Lecture 4: Cellular Level of Organization II Office hours: Tuesday and Thursday 1-2pm in Gittings 108 or by appointment Extra office hours for next week posted on d2l Claudia Stanescu, Ph.D.Objectives (pp. 59-73, sec. 3.3) 1. Discuss the influence of concentration gradient and distance on the rate of diffusion between two points. 2. Define osmosis. Given knowledge of the osmotic concentration of solutes in two solutions separated by a semipermeable membrane, predict the direction of net osmotic water flow. Compare and contrast the concepts of osmolarity and tonicity. 3. Compare and contrast the characteristics that distinguish passive diffusion from carrier-mediated transport; include a discussion of two diagnostic characteristics of carrier-mediated transport. 4. Compare and contrast the characteristics of facilitated diffusion and active transport. 5. Compare and contrast the characteristics of primary and secondary active transport. 6. List the categories of vesicular transport and describe a representative example of each.Membrane Functions: 1. Barrier 2. Organization 3. Transport 4. Reaction/ResponseTransport across the membrane: 1) Passive transport • Substances move down their concentration gradient (high to low concentration) without energy input from the cell 2) Active transport • Substances move against their concentration gradient (low to high concentration) using energy from the cell (ATP)Passive TransportPassive Transport Diffusion Beginning Intermediate Equilibrium [solute] [solute]Diffusion ‘take home points’ 1. Net diffusion is proportional to concentration gradient 2. Diffusion occurs rapidly over short (cellular) distances; but slowly over long (‘organismic’) distancesDiffusion across a membrane (‘Barrier’) To diffuse into (or out of) a cell, solutes must enter the lipid bilayer Hydrophilic (polar) solutes can’t… Hydrophobic (non-polar) solutes can…Passive Transport across the membrane: 1) Simple diffusion – of hydrophobic substances like: gasses (O2, CO2), fatty acids, steroid hormones, fat soluble vitamins 2) Osmosis – of water through channels called aquaporins 3) Channel mediated facilitated diffusion – of ions like K+, Na+, Ca2+, and Cl- 4) Carrier mediated facilitated diffusion – of glucose, fructose, galactose, and some vitamins? ? ?Simple diffusion Take Home Points 1. Net diffusion is proportional to concentration gradient 2. Hydrophobic solutes ‘permeate’ more rapidly than hydrophilic solutesPassive Flow of Water Across Membranes Osmosis: Net flow of water (across a semipermeable membrane) in response to a gradient in the chemical activity of waterT&D Figure 3.8 Osmosis vs. Hydrostatic PressureMeasuring Osmotic Pressure T&D Figure 3.8How does water cross lipid bilayers? "Animations". Nobelprize.org. 29 May 2012 http://www.nobelprize.org/nobel_prizes/chemistry/laureates/2003/animations.html through water channels called “aquaporins”Passive Transport: Channel-Mediated Facilitated DiffusionPassive Transport: Carrier-Mediated Facilitated Diffusion(J) [S] S1) Primary active transport (uses ATP) – Energy derived from hydrolysis of ATP changes the shape of the carrier protein and “pumps” the substance across the membrane against the concentration gradient (the Na+/K+ pump is a good example of this). 2) Secondary active transport (uses ion gradients) – Energy stored in the Na+ or H+ gradient is used to move other substances against their concentration gradients. 3) Bulk transport (transport in vesicles) – Endocytosis, exocytosis, transcytosis Active Transport across the membrane:Primary Active TransportSecondary Active TransportSecondary Active Transport by Antiporters & SymportersBulk Transport (Vesicular Transport) of Particles • Endocytosis is a vesicular transport of something into a cell • Exocytosis is vesicular transport (release) of something into the external environment (out of a cell) • Transcytosis is vesicular transport of something from the outside environment on one side of a cell to the outside environment on the other side of the cell Refer pp 71-73, sec. 3.3Suggested Learning Activities • Draw a graph to represent the process of passive diffusion • Draw a cell and determine what happens to the cell shape if different solutions are applied: 1) distilled water; 2) 0.9% salt solution; 3) 5% salt solution • Draw a plasma membrane and the different transport mechanisms that can occur across the membrane. For each mechanism list if it is: 1) active; 2) saturable; 3) selective • Draw antiporters and symporters in a plasma membrane. Label the concentrations of ions (high/low) across the membrane for each of the examples given and show which ion is moving with and against the