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Chapter 5 A Closer Look At Plasma Membranes Chapter 5 A Closer Look At Plasma Membranes Honors Biology.

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Presentation on theme: "Chapter 5 A Closer Look At Plasma Membranes Chapter 5 A Closer Look At Plasma Membranes Honors Biology."— Presentation transcript:

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2 Chapter 5 A Closer Look At Plasma Membranes Chapter 5 A Closer Look At Plasma Membranes Honors Biology

3 l It Isnt 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. l 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. l What mechanism is needed to selectively permit substances to enter or leave the cell? Phospholipid bi-layer with embedded proteins. l How does a cell maintain homeostasis? By controlling what enters and leaves the cell. l What are 2 examples of homeostasis with the human body?

4 Membrane Structure & Function lipid bilayer phospholipid molecule water Phospholipid molecules form a bilayer. Phosphate/glycerol head is polar & hydrophilic, two fatty acid tails are nonpolar & hydrophobic. Cholesterol (right) is another lipid molecule thats commonly found in the plasma membrane. Note: Do hydrophilic substances have an easier time passing thru the membrane? NO Question: What is the arrangement of the phospholipids? H – T - T - H

5 What is the Fluid Mosaic Model of the plasma membrane structure? What is the Fluid Mosaic Model of the plasma membrane structure? open channel proteins gated channel proteins transport protein lipid bilayer The lipid molecules are free to move and protein molecules float independently in the lipid bi-layer.The lipid molecules are free to move and protein molecules float independently in the lipid bi-layer.

6 protein molecules A wide variety of protein molecules float around in the lipid bi-layer and perform most of the functions of the membrane. cytoskeletal proteins (beneath the plasma membrane) ADHESION PROTEIN TRANSPORT PROTEINS EXTRACELLULAR ENVIRONMENT open channel protein gated channel protein (open) gated channel protein (closed) active transport protein RECEPTOR PROTEIN RECOGNITION PROTEIN LIPID BILAYER area of enlargement oligosaccharide groups phospholipid cholesterol

7 7 Types of Membrane Proteins (Note: Most of the plasma membrane functions are carried out by these proteins) internal support §1. Cytoskeletal Proteins - composed of microtubules. Needed for internal support and attachment. hold cells together §2. Adhesion Proteins - composed of glycoproteins attached to oligosaccharides. Serve as the glue to hold cells together. passive transport facilitated diffusion §3. Open-Channel Proteins- needed for passive transport and facilitated diffusion. directional flow §4. Gated Channel Proteins - help control the directional flow or transport of ions across the membrane.

8 7 types of membrane proteins..cont. active transportATP §5. Carrier Proteins - carry on active transport requiring energy (ATP) to actively pump their cargo across the membrane. binding sites for hormones and enzymes §6. Receptor proteins - these proteins have binding sites for hormones and enzymes, which allow them to do their work. fingerprints §7. Recognition Proteins -these proteins are the fingerprints of the cells. These self- recognizing proteins identify their own body cells or recognize invaders.

9 What will happen in the example above? What causes the reaction? What energy creates the reaction below? When will the reaction stop?

10 Concentration Gradients kinetic energy §Molecules are in constant motion, due to their own kinetic energy. concentration gradient §If there are more molecules of a substance in one area than another, a concentration gradient exists. highly concentrated low concentration §Random collisions of molecules cause them to move from an area where theyre highly concentrated to an area of low concentration. dynamic equilibrium Once the molecules have arranged themselves equally throughout two adjoining regions, its called dynamic equilibrium. At this point, a concentration gradient no longer exists.

11 Diffusion diffusion The 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: (a)Molecular size (a)Molecular size – smaller molecules move faster than larger ones. (b)Temperature (b)Temperature – heat energy causes molecules to move more rapidly & to collide more frequently. (c)Electrical gradients (c)Electrical gradients – the negative side of a membrane will attract positive ions & repel negative ions. (d)Pressure gradients (d)Pressure gradients – applying pressure can speed up the rate at which molecules move.

12 Osmosis osmosis §The movement of water across a selectively permeable membrane in response to concentration gradients, fluid pressure, or both is known as osmosis. selectively permeable membrane between two compartments water molecules protein molecules

13 Osmosis in a Plant Cell

14 Tonicity tonicity §The relative concentrations of solutes in two fluids is known as tonicity. solute concentrations are greater §Water tends to move to areas where solute concentrations are greater. isotonic §When solute concentrations in two fluids are equal, we say the two fluids are isotonic. no net movement §In an isotonic solution, there is no net movement of water in either direction.

15 Water moves from a hypotonic solution to a hypertonic solution. compartment 1 compartment 2 HYPOTONIC SOLUTION HYPERTONIC SOLUTION membrane permeable to water but not to solutes fluid volume increases In compartment 2

16 Tonicity 2M sucrose solution 1 liter of distilled water 10M sucrose solution 2M sucrose solution HYPOTONIC CONDITIONS ISOTONIC CONDITIONS HYPERTONIC CONDITIONS hypotonic A hypotonic solution has fewer solutes dissolved in it than an adjoining solution does. hypertonic A hypertonic solution has more solutes dissolved in it than an adjoining solution does. water molecules will move from a hypotonic solution to a hypertonic solution As a result, water molecules will move from a hypotonic solution to a hypertonic solution.

17 Plasma membranes areselectively permeable Plasma membranes are selectively permeable. X O 2, CO 2, other small nonpolar molecules, as well as H 2 O C 6 H 12 O 6, other large, polar water-soluble molecules, ions (such as H +, Na +, K +, Ca ++, CI - ) along with H 2 O (This means that some substances are able to enter the cell and others are not.)

18 high low concentration gradientconcentration gradient DIFFUSION ACROSS LIPID BILAYERS lipid-soluble substances as well as water diffuse across PASSIVE TRANSPORT Water-soluble substances, and water, diffuse through interior of transport proteins. No energy boost required. Also called facilitated diffusion ACTIVE TRANSPORT Specific solutes are pumped through interior of transport proteins. Requires energy boost Passive Transport vs. Active Transport

19 SPECIALIZED TYPE OF VACUOLE : CONTRACTILE VACUOLES: PROTISTS HAVE THESE ORGANELLES - THEY COLLECT EXCESS WATER AND EXCRETE IT SO THE CELL DOESNT BURST. (cytolysize) contractile vacuole (filled) contractile vacuole (emptied)

20 §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 THEYRE REPELLED OR TOO LARGE.

21 FACILITATED DIFFUSION : §PROTEINS PROVIDE CONVENIENT OPENINGS FOR PARTICLES TO PASS THROUGH - SUGARS AND AMINO ACIDS ARE MOVED THIS WAY... § THIS SPEEDS UP THE DIFFUSION RATE!

22 Facilitated Diffusion

23 §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. ACTIVE TRANSPORT (Requires energy)

24 § 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 Exocytosis

26 Active Transport § § EXOCYTOSIS : 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 19 EXOCYTOSIS Vesicle in cytoplasm moves to plasma membrane, fuses with it; contents released to the outside


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