Cell Membrane Structure and Function Goal: To be able to describe how the structure of the cell membrane regulates the flow of materials into/out of the cell. Anatomy of a Cell Membrane Phospholipid, Hydrophilic, hydrophobic, polar, nonpolar, phosphate, glycoprotein, protein “Selectively Permeable” • perme = “allow” • A characteristic of cell membranes that allows it to regulate the passage of molecules • Selective permeability depends on the structure of the membrane • Not to be confused with semi-permeability – Dialysis tubing is semi-permeable. What characteristic allows molecules to travel through the membrane? • Our cell membranes are “selective” due to: 1. Proteins embedded within membrane • decide what can pass: big, small, necessary, unnecessary, charged, etc. 2. Properties of the phospholipids that make up the layer • Nonpolar, hydrophobic Membrane Proteins Some molecules may need “help” (of a protein) to get through the cell membrane, so require help from transport proteins: – Large molecules – Charged molecules or ions (Na+ or Cl- ) – Molecules that may be traveling up their concentration gradient Cross-Section of the Cell Membrane Which molecules will allowed through the lipid bilayer and which ones may need the help of a protein? H2O, CO2, Glucose (C6H12O6), Starch (lots of glucoses), Potassium (K+), estrogen, Na+ Why or why not? Video Clip: Cell Membranes Recap: Cell Membranes Characteristics: – Selectively Permeable • Regulates what enters/exits cell • Helps transport certain molecules across with help of proteins – “Bilayered” • Hydrophobic • Hydrophilic – Embedded proteins (different functions) • • • • Cell identification Enzymes Transport of molecules Etc! Interchangeable terms • • • • • Cell Membrane Phospholipid Bilayer Lipid Bilayer Plasma Membrane Fluid Mosaic Model Types of Molecular Movement • Diffusion • Passive Transport – Simple diffusion – Facilitated diffusion – Osmosis • Active Transport high to low concentration high to low concentration high to low concentration high to low concentration low to high concentration Passive Transport Diffusion of solutes across a membrane Simple Diffusion Facilitated Diffusion • Molecules can easily pass through the membrane • Molecule characteristics allow it to pass hydrophobic part of cell membrane • • • Diffusion = high low concentration • Molecules have to pass through membrane proteins to cross membrane Molecule characteristics do not allow it to pass through hydrophobic part of cell membrane Diffusion = high low concentration Active Transport • Molecules pass through a protein to cross membrane • Not diffusion because active implies movement of solutes against their concentration gradient (i.e., low high) • Being “active” requires energy! ATP • Requires proteins or “pumps” to transport molecules across the membrane. Video Clip: Active Transport In Summary: Active Transport • Transport through a membrane • Requires energy (in the form of ATP) • Molecules move from low to high concentration With your group, organize the following terms into the T-chart below and justify their placement there. facilitated diffusion high low concentration low high concentration Passive Transport protein osmosis requires a membrane simple diffusion Energy ATP used Active Transport Your Tasks • Collect Day 2 data • Clean Up: – Solutions down sink – Cups rinsed and brought to cart up front – All containers rinsed and drying upside down Homework due Monday – Analysis Questions Homework due Tuesday? • Learn About Cell Membranes! Worksheet • Interested in extra credit? – Learn about how soap works! Research micelle formation and explain, in words and using a few diagrams, how soap works and how this relates to what we learned today about the phospholipid bilayer. Submit typed response with diagrams tomorrow.