Nuclei (yellow) and actin (red)

1. Nuclei (yellow) and actin (red) Figure 4.6x

2. THE CYTOSKELETON The cell’s internal skeleton helps organize its structure and activities • network of protein fibers Figure 4.17A

3. Intermediate filaments reinforce the cell and anchor certain organelles • Microtubules • give the cell rigidity • provide anchors for organelles • act as tracks for organelle movement • Microfilaments of actin enable cells to change shape and move

4. Tubulinsubunit Actin subunit Fibrous subunits 25 nm 7 nm 10 nm MICROFILAMENT INTERMEDIATEFILAMENT MICROTUBULE Figure 4.17B

6. How do cilia and flagella move? • A cilia or flagellum is composed of a core of microtubules wrapped in plasma membrane • Eukaryotes have “9+2” structure Cilia and flagella move when microtubules bend

7. FLAGELLUM Electron micrograph of sections: Outer microtubule doublet Plasmamembrane Flagellum Centralmicrotubules Outer microtubule doublet Plasmamembrane Basal body Basal body(structurally identical to centriole) Figure 4.18A

8. Slide 43

9. polar head P – cytosol hydrophobic molecules hydrophilic molecules nonpolar tails Phospholipid bilayer

10. Cell surfaces protect, support, and join cells Surfaces allow exchange of signals and molecules. • Plant cells connect by plasmodesmata

11. Walls of two adjacent plant cells Vacuole PLASMODESMATA Layers of one plant cell wall Cytoplasm Plasma membrane Figure 4.19A

12. Animal cells - extracellular matrix • sticky layer of glycoproteins • binds cells together in tissues • can also protect and support cells

13. Anchoring junctions link animal cells • Gap junctions allow substances to flow from cell to cell • Tight junctions can bind cells together into leakproof sheets TIGHTJUNCTION ANCHORING JUNCTION GAP JUNCTION Plasma membranes ofadjacent cells Extracellularmatrix Figure 4.19B

14. Eukaryotic organelles fall into 4 functional groups • 1. Manufacture and transport – dependent on network of membranes • Nucleus • Ribosomes • Rough ER • Smooth ER • Golgi apparatus

15. 2. Breakdown – all single-membrane sacs • Lysosomes (in animals, some protists) • Peroxisomes • Vacuoles (plants)

16. 3. Energy Processing – involves extensive membranes embedded with enzymes • Chloroplasts • Mitochondria

17. 4. Support, Movement, Communication • Cytoskeleton – includes cilia, flagella, filaments, microtubules • Cell walls • Extracellular matrix • Cell junctions

19. What do these have in common? • HIV infection • Transplanted organs • Communication between neurons • Drug addiction • Cystic fibrosis • hypercholesteremia

20. Membranes organize the chemical activities of cells • selectively permeable • hold teams of enzymes   Cytoplasm Figure 5.10

21. Plasma membrane • Contact between cell and environment • Keeps useful materials inside and harmful stuff outside • Allows transport, communication in both directions

22. Plasma membrane components • Phospholipid bilayer • Cholesterol • Proteins • Glycocalyx

23. polar head P – cytosol hydrophobic molecules hydrophilic molecules nonpolar tails Phospholipid bilayer

24. THE PLASMA MEMBRANE phospholipids cholesterol integral protein cytoskeleton peripheral protein Cholesterol blocks some small molecules, adds fluidity

25. Membrane Proteins • span entire membrane or lie on either side • Purposes • Structural Support • Recognition • Communication • Transport

26. Glycocalyx • Composed of sugars protruding from lipids and proteins • Functions • Binding sites for proteins • Lubricate cells. • Stick cells down.

27. Some proteins function as receptors for chemical messages from other cells • The binding of a messenger to a receptor may trigger signal transduction • Many membrane proteins are enzymes Messenger molecule Receptor Activated molecule Enzyme activity Signal transduction Figure 5.13

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

29. Diffusion and Gradients • Diffusion = movement of molecules from region of higher to lower concentration. • Osmosis = diffusion of water across a membrane

30. Molecule of dye Membrane EQUILIBRIUM • In passive transport, substances diffuse through membranes without work by the cell EQUILIBRIUM Figure 5.14A & B

31. (a) selectively permeable membrane H2O free water molecule: can fit through pore sugar pore bound water molecules clustered around sugar: cannot fit through pore (b) selectively permeable membrane sugar molecule bag bursts water molecule pure water

32. Osmosis = diffusion of water across a membrane Hypotonicsolution Hypertonic solution • water travels from an area of higher concentration to an area of lower water concentration Selectivelypermeablemembrane Solutemolecule HYPOTONIC SOLUTION HYPERTONIC SOLUTION Water molecule Selectivelypermeablemembrane Solute molecule with cluster of water molecules Figure 5.15 NET FLOW OF WATER

33. Water balance between cells and their surroundings is crucial to organisms osmoregulation = control of water balance • Osmosis causes cells to shrink in a hypertonic solution and swell in a hypotonic solution

34. 10 microns isotonic solution hypertonic solution hypotonic solution net water movement into cells net water movement out of cells equal movement of water into and out of cells

36. Passive transport = diffusion across membranes • Small nonpolar molecules - simple diffusion • Many molecules pass through protein pores by facilitated diffusion Solutemolecule Transportprotein Figure 5.17

37. Active transport • transport proteins needed • against a concentration gradient • requires energy (ATP)

38. FLUIDOUTSIDECELL Phosphorylated transport protein Transportprotein • Active transport in two solutes across a membrane • Na+/K+ pump • Protein shape change Firstsolute 1 First solute, inside cell, binds to protein 2 ATP transfers phosphate to protein 3 Protein releases solute outside cell Second solute 4 Second solute binds to protein 5 Phosphate detaches from protein 6 Protein releases second solute into cell Figure 5.18

39. Exocytosis and endocytosis transport large molecules exocytosis = vesicle fuses with the membrane and expels its contents FLUID OUTSIDE CELL CYTOPLASM Figure 5.19A

40. b

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

42. Phagocytosis, “cell eating” • —How the human immune system ingests whole bacteria or one-celled creatures eat. phagocytosis food particle 1 2 3 particle enclosed in vesicle

44. (extracellular fluid) pinocytosis 2 vesicle containing extracellular fluid (cytoplasm)

45. extracellular fluid plasma membrane cytosol vesicle coated pit receptors captured molecules vesicle bacterium pseudopodium vesicle

46. Receptor-mediated endocytosis

47. Cholesterol can accumulate in the blood if membranes lack cholesterol receptors Phospholipid outer layer LDL PARTICLE Receptor protein Protein Cholesterol Plasma membrane Vesicle CYTOPLASM Figure 5.20

49. What do these have in common? • HIV infection • Transplanted organs • Communication between neurons • Drug addiction • Cystic fibrosis • hypercholesteremia