BIO 2401 CELL BIOLOGY page 1 CELL BIOLOGY CELL STRUCTURE ORGANELLE AND MEMBRANE TRANSPORT Cells structural units of all living things recognize one another by their surface proteins called glycoproteins since all the cells of humans arise from one cell fertilized egg all the cells of an individual have exactly the same surface proteins and genetic information except for genetic mistakes different individuals you and me have slightly different cell surface proteins Principal parts of the cell cytoplasm consists of cytosol cell liquid viscous and dissolved molecules and organelles except for the nucleus organelles distinct structures or cell parts with specific functions nucleus has nuclear membrane is controlling center of cell has genetic information of cell in form of DNA nucleoli for ribosomal RNA synthesis and a gel like fluid called karyolymph ribosomes 106 cell small granules consisting of ribosomal RNA and protein are site of protein synthesis all cells start out with a nucleus but a few like RBCs lose them when mature free ribosomes float in cytoplasm and seem to function in protein production for cell use while ribosomes bound to the endoplasmic reticulum make protein for release or secretion endoplasmic reticulum ER consists of pairs of membrane folds enlcosing fluid filled cavities called cisternae running throughout the cell and connecting to the cell and nuclear membranes serves in the transport and packaging of molecules for secretion in association with the Golgi complex smooth ER has no ribosomes and catalyzes reactions involved in lipid metabolism synthesizes steroid hormones absorbs synthesizes and transports fat detoxifies drugs pesticides and carcinogens breakdown of stored glycogen rough ER has ribosomes and manufactures cell membranes Golgi complex specialized fold of membranes involved in the packaging of lipids and proteins in vacuoles and lysozymes lysozymes vacuole membrane sacs of hydrolytic enzymes formed by Golgi complex function in chemical digestion mitochondria double membrane sausage shaped organelles the powerhouse of the cell number of mitochondria in cells depends on supply and demand muscle liver and kidney cells have several thousand while inactive cells like skin cells have only a few have own DNA but is circular like that of bacteria can replicate and have ribosomes for their own protein synthesis projections on the inner membrane are cristae infolds location of Kreb s cycle enzymes and cytochrome system BIO 2401 CELL BIOLOGY cytoskeleton composed of filaments micro intermediate and microtubules filaments protein rods of actin that function in support and contractions actin and myosin microtubules hollow protein tubes functioning in support and transport of material through the cell centrioles paired can replicate function in cell division where they influence microtubular formation associated with cell division vacuoles membrane sacs used in storage and transporting secretory material plasma membrane outer limiting membrane that controls what gets in and out of a cell by being selectively permeable separates intracellular fluid from extracellular fluid and keeps ions in different proportions in these two compartments this sets up a membrane potential affects cellenvironment interactions membrane electric potential allows for excitability irritability and responsiveness of cells results from high concentration of sodium outside cell and high concentration of potassium inside the cell which leads to polarization one side other side of the cell membrane electric potential of about 70mV inside cell consists of two rows of phospholipids 60 and cholesterol 40 with proteins penetrating into and or passing through the membrane integral proteins and peripheral proteins that are loosely bound to the surfaces phospholipids form basic fabric of membrane have a polar head that is hydrophylic and a nonpolar tail that is hydrophobic arrangement of phospholipids encourages membrane to self assemble and reseal if torn cholesterols are a stabilizing force proteins float in the lipid bilayer to form a constantly changing mosaic pattern have 2 populations integral firmly inserted proteins most are transmembrane proteins but a few protrude from only 1 of the layers peripheral not embedded in the lipid bilayer attach loosely to integral proteins and are usually removed used in changing shape or providing cytoskeleton have specializations such as microvilli which are minute fingerlike extensions of membrane increase surface area for absorption Tranport through membranes page 2 basic concepts terminology solutions homeogenous mixtures of components that may be gases liquids or solids solute substance present in smaller amount BIO 2401 page 3 solvent substance present in greater amount dissolving medium usually a liquid concentration of solute in solvent expressed in a variety of ways molarity CELL BIOLOGY concentration gradient molecules move from areas of high concentration to areas of low concentration the greater the difference in concentration between the two areas the faster the movement DOWN the concentration gradient PASSIVE PROCESSES also called PASSIVE TRANSPORT 1 diffusion simple diffusion molecules will freely diffuse through a membrane IF they are lipid soluble charged molecules are not small enough to pass through membrane channels or assisted by a carrier molecule particles move from a high concentration to a low concentration due to their kinetic energy and each particle diffuses down its own concentration gradient or from more collisions to less collisions diffusion is a slow process especially in water is influenced by size of molecules and temperature raises kinetic energy 2 facilitated diffusion diffusion made easier because a carrier molecule integral protein in the cell membrane binds molecules like glucose and carries them across the cell membrane with NO expenditure of energy by the cell different molecules usually have different protein carriers changes in shape of carrier allow it to envelope and then release transported substance while shielding it from the non polar regions of the membrane 3 osmosis diffusion of a solvent through a selectively permeable membrane occurs because water is a small molecule and can squeeze between gaps in tails of phospholipids water can also move through pores or transmembrane proteins called aquaporins tonicity the ability of a solution to change the tone or shape of cells by altering their internal water