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1) Name the major molecules that make up the cell membrane. How thick is the membrane? 2) How does the fluid mosaic model proposed by Singer & Nicholson.

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Presentation on theme: "1) Name the major molecules that make up the cell membrane. How thick is the membrane? 2) How does the fluid mosaic model proposed by Singer & Nicholson."— Presentation transcript:

1 1) Name the major molecules that make up the cell membrane. How thick is the membrane? 2) How does the fluid mosaic model proposed by Singer & Nicholson (1972) compare with the Daveson & Danielli (1935) model? 3) Briefly explain how the membrane remains fluidic in lower temperatures? 4) What did the freeze fracture process and electron microscope reveal about the membrane? 5) How does cholesterol act as a buffer for the membrane? How does a hypotonic solution differ from a hypertonic solution? 5) What are the three forms of endocytosis? Explain how they are different.

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3 Amphipathic Lipids~ hydrophobic & hydrophilic regions Singer-Nicholson: fluid mosaic model proposed in 1972 (Current model)

4 The Phospholipid Bilayer Figure 5.11B Hydrophilic heads Hydrophobic tails Water l The heads face outward and the tails face inward l In water, phospholipids form a stable bilayer

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6 Approx. 10 nm thick Phospholipid Bilayer -Amphipathic molecules -Saturated and Unsaturated lipids Proteins: integral &* peripheral Cholesterol -acts as a buffer -increases membrane integrity -increases fluidity

7 Membranes organize the chemical reactions making up metabolism Cytoplasm Figure 5.10

8 l They control the flow of substances into and out of a cell l Membranes are selectively permeable **Small, Nonpolar molecules easily pass through the membrane: O 2, CO 2, H 2 O, Hormones, Steroids **Large, Charged do not pass through easily and must be helped in. These molecules would include: C 6 H 12 O 6, Proteins, and Ions Membranes regulate chemical reactions and can hold teams of enzymes that function in metabolism

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11 Phospholipids are the main structural components of membranes They each have a hydrophilic head and two hydrophobic tails Head Hydrophobic tail Hydrophilic head

12 Phospholipids~ membrane fluidity Cholesterol~ membrane stabilization Mosaic Structure~ Integral proteins~ transmembrane proteins Peripheral proteins~ surface of membrane Membrane carbohydrates ~ cell to cell recognition; oligosaccharides (cell markers); glycolipids; glycoproteins

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14 David Frye & Micheal Edin (1970)

15 To function properly : Lipids must be in a state of optimal fluidity Too much fluidity weakens the membrane -not enough cholesterol -too many unsaturated phospholipids Also, the membrane cannot be too rigid because transport through the membrane is inhibited Temperature changes can severely effect the membrane. HOW?

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19 Proteins: Six Major Functions Observed- Pg. 128 A B C,D FG G

20 See Pgs (Ch. 11- Cell Communication) Begins w/ signaling molecule called a Ligand Ligands-examples are hormones & proteins Involves several proteins: Receptor (1 st messenger) binds w/the ligand Protein Kinases: an enzyme that transfers phosphate groups from ATP to a protein (uses ATP & moves phosphates) G proteins & Adenylyl cyclase Cyclic AMP: 2 nd messengers

21 Lateral Transfer of Information Across the Membrane Figure 5.13 Ligand Receptor Enzymatic Rxns G Protein Adenylyl Cyclase 2 nd messenger cAMP

22 In passive transport, substances diffuse through membranes without work by the cell They spread from areas of high concentration to areas of lower concentration EQUILIBRIUM Molecule of dye Figure 5.14A & B Membrane EQUILIBRIUM

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25 Diffusion~ tendency of molecules to move from areas of high concentration to areas of low. Concentration gradient Passive transport~ diffusion of a substance across a biological membrane Osmosis~ the diffusion of water across a selectively permeable membrane

26 Osmosis is the passive transport of water In osmosis, water travels from an area of lower solute concentration to an area of higher solute concentration Hypotonic solution Figure 5.15 Solute molecule HYPOTONIC SOLUTION Hypertonic solution Selectively permeable membrane HYPERTONIC SOLUTION Selectively permeable membrane NET FLOW OF WATER Solute molecule with cluster of water molecules Water molecule

27 Two Models of Facilitated Diffusion

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30 Osmosis causes cells to shrink in a hypertonic solution and swell in a hypotonic solution The control of water balance (osmoregulation) is essential for organisms ISOTONIC SOLUTION Figure 5.16 HYPOTONIC SOLUTION HYPERTONIC SOLUTION (1) Normal (4) Flaccid (2) Lysing (5) Turgid (3) Shriveled (6) Shriveled ANIMAL CELL PLANT CELL Plasma membrane

