The Cell Membrane AP Biology

1. The Cell MembraneAP Biology

2. Helpful links as you go through this chapter… • http://student.ccbcmd.edu/courses/bio141/lecguide/unit3/eustruct/cmeu.html

3. Cell membrane defines the perimeter of the cell • Cell membrane _____________ living cell from aqueous environment • thin barrier = 8nm thick • Controls traffic in & out of the cell • allows some substances to cross more easily than others

4. Movement across cell membrane • Cell membrane is the boundary between inside & outside… • separates cell from its environment NO! Can it be an impenetrable boundary? OUT waste __________ ________ _______ _______ __________ IN food _____________ ______, ______ _____________ ____________ _____________ OUT IN cell needs materials in & products or waste out

5. ________________ Permeability • Barrier allows SOME substances to cross more easily than others • Also called _____________________ • Key aspect of membrane structure and function • Remember: selectively permeable membranes are important in _________ organelles as well as the plasma membrane of the cell itself.

6. Membrane Structure • Primary components • _________________ • Foundation molecules • Primarily ___________________________ • ______________ • _______________ within the lipids of the membrane • Important in carrying out most membrane functions • Remember: It’s the _____________ that do all the _____________!

7. Phospholipids Phosphate “_________ to water” • _______________ head • ______________ • _____________ tails • _______________ • Arranged as a _______ Fatty acid “__________ by water” Aaaah, one of thosestructure–function examples

8. Why the bilayer? • Water is attracted to hydrophilic ______ and NOT to hydrophobic _______ • Water pushes tails away and they end up pointed toward each other and AWAY from water. • Results in Bilayer • Animation – • Click HERE

9. Bilayer as Selective Barrier • Because of the close placement and polarity of the phosphate heads, there are some molecules that cannot penetrate and some that can.

10. What CANNOT penetrate • Phospholipid Bilayer? • _______/________ things • Ions (___, ____, _____) • ____________ • ___________ • Polar ____________ • Ions get large ____________ • ____________ in aqueous • Solution which makes them • Too large to fit b/t • Phospholipids • Also, polar/charged molecues • Become attracted and • stuck to ________________ • ______ attracted to nonpolar center • of bilayer • What CAN penetrate • Phospholipid Bilayer? • Anything ____________ • ___________ • ______________ • ________________ • NONPOLAR molecules do • NOT get attracted and • Stuck to polar heads; thus • They pass through.

11. Arranged as a Phospholipid bilayer • Serves as a cellular barrier / border ____ ____ ____ ________ hydrophilic heads __________ hydrophobic tails impermeable to polar molecules _________ hydrophilic heads _____ _____

12. How, then, can these polar, but necessary molecules pass through the membrane? • ______________ • Embedded in the bilayer

13. Permeability to polar molecules? • Membrane becomes semi-permeable via ______________________ • _______________ channels allow ____________ material across cell membrane • Thus ___________ is also maintained. Not just anybody can get in. inside cell ____ ___ _____ ____ outside cell ____

14. ____________ – A Protein Channel ____ water Conc. • Used to be thought that water could penetrate the phospholipid bilayer unaided • Now we know that a protein channel called aquaporin is found in nearly all cell membranes in large amounts • This is the channel that allows the passage of water. • Remember, water is polar and would NOT be attracted past the polar heads ____ water Conc.

15. Cell membrane is more than lipids… • ________________ proteins embedded in phospholipid bilayer • create semi-permeabe channels protein channelsin lipid bilyer membrane

16. Why areproteins the perfect molecule to build structures in the cell membrane?

17. Classes of amino acids What do these amino acids have in common? ______________ & ______________

18. Classes of amino acids What do these amino acids have in common? I like thepolar onesthe best! ________ & ___________

19. Protein’s regions _________ molecule Polar areas of protein • _________ membrane • _______ amino acids • Hydro__________ • anchors protein into membrane • On ______ surfaces of membrane in fluid • _______ amino acids • Hydro__________ • extend into extracellular fluid & into cytosol Nonpolar areas of protein

