BIO 3324 1st Edition Lecture 2 Outline of Last Lecture I. Fluid compartments II. Plasma MembraneIII. Channel proteinsIV. Mass balanceV. Law of diffusion Outline of Current Lecture II. Active TransportIII. Mediated transportIV. exocytosisV. osmosisVI. membrane potentialCurrent LectureActive transport:• Use of a carrier to transport across a membrane against the gradient• Binding site affinity is greater on the downstream side• Two types of active transport– Primary active transport – energy in the form of ATP is directly used to change carrier conformation and binding site affinity. • Many of the transporters are ATPases: Hydrolyze ATP → ADP + Pi• Transporters are often called “pumps”Secondary active transport – uses potential energy stored in the concentration gradient of one molecule to push other molecules against their concentration gradient. Ultimately is dependent on the gradients created by primary active transportActive Transport: Na+-K+ pump:• Transports Na+ out of cell and K+ into cell (against their gradients)• Mechanism of action– ATPase activity changes conformation and increases the affinity for Na+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.– Na+ binding induces carrier conformation change so that Na+ is transported to ECF– Dephosphorylation changes conformation so that carrier has a greater affinity forK+– K+ binding restores original conformation to allow K+ into ICF• Establishes a Na+ and K+ gradient across the plasma membrane of all cells. This is especially critical in nerves and muscles.• Regulates cell volume by controlling solute concentrations inside the cell• Potential energy stored in the new concentration gradients serve as the energy source for the cotransport of glucose and amino acidsSecondary Active Transport:• Example of the Na+-Glucose Co-transporter • Energy is indirectly used to facilitate the transportation of a substance against its gradient• Frequent utilization of co-transport carriers– Binding of molecule A increases the affinity for molecule B binding• Mechanism of action– Na+ binds to carrier protein when it is open to the ECF– A conformational change caused by Na+ binding increases the binding affinity for glucose– Binding of glucose results in conformation change towards inside of cell– Both Na+ and glucose are released• Na+ into low [Na+] environment• Glucose due to low affinity• Conformational change to be open towards ECFCarrier-Mediated Transport:• The characteristics that determine what kind and amount of material to be transported– Specificity – each carrier protein is specific to the molecule it is supposed totransport. Only very like/similar molecules (in some cases) may bind to the samecarrier.– Competition – if the carrier can bind more than one substance, then the rate oftransport is dependent on the presence of the number of molecules of bothsubstances– Saturation – a limited number of carrier binding sites are available within amembrane. Results in the transport maximumVesicular Transport:• The mechanism to move large macromolecules and particles that are too big to enter orleave cells through protein channels or carriers• Use of membrane-bound compartments created from the cell membrane• Two processes to intake and one to output material– Phagocytosis – intake– Endocytosis – intake– Exocytosis – outputExocytosis:• Vesicle containing substance, moves to the plasma membrane, fuses with plasmamembrane, then releases its contents into the ECF.– Used to excrete large polar molecules– Enables the cell to add specific components to the plasma membraneEpithelial Transport:• Movement of substances through cells.– Moving material from the lumen of an organ is called absorption– Moving material into the lumen of an organ is called secretion • Can occur either in between adjacent cells (Paracellular Transport) or through the cells(Transcellular transport)• Usually one step is uphill and the other is downhillTranscytosis:• Combination of Endocytosis and Exocytosis• Vesicle is transported through the cell via Cytoskeletal elementsOsmosis:• The net diffusion of H2O across a membrane• H2O moves to the area of higher solute concentration• When the membrane is permeable to both H2O and solute then both solute and H2O willequilibrate• When the membrane is permeable to H2O and not to solute– Water concentrations NOT equal– Solute concentrations NOT equal– So H2O moves into the area of higher solute concentrationOsmosis and osmotic pressure:• Tendency for water to diffuse by osmosis into side B is exactly balanced by opposingtendency for hydrostatic pressure difference to push water back into side A– Result: Osmosis Ceases– Concentration equilibrium is NOT met• Osmotic Pressure of the solution is the opposing pressure necessary to completely stoposmosisOsmolarity:• Describes the number of particles (ions, intact molecules, or both) in a given volume ofsolution• It says nothing about the composition of the particles• Examples:– One glucose yields one particle– One NaCl yields two particles: Na+ and Cl- Tonicity:• Tonicity is the ability of a solution to cause a cell to gain or lose water • Isotonic solution: equal non-penetrating solute concentration (and equal waterconcentration)• Hypertonic solution: higher non-penetrating solute concentration• Hypotonic solution: lower non-penetrating solute concentrationElectricity review:• Overall the human body is electrically neutral (e.g. for every + charge, there is a –charge)• Opposite charges attract, same charges repel• Separating charges requires energy• Separated charged move towards each other through material called “Conductors” andare kept separated from each other by insulators– Conductor in the body is H2O– Insulator is the plasma membraneMembrane Potential:• Separation of opposite charges across the Plasma Membrane• Difference in charge between the localized regions of the ECF and ICF on either side ofthe membrane– The difference in charge between two adjacent areas produces an ElectricalGradient– Electrochemical gradient is the simultaneous effect of concentration andelectrical gradients • Resting