31 Osmosis and Animal Cells CRENATION WILL LYSE NO CHANGE

32 OSMOSIS AND ANIMAL CELLS

33 The role of contractile vacuole in protists

34 HYPERTONIC SOLUTION= PLASMOLYSIS HYPOTONIC SOLUTION= NORMAL TURGOR PRESSURE

35 OSMOSIS IN PLANT CELLS (Elodea) Plasmolyzed cells

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37 Active Transport (Pg. 135)

38 Active transport in two solutes across a membrane Figure 5.18 Transport protein 1 FLUID OUTSIDE CELL First solute First solute, inside cell, binds to protein Phosphorylated transport protein 2 ATP transfers phosphate to protein 3 Protein releases solute outside cell 4 Second solute binds to protein Second solute 5 Phosphate detaches from protein 6 Protein releases second solute into cell

39 Utilizes ATP and a protein Moves substances against the concentration gradient (Low to High) Typical example is: Na/K pump (Observed in nerve cells)

40 Membrane potential: a charge difference across the membrane Most commonly seen in nerve cells (sodium & potassium pump) – see pg 135 Achieved through actively pumping ions on one side of the membrane. (Na + and K + ) All cells have a potential with a slight negative charge on the inside a positive charge on the outside. Why???

41 Transport proteins Facilitated diffusion~ passage of molecules and ions with transport proteins across a membrane down the concentration gradient Active transport~ movement of a substance against its concentration gradient with the help of cellular energy

42 1) Name the major molecules that make up the cell membrane. How thick is the membrane? 2) How does the fluid mosaic model proposed by Singer & Nicholson (1972) compare with the Daveson & Danielli (1935) model? 3) Briefly explain how the membrane remains fluidic in lower temperatures? 4) What did the freeze fracture process and electron microscope reveal about the membrane? 5) How does cholesterol act as a buffer for the membrane? How does a hypotonic solution differ from a hypertonic solution? 5) What are the three forms of endocytosis? Explain how they are different.

43 1) What did the freeze fracture process and electron microscope reveal about the membrane? 2) How is diffusion different from facilitative diffusion? 3) Name some factors that can affect diffusion rates of molecules. 4) Name the ions used to show how active transport works in a the cell membrane. What role does ATP play during this process? 5) What is the charge range difference across the membrane? Which side is positive and which side is negative?

44 Osmoregulation~ control of water balance Hypertonic~ higher concentration of solutes Hypotonic~ lower concentration of solutes Isotonic~ equal concentrations of solutes Cells with Walls: Turgid (very firm) Flaccid (limp) Plasmolysis~ plasma membrane pulls away from cell wall

45 Endocytosis~ import of macromolecules by forming new vesicles with the plasma membrane phagocytosis pinocytosis receptor-mediated Exocytosis~ secretion of macromolecules by the fusion of vesicles with the plasma membrane

46 To move large molecules or particles through a membrane a vesicle may fuse with the membrane and expel its contents Figure 5.19A FLUID OUTSIDE CELL CYTOPLASM

47 or the membrane may fold inward, trapping material from the outside (endocytosis) Figure 5.19B ENDOCYTOSIS

48 Three Types of Endocytosis

49 Three kinds of endocytosis Figure 5.19C Pseudopod of amoeba Food being ingested Plasma membrane Material bound to receptor proteins PIT Cytoplasm EXAMPLES OF ENDOCYTOSIS

50 Harmful levels of cholesterol can accumulate in the blood if membranes lack cholesterol receptors Figure 5.20 LDL PARTICLE Phospholipid outer layer Protein Cholesterol Plasma membrane CYTOPLASM Receptor protein Vesicle CHOLESTEROL

51 The plasma membrane of an animal cell Fibers of the extracellular matrix Figure 5.12 Glycoprotein Carbohydrate (of glycoprotein) Microfilaments of the cytoskeleton Phospholipid Cholesterol Proteins CYTOPLASM Glycolipid

52 1) What did the freeze fracture process and electron microscope reveal about the membrane? 2) How is diffusion different from facilitative diffusion? 3) Name some factors that can affect diffusion rates of molecules. 4) Name the ions used to show how active transport works in a the cell membrane. What role does ATP play during this process? 5) What is the charge range difference across the membrane? Which side is positive and which side is negative? 6) Name the three types of endocytosis observed in cells. (pg. 138)

53 Introductory Questions #4 1)Name the major molecules that make up the cell membrane. How thick is the membrane? 2)How does the fluid mosaic model proposed by Singer & Nicholson (1972) compare with the Daveson & Danielli (1935) model? 3)Briefly explain how the membrane remains fluidic in lower temperatures? 4)What did the freeze fracture process and electron microscope reveal about the membrane? 5)How does cholesterol act as a buffer for the membrane? How does a hypotonic solution differ from a hypertonic solution? 5)What are the three forms of endocytosis? Explain how they are different.


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