Presentation on theme: "Chapter 5 A Closer Look At Plasma Membranes"— Presentation transcript:
1 Chapter 5 A Closer Look At Plasma Membranes Honors Biology
2 HOMEOSTASIS……….. It Isn’t Easy Being Single? (why not) Concentrations of ions & other substances outside the cell may rapidly become too high or low. A mechanism is needed to selectively permit substances to enter or leave the cell.What is homeostasis?Homeostasis is the name given to the dynamic processes that enable optimum conditions to be maintained for constituent cells, in spite of continual changes taking place both internally and externally.What mechanism is needed to selectively permit substances to enter or leave the cell?Phospholipid bi-layer with embedded proteins.How does a cell maintain homeostasis?By controlling what enters and leaves the cell.What are 2 examples of homeostasis with the human body?It Isn’t Easy Being Single: (Concentrations on ions and other substances outside the cell may rapidly become too high or low; a mechanism is needed to selectively permit substances to enter or leave the cell.Cell involved in constant chemical activity.Take in: oxygen and nutrients to maintain metabolism (aerobic respiration)Release: Waste take could to toxic to the cell. (carbon dioxide, sodium, enzymes, end products of digestion)
3 Membrane Structure & Function Phospholipid molecules form a bilayer.Phosphate/glycerol head is polar & hydrophilic, two fatty acid tails are nonpolar & hydrophobic.phospholipid moleculeNote: Do hydrophilic substances have an easier time passing thru the membrane?NOlipid bilayerwaterCholesterol (right) is another lipid molecule that’s commonly found in the plasma membrane.Question: What is the arrangement of the phospholipids?H – T - T - H
4 What is the ‘Fluid Mosaic Model’ of the plasma membrane structure? The lipid molecules are free to move and protein molecules float independently in the lipid bi-layer.open channelproteinstransport proteingated channelproteinslipidbilayer
5 oligosaccharide groups A wide variety of protein molecules float around in the lipid bi-layer and perform most of the functions of the membrane.oligosaccharide groupscholesterolphospholipidEXTRACELLULAR ENVIRONMENTcytoskeletalproteins (beneaththe plasmamembrane)RECEPTORPROTEINRECOGNITIONPROTEINADHESIONPROTEINopenchannelproteingatedchannelprotein(open)gatedchannelprotein(closed)activetransportproteinLIPIDBILAYERarea ofenlargementTRANSPORTPROTEINS
6 7 Types of Membrane Proteins (Note: Most of the plasma membrane functions are carried out by these proteins)1. Cytoskeletal Proteins - composed of microtubules. Needed for internal support and attachment.2. Adhesion Proteins - composed of glycoproteins attached to oligosaccharides. Serve as the “glue” to hold cells together.3. Open-Channel Proteins- needed for passive transport and facilitated diffusion.4. Gated Channel Proteins - help control the directional flow or transport of ions across the membrane.
7 7 types of membrane proteins..cont. 5. Carrier Proteins - carry on active transport requiring energy (ATP) to “actively pump” their cargo across the membrane.6. Receptor proteins - these proteins have binding sites for hormones and enzymes, which allow them to do their work .7.Recognition Proteins -these proteins are the “fingerprints” of the cells. These self-recognizing proteins identify their own body cells or recognize invaders.
8 What will happen in the example above? What causes the reaction?What energy creates the reaction below?When will the reaction stop?
9 Concentration Gradients Molecules are in constant motion, due to their own kinetic energy.If there are more molecules of a substance in one area than another, a concentration gradient exists.Random collisions of molecules cause them to move from an area where they’re highly concentrated to an area of low concentration.Once the molecules have arranged themselves equally throughout two adjoining regions, it’s called “dynamic equilibrium.”At this point, a concentration gradient no longer exists.
10 Molecular size – smaller molecules move faster than larger ones. DiffusionThe net movement of like molecules down their concentration gradient is known as diffusion.The rate at which diffusion occurs can be affected by the following factors:Molecular size – smaller molecules move faster than larger ones.Temperature – heat energy causes molecules to move more rapidly & to collide more frequently.Electrical gradients – the negative side of a membrane will attract positive ions & repel negative ions.Pressure gradients – applying pressure can speed up the rate at which molecules move.
