BIOL 1411 1st Edition Lecture 7 Outline of Last Lecture I Cells II Membranes Outline of Current Lecture I Membrane Transport a Active Transport i Osmosis b Passive Transport Current Lecture I Membrane Transport The endomembrane system in dynamic and fluid Passive transport movement by diffusion no outside energy required concentration gradient is driving force high concentration to low concentration o Simple diffusion directly across the phospholipid bilayer o Facilitated diffusion across a membrane via channel or carrier proteins Active transport requires energy movement against concentration gradient via a protein pump that requires energy to operate Diffusion Rate The diffusion rate of each solute is independent Factors that influence the rate o Diameter of the molecule of ion o Electrical charge o Temperature of the solution o Concentration gradient Permeable for that solute steroids Impermeable for that solute ions Facilitated Diffusion Polar and charged solutes cant diffuse across a phospholipid bilayer so needs the aid of proteins These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute Carrier proteins membrane proteins that function as channels that must bind the transported solutes to speed their diffusion through the bilayer ex Sugar transporters Allows much faster diffusion of glucose than would be possible by simple diffusion through the bilayer Rate depends of concentration gradient Channel Proteins integral membrane proteins that form a central pore lined with polar amino acids Solute streams down the gradient Ex Gated ion channels aquaporin Gated Ion Channels o Open to allow ion passage o Gate opens when protein is stimulate to change shape Ligand gated channel Voltage Gated Ion Channel o Different ion channels Exist for different ions specificity o Several different human diseases result from mutations in K channel genes KCNQ ex Cardiac arrhythmias Membrane Potential electrical gradient across a membrane inside is typically more negative relative to outside o All cells maintains an imbalance of ion concentrations across a plasma membrane o Resting membrane potential Osmosis diffusion of water across a membrane that the solutes cannot pass through Depends on the number of solute particles present not the type of particles Water molecules will diffuse from the region of higher water concentration lower solute concentration to the region of lower water concentration higher solute concentration Hypertonic solution more solutes on the outside of the cell Hypotonic solution more solutes inside of the cell ex Turgor pressure Isotonic equivalent concentration inside and outside the cell in constant equilibrium Facilitated Diffusion by water channels Can cross a membrane directly or by hitchhiking with hydrated ions Cross through special water channels call aquaporins 100 million H2O per second Aquaporin increases membrane water permeability Active Transport opposite of diffusion low concentration of water to high concentration requires energy Example cystic fibrosis is a mutation with a defective chloride pump Uniporters transports one substance in one direction Symporters Antiporters Na K pump Sodium Potassium Pump present in all cells o Important for membrane potential o Higher Na outside of cell higher K inside of cell o Pumps Sodium out of cell against gradient o Pumps Potassium into the cell against gradient o 3 Na out 2 K in Net 1 out o ATP is broken down into ADP and Phosphate Active transport requires ATP adenine triphosphate Primary active transport direct hydrolysis of ATP provides energy Secondary active transport energy comes from an ion concentration gradient that is established by primary active transport o The glucose Na symporter found in intestinal and kidney cells o Glucose is transported across the membrane against its concentration gradient o Simultaneous diffusion of Na provides the energy to move glucose molecules o Works in parallel to Sodium Potassium Pump