Lecture 4 Cellular Level of Organization II Claudia Stanescu Ph D Office hours Tuesday and Thursday 1 2pm in Gittings 108 or by appointment Extra office hours for next week posted on d2l Objectives pp 59 73 sec 3 3 1 2 3 4 5 6 Discuss the influence of concentration gradient and distance on the rate of diffusion between two points 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 Compare and contrast the characteristics that distinguish passive diffusion from carrier mediated transport include a discussion of two diagnostic characteristics of carrier mediated transport Compare and contrast the characteristics of facilitated diffusion and active transport Compare and contrast the characteristics of primary and secondary active transport List the categories of vesicular transport and describe a representative example of each Membrane Functions 1 Barrier 3 Transport 2 Organization 4 Reaction Response Transport 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 Transport Passive Transport Diffusion solute solute Beginning Intermediate Equilibrium 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 distances Diffusion 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 solutes Passive Flow of Water Across Membranes Osmosis Net flow of water across a semipermeable membrane in response to a gradient in the chemical activity of water T D Figure 3 8 Osmosis vs Hydrostatic Pressure T D Figure 3 8 Measuring Osmotic Pressure How does water cross lipid bilayers through water channels called aquaporins Animations Nobelprize org 29 May 2012 http www nobelprize org nobel prizes chemistry laureates 2003 animations html Passive Transport Channel Mediated Facilitated Diffusion Passive Transport Carrier Mediated Facilitated Diffusion J S S Active Transport across the membrane 1 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 Primary Active Transport Secondary Active Transport Secondary Active Transport by Antiporters Symporters Bulk 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 3 Suggested 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 gradient