BIO 110 1st Edition Lecture 17Phospholipids - If the membrane were purely a phospholipid bilayer then it would be permeable to: o Nonpolar molecules o Small polar molecule And impermeable to o Large polar molecules o Charged molecules - Proteins in membrane modify properties - 2 kinds of membrane proteins: o Integral- span membrane, tightly bound to membrane  Typically divided into domains:  Intracellular domain  Transmembrane domain  Extracellular domain o Peripheral- on one surface of the membrane o Loosely bound to membrane - Proteins critical to membrane function Fluid mosaic model - Membrane lipids are not fixed, they can move laterally - Membrane proteins also not fixed, move materlly- Integral flat partially submerged in thin sea of lipids - Peripheral float on surface Membrane Fluidity - Membrane at physiological temp is fluid and dynamic - Frye/edideno Label membrane proteins in 2 different cells with filaments dye o Human cell-red o Mouse cell- green - Fuse cells and observe over time o If red/green stay separate, membrane isn’t fluid - Result- red/green do mix in about 10-20 minutes = fluid Control of membrane fluidity - Cells can maintain fluidity by changing faty acids in p-lipidso Unsaturated fatty acids increase fluidity o Shorter chains increase o Saturated longer decrease - Cells change membrane components to compensate for environmental changes - Goal- keep membrane fluidity constant o Original membrane is now less fluid o Cells makes new p-lipids with more unsaturated/shorter fatty acids - Practical componentso Fish oil pills o Where do oils vs fats come from originally  Solid fats from warm blooded animals  Oils from plants Type of membrane transport - Simple diffusion o If a membrane is permeable to substance and concentration differs across the membrane o Substance will show net movement from high to low concentration o “concentration gradient” o When concentrations equalize, no net movement - Facilitated diffusion- used when molecules cant cross by themselves o Charged or large polar molecules o Can cross membrane using carrier protein or chemical protein o Cells control what crosses the membrane o Some channels are