The CELL SURFACE AND CYTOSKELETON 3-D Journey

1. The CELL SURFACE AND CYTOSKELETON3-D Journey Chapter 5

2. The Cell Membrane and Cell Function

3. Cell Membrane recognizes “self” • Organ rejection • Name tags of proteins, carbs and lipids

4. Cytoskeleton • Cell’s interior scaffolding • Protein fibers

5. Cytoskeleton + cell membrane • Cells framework • Organizes interior of cell • Distinguishes on cell from another

6. A. Cell Membrane Structure Cell membrane is a phospholipid bilayer embedded with mobile proteins. – Sandwich-like layering repels both charged and uncharged particles Phosphate head of phospholipid is hydrophilic. Fatty acid tails are hydrophobic. Proteins

7. CM Structure, con’t • Proteins – embedded • Passageway for water soluable molecules and ions • Also act as carriers

8. CM Structure, con’t • Fluid mosaic – everything moves within the layer

9. CM Structure, con’t • Receptors – glycoproteins on or within the membrane surface

10. CM Structure, con’t Ratios of proteins to phospholipids reflect health • Upset = sickness • Multiple sclerosis – not enough fat in cell membranes (cell that are supposed to create mylin • TaySachs – excess lipid in cell membrane (cells that build TOO MUCH mylin Layers of plasma membrane wrapped around an axon

11. Diffusion: Passive Flow Across a Membrane • General terms: • Aquaeous solution – homogeneous mixture of solute + solvent (water) • Concentration – how much solute is in the solvent

12. Diffusion, con’t • Diffusion moves substances from high to low concentration • Membranes are selectively permeable • Oxygen, water and carbon dioxide freely cross membranes

13. Diffusion, con’t • Heat increases the rate of diffusion – kinetic energy is increasing

14. Diffusion, con’t • Concentration gradient – differences in concentration from low to high or vice-versa • Other types of gradients: • pH • Electrical • Pressure • ions

15. Diffusion, con’t • Dynamic equilibrium – equal movement back and forth

16. Osmosis • The diffusion of water • MUST be across a membrane • Controlled by solute concentration inside and outside the cell • Solutes can’t move, so water does

17. Osmosis, cont • Tonicity • Isotonic-solutes inside and outside have the same concentration

18. Osmosis, con’t • Hypotonic – hypertonic • Relative terms • Can refer to inside or outside of cell • Hypotonic - solution with the lowersolute concentration. • Hypertonic - solution with the highersolute concentration. • Red blood cell example Pg 70

19. What is effect of immersing an animalcell in a hypertonic or hypotonic solution?

20. Cells in solutions

21. What is effect of immersing a plant cellin a hypertonic or hypotonic solution? Cell immersed in hypertonic solution Cell immersed in hypotonic solution

22. Osmosis, con’t • Contractile vacuole – organ that regulates water movement in single cell critter (see video on previous slide) • Turgor pressure – how plant cells regulate how much water can flow into cell – water forced against the cell wall

23. Transport Proteins • Channels Allow Passive Movement at a faster Rate • Forms an opening (tube) for solutes to pass through • Charge and size regulate what passes • FAST -100 million ions or molecules /second • Form of facilitated diffusion

24. Transport Proteins, con’t • Carriers move cargo from one side to the other • Carrier protein binds to ion or molecule • Protein changes shape and forces particle to other side of membrane • Can be passive (no ATP- therefore another facilitaed diffusion) or active- uses ATP • Passive facilited 100-1000 per ssecond • Active – can move against the gradient

25. Transport Proteins, con’t • Pumps use energy to move molecules or ions against a gradient • Sodium potassium pump

26. Transport Proteins, con’t • Pumps, con’t • Co-transport- see diagram (figure 5.11) pg 72 • Creates gradient • Gradient used to transport substance • Symporter molecule responds to gradient movement

27. Transport Proteins, con’t • Vesicles perform mass movements by packaging substances • Exocytosis – fluids and large particles out of cell • Ex. Sperm – releases enzymes that penetrate egg

28. Transport Proteins, con’t • Vesicles, con’t • Endocytosis – capture large molecules and fluid on surface and move into cell • Pinocytosis – just water or solutes and water • Phagocytosis – captures and destroys debris, small organisms, bacteria • Endosome – phagocytic vesicle fuses with a lysosome

