1. Cell Junctions

2. “serve to anchor cells to one another or to provide a passageway for cellular exchange.” Three major types: Desmosomes Tight junctions Gap junctions Cell Junctions

4. Desmosomes Hold two cells together Intermediate filaments (made of protein keratin) Provide mechanical stability and strength Like rivets fastening cells into strong sheets Tissues: skin, uterus, heart

5. Desmosomes

6. Tight Junctions Create impermeable seals around cells Example: digestive tract tube does not allow enzymes from digestive tract to pass through bloodstream Animal cells only Prevents leakage of molecules

9. Communication junctions “passageways between cells that allow transfer of chemical or electrical signals” Two kinds: plasmodesmata gap junctions

10. Gap Junctions Narrow tunnels made of protein connexins Prevents cytoplasm of each cell from mixing Allows passage of ions/small molecules Tunnels-1.5 nm diameter Gap between cells- 2-3 nm Pattern of channel formation determines permeability

13. Endocytosis (endo = inside, cyto = cell) Capture of substances outside the cell when the plasma membrane merges to engulf it. ***There are three types of endocytosis 1. phagocytosis 2. pinocytosis 3. receptor-mediated

14. Pinocytosis (pino = to drink, cyto = cell) Pinocytosis occurs when dissolved materials enter a cell. The plasma membrane folds inward to form a channel allowing the liquid to enter. The plasma membrane closes off the channel, encircling the liquid inside a vesicle. Oils enter cells through pinocytosis

15. Phagocytosis (phago = to eat, cyto = cell) Phagocytosis occurs when undissolved solids enter a cell. The plasma membrane wraps around the solid material and engulfs it, forming a vesicle. Phagocytic cells, such as white blood cells, attack and engulf bacteria in the manner.

16. Receptor-Mediated Endocytosis Occurs when specific molecules bind to specialized “receptors” (proteins) in the plasma membrane. The membrane, the receptors, and the specific molecules, called ligands, fold inward forming vesicles. Hormones target special “target cells” by receptor-mediated endocytosis. Ligan d Receptor Protein Molecule being ingested

17. Exocytosis (exo = outside, Cyto = cell) moving substances outside the cell Process of vesicles fusing with the plasma membrane and releasing their content to the outside of the cell.

18. Passive Transport No energy expended by the cell Goes “downhill” with the concentration gradient Substances move from [HI] [LOW] Examples: diffusion, osmosis, facilitated diffusion

19. Diffusion Solution = solute + solvent Solute- substance that is dissolved Solvent- substance that does the dissolving (fluid) Solute particles dissolved in a solvent are constantly in motion. Temperature motion This constant motion causes DIFFUSION Diffusion- movement of particles from areas of high concentration to areas of low concentration

22. Osmosis and Tonicity Hypertonic- the solution that has [solute] Water flows toward the hypertonic environment Hypotonic- the solution that has [solute] Water flows away from a hypotonic environment Isotonic- the solutions have equal concentrations of solute (no net osmosis)

23. Osmosis and Tonicity

24. Facilitated Diffusion Down gradient No ATP used Carrier – Mediated Transport

25. Active Transport (Sodium-Potassium Pump) Needed because Na + and K + constantly leak through membrane One ATP utilized to exchange three Na + pushed out for two K + brought in to cell

26. Carrier – Mediated Transport Secondary Active Transport Sodium-Potassium Pump CYTOPLASM Glucose molecule Sodium ion Na + –K + pump + + Regulation of cell volume Heat production Maintenance of a membrane potential Secondary active transport (No ATP used)

27. Voltage-Gated Sodium Channels

28. Voltage-Gated Potassium Channel