BIO 110 1st Edition Lecture 18Carriers vs Channels - Transport kinetics- rate of transport vs concentration o Channel- linear kinetics  Open pathways for many molecules at once  Carry proportionally more as concentration increases o Carriers- saturation kinetics o Carriers one at a time o Become saturated when trying to move as concentration increase Active Transport - Cell can concentrate a molecule by using energy to actively more molecules from low to high concentration o Against the gradient - Requires specific transporter protein - Requires energy (ATP) - Allows active control of cell contents by expending energy o Glucose - Three types of transporters o Uniporters- transport single molecular species in one direction o Symporters- transport 2 molecular species in same direction o Antiporters – transport 2 molecular species in opposite directions  NA out of and K into cell at same time - All active transporter also saturate Coupled Transport - Active transport creates one gradient, use that gradient to make another molecule. Transports are “coupled” Osmosis - Membrane are permeable to water o Small permeability of pure PLBL enhanced by aquaporins o Not permeable to many common solutes - High concentration of impermeable solutes inside cell - Concentration of solutes outside cell changes - Since solutes can’t move, water moves in and out by OSMOSIS Tonicity and Cells - Hypertonic: higher concentration of solutes than inside the cell- loses water - Hypotonic – lower concentration of solutes than inside cell- gains water- Isotonic – same concentration of solutes as inside cell - Consider hospital IC solution injected into veins o Want isotonic solution Connections between Cells - 3 kinds of specialized connections o Tight junction- impermeable connections around the outside of cells. Found in epithelial cell layers  Separate lumen of organ from rest of the body, preventing organ content from leaking o Anchoring junction- close connection between 2 cells, provide mechanical strength, permeableo Desmosomes connect cytoskeleton of 2 cells o Hemidemosomes connect cytoskeleton to ECM o Communication junction- allow molecules and signals to move o Animal- gap junction o Plant-