Chapter 5: The Plasma Membrane

1. Chapter 5:The Plasma Membrane

2. Constantly interacting with the outer world Very thin 10,000 0f them stacked would equal a sheet of paper. Fluid and fatty makeup. Stable Flexible Constantly reformed Materials moving in and out Every 30 minutes 5.1 The nature of the Plasma membrane

3. PHOSPHOLIPIB BILAYER Largest component of the cell membrane Fatty Acid tails face each other and Phosphate-Glyceral heads point in the opposite directions CHOLESTERAL “patching” material Keeps the membrane fluid PROTEINS Intergrated in the membrane Are exposed at both sides Serve as Support Structure Signaling Identification markers Cellular passageways GLYCOCALYX Carbohydrate chain that is layered outside the membrane Important components of the plasma membrane

4. Recall: Phospholipid=Hydrophillic head (Phosphate)+ Hydrophobic tails (fatty Acid) Phospholipid bilayera chief component of the plasma membrane, composed of two layers of phospholipids, arranged with their fatty acid chains pointing toward each other. Consequences Oil like Two hydrophobic layers only allow other hydrophobic substances to cross First Component: The Phospholipid Bilayer

5. Lies between two phospholipid molecule “Patch up” keep small molecules from getting through Helps the membrane maintain an optimum level of fluidity Accomplishes this by not allowing the chain to lie to close together Without it at low temperatures the membrane would change from flexible substance hard substance At low temperatures keeps the membrane from becoming too fluid Second Component: Cholesterol

6. Found Embedded in Lying on Two types Integral proteinsare plasma membrane proteins that are bound to the membrane’s hydrophobic interior Can extend to either side of the membrane Peripheral proteins plasma membrane proteins that lie on either side of the membrane but that are not bounded to the hydrophobic interior. Third Component:Proteins

7. STRUCTURAL SUPPORT Peripheral proteins are attached to the cytoskeleton Anchors Gives cells their shape RECOGNITION Integral proteins Have binding site to tell Immune cells what kind of cell it is How does this apply to blood type? Role of Proteins

8. 3. COMMUNICATION Cells need to send messages to one another Accomplished by Hormones Signals are channeled through receptor proteins Plasma membrane proteins that binds with a signaling molecule Shape is specific to molecule (hormone) The signal is transferred internally a cascade of reactions follow Insulin  receptor Increases production of protein channels for glucose 4. TRANSPORT Integral proteins  Transport protein proteins that facilitate the movement of molecules or ions from one side of the plasma membrane to the other Have channels Hydrophillic opening Role of Proteins cont.

9. Carbohydrate chains short branched extensions protruding from the phospholipds and the proteins Binding site for many signals insulin Lubricates cells Allows them to stick together Collectively all these chains form the glycalyxan outer layer of the plasma membrane composed of short carbohydrate chains that attach to membrane proteins and phospholipid molecules Fourth Component: The Glycalyx

10. Plasma membrane a membrane, forming the outer boundary of many cells, composed of a phospholipid bilayer that is interspersed with proteins and cholesterol and coated on its exterior face with carbohydrate chains. Fluid Mosaic modela conceptualization of the plasma membrane as a fluid, phospholipid bilayer that has, moving laterally within it, a mosaic of proteins. The Fluid-Mosaic Membrane Model

11. Random movement and even distribution All molecules or ions Are constantly in random motion Law of thermodynamic states: Molecules will move from Initial ordered state to their most disordered state=evenly distributed throughout the container 5.2 Diffusion, Gradients, and Osmosis What is at work here?

12. DiffusionThe movement of molecules of ions from a region of higher concentration to a region of lower concentration Concentration gradientthe difference between the highest and the lowest concentration of a solute within a given medium Fig. 5.4 Solute dyeadded to solvent water Dye moves down its concentration gradient =from a high concentration to a lower one Random movement and even distribution

13. What happens to a solution that is divided by a membrane? If the membrane is permeable water and the soluble can freely pass through it, and the solute lies on one side of the membrane Solute moves down its concentration gradiant (high low) Moving to the opposing side, eventually becoming evenly distributed on both sides. Diffusion through membranes

