The Cellular Level of Organization

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)

8. PHOSPHOLIPID BILAYER

9. Cholesterol • weakly amphipathic

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

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

12. 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

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

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

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

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

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

18. 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

19. 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

20. Membrane Fluidity

21. 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

22. Membrane Permeability

23. 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

24. Membrane Potential

26. 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

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

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

29. 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

30. 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

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

32. Is Diffusing Material Polar or Nonpolar?

33. 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

34. RBCs in Solution

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

36. 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

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

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

39. 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

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

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

42. 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

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

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

47. Endocytosis

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

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