Topic list for Exam 2 – partial listChapter 51. Functions, properties and components of the plasma membraneThe plasma membrane is usually the outermost barrier of the cell. The plasma membrane (Fig5-1)The plasma membrane contains the cell but still allows the cell to interact with the environment. The plasma membrane functions:1. Isolate the cell environment2. Regulate exchanges between inside and outside3. Communicate with other cells4. Create attachments with other cells5. Regulates bio chemicals with other cells -Plasma membrane is the membrane at the boundary of every cell that acts as selective barrier thereby regulating the cell’s chemical environment.2. Fluidity of membranesSinger and Nicolson: FLUID-MOSAIC MODEL – each membrane consists of a mosaic of proteins that constantly shift and flow within a fluid formed by a double layer of phospholipids Factors which influence fluidity of membranes Fig. 5.4- lipid composition - -temperature3. Plasma Membrane Fig. 5.14. Membrane proteins (Receptor, recognition, carrier, and channel)Some functions of integral membrane proteins Transport proteins-channel proteins – pores -carrier proteins - selective revolving doors (Carrier proteins bind and release specific molecules)Receptors Cell to cell recognition - Some of the recognition keys of the surface of cells areglycoproteins, these are unique and identify the cells as self-cells(Glycoproteins are proteins which have a carbohydrate attached to them.)5. Movement of molecules (concentration gradient, passive transport, diffusion, facilitated diffusion) How do substances move across membranes ? Transport is movement . Movement of molecules requires two factors 1. Movement must be through a fluid. liquid or gas2. There must be a concentration gradient.-difference in the amount of molecules from one place to anotherMolecules in a fluid always move. If there is a concentration gradient then the movement has a specific direction.Concentration gradient - : The graduated difference in concentration of a solute per unit distance through a solution (Diffusion of a dye)Passive transport - Movement down a concentration gradientDiffusion - is the net movement of a substance down a concentration gradient. -movement is from greater concentration to lower concentration -the greater the concentration difference, the faster the diffusion -net movement continues until the system reaches equilibrium -usually occurs over short distancesMuch of the movement of substances across membranes occurs by diffusion and therefore is aform of passive transport (Fig. 5.7).Passive transport is diffusion of a substance across a biological membrane. -Does not require the cell to expend energy.-Depends on the permeability of the membrane6. How molecules pass the PMMembranes are built to be selectively permeable.--Selective permeability is the property of biological membranes which allows some substances to cross more easily than others.- Some molecules pass by simple diffusion, others require facilitated diffusion.- Water, oxygen and carbon dioxide AND lipid-soluble molecules (alcohol, vitamins A, D,and E and hormones) diffusion.- Ions and sugars form bonds with water and require the aid of transport proteins. Facilitated diffusion.7. Osmosis• Osmosis is the passive transport of water or diffusion of water across a membrane • Osmosis is the diffusion of water across a differentially permeable membrane.• The Principles of Osmosis1. Osmosis is the diffusion of water across a differentially permeable membrane.2. Water moves from high concentration to low concentration3. Dissolved substances decrease the amount of free water moleculesCellular survival depends on balancing water movementComparisons between the solution outside & solution inside cell determine water flowo Isotonic environmentso Isotonic solutions have equal concentrations of soluteo Hypertonic environment means there is more solute in the solution surrounding the cell o Hypotonic environments means there is less solute in environment (more free water)• ---Isotonic is an equal concentration of solute compared to the inside of a cell.---Hypertonic is a greater concentration of solute than the inside of a cell.---Hypotonic is a lower concentration of solute than the inside of a cell.Central vacuole –contains lots of solute and membrane is rich in aquaporin’s8. Active transportActive transport of solutes against a concentration gradient.Active transport is an energy-requiring process during which a transport protein pumps a molecule across a membrane against its concentration gradient.-Uses energy from ATP-Used to maintain ion gradients9. Endocytosis, ExocytosisEnergy is also required for Endocytosis and Exocytosis Endocytosis, the transport of large molecules--Endocytosis is the cellular uptake of large molecules (a.k.a. macromolecules) and particulate substances (food) by the localized pinching off of a region of the plasma membrane to form a vesicle. Three types: A. phagocytosis B. pinocytosis and C. receptor-mediated endocytosis Endocytosis - phagocytosis (large particles) Phagocytosis (cell eating) is the endocytosis of solid particles . Fig 5.14Endocytosis - pinocytosis (small particles). Pinocytosis (cell drinking) is the endocytosis of fluid droplets Fig. 5.12.Receptor-mediated endocytosisReceptor-mediated endocytosis is the process of importing specific macromolecules into the cell by the inward budding of vesicles formed from coated pits , occurs in response to the binding of specific nutrients to receptors on the cell’s surface.Exocytosis moves material out of the cell. (Ex. waste or hormones) ---Exocytosis is the cellular secretion of large molecules (a.k.a. macromolecules) by the fusion of vesicles with the plasma membrane. Fig 5.1510. Cell connections and communicationConnections between cells integrate cells into higher levels of structure and function (i.e., tissues and organs)Cells that get stretched are connected by desmosomes to avoid tearing (Fig. 5.17)Desmosomes are junctions which hold two cells togetherProteins are linked to the intermediate filament proteins of the cytoskeleton.If the connection between cells needs to be watertight, then tight junctions connect the cells -Tight junctions - Leak-proof junctions which hold two cells togetherCommunication between cells occurs via gap junctions and
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