Cell Transport Notes Unit 5

1. Cell Transport NotesUnit 5 Diffusion & The Cell Membrane Osmosis Transport with Proteins

2. Diffusion & The Cell Membrane

3. Ways materials can cross the membrane: • Diffusion • Osmosis • Facilitated Diffusion • Active Transport • Bulk Transport: Endocytosis and Exocytosis Passive transport (no energy)

4. What is diffusion? Spreading out of molecules from higher [ ] to lower [ ] until equilibrium is reached • Examples: • Perfume spill • Oxygen molecules equilibrium

5. Diffusion is due to the random motion of molecules within a substance. Movement of molecules is GREATEST when there is more SPACE between them. solid liquid gas

6. Factors that Affect Diffusion: Temperature • Increasing temp  faster diffusion Pressure • Increasing pressure  speeds up diffusion (more collisions)

7. Concentration Gradient – difference in concentration from one area to another Molecular size • Small molecules move faster than larger ones, therefore have faster diffusion **diffuses faster** 10 H20 5H20 2 H20 2 H20

8. Phospholipid Structure glycerol fatty acid #1 glycerol fatty acid #1 fatty acid #2 fatty acid #2 phosphategroup fatty acid #3 Polar Head

9. Vocabulary: O- O- polar molecule • Share e- unevenly • Have a + and - charge non-polar molecule • Share e- evenly • Have NO charge H+ H+ H+ H+

10. Hydrophobic = water fearing phosphate Polar head glycerol H20 Hydrophilic = water loving Fatty acid chains

11. The Plasma Membrane The plasma membrane controls the passage of materials in and out of the cell. This means that the plasma membrane is responsible for maintaininghomeostasisor the CHEMICAL BALANCEof the cell. [Amounts of water, glucose, amino acids, O2, and CO2, and wastes must be kept at appropriate levels for cell survival.]

12. Outside cell Inside cell

13. Composed of two layers of phospholipids. • Lipids are not soluble (cannot dissolve) in water, so they are a perfect material for the cell’s boundary. • Phospholipidbilayer is approximately 8 nm thick. • Cholesterol molecules exist in between some phospholipids to stabilize (solidify) the membrane’s structure.

14. cholesterol

15. Contains channels made of proteins. • Act as pores for certain molecules to travel through the membrane.

16. Protein (function depends on unique shape)

17. The outer surface of the membrane is covered with carbohydrates (glycocalyx). • Type and pattern of carbohydrate chains is unique in every person, acting like ID tags for the body to recognize its own cells from other cells. • If a cell with a different pattern of carbohydrates is present, the immune system will detect it as foreign and will seek to destroy it.

18. carbohydrate

19. Cell Membrane is semi-permeable. • It blockssome molecules, while others are allowed to pass through. • This allows the cell to control most of what gets in/out based on the size, charge, chemical structureof the molecules entering/leaving.

20. Osmosis The diffusion of water across a cell membrane.

21. Environment of Cells • Cells exist in an environment of mostly water. • Water can move across the phospholipidbilayer directly. • Cells are constantly subjected to the flow of water across the membrane; they CANNOT CONTROL IT because water is • Small • Fast • Always Around

22. Three Different Situations • More water on the outside of the cell: the cell is in a hypotonic solution. • More water on the inside of the cell: the cell is in a hypertonic solution. • Even amount of water inside and out: the cell is in an isotonic solution.

23. Hypotonic Solution A solution (environment) in which the concentration of water is higher on the outside of the cell. Outside the cell: 99% water, 1% other molecules Inside the cell: 97% water, 3% other molecules water (99%)

24. Hypotonic Solution – Result Water will diffuse into the cell (osmosis) until a state of dynamic equilibrium is reached. (a state in which molecules still move in and out, but at an equal rate) • Animal cells will swell and may burst (cytolysis). • They contain contractile vacuoles that help pump out excess water. Plant cells will experience high turgor pressure (water fills vacuole and the plasma membrane gets pushed against the cell wall). The plant is fresh – does not wilt.

25. Hypertonic Solution A solution (environment) in which the concentration of water is higher on the inside of the cell. Outside the cell: 95% water, 5% other molecules Inside the cell: 97% water, 3% other molecules water (95%)

26. Hypertonic Solution – Result Water will diffuse out of the cell (osmosis) until a state of dynamic equilibrium is reached. Animal cells In plant cells, water leaves the shrivel. vacuole and the plasma membrane shrinks away from the cell wall (plasmolysis). Turgor pressure is low – plant wilts.

27. Isotonic Solution A solution (environment) in which the concentration of water is equal inside the cell and out. Outside the cell: 97% water, 3% other molecules Inside the cell: 97% water, 3% other molecules water (97%) Remember: Water is ALWAYS moving.

28. Isotonic Solution – Result Water will move in and out of the cell at an equal rate. No net movement of water (osmosis) will occur. Animal cells and plant cells will maintain normal conditions.

29. Summary More water on the outside Water enters cell Cell swells, possible cytolysis High turgor pressure More water on the inside Water leaves cell Cell shrivels Plasmolysis Equal amt water inside and out Water enters and leaves at equal rate No change No change

30. Transport With Protein Channels

31. Proteins transport molecules and ions that cannot cross the membrane directly by diffusion either because of sizeor charge. Some proteins can also pump molecules and ions againstthe concentration gradient (from low to high concentration) if necessary.

32. The function of the protein channels is due to its shape (due to amino acid order and folding of polypeptide chains). • Because proteins are shape-specific (like puzzle pieces or locks and keys), there must be a unique protein for each type of molecule that crosses the membrane. • Some of these protein channels are gated, meaning they require certain signals in order for them to open or close.

33. Transport Across Membrane with Protein Channels, Method Number 1: FACILITATED DIFFUSION • Protein channel assists and speeds up diffusion • Does not require energy – movement of molecules is due to concentration gradient alone

34. Low [ ] High [ ]

35. Transport Across Membrane with Protein Channels, Method Number 2: ACTIVE TRANSPORT • Protein channel moves molecules AGAINST the concentration gradient (from an area of LOW concentration to an area of HIGH concentration) • Requires energy from ATP (the cell’s only usable energy source)

36. Osmosis (water)

37. Bulk Transport (Endocytosis and Exocytosis) ENDOCYTOSIS (endo = in) • Transport of large quantities of substances into a cell, requiring ATP energy. • The ingested material gets surrounded by the phospholipids of the cell membrane. Once inside the cell, it is considered to be a vacuole.

39. EXOCYTOSIS (exo = out) • Transport of large quantities of substances out of a cell, requiring ATP energy. • A vacuole inside the cell fuses with the plasma membrane and releases its contents outside of the cell.