1. CELL MEMBRANE Cell Membrane Structure

4. Cell Boundaries liquid environment Every cell is surrounded by a liquid environment liquid inside (cytoplasm) and has a liquid inside (cytoplasm) Two types of boundaries separate: –Cell membrane (inner) ALLThin, flexible layer that surrounds ALL cells –Cell wall (outer) Strong supporting layer outside the cell membrane made of carbohydrate (cellulose, chitin) Only in some organisms (plants, algae, fungi, prokaryotes) PorousPorous Cell Membrane Structure

5. Phospholipids Cell membranes are mostly built from fat molecules called phospholipids –Have a polar head and two nonpolar tails Polar heads  glycerol with phosphate attached –attracted to water = hydrophilic Nonpolar tails  –repelled by water = hydrophobic Glycerol with phosphate group attached 2 fatty acid tails

6. Lipid Bilayer Because there is water inside and outside the cell, the phospholipids form a double layer called the lipid bilayer. Polar heads facing the polar liquid environments, nonpolar tails on the inside away from the polar liquid environment Cell Membrane Structure

7. Membrane Components Membranes also have proteins embedded in the bilayer -act as tunnels or pumps across the membrane -others protect the cell membrane Contains carbohydrates, usually attached to the proteins -act as antennae/signals to other cells -If attached to proteins – glycoproteins -If attached to phospholipids - glycolipids Contains cholesterol -Stabilizes the membrane Cell Membrane Structure

8. Cell Membrane

9. Outside of cell Inside of cell (cytoplasm) Cell membrane Proteins Protein channel Lipid bilayer Carbohydrate chains Section 7-3 Figure 7-12 The Structure of the Cell Membrane Cell Membrane Structure

10. Inside of cell (cytoplasm) Cell membrane Proteins Protein channel Lipid bilayer Carbohydrate chains Section 7-3 Figure 7-12 The Structure of the Cell Membrane Fluid Mosaic Model Moveable/fluid Has proteins throughout –Can have carbohydrate “ID tags” http://www.susanahalpine.com/anim/Life/memb.htm Cell Membrane Structure

12. Cell Wall NOTCell wall – tough, porous boundary that lies outside the cell membrane; found in plant cells and in some bacteria but NOT in animal cells -Allow water, gases, and other substances to pass through easily Most cell walls are made of carbohydrates and proteins - Specifically composed of cellulose Cell Membrane Structure

13. FUNCTIONS FUNCTIONS of Cell Membranes Regulates what goes in and what goes out of a cell –Must be able to take in raw materials and eliminate waste products -Like a bouncer at a club Protects cell Supports cell, but also flexible Recognizes foreign material Communicates with other cells Cell Membrane Structure

14. Permeable Permeable – substance can pass through membrane Impermeable Impermeable – substance can not pass through membrane PERMEABILITY CREATES SPECIFICITY OF THE CELL

15. What goes in and out? (Transport) Cell membrane is selectively permeable,  it lets some things in, but not other things Transport depends on… size (smaller get through more easily) concentrations, & type of molecule trying to get through (lipid and nonpolar get through more easily) Substances keep moving till there are ~ equal amounts of them on both sides of the membrane DYNAMIC EQUILIBRIUM Cell Membrane Structure

16. To Move or Not To Move Through… Fig 3.2 p 79 Can Move Across Through the Phospholipids Small, hydrophobic molecules –Steroids, O 2, CO 2 Small, uncharged polar molecules –H 2 O Can Move Across The Membrane Either With HELP or Through Active Transport (endocytosis or exocystosis) Larger, uncharged polar molecules –Think monomers Ions