Today is Tuesday, October 21 st , 2014

1. In This Lesson: Cell Membranes and Transport (Lesson 4 of 5) • Stuff You Need: • Guided Reading On Your Desk Today is Tuesday,October 21st, 2014 Pre-Class: Have a seat. When your partner arrives, say hi, ask how they’re doing, and then tell them all about the cell membrane. Anything you recall. This works even better if you don’ttell them why you’re doing it.

2. Today’s Agenda • The Cell Membrane • Structure • Function • You know…osmosis? Diffusion? • It’s gonna get “insane in the membrane…” • Where is this in my book? • Chapter 7

3. By the end of this lesson… • You should be able to describe in detail the structure of the cell membrane and link it to its functions. • You should be able to predict the outcome of an osmotic process. • You should be able to use the water potential equation.

4. So now then… • Okay, you giant piles of cells you… • Where do we go from here? • Well, let’s think about our last two units: • Evolution turned into speciation when we considered the “interactive” perspective. • Ecology turned into community ecology when we considered the “interactive” perspective. • Cells are going to be turning into cell membranes and transport – it’s what allows multicellular organisms to be so darn interesting. • And yes, it’s how cells interact with their environments.

5. Cell Membrane Structure Overview • The cell membrane is around 8 nm thick. • For perspective, the thickness of human hair is around 99,000 nm. • It’s composed of: • Lipids • Mainly phospholipids and some cholesterol. • Carbohydrates • Signal molecules attached to… • Proteins • Embedded in the membrane. • How was it discovered? • TED: Ethan Perlstein– Insights into Cell Membranes Via Dish Detergent

6. The Phospholipid Bilayer • The cell membrane is primarily composed of phospholipids. • The cell is sitting in a water-based environment, therefore: • Each phospholipid has a polar (hydrophilic) head… • It’s a phosphate group. • …and a non-polar (hydrophobic) pair of tails. • They’re fatty acids. • Because it has hydrophilic and hydrophobic parts, it’s amphipathic. • Note: Amphoteric = acid/base. Different. Polar Non- polar

7. The Phospholipid Bilayer • These phospholipids are then arranged in a bilayer. • Key: Don’t confuse a bilayer for a “double membrane.” • A bilayer is one membrane with two layers. Polar Non- polar

8. Aside: Soap • Ever wonder how soap works? • Soap, like the cell membrane, is amphipathic. • Unlike the membrane, soap molecules form a micelle (basically a phospholipid monolayer). • Because it’s got a lot of non-polar regions, soap can dissolve cell membranes of other cells. • Like pathogens’. http://0.tqn.com/y/chemistry/1/S/L/5/1/micelle.jpg

9. The Phospholipid Bilayer • The bilayer acts as a semi-permeable barrier. • Polar molecules can’t get in or out. Salt H2O Sugar Polar Heads Polar Heads Non-Polar Tails Lipids Waste

10. Quick Note: Permeability • Some things are “impermeable:” • Raincoats, balloons, brick walls. • Some things are “permeable:” • Air, water. • Some things are “semi-permeable:” • Nets, gates, cell membranes. • Semi-permeability is sometimes called selective permeability.

11. Back to the Phospholipid Bilayer • Importantly, the composition of the bilayer is not constant. • A certain percentage is composed of phospholipids with unsaturated fatty acid tails; the rest with saturated tails. • Unsaturated hydrocarbons lead to increased fluidity. • The lower the temperature, the more unsaturated the membrane needs to be to prevent freezing. • Cholesterol is also in the membrane and acts to increase viscosity except at low temperatures.

