Key Concepts: Cell Membranes

1. Key Concepts: Cell Membranes • Structure of the cell membrane • Main functions of cell membrane • How things are transported across the membrane

2. Cell Membrane: Structure • Cell Membranes are a fluid mosaic of lipids and proteins. • http://www.youtube.com/watch?v=Qqsf_UJcfBc

3. Cell Membrane: Structure cont. • Fluid describes that cell membranes move • Fluid also describes that the membranes are usually in a liquid state, like salad oil. • Membranes must be fluid to work properly.

4. Cell Membrane: Fluidity Hydrophilic Head (polar-water loving) Hydrophobic Region Hydrophobic Tail (non-polar) Cholesterol

5. Cell Membrane: Structure cont. Mosaic describes the many proteins and lipids that make up the cell membrane. Proteins are embedded in and on top of the lipid bilayer. The proteins embedded in the cell membrane determine its function.

6. Cell Membrane: Mosaic

7. Cell Membrane: Functions • Regulates what goes in and out of the cell. • Provides support for the cell.

8. Cell Membrane: Selective Permeability • Cell membranes exhibit selective permeability, regulating what goes in and out of cell. • Selective permeability means some substances can pass across the cell membrane while others cannot.

9. Types of Molecules Passing Through Cell Membrane • Hydrophobic molecules (non polar) like CO2, O2 and other hydrocarbons (fatty acids) • Can move across the lipid bilayer easily. • Hydrophilic molecules (polar) like sugars (glucose), salts, and water • Have trouble passing through the non-polar centers of the lipid bilayer. • Size and polarity prevents them from moving across the lipid bilayer so use a protein channel/pump.

10. Two Ways for Molecules to Enter Cell • Active Transport • Passive Transport

11. Passive Transport • Passive Transport is when the cell does not expend energy to move across the membrane. • Movement comes from kinetic energy of molecules • http://www.youtube.com/watch?v=6VdMp46ZIL8&feature=related • http://www.youtube.com/watch?v=2Vdjin734gE

12. Types of Passive Transport • 1. Diffusion • 2. Facilitated Diffusion • 3. Osmosis

13. Passive Transport: Diffusion • 1. Diffusion is the tendency for molecules to spread out evenly (reach dynamic equilibrium) and move from an area of high concentration to low concentration.

14. Passive Transport: Facilitated Diffusion • 2. Facilitated Diffusion is when molecules use channel proteins or carrier proteins to pass through the bilayer.

15. Passive Transport: Osmosis • 3. Osmosis is the special name given to the diffusion of water molecules. • Water like other substances moves from a higher concentration of water molecules to a lower concentration of water molecules.

16. Water Balance in Cells • Why would a cell gain or lose water? • It depends on the concentration of solutes inside and outside the cell.

17. Water Balance in Cells • Tonicity = the ability of a cell to gain or lose water. • Three Types of Tonicity • Isotonic • Hypertonic • Hypotonic • Always in terms of relationship between the solute concentration in solution and the solute concentration in the cell

18. Solutes Suck!

19. Water Balance in Cells • Hypertonic Environment • Hyper = more • If there are more solutes outside the cell, the cell will lose water. • Water moves outside the cell to equalize the concentration of water molecules, causing the cell to shrink.

21. Elodea in a Hypotonic Solution Water Balance in Cells • Hypotonic Environment • Hypo = less • If there are less solutes outside the cell, the cell will gain water • Water moves inside the cell to equalize the concentration of water molecules, causing the cell to swell.

23. Water Balance in Cells • Isotonic Environment • iso = same • No net movement of water across the membrane because the solute concentration is equal inside and outside of the cell.

25. Water Balance in Cells • Osmotic Pressure: The force exerted on the cell from an imbalance of water and solutes. • High Osmotic pressure means water moving into the cells • Low Osmotic pressure means water moving out of the cells

26. Adaptations for Osmotic Pressure • Large organisms deal with this by living in isotonic environments like blood. • Plants, fungi, bacteria and protista have rigid cell walls to protect the cell from bursting in a hypotonic environment.

27. Active Transport • Cellular energy (ATP) is used to move solutes in and out of a cell.

28. Types of Active Transport • Solute Pumping • Using Carrier Proteins • Engulfing Large Molecules • Exocytosis • Endocytosis • Phagocytosis • Pinocytosis

29. Active Transport: Solute pumping small molecules • Carrier Proteins are used to move small molecules against the concentration gradient. • Example: Potassium Pump Active Transport

30. Active Transport: Large Molecules • Exocytosis • Dumping large molecules outside of the cell. • Insulin is secreted into the blood this way. • Cell walls are formed by proteins and carbohydrates transported outside the cell. • Exocytosis

31. Active Transport: Large Molecules • Endocytosis • Forming of vesicles to take in large substances into the cell (macromolecules or other cells). • Phagocytosis: cell eating (phago- means to eat) • Pinocytosis: cell drinking (pino- means to drink…think vino, pino) • Endocytosis • Pinocytosis • Phagocytosis

32. End

33. Passive Transport: Facilitated Diffusion • Channel Proteins = Open tunnels with hydrophilic centers that allow hydrophilic substances (i.e. water) to pass through the membrane rapidly.

34. Passive Transport: Facilitated Diffusion • Carrier proteins = help other hydrophilic molecules (i.e. glucose and salt ions) to enter the cell. • When the molecule enters the carrier protein, the protein undergoes a shape change so the molecule can pass through. • Molecule specific.