8-1 Cell Membrane

1. 8-1 Cell Membrane Provides structural support Cell Membrane – controls what enters and leaves the cell Selectively Permeable (Semi-Permeable) allows some materials into the cell while keeping other materials out “Gate-keeper” Useful in maintaining homeostasis (a constant internal environment.)

2. Ways a cell maintains homeostasis Transports substances (controls in/out) Recognizes foreign material Communicates with other cells

3. Structure of the Cell Membrane • Double layer sheet called a lipid bilayer. • Has proteins embedded throughout it for channels and pumps to help move materials across the membrane. Made of phospholipids that form a strong barrier around the cell.

4. Fluid Mosaic Model “Fluid” –phospholipids and proteins are able to move sideways “Mosaic” (a surface of small fragments) – many different protein molecules with various organic substances attached to them

5. Membrane Proteins • 1. Glycoproteins- Cell surface markers – carbohydrate and protein,identify each cell type • 2. receptor proteins- recognize and bind to substances outside the cell • 3. Enzymes –assists chemical reactions inside cell • 4. Transport Proteins – help substances move across the cell membrane

6. What passes through a membrane? Small, nonpolarsubstances can pass Ions and most polar molecules are repelled by the nonpolar interior Water is small enough to pass through even though it is polar Substances that cannot pass through by themselves that the cell needs are passed through the membrane by TransportProteins.

7. Stop and Think • 1.State the four roles (functions) of the cell membrane. • Structure support, recognizes foreign material, communicates with other cells, transports substances • 2. Why can’t ions pass through the lipid bilayer? • They are repelled by the nonpolar interior of the lipid bilayer

8. Diffusion Cells are made up mostly of water surrounded by a watery environment Cytoplasm and its external environment are made up of many different solute particles dissolved in water. The concentration of a solution is the mass of a solute in a given volume of solution. In a solution, molecules move constantly – colliding and spreading out. http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__how_diffusion_works.html

9. 8.2 Diffusion Cells are made up mostly of water surrounded by a watery environment Cytoplasm and its external environment are made up of many different solute particles dissolved in water. The concentration of a solution is the mass of a solute in a given volume of solution. In a solution, molecules move constantly – colliding and spreading out. http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__how_diffusion_works.html

10. Parts of a solution Review: Solute = Dissolved substance Solvent = Substance doing the dissolving (usually water) Solution = combination of solute + solvent

11. Diffusion Diffusion – the tendency of molecules to move from areas of high concentration (a lot of solute particles) to areas of low concentration (fewer solute particles.) Used to help maintain homeostasis.

13. Diffusion Eventually the molecules will reach equilibrium where the two concentrations are equal on both sides or in both areas. Diffusion of molecules across the cell membrane is a process that does not require energy. Passive transport Molecules move down a concentration gradient (from high to low concentration.) http://www.wisc-online.com/objects/index_tj.asp?objID=AP1903

14. Osmosis The diffusion of water through a selectively permeable membrane Water moves from areas of high to low concentration. Concentration = mass of solute in a given volume of soultion In a solution… High water = Low solutes Low water = High solutes Water will move across the membrane until the concentrations are equal on each side

15. Osmosis http://www.stjohn.ac.th/Department/school/bio_pix/osmosis.gif

16. Types of Solutions: Isotonic Solutes and water are equal inside and outside of the cell. No net movement of water - water moves in and out of the cell in equal amounts.

17. Types of Solutions: Hypotonic Low solute concentration (High water) outsideof the cell. More water outside than inside the cell. Causes water to moveinto the cell.

18. Hypotonic Solutions cont’d • Water entering the cell causes an increase in turgor (osmotic) pressure on the membrane. • Plants can withstand this increase because they have cell walls. • Animal cells do not have cell walls, and they run the risk of bursting – Lysis. • Some animal cells have special organelles – contractile vacuoles – that pump excess water from their cells.

19. Types of Solutions: Hypertonic High solute concentration (low water) outside of the cell. More water inside the cell than outside the cell. Causes water to move out of the cell.