12. The Phospholipid Bilayer • And why the fluidity? To allow for movement of embedded membrane proteins. • This view of the membrane is the Fluid Mosaic Model:

13. Another View

14. Membrane Proteins • Membrane proteins provide the bulk of the cell-specific (or organelle-specific) functions. • There are two main types: • Peripheral Proteins • They’re stuck to the outside of the cell. • Example: Antigens (cell markers) • Integral Proteins • They’re stuck within and usually span the membrane. • Example: TransmembraneProteins or Transport Proteins

15. So why proteins? Polar areas of protein • What do you see in the picture to the right? • What are the blue things with two tails? • Phospholipids • What’s the yellow thing wedged in there? • Cholesterol • What are the red squiggly lines? • -Helices Non-polar areas of protein

16. So why proteins? Polar areas of protein • Remember how amino acids can be polar or non-polar? • That makes proteins (also amphipathic) a great candidate for transmembrane proteins. • The hydrophobic regions act as anchors to the membrane. Non-polar areas of protein

17. Fluid Mosaic Model • Those anchors are needed because the phospholipids move frequently. • It’s the Fluid Mosaic Model, remember? • Studies of hybrid cell membranes made of a combination of human and mouse cells confirmed this:

18. What do they do? Example: Channel Protein Signal Transduction Protein Cell Surface Receptor Enzymes Transport Example: Antigen Attachment to cytoskeleton Cell Cohesion Cell-Cell Recognition

19. Cell Surface Proteins • Cell surface proteins play a key role in recognition between cells. • This aids in development of organs and tissues. • Antigens are proteins on the cell surface that cause a response from the immune system. • They’re how the body “rejects” cells that are foreign.

20. Cell Surface Proteins • Take a look at the image to the right. See those two orangey things? • They’re carbohydrate chains. • One’s coming from a lipid, making it a glycolipid. • The other is coming from a protein, making it a glycoprotein. • These carbohydrate chains make the cell identifiable to other cells.

21. Cell Membrane Function Overview • Cells must take in and release substances: • Food in, products and waste out. • They can do it with one of two general modes: • Passive Transport (does not require energy) • Diffusion • Facilitated Diffusion • Osmosis • Active Transport (requires energy) • Endocytosis • Exocytosis • Molecular Transport • To fully understand these, we need to understand concentration gradient.

22. Concentration Gradient • Concentration refers to the amount of a substance in a certain area. • Particles diffusedown their concentration gradient. • What does that mean? • In passive transport, particles always go from an area of high concentration to an area of low concentration. • Fun Fact: Passive transport occurs in part to satisfy the second law of thermodynamics, AKA entropy.

23. Concentration Gradient High Warning: Steep Grade Low

24. Concentration Gradient High Concentration In Passive Transport, particles move from areas of high concentration to areas of low concentration. Substance Concentration Gradient Low Concentration

25. Diffusion Demo Diffusion in Air

26. What can diffuse? • Can diffuse: • Lipids • CO2 • O2 • Can’t diffuse: • H2O and other polar molecules • Ions and other charged particles • Large molecules (like starches and proteins)

27. HIGH LOW Facilitated Diffusion • Simply put, it’s diffusion with help. • Those particles that can’t diffuse can get through channel proteins. • No energy needed. • This leads to semi-permeability for molecules that can’t otherwise diffuse. • There are specific channels for specific molecules, too. inside cell H2O aa sugar salt outside cell NH3

28. Summary of Passive Transport

29. Osmosis • Osmosis is basically the same thing as diffusion, only with water molecules and some form of a barrier. • Osmosis is another form of passive transport. • Just like in diffusion, in osmosis, water moves from areas of high water concentration to low water concentration. • Or, water moves from areas of low solute concentration to areas of high soluteconcentration.

30. Osmosis • Which drink has more liquid in it? ICE ICE ICE ICE Drink A Drink B

31. Osmosis in a U-Tube Side A Side B Which side has more water on it? http://www.biologycorner.com/resources/osmosis.jpg

32. Tonicity • Hypertonic solution • Relativelymore solute than surroundings. • Relativelylessfree water than surroundings. • Free water is water not busy hydrating a dissolved solute. • Hypotonic solution • Relatively less solute than surroundings. • Relativelymorefree water than surroundings. • Isotonic solution • The same amount of solute as the surroundings. • No net water change.

