1. Thursday, 9/27  Discuss SA:Volume Ratio Lab l Any questions? l Collect Lab sheet  Chp.6 Quiz l 15 multiple choice/matching l 1 short answer  Start Chp.7 l Draw model of the cell membrane (plasma membrane)  use diagram in class, book fig.7.5??? Label all of the parts Color your diagram This goes in your notes l Bring textbook tomorrow, HW due Monday

2. Friday, 9/28  Cell Transport Notes  Homework = Chp.7 Reading Notes l Due Monday  AP Lab: Diffusion & Osmosis next week l Set up Monday, Lab Tues - Thursday l Lab debrief/Review Friday l Chp.6&7 Test will be next MONDAY!

3. Chapter 7 ~ Membrane Structure & Function

4. Cell Membrane (Notes)

5.  Is the boundary that separates the living cell from its nonliving surroundings  exhibits selective permeability l It allows some substances to cross it more easily than others The plasma (cell) membrane:

6. Cellular membranes  are fluid mosaics of lipids and proteins l Fluid Mosaic Model  Phospholipids l Are the most abundant lipid in the plasma membrane l Are amphipathic, containing both hydrophobic and hydrophilic regions

7. The Fluidity of Membranes  Phospholipids in the plasma membrane l Can move within the bilayer Figure 7.5 A Lateral movement (~10 7 times per second) Flip-flop (~ once per month) (a) Movement of phospholipids

8. Membrane structure  Cholesterol~ membrane stabilization  “Mosaic” Structure~ l Integral proteins~ transmembrane proteins l Peripheral proteins~ surface of membrane l Membrane carbohydrates ~ cell to cell recognition; oligosaccharides (cell markers);glycolipids; glycoproteins

9. Membrane protein function: 1.transport 2.enzymatic activity 3.signal transduction 4.intercellular joining 5.cell-cell recognition 6.ECM attachment

10.  Membrane proteins and lipids l Are synthesized in the ER and Golgi apparatus ER Figure 7.10 Transmembrane glycoproteins Secretory protein Glycolipid Golgi apparatus Vesicle Transmembrane glycoprotein Membrane glycolipid Plasma membrane: Cytoplasmic face Extracellular face Secreted protein 4 1 2 3

11.  Membrane structure results in selective permeability l A cell must exchange materials with its surroundings, a process controlled by the plasma membrane

12. The Permeability of the Lipid Bilayer Figure 7.2 Hydrophilic head Hydrophobic tail WATER  Hydrophobic molecules l Are lipid soluble and can pass through the membrane rapidly  Polar molecules (hydrophillic) l Do not cross the membrane rapidly  Transport proteins l Allow passage of hydrophilic substances across the membrane

13.  Passive transport is diffusion of a substance across a membrane with no energy investment l Movement of a substance from [high] to [low] (down a concentration gradient)

14. 1.Diffusion~ tendency of any molecule to spread out into available space 2.Osmosis~ the diffusion of water across a selectively permeable membrane

15. Water balance : Osmoregulation= control of water balance  Isotonic~ l The concentration of solutes is the same as it is inside the cell l There will be no net movement of water  Hypertonic~ l The concentration of solutes is greater than it is inside the cell l The cell will lose water  Hypotonic~ l The concentration of solutes is less than it is inside the cell l The cell will gain water Hypotonic solution Isotonic solution Hypertonic solution H2OH2O H2OH2O H2OH2O H2OH2O

16. Cells with Walls:  Walls help maintain water balance  Turgid (very firm)  Flaccid (limp)  Plasmolysis~ plasma membrane pulls away from cell wall Plant cell. Plant cells are turgid (firm) and generally healthiest in a hypotonic environ- ment, where the uptake of water is eventually balanced by the elastic wall pushing back on the cell. (b) H2OH2OH2OH2O H2OH2O H2OH2O Turgid (normal)Flaccid Plasmolyzed Figure 7.13

17.  Facilitated Diffusion = Passive Transport Aided by Proteins l Transport proteins speed the movement of molecules across the plasma membrane

18.  Channel proteins l Provide corridors that allow a specific molecule or ion to cross the membrane Figure 7.15 EXTRACELLULAR FLUID Channel protein Solute CYTOPLASM A channel protein (purple) has a channel through which water molecules or a specific solute can pass. (a)

19.  Carrier proteins l Undergo a subtle change in shape that translocates the solute-binding site across the membrane Figure 7.15 Carrier protein Solute A carrier protein alternates between two conformations, moving a solute across the membrane as the shape of the protein changes. The protein can transport the solute in either direction, with the net movement being down the concentration gradient of the solute. (b)

20.  Active transport = uses energy to move solutes against their gradients l Moves substances against their concentration gradient l Requires energy, usually in the form of ATP l Example: Sodium-Potassium Pump

21. Na-K Pump

22. Review

23. Maintenance of Membrane Potential by Ion Pumps  An electrochemical gradient l Is caused by the concentration electrical gradient of ions across a membrane  An electrogenic pump l Is a transport protein that generates the voltage across a membrane EXTRACELLULAR FLUID + H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ Proton pump ATP CYTOPLASM + + + + – – – – – +

24.  Bulk transport (Large proteins) across the plasma membrane occurs by exocytosis and endocytosis  In exocytosis l Transport vesicles migrate to the plasma membrane, fuse with it, and release their contents  In endocytosis l The cell takes in macromolecules by forming new vesicles from the plasma membrane

25. EXTRACELLULAR FLUID Pseudopodium CYTOPLASM “Food” or other particle Food vacuole 1 µm Pseudopodium of amoeba Bacterium Food vacuole An amoeba engulfing a bacterium via phagocytosis (TEM). PINOCYTOSIS Pinocytosis vesicles forming (arrows) in a cell lining a small blood vessel (TEM). 0.5 µm In pinocytosis, the cell “gulps” droplets of extracellular fluid into tiny vesicles. It is not the fluid itself that is needed by the cell, but the molecules dissolved in the droplet. Because any and all included solutes are taken into the cell, pinocytosis is nonspecific in the substances it transports. Plasma membrane Vesicle In phagocytosis, a cell engulfs a particle by Wrapping pseudopodia around it and packaging it within a membrane- enclosed sac large enough to be classified as a vacuole. The particle is digested after the vacuole fuses with a lysosome containing hydrolytic enzymes.  Three types of endocytosis Figure 7.20 PHAGOCYTOSIS

26. 0.25 µm RECEPTOR-MEDIATED ENDOCYTOSIS Receptor Ligand Coat protein Coated pit Coated vesicle A coated pit and a coated vesicle formed during receptor- mediated endocytosis (TEMs). Plasma membrane Coat protein Receptor-mediated endocytosis enables the cell to acquire bulk quantities of specific substances, even though those substances may not be very concentrated in the extracellular fluid. Embedded in the membrane are proteins with specific receptor sites exposed to the extracellular fluid. The receptor proteins are usually already clustered in regions of the membrane called coated pits, which are lined on their cytoplasmic side by a fuzzy layer of coat proteins. Extracellular substances (ligands) bind to these receptors. When binding occurs, the coated pit forms a vesicle containing the ligand molecules. Notice that there are relatively more bound molecules (purple) inside the vesicle, other molecules (green) are also present. After this ingested material is liberated from the vesicle, the receptors are recycled to the plasma membrane by the same vesicle.