Mod. 4 Function of the cell membrane
- 1. MODULE 4 FUNCTION OF THE CELL MEMBRANE CELL AND MOLECULAR BIOLOGY LAB. MEB 3RD YR / BIO 4TH YR.
- 2. MEMBRANE STRUCTURE Eaton, Louise, and Kara Rogers. Examining Cells. Britannica Educational Publishing, 2018
- 3. Small molecules and larger hydrophobic move through easily. e.g. O2, CO2, fats & other lipids Ions, hydrophilic molecules larger than water, and large molecules such as proteins do not move through the membrane on their own. Semi-permeability
- 4. Channels through cell membrane • Membrane becomes semi-permeable with transport protein • specific transport proteins allow specific material across cell membrane inside cell outside cell sugar aa H2O salt NH3
- 5. Membrane Transport Proteins: Carrier Protein and Channel Protein Carrier proteins can change shape to move material from one side of the membrane to the other Channel proteins are embedded in the cell membrane & have a pore for materials to cross
- 6. 3 Types of CARRIER-mediated transport Coupled carriers Uniport (facilitated diffusion) carriers mediate transport of a single solute. GLUT1 glucose carrier (CM of RBCs) Symport (cotransport) carriers bind two dissimilar solutes (substrates) & transport them together across a membrane. glucose-Na+ symport Antiport (exchange diffusion) carriers exchange one solute for another across a membrane. Na+,K+-ATPase pump
- 7. Ion Channels: Transmembrane Proteins That Allow Rapid Passage of Specific Ions Leakage channels are channels that are always open, making the membrane per meable to ions. Ligand-gated channels are triggered by the binding of specific substances to the channel protein. Mechanosensitive channels respond to mechanical forces that act on the membrane. Voltage-gated channels open and close in response to changes in the membrane potential.
- 8. Membrane Transport Passive Transport does not require an extra expenditure of metabolic energy, and materials flow down the concentration gradient Examples are diffusion, osmosis, and facilitated diffusion Active Transport uses energy (in the form of ATP), and materials flow against the concentration gradient.
- 9. Three Forms of Transport Across the Membrane
- 11. Osmosis Diffusion of water across a membrane Moves from HIGH water potential (low solute) to LOW water potential (high solute) H20 moves from regions of low solute conc. (high free energy) to high solute conc. (low free energy) High H2O potential Low solute concentration Low H2O potential High solute concentration
- 12. Aquaporins Water Channels Protein pores used during OSMOSIS WATER MOLECULES
- 13. Transport mechanisms Important transport processes of the RBC
- 14. Other forms of membrane transport Gap junctions A primitive type of intercellular communication mean present in animal and plant cells. Allows transmembrane movement of small solutes like ions, sugars, amino acids, and nucleotides while preventing migration of organelles and large polymers like proteins and nucleic acids
- 15. ACTIVE TRANSPORT DEMONSTRATION IN FROG/TOAD SKIN BAG
- 16. Amphibian skin https://th.bing.com/th/id/OIP.5QlGKCpVdiTWaF8x3tD41QHaE-?pid=ImgDet&rs=1 • Has a high permeability to water and electrolytes • For osmoregulation and electrolyte and fluid homeostasis. • Aquaporin water channels • AQP-h2 and AQP-h3
- 18. FROG SKIN APICAL surface SEROSAL surface Stratum corneum Stratum granulosum Stratum spinosum Stratum germinativum Tight junction Gap junction Aquaporin
- 19. APICAL surface Na+ Na+ Na+ Na+ Na channels or Epithelial Na channels (ENaC) Na+K+ATPase pump ATP-gated K+ channel (KATP channel) Cl- entry (Paracellular path) + + + + + + + + + + + + K+ - - - - - - - - K+ (K ATP) Na+ Na+ Na+ Na+ Na+ SEROSAL surface Water molecules Aquaporin water channel Na+ Na+ Na+ Na+ K+ K+ All four layers of the epidermis communicate with each other via gap junctions, thereby forming a functional syncytium.
