Ch. 8 Exchanging Materials with the Environment

1. Ch. 8 Exchanging Materials with the Environment Chapter Objectives: Discuss the structure & function of membranes in living organisms Describe how materials are exchanged across membranes

2. “Gate-keeper” 8-1 Cell Membrane What’s the purpose of the cell membrane? Adds protection and support for a cell Cell Membrane – controls what enters and leaves the cell Selectively Permeable (Semi-Permeable) allows some materials into the cell while keeping other materials out

3. Useful in maintainingHomeostasis: the tendency of an organism to maintain a relatively stable internal environment by regulating its metabolism & adjusting to its environment. Other ways cell maintains homeostatsis • Recognizes foreign material • Communicates with other cells

4. What exactly needs to ENTER cells? • WATER – most chemicals require water as the material to undergo a reaction within • OXYGEN (some cells do NOT take in this) • IONS = Na+, Mg+2, Ca+2, H+, Cl-, K+ • CO2 (some cells do NOT take this in) • NUTRIENTS = sugars, amino acids, lipids • HORMONES

5. What exactly needs to LEAVE cells? • WASTES = Ammonium ion (NH+4), CO2, O2, excess salts, excess H2O etc . . . • Cell Products = Hormones & other chemical products (ex: Proteins)

6. Membrane as a Barrier • Membranes are composed of a Phospholipid bilayer -2 layers of phospholipids & proteins • SELECTIVELY PERMEABLE, so NOT all substances are allowed to pass • Molecules that are SOLUBLE in the lipid bilayer pass easily, (small, nonpolar substances) but other molecules, like charged Ions, and most polar molecules are repelled by the nonpolar phospholipid tails

7. “Water Fearing” Always NONPOLAR Repelled by water – Insoluble in water Cannot make hydrogen bonds with water These molecules tend to cluster together in water, forming droplets/bubbles Ex: Lipids, O2 gas . . . Hydrophilic = “Water Loving” Typically POLAR Mostly soluble in water Capable of hydrogen bonds with water Ex: Salts, Sugars . . . Hydrophobic vs. Hydrophilic

8. A molecule’s permeability is determined by: 1. Size 2. Electric Charge 3. Polarity Transport Protein are embedded on the membrane surface, help ions, amino acids & sugars to enter the cell that can’t pass through the lipid bilayer

9. Selectively permeable membrane

10. 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

11. 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

12. Cell Membrane Components

13. Passage of Charged Molecules (Ions) • Transport Protein are embedded on the membrane surface, help ions across • The Protein “gateways” also help amino acids & sugars to enter the cell • Large Proteins use different mechanism (explained later) • Glycoproteins = specialized protein receptor on the cell surface with an attached sugar • Glycolipids = specialized lipid-sugar molecules in the cell membrane – receives chemical messages from outside the cell

14. 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

15. Ch. 8.2 Diffusion & Osmosis • Diffusion = natural movement of molecules from an area of high concentration to an area of low concentration • This difference in the concentration over a distance is called aConcentration Gradient • The end goal of diffusion is to achieve Equilibrium = when all molecules are equally spread apart (balance) molecules are equally spread apart • molecules still move, but in equal #’s across the membrane

17. 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 Water will move across the membrane until the concentrations are equal on each side

18. Osmosis – The Diffusion of H2O • Parts of a solution: • Solute = Dissolved substance • Solvent = Substance doing the dissolving (usually water) • Solution = combination of solute + solvent • In a solution… • High water = Low solutes • Low water = High solutes

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

20. 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, at the same rate.

21. 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.

22. 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 – cytolysis. • Some animal cells have special organelles – contractile vacuoles – that pump access water from their cells. Hypotonic Solutions cont’d

23. 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.

24. 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.

25. Hypo-, Iso-, & Hypertonic Hypotonic = “below strength” Isotonic = “same strength” Hypertonic = “above strength” Hypotonic Isotonic Hypertonic Plasmolysis!

26. 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

27. 8.2 Means of Transport 1.) Passive Transport Is diffusion without any input of energy 2.) Active Transport Moves substances against their concentration gradients and thus requires energy

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

29. 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

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

31. 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

32. 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

33. 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

34. Sodium-Potassium Pump http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__how_the_sodium_potassium_pump_works.html • Na/K Pump = an enzyme protein that moves 3 sodium ions out of a cell while moving 2 potassium ions in. • Prime example of how electrolytes are critical to health • Essential to muscle contraction & nervous system conduction

35. THE END

36. What types of molecules can cross the lipid bilayer? • Can Cross • Small hydrophobic molecules like gases • Small uncharged polar molecules like water (small hydrophilic molecules) • Can’t Cross • Larger uncharged polar molecules like amino acids, glucose and nucleotides • Ions or charged molecules like H+

37. 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!

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

39. ATP – ADP Cycle:

40. Materials that Pass & Do Not Pass

41. Passage of Charged Molecules (Ions) • Transport Protein are embedded on the membrane surface, help ions across • The Protein “gateways” also help amino acids & sugars to enter the cell • Large Proteins use different mechanism (explained later) • Glycoproteins = specialized protein receptor on the cell surface with an attached sugar • Glycolipids = specialized lipid-sugar molecules in the cell membrane – receives chemical messages from outside the cell

42. Diffusion, cont . . . • Due to this natural movement, substances diffuse across cell membranes without the need for metabolic energy (ATP) to be spent by the cell • At equilibrium, molecules still move, but now they move in equal #’s across the membrane • Rate of diffusion depends on: size of concentration gradient, surface area • of membrane & • temperature.

43. Ch. 2.8 Energy Transfer & ATP • Decomposition rnxs release free energy thru a process called OXIDATION • Oxidation is the removal of electrons from a molecule & then certain bonds are broken & rearranged • Energy is then released as free energy & heat • The free energy ultimately ends up in a molecule called ATP  Adenosine Triphosphate • ATP is the “energy currency” your cells “spend” for all metabolic reactions

44. ATP  ADP • The way free energy is released from ATP is when the chemical bond between the 2nd & 3rd phosphate groups is broken: • ATP now becomes ADP (Adenosine Diphosphate)