33. Isotonic Solutions • Water does not experience a net movement in isotonic solutions. • There is no concentration gradient. Substance No concentration gradient No net movement of water

34. And now, I present to you… • …the key to EVERYTHING!!!!!!* • *osmosis-related. • Draw this in your notebook. Make it BIG. Hypotonic Hypertonic H2O Flow

35. Osmosis in Plant Cells • As we have learned, plant cells are good at holding water. • If they’re placed in a hypertonic solution, however, they lose water and wilt. • Their cells undergo plasmolysis. • Place them in a hypotonic solution and they will swell slightly, like a garden hose with water. • Their cells become turgid. • In animal cells, without a cell wall, the cell may burst in a process called cytolysis.

36. Osmosis – The Big Idea http://upload.wikimedia.org/wikipedia/commons/thumb/a/ab/Turgor_pressure_on_plant_cells_diagram.svg/2000px-Turgor_pressure_on_plant_cells_diagram.svg.png

37. Osmosis – The Big Idea Blood hypertonic, surroundings hypotonic Isotonic solutions Blood hypotonic, surroundings hypertonic http://upload.wikimedia.org/wikipedia/commons/thumb/e/e3/Erythrozyten_und_Osmotischer_Druck.svg/450px-Erythrozyten_und_Osmotischer_Druck.svg.png

38. Managing Water Balance • Animals: • Kidneys. • Methods to either remove salt or pump in water. • Unicellular Organisms: • Contractile Vacuoles • Pump water out at a cost of ATP (energy). • Maintaining water balance is just another aspect of homeostasis.

39. Osmosis in Kidneys http://classes.midlandstech.edu/carterp/Courses/bio211/chap25/Slide18.GIF

40. Osmosis in Kidneys • The proximal Loop of Henle is the part of the nephron (kidney component) responsible for re-absorbing water from urine. • With this in mind, would you guess that desert animals have larger or smaller Loops of Henle than other animals?

41. Osmosis in Kidneys http://www.answersingenesis.org/assets/images/articles/cm/v26/i3/rats.jpg

42. Osmosis in Merriam’s Kangaroo Rats http://www.bio.davidson.edu/Courses/anphys/1999/Chisholm/nephron1copy.wc2.jpg

43. Osmosis Supplements • Egg Osmosis • Gummi Bear Osmosis • Woman Dies After Water Drinking Contest • CrashCourse – In Da Club – Membranes and Transport

44. Stop everything, you liar! • “You said at the beginning of this PowerPoint that polar substances like H2O can’t diffuse into the cell through the membrane, yet now you’re talking about osmosis being like water diffusion. How could that be?” said the student. • “For a while scientists noticed the same thing. Water clearly efficiently enters a cell, but how?” replied the teacher, quietly appreciative of his student’s skepticism.

45. Aquaporins • Aquaporinsare channel proteins that move water rapidly into the cell through facilitated diffusion. • They were discovered by these two in 1991. • They shared the 2003 Nobel Prize in Chemistry. Roderick MacKinnon Rockefeller Peter Agre Johns Hopkins

46. Equilibrium • For things like diffusion and osmosis, eventually the solutes reach a point where there is no net change in molecule movement. • This is equilibrium. • We call it “dynamic equilibrium” because the molecules are still moving, but there is no net change in concentration or movement.

47. Equilibrium • When dynamic equilibrium is reached, diffusion and osmosis stop. • Molecular motion continues, though. Net Water Flow Inward No Net Water Flow 1.0% Sugar 0.75% Sugar WATER WATER 0.50% Sugar 0.75% Sugar WATER WATER

48. Osmosis Practice Problems • We’re going to talk about water potential soon, but for now, let’s get the concept of osmotic movement under our belts. • Following this slide are four osmosis practice problems, all multiple choice. • Get them all correct on the whiteboards and, uh… • …um… • 

49. Osmosis Practice Problem SAMPLE • Suppose a human blood cell (saline concentration 0.9%) is sitting in a beaker of 2% NaCl. Will it shrink, expand, or remain unchanged? • Make a sketch! The blood cell will shrink. Hyper Hypo 0.9% 2%

50. Osmosis Practice Problem #1 • If you soak your hands in dishwater, you may notice that your skin absorbs water and swells into wrinkles. This is because your skin cells are _______________ to the _______________ dishwater. • hypotonic…hypertonic • hypertonic…hypotonic • hypotonic…hypotonic • isotonic…hypotonic • hypertonic…isotonic