Chapter 5 BCS 1005 Mr Tidwell There are 2 types of Transport Proteins o These proteins regulate the movement of hydrophilic molecules through the o Channel Proteins form channels whose central pores allow specific ions or water plasma membrane molecules to pass through the membrane molecules on one side of the membrane and then move them through the membrane to the other side have binding sites that can temporarily attach to specific o Carrier Proteins A substance whose molecules can flow past one another and therefore have no Fluid defined shape Solute A substance that can be dissolved in a solvent Solvent A fluid capable of dissolving a solute Concentration The amount of solute in a given amount of solvent Gradient A physical difference in temperature pressure charge or concentration of a particular substance in a fluid between two adjoining regions of space Movement through membranes occurs by passive transport and energy driven transport o Concentration gradients of ions and molecules exist across the plasma o Plasma membranes are selectively permeable because they only allow certain membranes of all cells ions or molecules to permeate Passive transport concentration gradients and doesn t require energy is the diffusion of substances across cell membranes down o Passive transport includes simple diffusion facilitated diffusion and osmosis o Simple Diffusion Net movement of substances down their concentration gradients across a membrane Molecules that move across membranes by simple diffusion include water oxygen carbon dioxide and lipid soluble molecules like alcohol and vitamins A D and E For diffusion to occur there must be a gradient o Facilitated Diffusion Uses the aid of a channel and transport protein Water soluble molecules like ions amino acids and sugars diffuse o Osmosis through facilitated diffusion The diffusion of water across selectively permeable membranes Dissolved substances reduce the concentration of free molecules in a solution Page 1 of 3 Chapter 5 BCS 1005 Mr Tidwell A hypertonic solution is one with a greater solute concentration Water moves across a membrane toward the hypertonic solution When cells are placed into a hypertonic solution they shrivel owing to water loss A hypotonic solution has a lower solute concentration Water moves across a membrane away from the hypotonic solution When cells are placed into a hypotonic solution they swell owing Isotonic to water entry solutions have equal concentrations of dissolved substances No net water movement occurs across the membrane Cells in isotonic solutions remain unaffected Energy requiring transport occur is transport that requires the use of cellular energy to o Active transport ions across plasma membranes against their concentration gradient Membrane proteins use cellular energy to move molecules or They often have a molecule binding site and an ATP binding site Cells engulf particles or fluids by endocytosis Active transport proteins span the entire membrane o Endocytosis Receptor mediated endocytosis Pinocytosis through the use of receptors on the membrane Phagocytosis cell drinking moves liquids into the cell cell eating moves large particles into the cell moves specific molecules into the cell o Exocytosis Moves materials out of the cell Cells use energy to dispose of undigested particles of waste or to secrete substances into the extracellular fluid by exocytosis Example secretion of hormones Exchange of material across membranes influence cell size and shape o As a sphere enlarges its innermost parts get farther away from the plasma membrane As the cell gets larger diffusion which is relatively slow can take too long to supply important processes deep within the cell Because its volume increases more rapidly that its surface area a larger cell has a relatively smaller area of membrane for acquiring nutrients and eliminating waste products than a smaller cell o Nerve and muscle cells and microvilli overcome size restraints by elongating thus keeping the ratio of surface area to volume relatively high Specialized Junctions o Desmosomes allow cells to connect and communicate attach cells together Page 2 of 3 Chapter 5 BCS 1005 Mr Tidwell Desmosomes are found where cells need to adhere tightly together under the stresses of movement Examples skin intestines and urinary bladder make cell attachments leak proof are found where tubes and sacs must hold contents Tight junctions without leaking Examples skin and urinary bladder and Plasmodesmata plants only allow direct communication o Tight junctions o Gap junctions between cells Cell to cell protein channels allowing for passage of hormones nutrients and ions in animal cells are gap junctions Plant cells have holes in the walls of adjacent cells forming cytoplasmic connections called Plasmodesmata Page 3 of 3