Chapter 4 Lecture Notes PDF

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BIO 370 Chapter 4 lecture guide. SLIDE 1: Chapter 4: Membranes, Channels and Transport  Plasma membrane regulates molecular travel between the interior of the cell and external environment  Concentration Gradient: different amounts of ions on either side of the plasma membrane o helps maintain stable intracellular environment to balance catabolic and synthetic chemical reactions of the cell  Lipid Bilayer: double layer that is impermeable for most water-soluble molecules SLIDE 2: Osmotic Properties of Cells, Figure 4-12  Homeostatic process is important in maintaining cell membrane and interior/exterior concentration (figure 4.2)  Most prevalent ions = Na+, K+, Ca+, Cl Potassium (K+) is the most prevalent cell – more than sodium (Na+)  Membrane allow for passage through distinct interior and exterior environments  Na+ is the most common extracellular ion  Ionic environment is responsible for a lot of physiology TEXT SECTIONS: Biological membranes, Figure 4-2  Biological membranes have multiple components based on a lipid bilayer  Globular integral proteins: provide mechanism for transmembrane transport o Integral proteins: passive-transport pores and channels / active-transport pumps and carriers / membrane-linked enzymes / chemical signal receptors and transducers  Glycoproteins have oligosaccharide side chains that are important in cell recognition and communication  Cholesterol can be find in the heads of phospholipids and reduce membrane flexibility  Inner ends of phospholipids are very mobile helping with fluidity Mechanisms of Transport, Figure 4-17  Three mechanisms help crossing over of plasma membrane o Passive diffusion: simple diffusion of substance across membrane o Passive transport (facilitated diffusion): substance moves through channel down electrochemical gradient  Ionophores: carrier proteins that help specific ions o Active transport:  Primary: uses ATP to move substance (usually ion) against electrochemical gradient  Secondary: uses electrochemical gradient created by primary AT to move substance against concentration gradient  Doesn’t consume energy by itself In addition to the chapter reading, complete the following unit in Khan academy:

https://www.khanacademy.org/science/biology/membranes-and-transport SLIDE 3: Donnan equilibrium, Figure 4-10  Textbook definition: If diffusible solutes are separated by membrane that is freely permeable to water and electrolytes but totally impermeable to one ionic species, the diffusible solutes become unequally distributed between two compartments  Unequal distribution of ions = unequal distribution of charge o All at equilibrium (no net flux)  The forces that predict the movement of ion has to do with its concentration  KCl is permeable  The various permeability of solutes/ions to the cell membrane causes Donnan equilibrium  Diffusion of substrates through membranes  Modeled using Fick’s 1st Law o J = DA (C/X) o Tells you the flux rate at membranes and ionic movements and their concentrations Factor Effect on Rate of J (flux) Increased delta C Increases Increased Permeability Increases Increased Surface Area (A) Increases Increased Molecular Weight Decreases Increased Membrane Thickness Decreases

This is a good Donnan equilibrium animation Keeley, L. “Gibbs-Donnan Equilibrium and the Mebrane Potential.” https://www.youtube.com/watch?v=SNvA7VDCmKQ SLIDE 4: Diffusion of Substances through the membrane can be modeled using Fick’s 1st Law. (Slide provided in supplemental powerpoint file) TEXT SECTION: Membrane permeability, Figure 4-18  Membrane permeability of nonelectrolyte depends on its oil and water partition coefficient o Measure of ability to dissolve and diffuse through lipid bilayer Questions to answer from text reading in this section: 1. What property must a substance have if it is to pass through the phospholipid bilayer portion of the membrane? o it must be permeable to oil and water 2. How can this property be measured in an experiment? (See Fig 4-18) o It can be measured by testing its oil and water partition coefficient based on its permeability – oil/water partition coefficients effects on permeability

3. What chemical characteristic does a substance have if it can easily pass through the membrane? o I do not know!!!!!!!!!! SLIDE 5: Cell Volume is regulated, Figure 4-16 Read more about water movement across membranes through website link: http://www.anaesthesiamcq.com/FluidBook/fl1_2.php