20. Porin monomer H+ Retinal chromophore b-pleated sheets NH2 Bacterial outer membrane Nonpolar (hydrophobic) a-helices in the cell membrane COOH Cytoplasm H+ Examples __________ = water channel H2O H+ H+ proton pump channel in photosynthetic bacteria function through _______________ change = protein changes _________ H2O

21. Membrane Proteins do LOTS of different jobs!! “_______” Outside Plasma membrane Inside Transporter __________activity Cell surface__________ “_______” Cell _______ Cell surface _________ marker Attachment to the_____________

22. Membrane Proteins • Proteins determine membrane’s specific __________________ • cell membrane & organelle membranes each have unique collections of proteins • Classes of membrane proteins: • __________________ proteins • loosely bound to surface of membrane • ex: cell surface identity marker (antigens) • ____________________ • penetrate lipid bilayer, usually across whole membrane • _____________________ protein • ex: transport proteins • channels, permeases (pumps)

23. Cell membrane must be more than lipids… • In 1972, S.J. Singer & G. Nicolson proposed that membrane proteins are inserted into the phospholipid bilayer • _______________Model • Made up of lots of little pieces – like a mosaic • Pieces can slide past each other – like a soap bubble – like a fluid • Click here for an animation

24. Don’t forget _____________ • Embedded in membrane b/t phospholipids • Keeps membrane _____ yet ______ • Important for cell membrane structure • Even though we often think of cholesterol as being “bad”…

25. _______________ ______________ _____________ __________ Peripheral protein Filaments of____________ Membrane is a collage of proteins & other molecules embedded in the fluid matrix of the lipid bilayer _________________ _____________ _____________ _____________ 1972, S.J. Singer & G. Nicolson proposed Fluid Mosaic Model

26. Membrane ________________ • Play a key role in cell-cell ____________ • ability of a cell to distinguish one cell from another • ______________ • important in organ & tissue development • basis for rejection of foreign cells by __________system

27. Any Questions??

28. Movement across the Cell Membrane

29. Movement of Molecules Across a Membrane • 2nd Law of Thermodynamics governs biological systems • universe tends towards disorder (__________) • Remember that molecules are always ___________…they don’t have any “brains” to move in a particular direction…they are just moving – _____________. (entropy – no order) • What can affect this random movement? • The size/attractiveness of the openings available for molecules to pass through • “hands” that physically GRAB molecules and FORCE them to go places they might not go just due to random motion.

30. Types of Transport Across a Membrane • Two major types • _____________ • Does ____ require energy from the cell • Substances move ____ their concentration gradient • ______ to ______ • ______________ • DOES require _________ from the cell • Substances move _____________ their concentration gradient • _______ to ________

31. Note: At equilibrium Molecules are ________ MOVING… Movement just can’t be perceived b/c there is no conc. difference on either side. Diffusion • The movement of any substance… • Due to its _____________ molecular motion… • From an area of _____ concentration to an area of ______ concentration. • Diffusion • movement from HIGHLOW concentration

32. Simple Diffusion • Move from _______ to ______ concentration • “______________ transport” • _______ energy needed • ______ molecule type can do this diffusion

33. movement of water osmosis Osmosis • Specialized Diffusion • Movement of ___________ from an area of ________ water concentration to an area of ___________ water concentration • Across a _________

34. HIGH LOW _____________ ______________ • Diffusion through _________ _____________ • channels allow ____________ molecules across cell membrane • Very selective “doors” • _______ energy needed facilitated = with help diffusion = WITH conc. gradient

35. ______ ______ _________ Transport • Cells may need to move molecules ____________concentration gradient • From ________ concentration to ___________ • Protein ______ attracts the molecules and undergoes _____ change which moves the molecule from one side of membrane to other • _______________ change = ____________ change • “costs” energy = _____ conformationalchange ATP

36. Active Transport - Types of Pumps • _________________ Pump • Na+/K+ Pump • Classic example • Important in _________ cell and nerve impulse transmission (among others) • Generates ___________ difference across the membrane of the neuron • For animations click • Here or Here