11 selectively permeable membrane between two compartments Osmosisselectively permeable membranebetween two compartmentsThe movement of water across a selectively permeable membrane in response to concentration gradients, fluid pressure, or both is known as osmosis.watermoleculesproteinmolecules
13 TonicityThe relative concentrations of solutes in two fluids is known as tonicity.Water tends to move to areas where solute concentrations are greater.When solute concentrations in two fluids are equal, we say the two fluids are isotonic.In an isotonic solution, there is no net movement of water in either direction.
14 Water moves from a hypotonic solution to a hypertonic solution. compartment1compartment2HYPOTONICSOLUTIONHYPERTONICSOLUTIONmembrane permeable towater but not to solutesfluid volume increasesIn compartment 2
15 Tonicity2M sucrosesolutionA hypotonic solution has fewer solutes dissolved in it than an adjoining solution does.A hypertonic solution has more solutes dissolved in it than an adjoining solution does.As a result, water molecules will move from a hypotonic solution to a hypertonic solution.HYPOTONICCONDITIONSHYPERTONICCONDITIONSISOTONICCONDITIONS1 liter ofdistilled water10M sucrosesolution2M sucrosesolution
16 Plasma membranes are selectively permeable. (This means that some substances are able to enter the cell and others are not.)O2, CO2, other smallnonpolar molecules,as well as H2OC6H12O6, other large, polarwater-soluble molecules,ions (such as H+, Na+, K+,Ca++, CI-) along with H2OX
17 Passive Transport vs. Active Transport concentration gradientPassive Transport vs. Active TransporthighlowDIFFUSION ACROSSLIPID BILAYERSlipid-solublesubstances aswell as waterdiffuse acrossPASSIVETRANSPORTWater-soluble substances, and water,diffuse through interior of transportproteins. No energy boost required.Also called facilitated diffusionACTIVETRANSPORTSpecific solutes arepumped through interiorof transport proteins.Requires energy boost
18 SPECIALIZED TYPE OF VACUOLE: CONTRACTILE VACUOLES: PROTISTS HAVE THESE ORGANELLES - THEY COLLECT EXCESS WATER AND EXCRETE IT SO THE CELL DOESN’T BURST. (cytolysize)contractilevacuole(emptied)contractilevacuole (filled)
19 PLASMOLYSIS: LOSS OF WATER FROM A CELL RESULTING IN A DROP IN TURGOR PRESSURE. Turgor pressure: Water pressure inside the plant cell. (turgidity)PASSIVE TRANSPORT:REQUIRES NO ENERGY TO MOVE SUBSTANCES ACROSS A MEMBRANE = DIFFUSION , EXAMPLE: WATER, NON-POLAR MOLECULES, AND LIPID-SOLUBLE SUBSTANCES.LIPID BILAYER KEEPS MOST SUBSTANCES OUT BECAUSE THEY’RE REPELLED OR TOO LARGE.
20 FACILITATED DIFFUSION: THIS SPEEDS UP THE DIFFUSION RATE! PROTEINS PROVIDE CONVENIENT OPENINGS FOR PARTICLES TO PASS THROUGH - SUGARS AND AMINO ACIDS ARE MOVED THIS WAY...THIS SPEEDS UP THE DIFFUSION RATE!
22 ACTIVE TRANSPORT (Requires energy) FROM LOW CONC. TO HIGHER CONC.In active transport, SOLUTES MOVE AGAINST THE CONCENTRATION GRADIENT!Ex- Sodium-Potassium Pump-helps nerve cells transfer electrical impulses by maintaining an electrical gradient on the plasma membrane.Ex- Calcium Pump - helps keep the calcium concentration high in cells.
23 ENDOCYTOSIS: a form of active transport in which the cell uses energy to bring materials into the cell by engulfing.A. PHAGOCYTOSIS: (“CELL EATING”) Cell takes in large molecules by pinching in the plasma membrane.B. PINOCYTOSIS: (“CELL DRINKING”) Cell takes in fluid by pinching in the plasma membrane.
25 Active TransportEXOCYTOSIS: a form of active transport in which the cell excretes wastes or secretes substances needed elsewhere in the organism. These substances do not move through the plasma membrane itself.Slide 19EXOCYTOSISVesicle in cytoplasm moves to plasma membrane,fuses with it; contents released to the outside