Cell Membrane Structure • two layers of phospholipid molecules (lipid containing a glycerol and two chains of fatty acids) • proteins embedded throughout the phospholipidbilayer • See page 52 fig. 2.24 • responsible for maintaining homeostasis inside the cell ANIMATION YOUTUBE (FIRST IS SHORT) http://www.youtube.com/watch?v=Rl5EmUQdkuI&feature=related http://www.youtube.com/watch?v=moPJkCbKjBs Homeostasis: a constant internal environment • Selectively Permeable: allowing some molecules to pass through the cell membrane while preventing others.
Methods of Transport • Passive Transport: no energy required to move materials. • Diffusion: is the movement of molecules from a region of high concentration to a lower concentration. Pg. 53 fig. 2.25 • When there is a difference in concentrations a concentration gradient results. • ANIMATION: http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__how_diffusion_works.html
Methods of Transport • Osmosis: diffusion of water across a semi-permeable membrane from a region of higher water concentration to a region of lower concentration. (with the concentration gradient) • Direction of osmosis depends on the concentration of water molecules on either side of the membrane. Three possible scenarios:
Osmosis (Passive) A. Isotonic: the water concentration is equal on both sides of the cell membrane. As a result, equal amounts of water move in and out of the cell. B. Hypotonic: the water concentration outside the cell is greater than that inside the cell. As a result, water moves into the cell. C. Hypertonic: the water concentration inside the cell is greater than that outside the cell. As a result, water moves out of the cell. Draw fig. 2.26 pg. 55 http://www.youtube.com/watch?v=7-QJ-UUX0iY
Methods of Transport (passive) • Facilitated Diffusion: movement of molecules in or out of the cell along a concentration gradient through a transport protein molecule. • A transport protein will recognize and help to move only one type of dissolved molecule or ion based on its shape, size, and electrical charge. • Fig. 2.27 pg. 57 • http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__how_facilitated_diffusion_works.html
Methods of Transport (Active) Active Transport: energy required to move materials against (ATP) the concentration gradient. (low ➙ high) 1. Endocytosis: the process of the cell membrane folding in on itself to form a vesicle that brings a substance into a cell. Fig. 2.34 page 63 A. Pinocytosis: (“cell drinking”) taking in fluid and dissolved substances. Fig. 2.33 B. Phagocytosis: (“cell eating”)taking in a cell, bacterium, or organic material. Fig 2.33 • http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__phagocytosis.html C. Receptor-assisted endocytosis - the intake of specific molecules that attach to special proteins in the cell membrane that serve as receptors. The receptors have a special shape that only specific molecules will fit into. Ex: animals bring in cholesterol using this method. Fig. 2.34 page 63. • http://bcs.whfreeman.com/thelifewire/content/chp05/0502003.html • Exocytosis: process used in the secretion of cell products in which a vesicle from the inside the cell moves to the cell surface and fuses with the cell membrane, releasing its contents outside the cell.