Lecture 5 unit2 lecture1 movement of materials through the plasma membrane cells surrounded by interstitial fluid cells must bring in substances needed for metabolism movement of materials through plasma membrane is controlled by plasma membrane selectively permeability passive processes o diffusion the tendency of a molecule or ion to scatter evenly throughout its environment to establish equilibrium allowed to occur because molecules in gases and liquids are constantly in motion collide and bounce off each other in all directions molecules move from high concentration to low increase number of molecules increase collisions factors that influence o o concentration gradient higher concen faster size of molecules smaller move faster temperature higher temp faster molecules o facilitated diffusion o o requires carrier molecule and concentration gradient e g glucose no ATP used solute binds to carrier it changes shape then releases solute on other side of membrane osmosis a special case of diffusion diffusion of water across a selectively permeable membrane just the water passes through important because of water content in cells and extracellular fluids for osmosis to occur selectively permeable membrane concentration gradient for water o means more water and less solute on 1 side of membrane less water and more solute on other side of membrane o creates concentration gradient for water o selectively permeable membrane does not allow solute to pass continues until one of two things occur equilibrium is reached for water means percentage of water and solute is equal on each side of membrane osmotic pressure stops movement of water osmotic pressure potential pressure due to amount of nondiffusible solute more solute less water creates a greater concentration gradient for water causes water to move in more water requires more osmotic pressure to stop its movement pressure to stop osmosis boundaries cell membrane water into cell increases volume creates pressure against plasma membrane to stop flow of water into cell hydrostatic pressure weight of water o filtration movement of particles through a selectively permeable membrane by hydrostatic pressure which forces materials nutrients and oxygen into interstitial spaces surrounding cell examples coffee pot pressure forces water through filter filter keeps out large particles filtration of nutrients from blood capillaries into tissue fluids filtration of wastes from blood in kidneys active processes o o materials moved against concentration gradient o large materials require use of cellular energy ATP 2 major processes o active transport or solute pumping o enzyme like protein carriers serve as solute pumps o move solutes in or out of cell against concentration gradient o examples sodium potassium pump calcium pump bring amino acids into cell bulk transport o large particles through membrane o energy required ATP o types of bulk transport o exocytosis substances moved out of cell into extracellular space 1 2 3 4 packed in vacuole or vesicle golgi vacuole migrates to plasma membrane fuses with plasma membrane fused area ruptures spilling contents into extracellular fluid ex secretory materials packed by golgi complex o endocytosis o plasma membrane invaginates o forms vesicle o brings material into cell o three types 1 pinocytosis cell drinking occurs in human cells bring droplets of fluid into cell 2 phagocytosis means cell eating surrounding solid material and bring into cell usually occurs in conjunction with lysosomes first engulfs foreign materials then destroys with digestive enxymes in lysosomes 3 receptor mediated endocytosis involves a receptor protein on plasma membrane receptor site for specific material material s presence triggers invagination allows cell to take in specific substances from outside of the cell that may be present in low concentrations materials that diffuse through a plasma membrane fall into 3 categories o o lipid soluble materials oxygen carbon dioxide fats lipid insoluble small molecules diffuse through pores in channel proteins some channel proteins tend to be selective some channels are always open some channels open and close gated channels o facilitated diffusion neither lipid soluble or small ex glucose requires carrier molecule and concentration gradient no ATP used solute binds to protein carrier it changes shape pumped a little energy into it so that it fits better with substrate to move through then releases solute on other side of membrane where there is low concentration and releases from enzyme high concentration of substrate anything that combines with an enzyme favors dissociation of carrier with substrate low concentration of substrate favors process limited by number of carriers relationship cell surrounding fluids o o tonicitiy of solution measure of the ability of a solution to cause change in cell shape or tone volume or pressure by promoting osmotic flow of water isotonic solution concentration of solute in extracellular fluid is same as in cell no osmosis occurs fluid around cell is same as fluid inside cell hypotonic solution less solute than found in cell solution has more water than cell hypo refers to less solute water rush into cell cell volume increases cell may burst lysis hypertonic solution more solute than found in cell solution has less water than cell hyper refers to more solute water rushes out of cell leaves cell shrunken or crenated isotonic saline solution concentration of saline salt in blood is 9 isotonic saline is 9 saline o o when isotonic saline is introduced into body no osmosis occurs fluid equilibrium o o o o o o o o maintained effects of tonicity of RBCs hypotonic isotonic and hypertonic solutions affect fluid volume of a red blood cell crenated and swollen cells o must have two solutions o water always flows towards more concentrated solution transcytosis transport of a substance across a cell o receptor mediated endocytosis moves it into cell and exocytosis moves it out the other side insulin resting membrane potential RMP total body cytosol extracellular fluids are electrically neutral electrical potential differences voltage across cell s plasma membrane intracellular fluid is more negative than extracellular fluid voltage differences ranges from 20 to 200mV voltage difference called Resting Membrane Potential RMP voltage difference is important for function of nerve cells conducting information muscle cells causing contraction receptors gathering