29. Transport Proteins, con’t • Vesicles, con’t • Endocytosis, con’t • Receptor mediated endocytosis • Receptor protein binds to ligand, membrane indents, pulling ligand into the cell • Ex. Liver cells take in cholesterol this way

30. Transport Proteins, con’t • Trancytosis – combination of endo and exocytosis • Moves particles from one side of the cell to another

31. The Cytoskeleton • Tubules and filaments guide organelle movement, provide shape and link molecules

32. The cytoskeleton, con’t Compare Microtubules and both filaments (figure 5.14 pg 75 aka microfilaments

33. The cytoskeleton, con’t Microtubules – hollow, thick elements made of the protein tubulin- protein dimmers (pairs) Length adjustable + or – molecules of tubulin Number and arrangement changes based on cell cycle (spindles) Cancer treatments – some effect tubule assembly

34. The cytoskeleton, con’t Other Functions: • move chromosomes apart during cell division • form cilia & flagella • Cilia- have wave-like motion • 9 microtubule pairs around a central pair (9+2) pattern • Dynein – connects inner and outer proteins (wheel-like) pg 76

35. The cytoskeleton, con’t • Bad dynein arrangement leads to disease • Clean respiratory track, move egg down fallopian tube, single celled critters swim Leads to Alzheimer’s plaques and tangles

36. The cytoskeleton, con’t • Flagella • 9+2 arrangement but longer • Whiplike – propulsion • Sperm cells – humans 1, cycad tree - thousands

37. The cytoskeleton, con’t • Another function – track-way in cell • Moves organelles and proteins within • Squid color changes – rearrange pigment

38. The cytoskeleton, con’t Microfilaments - long, thin elements made of the protein actin. • Not hollow • Smaller than microtubules Functions: • Strength to cells – withstand stretching and bending) • connect cells to each other • move vesicles & organelles within cytoplasm • Muscle contractions • Actin and myosin interact in sliding filament

39. The cytoskeleton, con’t Intermediate filaments - elements with diameters in between that of microtubules & microfilaments. Made of various proteins (ie. keratin) Dimers entwined into coiled rods Functions: • maintain cell shape • Inner framework of cell • connect cells to each other & to underlying tissue (skin cells) • Epidermolysis bullosa • Intermediate filaments abnormal – skin blisters easily

40. Cell Signaling and Response • Cell to Cell communication Intercellular Junctions Structures that connect cells of multicellular organisms to form tissues

41. Cell Signaling and Response, con’t . Animal cell Connections- types depend on functions Tight Junctions- cell membranes of adjacent cells are fused, creating a tight seal – like a belt Create sheets Ex. cells lining small intestine; cells lining capillaries in brain

42. Cell signaling and Response, cont • Blood vessels (capillaries) in brain (400 mile-blood brain barrier) • Lipids are chemically soluble – heroin, valium, nicotine, cocaine, alcohol • Oxygen passes • Water soluble – different pathway

43. Cell Signaling and Response, con’t Desmosomes - intermediate filaments weld cell membranes of adjacent cells together in isolated spots. hold skin cells in place (cell to extrcellular matrix) Ex. skin cells

44. Cell Signaling and Response, con’t Gap Junctions - channels that link the cytoplasm of adjacent cells, allowing exchange of materials. Ex. heart muscle cells, and muscle cells in digestive track

45. Cell Signaling and Response, con’t • Cell Walls add structure and allow interactions • Around cells of bacteria, archaea, fungi, algae and plants • Provide shape and volume AND interact

46. Cell Signaling and Response, con’t • Cell walls, con’t • Composition depends on function of cell, surrounding or life cycle of cell • Plants – mostly cellulose and pectin (like glue)

47. Cell Signaling and Response, con’t • CW is layers. Oldest layer is most outside layer • Where cell walls meet: middle lamella • Plasmodesmata – link plant cells (tunnels to cells)

49. Cell Signaling and Response, con’t Cell Adhesion Process that uses membrane proteins called cellular adhesion molecules (CAMs) to direct the migration of cells. Various CAMs function in sequence to: • guide WBCs to injury sites • guide embryonic cells to help form placenta • establish nerve connections involved in learning & memory

50. CAMs directing WBCs to injury sites.