20. Hypertonic Solutions cont’d Plasmolysis – the loss of water from a cell Results in the drop of osmotic pressure In plant cells, the central vacuole shrinks, loses support, and begins to wilt. http://www.youtube.com/watch?v=gWkcFU-hHUk&feature=PlayList&p=597DCBAA391B9074&playnext=1&playnext_from=PL&index=29 http://www.youtube.com/watch?v=H6N1IiJTmnc&feature=fvw Animal cells can eventually shrink and die.

22. Review Questions Label the following solutions as isotonic, hypertonic, or hypotonic. A cell with 97% water is placed into an environment with 100% water. Hypotonic A cell shrinks and becomes weak. Hypertonic A plant cell develops turgor pressure. Hypotonic A fresh water cell (97% water) lives in a pond that is 97% water. Isotonic A fresh water cell (97% water) is placed into the ocean (88% water.) Hypertonic An animal cell bursts. Hypotonic

23. Means of Transport • 1.) Passive Transport -Type of diffusion, and does not require any input of energy • 2.) Active Transport -requires energy

24. Diffusion WITHOUT energy (ATP) Moves molecules DOWN/WITH the concentration gradient (high->low) Ex: Simple diffusion, Facilitated diffusion & Osmosis Requires energy (ATP) Moves molecules AGAINST the concentration gradient(low->high) Ex: Endocytosis & Exocytosis Passive vs. Active Transport

25. Facilitated Diffusion • A form of Passive transport • Uses transport proteins in cell membrane to move molecules • Either through an open channel or carry specific molecules across • Molecules move with the concentration gradient, therefore do not need ATP • Makes transport more specific & speeds up rate

26. Facilitated Diffusion cont. • Carrier Proteins- transprot substances that fit in their binding site • Binding causes protein to change shape • Change moves substance aross membrane • Channel proteins- tunnels through lipid bilayer • Allows diffusion o f specific substances with right size and shape

27. Active transport of substances INTO cell Useful way for unicellular organisms to acquire food Cell literally surrounds particle with its cell membrane & engulfs the particle into itself Active transport of substances OUT of cell Mostly for waste removal & export of enzymes or hormones Vesicles carrying substances fuse with inside of cell membrane & open up to external environment, releasing material Endocytosis vs. Exocytosis

28. Sodium-Potassium Pump • Type of active transport • Requires energy (ATP) to “pump” substances across membrane • Uses carrier proteins • Prevents sodium (Na+) from building up in cell • Cells would swell or burst if too much water enters through osmosis

29. Sodium-Potassium pump steps • 3 Na+ ions bind to pump • Phosphate from ATP also binds to give energy • Pump changes shape and releases 3 Na+ ions to outside of cell • 2 K+ ions bind to pump and cross membrane • Phosphate group released, pump returns to original shape • K+ is released into the cell

31. Cellular Energy • Cells use a form of chemical energy called Adenosine Triphosphate (ATP) • Cells store & use ATP to fuel necessary metabolic reactions • Such as maintaining internal chemical conditions (homeostasis) • 10 MILLION molecules of ATP are consumed & regenerated per second per cell!

32. Adenosine Triphosphate (ATP) Nucleotide 3 Energy Rich Phosphate Bonds Sugar

33. ATP – ADP Cycle:

34. 8.3 Membrane Receptor Proteins • Cells must be able to communicate and distinguish between important and unimportant information • Cell communicate by sending chemical signals • Signaling cell- produces a signal (molecule) • Target cell- cell that receives the signal (molecule) because it has the correct surface protein • Hormones and nerve cells send signals over long distances

35. Receiving signals • Cells are bombarded by hundreds of signals but only responds to the few signals that relate to its function • Receptor proteins- in membrane, determine which signals cell responds • Only responds to signals that match the specific shape of its binding site • When a signal does bind the receptor protein changes shape which passes the information into the cell

36. Membrane Receptor Proteins Responses to Signals • Functions: • 1. Changes in Permeability - binding of a signal molecule to the receptor protein causes an ion channel to open and allows specific ions to cross membrane. • 2.Second Messengers - receptor protein may cause the formation of a second messenger inside the cell. The second messenger acts as a signal molecule and amplifies the signal of the first messenger—that is, the original signal molecule. • 3.Enzyme action - receptor protein may act as an enzyme. When binding occurs, receptor protein may speed up chemical reactions inside cell.

37. Changes in Permeability

38. Second Messengers