Ch. 5 pre-reading.docx

Khadijah IsaacsPeriod 7th10/13 /2013 RAVEN CHAPTER 5 GUIDED NOTES: MEMBRANES1. Describe the structure of a phospholipid molecule. Be sure to describe their behavior inrelationship to water. Phospholipids have large polar heads and non-polar tails (due to hydrocarbons). Water molecules are attracted to the polar heads (because water has polar bonds where Oxygen is more negative and H are more positive). The non-polar tails do not like to be in water because of water's polarity. So when phospholipids are dumped into water, they will spontaneously arrange themselves so that the polar heads are in water, but the non-polar tails are not. This can take form as a bilayer 2. What happens when a collection of phospholipids molecules are placed in water? They would arrange themselves into two layers. The hydrophilic heads would face the water [or whatever the liquid may be] while the hydrophobic tails would hide inside the layers. Since the phospholipid molecules aren't bonded to one another, the layer would be fluid and individual molecules would easily move around.3. Explain the significance of this behavior in relationship to the evolution of life. The fact that it will spontaneously arrange itself into a bilayer. Heads in toward each other, tails facing out. It becomes a semi-permeable membrane.Not only to they form a bilayer but in smaller amounts they will form a micelle. A micelle allows entrapment of other molecules inside it and forces these other molecules to interact together. 4. What is meant by the phrase the plasma membrane is fluid? The plasma membrane is "fluid" because of movement of substances across the membrane. c. The bilayer permits diffusion of certain lipid-soluble substances. 5. Explain the fluid mosaic model. The fluid mosaic model explains how proteins and other components of the cell membrane diffuse.6. How is the fluidity of the cell membrane altered? It can be altered depending on the type of hydrophobic molecules that make up the membrane!The fluidity of the membrane can then affect the proteins that are found embedded in it.. it can change their activity and kinetics (how they work)The fluidity of the membrane can also be altered by some hormones found in circulation7. Describe the components of the cell membrane. Explain the function of each and give anexample a. The most fundamental "backbone" if you will is the phospholipid. They have two fatty acid nonpolar tails (hydrophobic = avoid water) and polar heads (hydrophilic - water loving). They form a bilayer with the tails facing the middle and the heads facing the outside (since outside cytosol is water). b. Integral Proteins - transverse the membrane and serve many functions such as transporting things acrossc. Cholesterol - tons of these molecules in the membrane help maintain the fluidity d. Glycocalyx - oligosaccharide (carb / sugar) molecule that are often attached to either the phospholipid or various proteins. They are involved in cell - cell recognition.8. List and briefly describe the different classes of membrane proteins and the roles they play.1. They serve as channels across the lipid bilayer. 2. They serve as carrier molecules which transfer substances across the membrane. 3. They serve as docking-marker acceptors that bind lock and key fashion with the docking markers of secretory vesicles. 4. They serve as membrane bound enzymes that control specific chemical reactions at either the inner or outer cell surface. 5. They serve as receptors that recognize and bind with specific molecules in the cell's environment. 6. They serve as cell adhesion molecules. 7. They are important is the cell's ability to recognize "self" as in cells of the same type.9. Describe how the structure of membrane proteins allows some proteins to be permanently anchored within the cell membrane as a transmembrane protein whereas other proteins can move freely about the surface of the membrane. Membrane-bound proteins have short hydrophobic stretches (usually helices) that allow the membrane to be stably anchored in the membrane. This does not preclude these proteins from moving laterally across the membrane surface. Some membrane proteins might be anchored to cytoplasmic structures that restrict this lateral movement. Such lateral movement is important in membrane-protein functions, which often require cross-linking for activation.