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Any cell that moves things in and out will affect its H2O volume Cell regulates volume by transporting solutes o H2O moves freely Maintenance of cell volume is disturbed by metabolic inhibitor that interferes with Na+ pumping Na+ levels are usually maintained at equilibrium as ion passively enters the cell and is pumped out When metabolic inhibitor is added and actively blocks transport of Na+ out of cell, the intracellular concentration of Na+ rises and H2O enters osmotically o This increases cell volume Eventually cell bursts because of high volume of H2O inside cell

SLIDE 6: Comparing mechanisms of transport, Figures 4-20 & 4-23. Review mechanisms of transport (figure 4-17)  Transporters vs. Channels  Permeable solute increases flux with increased concentration o Some due at lesser amounts  different permeability o Always a linear trend 1. Diffusing across membrane (only if you’re hydrophobic) 2. Transports (hydrophilic) 3. Channels (hydrophilic)  Passive diffusion through membrane (Figure 4-20 a) o gives linear positive relationship o The rate of influx is proportional to the extracellular concentration of substance  Concentration and permeability are important for flux  Passive Transport through channels ((Figure 4-20 b) o Most permeable is blue line o There are no carriers being used o When there is leveling off steady curved incline shows not as lipid permeable  Exhibits saturation kinetics  Carrier-Mediated (facilitated diffusion – passive transport) (Figure 4-20 c) o Transporters have slower and less efficient mechanisms than channels o Transporters exhibit Michaelis-Menton kinetics – like enzymes o Tells us there is carrier involved and the efficiency of transporter  Kinetics of influx of substance crossing plasma membrane and entering cell depends on mechanism of substance’s movement!!!

TEXT SECTION: Ion gradients as a source of energy, Figures 4-27 & 4-28. Figure 4-27  Chemiosmotic Coupling Hypothesis: energy transduction from membrane o Membrane-embedded protein complex of respiratory chain uses energy to pump H+ against concentration gradient outside of mitochondrial matrix o H+ enters into mitochondrial matrix through ATP synthase in the inner mitochondrial membrane o Energy released by movement of H+ down into concentration gradient catalyzes ATP formation from ADP and inorganic phosphate (Pi) o Inner membrane is impermeable to H+  Answering to hypothesis: energy stored in the H+ concentration gradient (low concentration inside the matrix, high outside) is preserved until H+ is channeled through ATP synthase Figure 4-28  Phosphate and ATP-ADP transport system that makes ATP is in inner mitochondrial membrane  Every 4 H+ translocated outward, 3 are used to synthesize 1 ATP molecule and 1 is used to export ATP in exchange for ADP and Pi. These are examples of how the energy in ion gradients are used to do cellular work!!!!!!!! SLIDE 7: Channels are selective for their ions, Figure 4-29.  Selectivity: size, charge, hydration  Positive changes lining the channel pore allow anions to pass  But it slows the diffusion of cations through the channel SLIDE 8: Epithelial tissues. Figure 4-34.  GI tract and kidney have epithelial cells  Composed of sheets of epithelial cells connected by tight junctions o Tight junctions seal cells together into an epithelial sheet but do not provide a channel  Found in line cavities and hollow organs (absorption)  Form barriers affecting transport, etc.  Facilitates regulation of substance flux across body o Barrier between external and internal environment o Exterior = mucosal side o Interior = serosal side o Tight junctions limit paracellular path In addition to the chapter reading, follow this link in Khan academy: https://www.khanacademy.org/science/biology/structure-of-a-cell#cytoskeletonjunctions-and-extracellular-structures read the “Cell-cell junctions” section under “Extracellular structures and cell to cell junctions”

SLIDE 9: Epithelial tissues facilitate regulation of substance flux across body compartments, Figure4-35.  Substances can cross epithelial layer by either paracellular or transcellular pathways  Active transport only happens across plasma membranes o Actively transported molecules follow the transcellular pathway  Transcellular pathway: substances can pass through ends of the cell  Paraceullar pathway: substances can pass around the ends of the cell SLIDE 10: Example: Na+ transport across epithelia, Figure 4-37.  Trans-epithelial Na+ transport depends on diffusion and active transport SLIDE 11: Cells move solutes, resulting in osmosis (solute-coupled water transport), Figure 4-39.  Wherever Na+ goes, H2O goes!!!  Salts transported actively into intercellular clefts produce high osmolarity within the clefts...