14. If the membrane is semipermeable Water can move not the solute If there is a high concentration of solute on one side of the membrane The water will move to the area where the solute occurs at higher concentrations and thus making both sides of the membrane have equal concentrations of solution. What had been demonstrated?Osmosis The movement of water across a semipermeable membrane from an area of lower concentration of solute to an area of higher concentration of solute Why does this occur? water wants to bond with the salt ions. Diffusion through membranes

15. Lipid bilayer Permeable to Somewhat permeable to water Primary need for the uptake of water by plants Metabolic process in animals Lipids Not permeable to Large molecules Example:Blood Driven out of the capillaries by high blood pressure How is the fluid regained back into the circulatory system? Proteins in the capillaries are polar and attract the fluid to reenter the bloodstream by osmosis The Plasma Membrane as a Semipermeable Membrane

16. Cells can either Loose water to their environment Gain water from their environment Or have a balanced flow of water (in and out) These conditions exist due to the amount of concentration inside and outside the cell Hypertonic solutiona fluid that has a higher concentration of solutes Isotonictwo solutions that have equal amounts of concentration of solutes Hypotonic solution a solution that has lower concentration of solutes than another Osmosis and Cell Environments

17. Substances (molecules, ions) move through diffusion and osmosis Others need the assistance of the latter forces, protein channels, other channels, and energy. Two Different kinds of transport Active transport any movement of molecules or ions across a cell that requires the expenditure of energy. A in Active for ATP Passive movement any movement of molecules or ions across a cell membrane that does not require the expenditure of energy. 5.3 Moving Smaller Substances In and Out

18. Simple Diffusion Small molecules move down their concentration gradient Oxygen Left by the capillaries outside the cell Oxygen diffuses inside the cell (lower concentrations inside) Carbon dioxide Diffuse out of the cell (lower concentration outside) Fat soluble (Steroid hormones) Simple diffusion diffusion through a cell membrane that does not require a protein channel Passive Transport: Two Types

19. 2. Facilitated Diffusion: Help from Proteins Polar molecules larger then water need help crossing the membrane Glucose Amino acids Facilitated diffusion passage of materials through a plasma membrane that is aided by a concentration gradient and a transport protein Each protein only allows one substance May allow a small group of associated substances Transport process: Glucose binds to a transport protein Binding causes the protein to change shape The glucose passes through

20. Aids to moves substances That occur at equal concentrations on either side That need to move against their concentration gradient (Low  high concentration) Why do they need to move against their concentration? The cell needs them Solution Pumps Molecules are pumped by proteins against their concentration gradient and energy is expended Energy source ATPAdenosine Triphosphate Active Transport

21. Allows the cell to maintain High concen. of Potassium inside the cell High concen. of Sodium outside the cell They both “leak” K+ out and Na+ in Why? they are following their concentration gradient from Highlow The cell pumps these ions in order to produce a nerve signal. The Sodium-Potassium Pump

22. Immune cells Need to take in large particles like bacteria Can not be accomplished by transport Movement out: Exocytosis A movement of material outside the cell through the fusion of a vesicle with the plasma membrane Proteins or wastes products Single celled organisms may use this to release waste products 5.4 Getting the Big Stuff In and Out

23. The movement of a relatively large material into the cell by the infolding of the plasma membrane Three forms Pinocytosis Receptor-mediated endocytosis Phagocytosis Movement In: Endocytosis http://www.ibiblio.org/virtualcell/textbook/chapter3/movies/endo.gif

24. Pinocytosis form of endocytosis that brings into the cell a small volume of extracellular fluid and the materials suspended in it “cell drinking” Harbors are created Pinched off and becomes a vesicle Receptor-mediated endocytosis Depends on receptors, whose role is to bind to specific molecules and then hold on to them Receptors move laterally Congregate in an area Are pinched off Phagocytosis The process of bringing relatively large materials into a cell by means of wrapping extensions of the plasma membrane around the material and fusing the extensions together “cell eating” Immune cells ingests a whole bacteria Single celled organisms obtain their food Psuedopods”false feet” aid in capturing food Lysosomes help break down organism or food particle Three Forms of Endocytosis

27. Essay How Did We Learn? The Fluid-Mosaic Model of the Plasma Membrane