10. The cell membrane is selectively permeable. Explain what that means. Which molecules easily cross the membrane? How are molecules transported that do not easily cross the membrane? Selective permeability means that the cell membrane has some control over what can cross it, so that only certain molecules either enter or leave the cell. Molecules can cross the plasma membrane in three main ways.Molecules that are not polar or ion molecules. That is because they won't be stopped by the hydrophobic tails and they will have the acknowledgement to pass through the cell membrane thanks to little resistance. The large, hydrophilic molecules are the molecules that have difficulty passing through the membrane. The transport proteins have a hydrophilic channel which is used as a tunnel to allow the molecule to pass through by avoiding the lipid bilayer.11. Define the following a. Diffusion - the process of passively(without loss of energy) movement of any substance from higher concentration to the lower concentrationb. Facilitated Diffusion - a type of passive transport that allows substances to cross membranes with the assistance of special transport proteins.c. Osmosis - the process that causes a liquid (especially water) to pass through the wall of a living celld. Hypotonic - has a low osmotic concentration pressure.e. Hypertonic- has a high osmotic concentration pressure.f. Isotonic- Having the same concentration of solutes as the blood: an isotonic saline solution.

12. What is happening in the diagram below? The diagram looks like it is going through the process of osmosis which is from hypotonic to hypertonic low to high concentration.

13. Explain how facilitated diffusion works and give an example. Facilitated diffusion is the spontaneous passage of molecules and ions, bound to specific carrier proteins, across a biological membrane down their concentration gradient.Glucose, sodium ions and chloride ions are just a few examples of molecules and ions that must efficiently get across the plasma membrane but to which the lipid bilayer of the membrane is virtually impermeable. Their transport must therefore be "facilitated" by proteins that span the membrane and provide an alternative route or bypass.14. What is the function of aquaporins? Why are they necessary? Aquaporins are protein molecules embedded in the phospholipid bilayer of some cells.They transport water across the cell membrane. is necessary to keep cells hydrated during periods of drought .

15. What do animal & plant cells do when placed in solutions that are:a. Hypotonic -when a animal cell is placed in a hypotonic solution (a solution containing less solute particles than inside cell e.g water) molecules move from a high water potential to a low one because diffusion. net movement is into the cell. because of this the cell swells and eventually burst. this is osmotic shock. plant cell have a cell wall so in a hypotonic solution the cell swells but doesn't not burst because of the strong structure of the cellulose cell wall.the cell becomes turgid. b. Hypertonic- in a hypertonic solution the net movement is out of the cell. the cell shrinks this is called crenation.- Animal Cell in a hypertonic solution the net movement is out of the cell because of the high solute conc outside the cell. the cell membrane begins to pull away from the cell wall. the cell is plasmolysed. when fully plasmolysed it is irreversible. - Plant cellc. Isotonic -isotonic solution is when the cell content has the same solute potential as the solution the cell is in. therefore no net movement of molecules. 16. How does the Paramecium maintain osmoregulation? A Paramecium has a plasma membrane that is much less permeable to water than other membranes of most cells. it uses contractile vacuoles to pump out excess water that enters because it is in a hypotonic solution(fresh water).

17. What is the difference between exocytosis and endocytosis? Endocytosis takes material into the cell by infolding of the cell membrane. Exocytosis releases large amounts of material.18. Distinguish between pinocytosis and phagocytosis. Phagocytosis means to engulf a solid objects and pinocytosis means to engulf a liquid object but both forms of endocytosis.19. Describe an example of receptor-mediated endocytosis. Receptor-mediated endocytosis (RME) is a process by which cells internalize molecules (endocytosis) by the inward budding of plasma membrane vesicles containing proteins with receptor sites specific to the molecules being internalized. One example of receptor-mediated endocytosis important in human physiology is the main mechanism by which cholesterol is taken up by cells, in particular, liver cells.20. How do active and passive transport differ? Active transport uses energy and passive transport doesn't.Active transport requires the cell to use its own energy,while passive transport doesn't.Active transport is the flow of substances from a lower concentration to a higher concentration gradient which uses energy in the form of ATP whereas Passive Transport in contrast, is the flow of substances from higher concentration to a lower concentration gradient without using energy and it continues until an equilibrium is reached.

21. The sodium-potassium pump uses to pump out of the cell and into the cell.22. Define coupled transport and give an example. uses ATP-ase and that it pumps three sodium ions out of the cell for every two potassium ions pumped in.

23. Define countertransport and give an example. it's also called second type active transport, that can move a substance along its electrochemical gradient, while an other substance is carried in the opposing direction of its electrochemical gradient. It is Antiport only if one of the substances are getting out, and the other, getting in.