37. Active Transport – Types of Pumps • ______________ Pumps • Pump Hydrogen ions (___+) across a membrane • Can also generate membrane potential (like Na/K pump) • Difference in voltage from one side of the membrane to the other • Proton pumps are VERY important in mitochondrion – cell respiration • _________________ • Also called_________ transport

38. __________________ • Membrane proteins couple the transport of one solute to another • A combination of both ________ transport and ______________ (passive). • Pump (active) • Transport channel (passive)

39. Cotransport – Example – in plants • Proton Pumps pump __+ _______ the concentration gradient and OUT of the cell. • Creates a very _____ concentration of H+ ______________ the cell. • ___________ transport • That means, if given an opportunity, H+ would flow ________ its concentration gradient back __________ the cell.

40. Cotransport – Example – in plants • In plants, sucrose is in ________ concentration _____ the cells, but plants need to get even even ________ ________ into cells for storage. • Thus, sucrose must move into a plant cell _________ its concentration gradient.

41. Cotransport – Example – in plants • “_______hill” (WITH concentration) movement of H+ is coupled with the “_____hill” (AGAINST concentration) movement of sucrose into the cell. • Sucrose MUST ________ to an H+ ion. “Rides” with the H+ as H+ flows INTO the cell through the cotransport channel WITH it’s concentration gradient. • Remember, the H+ concentration gradient is maintained by the proton ________ • The only way that sucrose can enter is if it is bound to H+. Then the very specific cotransport channel will allow both to “diffuse” through. • PUMP to maintain H+ conc. = __________ • Cotransport channel = facilitated diffusion = _____________

42. Getting through cell membrane • _____________ Transport • _______________diffusion • diffusion of nonpolar, hydrophobic molecules • lipids • HIGH  LOW concentration gradient • _______________ diffusion • diffusion of polar, hydrophilic molecules • through a protein ____________ (“door”) • HIGH  LOW concentration gradient • _________________ transport • pump ______________ concentration gradient • LOW  HIGH • uses a protein pump • requires _________ ATP

43. Transport summary NONPOLAR cmpds. Lipids; oxygen; Carbon dioxide simplediffusion ___ ___ facilitateddiffusion ___ ___ POLAR cmpds. Water; Ions – Na+, Cl-; Glucose, etc. _____ activetransport ___ ___ REQUIRED

44. How about large molecules? • Moving _________ molecules into & out of cell • through ___________ & ________________ • _________________ – taking _______ • _______________ = “cellular eating” - __________ • _______________ = “cellular drinking” - __________ • __________________ • Expelling / ______________ substances exocytosis

45. Endocytosis Solids fuse with _________ for digestion _____________ Liquids Both are ____-specificprocesses ______________ ___________________ is taken Into the cell this way. ___________ ___________________ endocytosis _______ – substance that fits receptor

46. The Special Case of WaterMovement of water across the cell membrane

47. Osmosis is just _______ of ______ • Water is very important to life, so we talk about water separately • Diffusion of water from ______ concentration of ________ to ______ concentration of _________ • across a ______-permeable membrane

48. hypotonic hypertonic Concentration of water • Direction of osmosis is determined by comparing total solute concentrations • _______________ - more _________, less _________ • _______________ - less _________, more __________ • _______________ - ________ solute, _________ water • Water moves from a ____________ (HIGH Concentration of water) solution to a ____________ (LOW Concentration of water) solution LESS water MORE water LESS solute MORE solute Yellow dot = SOLUTE water Blue = WATER net movement of water

49. Managing water balance • Cell survival depends on balancing water uptake & loss freshwater balanced saltwater

50. 1 Managing water balance • ____________ • a cell in _________ water • ______ concentration of ______ around cell • problem: cell ________ water, swells & can ________(lysis) • example: Paramecium • ex: water continually enters Paramecium cell • solution: ______________________ • ___________ water out of cell • ________ • plant cells • ____________ = full • ____________ protects cell from bursting KABOOM! ATP No problem,here – I love it! freshwater