Understanding Cell Membrane Function

1. 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.

2. Anatomy of a Cell Membrane

3. Phospholipid, Hydrophilic, hydrophobic, polar, nonpolar, phosphate, glycoprotein, protein

5. “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: • Proteins embedded within membrane • decide what can pass: big, small, necessary, unnecessary, charged, etc. • Properties of the phospholipids that make up the layer • Nonpolar, hydrophobic

6. Membrane Proteins Some molecules may need “help” (of a protein) to get through the cell membrane, so require help from transportproteins: • Large molecules • Charged molecules or ions (Na+ or Cl- ) • Molecules that may be traveling up their concentration gradient

7. 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?

8. Video Clip: Cell Membranes

9. 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!

10. Interchangeable terms • Cell Membrane • Phospholipid Bilayer • Lipid Bilayer • Plasma Membrane • Fluid Mosaic Model

11. Types of Molecular Movement high to low concentration • Diffusion • Passive Transport • Simple diffusion • Facilitated diffusion • Osmosis • Active Transport high to low concentration high to low concentration high to low concentration Requires energy by the cell “ATP” low to high concentration Requires a transport protein

12. Passive TransportDiffusion of solutesacross a membrane Simple Diffusion • Molecules can easily pass through the membrane • Molecule characteristics allow it to pass hydrophobic part of cell membrane • Diffusion = high  low concentration Facilitated Diffusion • 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

13. 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! • Requires proteins or “pumps” to transport molecules across the membrane. ATP

14. Video Clip: Active Transport

15. In Summary: Active Transport • Transport through a membrane • Requires energy (in the form of ATP) • Molecules move from low to high concentration

16. With your group, organize the following terms into the T-chart below and justify their placement there. facilitated diffusion protein simple diffusion high  low concentration osmosis Energy low  high concentration requires a membrane ATP used

17. 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

18. 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 responsewith diagrams tomorrow.