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Transcript
3.3 Cell Membrane KEY CONCEPT The cell membrane is a barrier that separates a cell from the external environment. 3.3 Cell Membrane The cell membrane has two major functions – forms a boundary between inside and outside of the cell cell membrane inside cell outside cell 3.3 Cell Membrane The cell membrane has two major functions – forms a boundary between inside and outside of the cell – controls passage of materials cell membrane inside cell outside cell 3.3 Cell Membrane Cell membranes are composed of two phospholipid layers. • Polar Head is charged PO4 • Nonpolar tail of two fatty acid chains 3.3 Cell Membrane The fluid mosaic model describes the membrane • The arrangement of molecules making the membrane • Flexible like fluid with a variety (mosaic) of molecules cell membrane carbohydrate chain cholesterol protein protein channel protein 3.3 Cell Membrane There are other molecules embedded in the membrane • Cholesterol – strengthens • Proteins – movement and signaling • Carbohydrates – identify the cell cell membrane carbohydrate chain cholesterol protein protein channel protein 3.3 Cell Membrane The cell membrane is semipermeable Some molecules can cross the membrane while others cannot. 3.3 Cell Membrane Selective Permeability -some things can cross while others cannot -semipermeable -maintains homeostasis -molecules can cross in a variety of ways 3.3 Cell Membrane Chemical signals are transmitted across the cell membrane. • Receptors bind with ligands and change shape. • There are two types of receptors. 3.3 Cell Membrane Receptors: communicate between cells by detecting a signal molecule to perform an action • There are two types of receptors. – intracellular receptor: bind to molecules to cross the membrane 3.3 Cell Membrane • Membrane Receptor: binds to molecules that cannot cross the membrane; change shape and transmit the message 3.3 Cell Membrane Person A Person B What is the function of the cell membrane? What is a phospholipid? Why is it called that? Describe the fluid mosaic model. What is selective permeability? How does the fluid mosaic model and phospholipids make the cell membrane semipermeable? 3.3 Cell Membrane Page 80 Formative Assessment Questions 3.3 Cell Membrane 3.3 Cell Membrane KEY CONCEPT Materials move across membranes because of concentration differences. 3.4 and Osmosis 3.3Diffusion Cell Membrane Passive transport does not require energy input from a cell. • Takes NO energy • Substances move DOWN their concentration gradient 3.4 and Osmosis 3.3Diffusion Cell Membrane Diffusion is a type of passive transport. • Molecules diffuse down a concentration gradient. • -small • -nonpolar molecules • -for example: • O and CO2 3.4 and Osmosis 3.3Diffusion Cell Membrane Osmosis is a type of passive transport. • Osmosis is the diffusion of water molecules across a semipermeable membrane. 3.4 and Osmosis 3.3Diffusion Cell Membrane Diffusion and osmosis are types of passive transport. • There are three types of solutions. • isotonic • hypertonic • hypotonic 3.4 and Osmosis 3.3Diffusion Cell Membrane Facilitated Diffusion = some molecules can only diffuse through transport proteins. • Some molecules cannot easily diffuse across the cell membrane. • Large, Polar molecules • Facilitated diffusion is diffusion through transport proteins. • Does NOT require energy 3.3 Cell Membrane Person A Person B What is diffusion? What types of substances move through diffusion? What is osmosis? What types of substances move through osmosis? Make a Venn diagram to compare/contrast osmosis and diffusion 3.3 Cell Membrane Person A Person B Describe what happens to a cell in a hypertonic solution. Describe what happens to a cell in a hypotonic solution The hospital gives patients’ a saline (slightly salty) solution to keep them hydrated. In terms of hypo- hyper- and isotonic solutions explain why a pure water solution isn’t given instead? 3.3 Cell Membrane Page 83 Formative Assessment Questions