BIOL 1441 1st Edition Lecture 12 Outline of Last Lecture I Plasma membrane a Fluidity b Cholesterol II Membrane proteins a 6 major functions III Permeability of the lipid bilayer a Polar vs nonpolar b Transport proteins IV Types of transport a Diffusion b Osmosis Outline of Current Lecture I Osmoregulation a With cell walls II Facilitated diffusion III Active transport IV Membrane potential V Electrochemical gradient 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 VI Electrogenic pump Current Lecture I II III Osomoregulation water balance a To maintain their internal environment osmoregulate b Control the balance of water within themselves and the outside environment c Paramecium lives in a hypotonic environment pond water i Contractile vacuole that acts as a pump ii SINCE IT LIVES IN HYPOTONIC ENVIRONMENT PARAMECIUM HYPERTONIC d Water Balance with Cell Walls i Hypotonic environment plant cell swells cell wall exerts pressure opposes uptake turgid firm 1 Water flows INTO plant cell stands straight up ii Isotonic environment no net movement of water flaccid wilt iii Hypertonic environment plant cells lose water 1 Water flows out of cell Shrivels up 2 Plasmolysis plasma membrane pulls away from the wall e Tonicity and Osmoregulation i Tonicity ability of a solution to cause a cell to gain or lose water 1 how a solution gains loses water ii Osmoregulation animals plants control the balance of water within themselves and the outside environment 1 how we manage water balance iii ANIMAL CELLS LIKE ISOTONIC SOLUTIONS iv PLANT CELLS LIKE HYPOTONIC SOLUTION Facilitated Diffusion Passive diffusion aided by transport proteins a Transport proteins speed movement of polar molecules across the plasma membrane i Very specific water or small ions b Channel proteins provide corridors that allow a specific molecule or ion to cross the membrane c Ion channels gated channels stimulus causes them to open close i Stimulus chemical or electrical ii Chemical not the substance that will be transported 1 Neurotransmitter can open Na ion channels d Carrier proteins undergo change in shape that translocates the solute binding site across the membrane Active Transport Moves solutes against their gradients a Moving solutes from LOW concentration to a HIGH concentration i AGAINST THE GRADIENT b Active transport requires energy usually ATP c Performed by carrier proteins only IV V VI i Channels are just open passage ways d Sodium potassium pump higher concentration of K and lower concentration of Na inside the cell compared to environment i Both cations ii Is a transport protein iii Maintains concentration gradients of sodium and potassium across cell membranes 1 Pumps 3 Na OUT of cell 2 Pumps 2 K INTO cell 3 Inside of cells are NEGATIVE 4 Inside of cell has LOW sodium Na 5 Inside of cell has HIGH potassium K 6 If Na channels are opened Na diffuses INTO cell 7 If K channels are opened K diffuses OUT of the cell Membrane Potential a All cells have voltage across their plasma membranes b Voltage electrical potential energy separation of opposite charges c Cytoplasm has a negative charge compared to extracellular fluid i Unequal distribution of anions ions cations ions d Membrane potential voltage difference across a membrane i Separate charges across a membrane e Range 50 to 200 mV i Minus sign indicated negative inside the cell compared to outside f Acts like a battery energy source that affects the trafficking of all charged substances across the membrane g Inside cell is negative membrane potential favors the passive transport of cations in to the cell anions out of the cell Electrochemical Gradient a Two combined forces drive the diffusion of ions across a membrane i Ion s concentration gradient chemical force ii Effect of the membrane potential on the ion s movement electrical force b Passive diffusion ion moves down its electrochemical gradient i Includes concentration as well as charge across membrane c Example i Resting nerve cell Na lower inside cell than out ii Stimulated gated Na channels open up iii Na ions fall down electrochemical gradient 1 Driven by concentration gradient of Na 2 Driven by the attraction of cations to the negative interior of the cell charge Electrogenic Pump a Membrane proteins contribute to membrane potential difference of voltage across the membrane b Sodium potassium pump pumps 3 Na ions out for every 2 K ions pumps in i Net transfer of 1 charge to extracellular environment ii Stores energy in form of voltage c Electrogenic pump proton pump transport protein that generates the voltage across a membrane