The Cell’s Plasma Membrane

1. The Cell’s Plasma Membrane

2. The Plasma Membrane Is Selectively Permeable Waste Removal Won’t Allow just anything in or out Maintains Homeostasis Selective about what crosses the membrane Excess nutrients and materials when concentration is too high Balance of water ,glucose, amino acids, lipids regardless internal and external cell conditions. Small particles diffuse across; Large have to be “helped”

3. Structure of the Plasma (Cell) Membrane *Referred to as a phospholipid bilayer (2 layers of phospholipids) in a fluid mosaic **Phospholipids  lipids with a phosphate head. Non-Polar, lipid Tails – “hate” water and keep extra water out of the cell; hydrophobic Phosphate Polar heads “love” water; hydrophilic

4. Other components of the plasma membrane: • Cholesterol prevents fatty acid chains of the phospholipids from sticking together and collapsing the membrane! Phospholipid Cholesterol Molecule

5. Carrier proteins will “carry” specific particles, particularly ions, across membrane • Channel Proteins  allows small things like polar molecules directly through the membrane • Cholesterol  Stabilizes membrane; prevents fatty acid chains of phospholipids from sticking together • Carbohydrates  Helps cells identify each other Carbohydrates Channel Proteins Cholesterol Carrier Proteins

6. Transport Across the Semi-Permeable Membrane

7. Transport Across the Plasma Membrane Transport of Materials Across The Plasma (Cell) Membrane2 Kinds:* Passive (No energy required)*Active (Energy in the form of ATP is Required)

8. Passive Transport

9. Proteins and Diffusion

10. Facilitated Diffusion Requires Proteins

11. Channel Proteins • Like a hollow tube. • Allows very small molecules diffuse down a concentration gradient (high concentration to low concentration)

12. Carrier Proteins **Polar molecules and charged ions can not diffuse freely across the plasma membrane  hydrophobic nature of the fatty acid tails **Carrier Proteins “help” these through the membrane without using any ATP ** The molecule changes the shape of protein http://highered.mcgraw- hill.com/sites/0072495855/student_view0/chapter2/animation__how_facilitated_diffusion_works.html

13. Passive Transport Continued: NO Proteins Required in Simple Diffusion and Osmosis

14. Passive Transport That Requires NO Proteins • Osmosis – water simply diffuses across the plasma membrane without any help • Simple Diffusion – Small molecules such as O2 and CO2 will readily diffuse as well • Both depend on Solute Concentration!!

15. Diffusion and Osmosis **Goes WITH the concentration gradient – High to low Plasma membrane

16. A Little Vocab…………….. • SOLVENT: A usually liquid substance (such as water) that is capable of dissolving or dispersing one or more substances. Water is the universal solvent • SOLUTE: A substance (such as salt) that dissolves in a solvent. • SOLUTION: The combination of a solute with a solvent, when the solute has been evenly dissolved in the solvent. Such as saline solution for contact lenses

17. Tonicity Drives Osmosis

18. Tonicity • Solutions In Which Cells are in (Extra-Cellular Fluid) can be: • Hypertonic • Hypotonic • Isotonic

19. A Cell in a Hypertonic Solution • Solute concentration of a solution is higher OUTSIDE of the cell than inside cell • Causes water to diffuse OUT of the cell • The sell shrinks

20. A Cell in Hypotonic Solution • Solute concentration of solution is low thus MORE H2O!! • Causes water to diffuse INTO the cell • The cell swells

21. A Cell in an Isotonic Solution • Solute concentration of solution equal to that of cell • No net movement of water  Dynamic Equilibrium

23. Tonicity • Things to remember: • If: It’s hypertonic OUTSIDE of the cell, the CELL itself is considered to be hypotonic • If: It’s hypotonic OUTSIDE of the cell, the CELL itself is considered to be hypertonic • Water would flow from HYPO- to HYPER

24. Osmotic Pressure

25. Osmotic Pressure • Osmosis always moves a solvent in one direction only, from a less concentrated solution to a more concentrated solution(Hypo – to Hyper - ) • As osmosis proceeds, pressure builds up on the side of the membrane where volume has increased. Ultimately, this pressure prevents more water from and osmosis stops. • THUS, Osmotic Pressure of a solution is the pressure needed to be applied to the solution in order to STOP osmosis!!

26. Solutions with LOW Osmotic Pressure • These are cells are in a hypotonic solution • The SOLUTION has a low osmotic pressure. • SOLUTIONS with low osmotic pressure have a tendency to LOSE water • Water enters the cells!!

27. Solutions with HIGH Osmotic Pressure • These are cells in a hypertonic solutions. • The solution OUTSIDE the cell has a high osmotic pressure. • Solutions with a high osmotic pressure have a tendency to GAIN water • The cell itself has a LOW osmotic pressure • Not enough pressure to stop water from leaving (osmosis) • The cells shrink!!

28. Isotonic Solution • The solution and the cell both have equal osmotic pressures. • No net movement of water

29. Osmotic Pressure – Gummy Bear

30. Osmotic Pressure – U Tube

31. Facilitated Diffusion • Passive Transport • Carrier proteins “help” molecules across

32. Classwork/Homework Time!! • Diffusion and Osmosis Crossword • Answer “Science Organizer” questions about passive transport. Use terms we’ve used in class; hypertonic, hypotonic, isotonic, solute, solvent, diffusion, osmosis, concentration gradient etc. • Use a separate sheet of paper if you run out of room!!

33. Active TransportNEEDS ENERGY (ATP)

34. Active Transport • In some cases, particles such as ions (charged particles) move AGAINST the concentration gradients going from low to high!!! • Requires Transport (carrier) proteins and ATP

36. Active Transport • In some cases, ions such as K+ (potassium ion), must move across the membrane from LOW concentration to HIGH concentration • Called going against the concentration gradient http://www.wisc-online.com/objects/ViewObject.aspx?ID=AP11203

37. Active TransportBrainPopwww.brainpop.com

38. Cells Maintain Homeostasis – A Steady Internal Environment • Maintain pH levels • Temperature • Active and Passive Transport of particles • Water balance • Glucose balance

39. Buffers and Maintaining pH • pH balance Acids and bases. Remember them??? • Buffers are used A buffer is an aqueous solution (a chemical dissolved in water) that resists major changes in the pH of the solution. • Acidosis occurs when acid builds up • Alkalosis occurs when bases build up • Blood maintains a pH between 7.38 and 7.42 (slightly above neutral)

40. pH – Remember Acids and Bases?? • An acid is basically a solution with numerous hydrogen ions (H+) • A base is a solution with hydroxide (OH-) ions • Blood pH is regulated by the lungs and the kidneys • Blood contains large amounts of carbonic acid, a weak acid, and bicarbonate, a base. • If blood pH falls below 6.8 or rises above 7.8, one can become sick or die. • The bicarbonate neutralizes excess acids in the blood while the carbonic acid neutralizes excess bases.

41. High Blood Temperature • If blood temperature rises too high, blood vessels dilate, more blood flows close to the body surface and excess heat radiates from the body. • If it doesn’t cool enough, the brains induces sweating

42. Low Blood Temperature • If the blood temperature falls too low, arteries that supply blood to the skin constrict and warm blood is retained. • If it gets too cold, the brain activates shivering. Each muscle tremor in shivering releases heat energy and helps warm the body.

43. Glucose Levels • Monitored by cells in the pancreas • Hormones  chemicals that carry messages from organs of your body to your cells. Work in large part to keep the body’s natural balance in check. • Glucagon secreted by the pancreas – RAISE blood glucose levels • Insulin – Helps to LOWER blood glucose levels