- 20. APICAL surface Na channels or Epithelial Na channels (ENaC) Cl- entry (Paracellular path) + + + + + + + + + + + + K+ - - - - - - - - K ATP) Na+ Na+ Na+ Na+ SEROSAL surface Na+ Na+ Na+ Na+ K+ K+ ATP-gated K+ channel (KATP channel) K ATP)
- 21. APICAL surface Na+K+ATPase pump Cl- entry (Paracellular path) + + + + + + + + + + + + 3 Na+ 2K+ K+ - - - - - - - - Na+ Na+ Na+ Na+ Na+ Na+ Na+ Na+ Na+ 3 Na+ 2K+ SEROSAL surface Na+ Na+ Na+ Na+ K+ K+ K+ K+ K ATP)
- 22. APICAL surface Na channels or Epithelial Na channels (ENaC) Na+K+ATPase pump ATP-gated K+ channel (KATP channel) Cl- entry (Paracellular path) + + + + + + + + + + + + 3 Na+ 2K+ K+ - - - - - - - - K+ (K ATP) Na+ Na+ Na+ Na+ Na+ Na+ Na+ Na+ Na+ 3 Na+ 2K+ SEROSAL surface Water molecules Aquaporin water channel Na+ Na+ Na+ Na+ K+ K+ K+
- 23. Active transport demonstration in frog/toad skin bag MATERIALS:
- 24. Procedure: 1. Double pith the frog/toad. Hold the head between your thumb and index finger to pith (a) its brain and (b) its spinal cord. When the spinal cord and brain are severed, the toad will eventually become paralyzed. 2. Prepare a frog / toad skin bag by cutting the skin around the leg. Pull out the skin and turn inside out.
- 25. 3. Tie the frog/ toad skin bag at both ends. This is an empty skin bag. 4. Weigh the empty frog / toad skin bag in an analytical balance. This will serve as your initial reading.
- 26. 5. Immerse the skin bag in a beaker of Ringer’s solution for 10 mins with occasional stirring. 6. After 10 mins, lift the bag and blot dry with tissue paper. Place it in a small beaker and weigh. 7. Quickly immerse in Ringer’s solution again and weigh at 10-min interval for 1 hr. 8. Tabulate the data.
- 27. Use another toad skin bag and fill in with Ringer’s solution. Ringer’s solution solution of salts in water shown to prolong greatly the survival time of excised tissue. NaCl, KCl, CaCl2 and NaHCO3 in water.
- 28. Weigh the bag in an analytical balance. This will serve as your initial reading. Immerse the skin bag in a beaker of Ringer’s solution for 10 mins with occasional stirring. After 10 mins, lift the bag and blot dry with tissue paper. Place it in a small beaker and weigh. Quickly immerse in Ringer’s solution again and weigh at 10-min interval for 1 hr. Tabulate the data.
- 29. Repeat the same procedure, but this time fill the toad skin bag with 1:1 mixture of Ringer’s solution and 0.02M NaCN. Immerse the bag in a beaker with Ringer’s solution. 25 mL Ringer 25 mL NaCN
- 30. 3 set-ups Experimental set-up: Inner Envi. (Toad skin bag) Outside Envi. (Beaker) A Empty Ringer Solution B Ringer Solution Ringer Solution C 1:1 Ringer sol'n : NaCN Ringer Solution
- 31. Tabulate Data: Time in (mins) A B C 0 10 20 30 40 50 60 Area Rate
- 32. Calculation of Active transport Get the AREA of the skin bags by opening each and cutting the lines of ligature. Calculate the rate of active transport using the formula: Where: R = Rate of active transport Wi = initial weight Wf = Final weight t = Time A = Area of the bag
- 33. Sample: Time (mins) A 0 20.8 10 20.81 20 20.81 30 20.82 40 20.82 50 20.82 60 20.83 Area (cm2 ) 34.50 Rate (cm/min) Wf-Wi t R = 1 A 20.83-20.8 cm3 60 min R = 1 34.5 cm2 0.00001449 cm/min R = 1.449 x 10-5 cm/min R =
- 34. Answer Worksheet 3 - Function of the Cell Membrane: ACTIVE TRANSPORT Start: Oct.11 Due: Oct.18
- 35. References: Campbell CR. , Voyles J, Cook DI, Dinudom A. 2012. Frog skin epithelium: electrolyte transport and chytridiomycosis. Int J Biochem Cell Biol. 44(3): 431–434. doi:10.1016/j.biocel.2011.12.002 Eaton L, Rogers K. 2018. Examining Cells. New York (NY): Britannica Educational Publishing. Hardin J, Bertoni G, KleinsmithL. 2016. Becker's world of the cell: technology update. Boston (MA): Pearson Jared SR, Rao JP . 2017. Transepithelial sodium transport across frog skin. Adv Physiol Educ 41: 444–447; doi:10.1152/advan.00115.2016.