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The Cellular Level of Organization

The Cellular Level of Organization. Honors Anatomy & Physiology. Cells . ~200 different types cells in body all arise from cell division each type has unique role in supporting homeostasis . Parts of a Cell. Plasma Membrane separates inside from outside

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The Cellular Level of Organization

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  1. The Cellular Level of Organization Honors Anatomy & Physiology

  2. Cells • ~200 different types cells in body • all arise from cell division • each type has unique role in supporting homeostasis

  3. Parts of a Cell • Plasma Membrane • separates inside from outside • selective barrier that helps establish & maintain appropriate environment for normal cell activities • key role in cell-to-cell communication

  4. Plasma Membrane • fluid mosaic model • lipid bilayer makes up basic structural framework • 3 lipid molecules • Phospholipids (~75% of membrane) • Cholesterol (~20%) • Glycolipids (~5%)

  5. Simplified Plasma Membrane

  6. Phospholipids • *amphipathic: have both polar & nonpolar parts • made of • phosphate head (polar) • two long fatty acid (f.a.) chains (nonpolar)

  7. PHOSPHOLIPID BILAYER

  8. Cholesterol • weakly amphipathic

  9. Membrane Proteins • Integral Proteins • most transmembrane • amphipathic • hydrophobic a.a. extend among f.a. tails

  10. Membrane Proteins • Peripheral Proteins • not embedded in membrane • ass‘c loosely with polar heads or integral proteins • inner or outer surface

  11. Glycoproteins • protein + carbohydrate group attached that protrudes in ECF (never inside cell) • glycocalyx: all carbs attached to proteins or lipids on exterior surface of plasma membrane

  12. Functions of Membrane Proteins • 1. Ion Channels • selective pores or holes (think straws) thru which specific ions can flow in/out of cell

  13. Functions of Membrane Proteins • 2. transporters • selectively move a polar substance or ion across membrane

  14. Functions of Membrane Proteins • 3. receptors • integral proteins that serve as cell recognition sites • recognize specific type of molecule called a ligand

  15. Functions of Membrane Proteins • 4. enzymes • some integral (or peripheral) proteins catalyze specific chemical rx on inside or outside of cell

  16. Functions of Membrane Proteins • 5. linkers • integral (or peripheral) proteins that anchor proteins in plasma membrane of neighboring cells to each other

  17. Functions of Membrane Proteins • 6. cell-identity markers • glycoproteins (or glycolipids) • enable cell to recognize other cells of same kind during tissue formation • or to recognize & respond to foreign cells • ex: ABO bld type

  18. Membrane Fluidity • individual molecules not static in membrane • *fluidity greater when there are more dbl bonds in the f.a. tails of phospholipids • cholesterol makes membrane stronger but less fluid @ normal body temps

  19. Membrane Fluidity

  20. Cell Membranes are Selectively Permeable • lipid bilayer permeable to most nonpolar, uncharged small molecules • & impermeable to ions & most charged or polar molecules • # of ion channels alters the membrane permeability

  21. Membrane Permeability

  22. Concentration Gradients • because membranes are selectively permeable, differences in concentrations of chemicals between inside/outside of cell can exist • differences in charge across membrane = electrical gradient called a membrane potential

  23. Membrane Potential

  24. Transport Across Membrane • all ions & molecules have KE & each will move down its concentration gradient passively • diffusion • osmosis • active transport: material moves against its concentration gradient so cell must spend nrg • pumps • endo- & exo- cytosis

  25. Passive Transport is diffusion of substance across membrane w/no nrg investment

  26. Diffusion • higher concentration  lower concentration • equilbrium reached when concentration same • movement continues

  27. Rate of Diffusion Across a Membrane • affected by: • steepness of concentration gradient • temperature • mass of diffusing substance • surface area available for diffusing • distance material is diffusing thru

  28. Materials That Diffuse Thru Plasma Membrane • nonpolar, hydrophobic molecules, fat-soluble vitamins, small alcohols, ammonia, small amts water and urea • gases: O2, CO2, N2, • steroids, • vit. A, D, E, K

  29. Diffusion of Ions Across Plasma Membrane • ion channels: allow K+, Na+, Cl-, & Ca++ to move down concentration gradients when open

  30. Is Diffusing Material Polar or Nonpolar?

  31. Osmosis • diffusion of water across semi-permeable (selectively permeable) membrane • water moves not the solute • Isotonic solution: • cell has same concentration of solutes as solution • Hypotonic solution: • cell has higher concentration of solutes than solution • Hypertonic solution: • cell has lower concentration of solutes than solution

  32. RBCs in Solution

  33. http://www.stolaf.edu/people/giannini/movies/paramecium/para%20cont.movhttp://www.stolaf.edu/people/giannini/movies/paramecium/para%20cont.mov

  34. Facilitated Diffusion • solute moves passively by diffusion but requires a protein channel to cross membrane • *glucose binds to a specific transporter  protein changes shape  glucose crosses membrane thru transporter  protein returns to its original shape

  35. Facilitated Diffusion • http://programs.northlandcollege.edu/biology/Biology1111/animations/passive3.swf

  36. Active Transport • used to move materials from high concentration side of membrane  lower concentration side • ex: some ions, a.a., monosaccharides

  37. Energy for Active Transport • 2 sources: • ATP • pumps • Na+/K+ pump • nrg stored in Na+ or H+ concentration gradient • 1 substance moves in down its concentration gradient & brings along 2nd material

  38. Na+/K+/ATPase Pump • #1 pump in body cells

  39. Na+/K+/ATPase Pump • http://www.brookscole.com/chemistry_d/templates/student_resources/shared_resources/animations/ion_pump/ionpump.html

  40. Digitalis • medication given to patients with heart failure (weakened pumping action of heart) • action: • slows action of the Na+/K+ pumps which lets more Na+ accumulate inside cardiac muscle fibers  decreased Na+ concentration gradient across plasma membrane  Na+/Ca++ antiporters in these cells to slow down  increases intracellular concentrations of Ca++  increases force of contractions

  41. Secondary (2°) Active Transport • uses both symporters & antiporters that are powered by an ion concentration gradient (usually Na+ or H+)

  42. Bulk Transport Across the Membrane used by large macromolecules or large volumes of smaller molecules Exocytosis Endocytosis

  43. Endocytosis

  44. Phagocytosis • cell eats solid particles • neutrophils & macrophages are phagocytes

  45. Pinocytosis • bulk-phase endocytosis • cell takes in ECF

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