Understanding Cell Membrane Structure and Function: Phospholipids and Transport Mechanisms

1. February 7, 2014 • Objective: • To create a model of the cell membrane • To explain the structure of the cell membrane • Journal: What does it mean to have a phobia of something? What is an example of a phobia?

2. Key Terms • What do you think are the definitions of the following words? • Hydrophobic • Hydrophilic

3. Key Terms Defined • Hydrophobic: • Literally means fear of water • Molecules that are hydrophobic repel water and try to stay away from water • Hydrophilic: • Literally means water loving • Molecules that are hydrophilic are attracted to water and tend to be found next to water

4. Phospholipids • The structure of the phospholipid molecule generally consists of two hydrophobic tails and a hydrophilic head.

5. Phosphate Head • Hydrophilic • Polar (has a charge) • Made of phosphate

6. Two Fatty Acid Tails • Hydrophobic • Nonpolar (doesn’t have a charge) • Made of fatty acids

7. Structure of the Cell Membrane • Phospholipids make up the cell membrane of cells.

8. Phospholipid Cell Membrane Activity • Both inside and outside the cell contain water, so how do you think phospholipids are arranged to make a cell membrane? • Keep in mind that phospholipids contain hydrophilic heads and hydrophobic tails.

9. Cell Membrane Structure • Phospholipids form a double layer called a Phospholipid Bilayer with the phosphate groups on the outside and the fatty acid tails in the middle • This happens because there is water inside and outside of the cell, so the water loving phosphate end is always by the water

10. Structure Determines Function • The cell membrane structure helps it regulate what can and cannot pass through the phospholipid bilayer

11. Selectively Permeable • The cell membrane is selectively permeable, meaning that not everything can go across it. • Only certain things can get into the cell and only certain things can leave the cell

12. What can pass through the membrane? • This allows only small, nonpolar substances to pass directly through the phospholipid bilayer • All other substances are repelled by the nonpolar fatty acids, so they cannot go directly through the phospholipid bilayer

13. Other Ways to Pass Through the Phospholipid Bilayer • The cell needs to let other things in and out of the cell so it uses membrane proteins to allow specific substances across the membrane at specific times • Membrane proteins can be found on top of or within the phospholipid bilayer • http://www.youtube.com/watch?v=LKN5sq5dtW4

14. Types of Membrane Proteins

15. Receptor Proteins • Found on the outside of your cells • Enable a cell to sense its surroundings by binding substances outside the cell • Allows the cell to react to its surroundings

16. Cell-Surface Proteins • Similar to a nametag • Protein attached to a chain of carbohydrates attached to the cell membrane used to identify each type of cell

17. Transport Proteins • Allows certain necessary substances that cannot pass through the cell membrane into and out of the cell

18. Transport Proteins • Channel Proteins: Serve as a tunnel through the lipid bilayer that allow SPECIFIC ions, sugars, and amino acids to pass through the membrane • Ex: The channel for sodium ions does not allow sugars to pass through

19. Transport Proteins • Carrier Proteins: Only transport substances that fit within their binding site through the cell membrane • Carrier protein binds to a specific substance on one side of the cell membrane, changes shape and allows the substance out on the other side of the cell membrane

20. Daily Activities • Day 1 – Egg Lab • Begin Cell Membrane Model • Homework: • Cell Membrane Labeling Worksheet

21. February 7, 2014 • Objectives: • To differentiate between osmosis and diffusion • To describe how molecules can move down a concentration gradient • Journal: • What do you think the following words mean? • Equal • Concentration • Diffuse • If the Monksville dam broke, what would happen to the water in the Monksville Reservoir?

22. Cell Transport

23. Passive Transport Vocabulary • Equilibrium: when there is an equal number of molecules on both sides of the cell membrane • Concentration: the amount of a particular substance in a given volume • Concentration Gradient: When there is a higher concentration of a substance on one side than the other • Diffusion: When a substance moves from an area of higher concentration to an area of lower concentration

24. Types of Transport • Passive Transport: does not require energy to move substances across the cell membrane • Active Transport: requires energy to move substances across the cell membrane

25. Passive Transport • When substances enter or leave the cell by diffusing across the cell membrane down their concentration gradient • The direction the substances move depends on the concentration gradient

26. Types of Passive Transport • Simple Diffusion • Facilitated Diffusion • Osmosis

27. Simple Diffusion • When small, nonpolar (uncharged) substances pass directly through the phospholipid bilayer from an area of higher concentration to an area of lower concentration • Ex: If there is more oxygen outside the cell than inside the cell, it will diffuse across the lipid bilayer and into the cell.

29. Facilitated Diffusion • Substances that cannot pass directly through the membrane are helped to diffuse through the membrane using transport proteins

30. Osmosis • Facilitated diffusion of water from an area of higher concentration to an area of lower concentration • Allows the cell to maintain water balance as their environment changes

31. Water Channels • Since water is a polar substance, it does not directly diffuse across the cell membrane • So the cell has specific protein channels that only allow water to pass through called aquaporins

32. Predicting Water Movement • The direction the water moves depends on the concentration of the cell’s environment

33. Hypertonic • Water moves out of the cell • There is more solute outside the cell than inside the cell • The cell loses water and shrinks

34. Hypotonic • Water moves in • There is more solute inside the cell than outside the cell • Cell gains water and expands

35. Isotonic • There is the same concentration of water inside the cell and outside the cell • Equilibrium is reached • Cell stays the same size

36. Daily Activities • Egg Lab Day 2 – Place eggs in various solutions • Finish Cell Membrane Model

37. February 11, 2014 • Objectives: • To differentiate active transport from active transport • To describe how active transport moves molecules • Journal: • How is active different than passive?

38. Active Transport • Transport of substances against their concentration gradients • Requires energy usually in the form of ATP

39. Use of Carrier Proteins as Pumps • Carrier proteins require energy to pump substances across their concentration gradient

40. Sodium-Potassium Pump • Sodium ions inside the cell bind to the carrier protein which changes shape and releases sodium ions outside the cell membrane • As a result a phosphate group is released from the pump, returning the channel protein to its original shape, and releasing potassium ions inside the cell • For every three sodium ions pumped out, two potassium ions are brought inside • This prevents sodium from building up inside the cell, which would cause the cell to burst due to osmosis bringing in too much water

41. Vesicles • Large substances are too big to cross the membrane in channel proteins so they use vesicles • Vesicle membranes are lipid bilayer, so they can bud off from the cell membrane or fuse with it to move large substances in or out of the cell

42. Endocytosis • The movement of large substances into a cell using a vesicle • The cell membrane forms a pouch around the substance that closes and then pinches off inside the cell • Pinocytosis: also known as cellular drinking, engulfing liquid particles • Phagocytosis: engulfing solid particles

43. Exocytosis • The movement of large substances out of a cell using a vesicle • Vesicles inside the cell fuse with the cell membrane and are released outside the cell • Used to transport proteins modified by the Golgi apparatus, excrete wastes, or remove bacteria

44. Daily Activities • Day 3 – Finish Egg Lab