Cell Membrane and Transport

1. Cell Membrane and Transport

2. Cell Membrane AKA plasma membrane **All cells have a cell membrane Made up of a lipid bilayer (phospholipids) Controls what enters and leaves the cell to maintain internal balance called homeostasis

3. Cell Membrane Selectively permeable - Some molecules can pass through the cell membrane but some cannot In: Glucose, water, oxygen Out: Waste and carbon dioxide * Small molecules can pass through the membrane easily (contains pores)

4. Cell Membrane Structure Lipid Bilayer - two layers of phospholipids make a flexible barrier. Phospholipids are composed of a: Phosphate head (polar - water loving) Fatty acid tail (nonpolar - water fearing)

5. Cell Membrane Structure Proteins are embedded in the membrane Called a fluid mosaic because it is composed of many different organic macromolecules that can move Cell Membrane Fluid Mosaic Model

6. Cell Membrane Structure Lipids act as a barrier between the inside and the outside of the cell Carbohydrates act as receptors to decide if some materials can pass through the membrane or not. Proteins act as pumps or channels for larger molecules

7. Cell Transport Two categories of cell transport: Passive Transport (High → Low) *cell does NOT use energy to move molecules • Diffusion 3. Facilitated Diffusion • Osmosis Active Transport (Low → High) *cell DOES use energy to move molecules • Protein pumps • Endocytosis and exocytosis

9. Cell Transport Particles move in response to a concentration gradient *Difference between concentration (number of molecules) in a space [Solutes = substance being dissolved (ex: sugar); Solvent = Dissolver (ex: water)] Equilibrium - When particles are evenly distributed over a given space High Low Equal Low High

10. Equilibrium • All molecules move so they can reach equilibrium (equal on both sides or balance). • Once it is reached there is equal movement in both directions. • Molecules never stop moving!

11. Concentration Gradient • Concentration gradient is created when there is a difference in the amount of molecules on each side of the cell membrane (not at equilibrium) • It causes particles move!

12. Passive Transport - Diffusion • Diffusion - the random movement of any molecule across the cell membrane High to low concentration gradient Does NOT require energy Example: Food coloring in water

13. Passive Transport - Diffusion Diffusion continues until all molecules are evenly spread out → equilibrium! **Molecules will still move around but stay spread out

14. Passive Transport - Diffusion Practice!! Which way would the molecules move across the membrane? 1 2 1 2

15. Passive Transport - Diffusion Practice!! Which way would the molecules move across the membrane?

16. Passive Transport- Diffusion Let’s try some more diffusion practice problems using percentages: Inside a cell is 40 percent salt and outside the cell is 60 percent salt. Inside a cell is 50 percent salt and outside the cell is 50 percent salt. Inside a cell is 75 percent water and outside the cell is 55 percent salt.

17. Passive Transport - Osmosis 2. Osmosis - the diffusion of WATER molecules across the cell membrane High to low concentration gradient Does NOT require energy Ex: Fingers wrinkle in bath tub *SALT (Solute) SUCKS WATER!!!

18. Passive Transport - Osmosis More solute outside of the cell Outside=inside More solute inside the cell Water leaves cell Equilibrium Water enters the cell Cell shrinks Cell expands ***can burst!

19. Passive Transport - Osmosis Practice! Which way would the water molecules move? = water molecule = salt molecule

20. Passive Transport - Osmosis Osmosis Video Virtual Lab??

21. Osmotic Pressure Turgor Pressure - The pressure of water pushing the inside of the cell membrane against the cell wall of a plant cell. **Organisms have mechanisms for dealing with osmotic pressures. Ex: Bacteria and plants have a cell wall that prevent them from over expanding. Ex: Kidneys help remove excess water from the blood Ex: Saltwater fish pump salt out of their specialized gills so they do not dehydrate Video

22. Passive Transport- Facilitated Diffusion Facilitated Diffusion is the movement of LARGE molecules across the cell membrane through a protein High to low concentration Goes with the gradient Does NOT require energy

23. Active Transport Active Transport - the movement of molecules against a concentration gradient Requires energy (ATP) since molecules are moving from a low concentration to a high concentration. Uses a protein pump. Purposefully moves the molecule. High Cell Membrane Low Watch video clip

24. Sodium Potassium Pumps (Active Transport using proteins) Types of Active Transport 1. Protein Pumps -transport proteins that require energy to do work • Example: Sodium / Potassium Pumps are important in nerve responses. Protein changes shape to move molecules: this requires energy!

25. Types of Active Transport • 2.Endocytosis: taking bulky material into a cell • Uses energy • Cell membrane in-folds around food particle • “cell eating” • forms food vacuole & digests food • This is how white blood cells eat bacteria!

26. Types of Active Transport Endocytosis & Exocytosis animations 3. Exocytosis:Forces material out of cell in bulk • membrane surrounding the material fuses with cell membrane • Cell changes shape – requires energy • EX: Hormones or wastes released from cell