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BIOLOGY SEMESTER ONE UNIT 7 CHECKLIST UNIT 7: MEMBRANE STRUCTURE AND FUNCTION In this module you will investigate cellular membrane structure and function. Cellular membranes are made of a fluid phospholipid bilayer embedded with proteins. The proteins function in transport, enzymatic activity, signal transduction, cell-cell recognition, and intercellular joining. The phospholipid bilayer functions to separate the interior of the cell from the extracellular matrix in which it resides. This separation of the interior of the cell from its environment allows for controlled exchange of substances between the cell and its surroundings. The cell membrane is selectively permeable, allowing certain substances easy access in and out while limiting others. Passive transport of materials across the membrane does not have an associated energy cost. Such transport includes diffusion (referred to as osmosis when water is the substance moving across the membrane) and facilitated diffusion (when transport is aided by proteins). Active transport occurs when the cell uses energy to transport materials across its membrane. Transport is active when ATP fuels the movement of substances against their electrical or concentration gradients. Ion pumps and co-transport are two mechanism of active transport. Materials may also be moved across the cell membrane by means of exocytosis and endocytosis. These are usually used for bulk transfer (when there is more than one molecule to be move at a time). During exocytosis, vesicles bring materials to the cell, fuse with the cell membrane and release their contents into it. During endocytosis, molecules enter the cell as the membrane pinches inward, creating a vesicle to the inside containing the desired molecules. The three types of endocytosis are phagocytosis, pinocytosis, and receptor mediated endocytosis. LEARNING OBJECTIVES At the end of this module you should be able to: 1. Explain how the fluid mosaic model of membrane structure explains experimental findings: a. Actual membranes adhere more strongly to water than do artificial membranes composed only of phospholipids. b. Membranes with different functions may differ in type and number of membrane proteins. c. Membrane proteins are not very water-soluble. Creative Commons Attribution 3.0 Unported License 1 BIOLOGY SEMESTER ONE UNIT 7 d. EMs of freeze-fracture membrane preparations show protein particles interspersed in a smooth matrix. 2. Explain how membrane fluidity is influenced by temperature and membrane composition, and explain how cholesterol resists changes in membrane fluidity as temperatures change. 3. Understand the various functions of membrane proteins. 4. Explain the role of membrane carbohydrates in cell-cell recognition. 5. Define diffusion and understand why it is a passive and spontaneous process; compare with osmosis, facilitated diffusion, and active transport. 6. Explain why a concentration gradient of a substance across a membrane represents potential energy. 7. Describe how living cells with and without cell walls regulate water balance. 8. Describe the two forces that combine to produce an electrochemical gradient. 9. Explain how an electrogenic pump creates voltage across a membrane. 10. Describe the process of cotransport. 11. Explain how large molecules are transported across a cell membrane. 12. Distinguish between exocytosis and receptor-mediated endocytosis. CHECK LIST Read Chapter 7: Membrane Structure and Function of Campbell and Reece’s Biology, 8th Ed. As you are reading, address each of the learning objectives listed above. It is recommended that you make flash cards for the terminology list provided. This will be beneficial for studying for the midterm and final exams later in the semester. Review the Power point Lecture “Bio 103 Lecture 3b: Membrane Structure and Function. “ Review the BioFlix Video “Membrane Transport” from the Mastering Biology Website and complete the study Sheet associated with the vido. For extra practice try the Self Quiz or Practice Test on the Mastering Biology Website. To log onto the website, use the access code provided in your textbook. You will also find other resources, such as downloadable MP3 tutorials for each chapter, a glossary, and an electronic copy of your text- you can catch up on your reading anywhere! KEY TERMS active transport adenosine triphosphate (ATP) amphipathic aquaporin carbohydrate concentration gradient diffusion electrochemical gradient electrogenic pump Creative Commons Attribution 3.0 Unported License endocytosis exocytosis facilitated diffusion flaccid gated channel 2 BIOLOGY SEMESTER ONE UNIT 7 glycogen glycolipid glycoprotein hypertonic hypotonic integral protein ion channel isotonic ligand low-density lipoprotein (LDL) membrane potential model myosin osmoregulation osmosis passive transport peripheral protein phagocytosis pinocytosis plasma membrane plasmolysis proton pump receptor-mediated endocytosis selective permeability sodium-potassium pump tonicity transport protein turgid ROOT WORDS TO KNOW amphi- = dual (amphipathic molecule: a molecule that has both a hydrophobic and a hydrophilic region) aqua- = water; -pori = a small opening (aquaporin: a transport protein in the plasma membrane of a plant or animal cell that specifically facilitates the diffusion of water across the membrane) co- = together; trans- = across (cotransport: the coupling of the "downhill" diffusion of one substance to the "uphill" transport of another against its own concentration gradient) electro- = electricity; -genic = producing (electrogenic pump: an ion transport protein generating voltage across a membrane) endo- = inner; cyto- = cell (endocytosis: the movement of materials into a cell; cell eating) exo- = outer (exocytosis: the movement of materials out of a cell) hyper- = exceeding; -tonus = tension (hypertonic: a solution with a higher concentration of solutes) hypo- = lower (hypotonic: a solution with a lower concentration of solutes) iso- = same (isotonic: solutions with equal concentrations of solutes) phago- = eat (phagocytosis: cell eating) pino- = drink (pinocytosis: cell drinking) Creative Commons Attribution 3.0 Unported License 3 BIOLOGY SEMESTER ONE UNIT 7 plasm- = molded; -lyso = loosen (plasmolysis: a phenomenon in walled cells in which the cytoplasm shrivels and the plasma membrane pulls away from the cell wall when the cell loses water to a hypertonic environment) SOURCES Campbell, N. A. (2008). Biology, Eighth Edition. San Francisco: Pearson, Benjamin Cummings. Krogh, D. (2000). Biology, A Guide to the Natural World. Upper Saddle River: Prentice Hall. Pearson Education. (2010). Retrieved 2010, from Mastering Biology : http://session.masteringbiology.com NANSLO Biology Core Units and Laboratory Experiments by the North American Network of Science Labs Online, a collaboration between WICHE, CCCS, and BCcampus is licensed under a Creative Commons Attribution 3.0 Unported License; based on a work at rwsl.nic.bc.ca. Funded by a grant from EDUCAUSE through the Next Generation Learning Challenges. Creative Commons Attribution 3.0 Unported License 4