the ability of a surrounding solution to cause a cell to gain or lose water Isotonic Solution: solute concentration is the same as that inside the cell; no net water movement across the plasma membrane Hypertonic Solution: solute concentration is greater than that inside the cell; cell loses water Hypotonic Solution: solute concentration is less than that inside the cell; cell gains water Osmoregulation: the control of solute concentrations and water balance, is a necessary adaptation for life in such environments Water Balance of Cells Without Cell Walls Turgid (firm): a plant cell in a hypotonic solution swells until the wall opposes uptake Flaccid (limp): if a plant cell and its surroundings are isotonic, there is no net movement of water into the cell Plasmolysis: in a hypertonic environment, plant cell loses water, the membrane pulls away from the cell wall causing the plant to shrink Facilitated Diffusion: transport proteins speed the passive movement of molecules across the plasma membrane Transport Proteins: - Channel proteins (ion channels) - Carrier proteins - Aquaporins Active Transport: moves substances against their concentration gradients, requires energy usually in ATP form Cotransport: when active transport of a solute indirectly drives transport of other substances; active transport driven by a concentration gradient Bulk Transport: requires energy and occurs by exocytosis and endocytosis Exocytosis: cell takes in macromolecules by forming vesicles from the plasma membrane 3 Types of Endocytosis - Phagocytosis - Pinocytosis - Receptormediated endocytosis Phagocytosis: cell engulfs a particle in a vacuole, which then fuses with a lysosome to digest the particle Pinocytosis: molecules dissolved in droplets are taken up when extracellular fluid is “gulped” into tiny vesicles ReceptorMediated Endocytosis: binding of ligands to receptors triggers vesicle formation Ligand: any molecule that binds specifically to a receptor site of another molecule