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Cell Biology 225 Lecture 11 - Membrane Summary

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by: MelLem

Cell Biology 225 Lecture 11 - Membrane Summary BIOL 225

Marketplace > Simmons College > Biology > BIOL 225 > Cell Biology 225 Lecture 11 Membrane Summary
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Membrane summary and transportation of molecules.
Cell Biology
Dr. Lopilato
Class Notes
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Samuel Croteau

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This 3 page Class Notes was uploaded by MelLem on Monday April 4, 2016. The Class Notes belongs to BIOL 225 at Simmons College taught by Dr. Lopilato in Fall 2016. Since its upload, it has received 20 views. For similar materials see Cell Biology in Biology at Simmons College.

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Date Created: 04/04/16
Cell  Biology   Lecture  11   Summary  of  Membrane  Functions     Summary  of  Membrane  functions:   • Compartmentalization   • Scaffold  for  biochemical  activities   • Providing  a  selectively  permeable  barrier   • Transporting  solutes   • Responding  to  external  stimuli   • Intercellular  interaction   • Energy  transduction     Differentiated  functions  of  the  plasma  membrane  of  an  epithelial  cell   • Apical  plasma  membrane   o Regulation  of  nutrient  and  water  intake   o Regulated  secretion   o Protection   • Lateral  plasma  membrane   o Cell  contact  and  adhesion   o Cell  communication   • Basal  membrane   o Cell  substratum  contact   o Generation  of  ion  gradients   • Plasma  membrane  is  only  5-­‐10  nm  wide,  extremely  thin.  Need  ~  5000   membranes  to  equal  the  thickness  of  a  page  of  paper.     Membranes   • Lipid  composition   o Prokaryotes  lack  cholesterol   o T  cells  recognize  bacterial  by  lack  of  cholesterol   • Membrane  proteins   o Integral   o Peripheral   o GPI  anchored     The  asymmetry  of  the  membrane  lipids  inner  and  outer  leaflets   • Glycolipids  are  in  the  outer  leaflet  where  they  act  as  receptors  for  ligands.   • PE  (inner)  promotes  membrane  curvature  for  membrane  budding  and   fusion.   • PS  (inner)  has  a  negative  charge  to  bind  positively  charged  lysine  and   arginine  residues  on  adjacent  proteins.   • PS  (outer)  on  aging  lymphocytes  marks  the  cells  for  desctruction  by   macrophages   • PI  (inner)  can  be  phosphorylated  which  converts  the  lipid  into   phosphoinostitide  for  signal  transduction  pathways.   (Figure  4.10  The  asymmetric  distribution  of  phospholipids  (and  cholesterol)  in   the  plasma  membrane  of  human  erythrocytes.  (SM,  sphingomyelin;  PC,   phosphatidylcholine;  PS,  phosphatidylserine;  PE,  phosphatidylethanolamine;  PI,   phosphatidylinositol;  Cl,  cholesterol.)     Types  of  membrane  proteins   • Integral  membrane  proteins   • Peripheral  membrane  proteins   • GPI  anchored  protein  (GPI  =  glycosylphosphatidyl-­‐inositol)     Studying  membrane  proteins   • Hydropathy  Index   • Solubilization  by  detergents   o SDS  –  denaturing   o Triton  X100  –  nonionic  and  generally  nondenaturing   • Gel  electrophoresis   • Location  –  trypsin  digests   • Hydropathy  index  –  theres  4  peaks  in  this  diagram,  show  tha  it  crosses  the   membrane  4  times.       Ways  solutes  go  across  membranes   • Passive  –  does  not  require  energy  input   o Nonmediated   o Transported  mediated   • Active  –  requires  the  addition  of  energy   o Uses  ATP   o Uses  ion  gradients     Types  of  Transport   • Diffusion  –  movement  of  a  solute  from  an  area  of  high  concentration  to  an   area  of  low  concentration.   • Facilitated  diffusion   o Carrier  proteins  undergo  conformational  changes  upon  transfer  of   solute   o Channel  proteins  –  no  conformational  change  of  protein  with  transfer   of  solute   • Active  transport  –  requires  the  addition  of  energy,  typically  against  the   concentration  gradient.     Diffusion   • Simple  Diffusion   • Osmosis  –  flow  of  H2O   o Hypotonic  –  water  flows  into  the  cell/  area  of  higher  solute   concentration     o Hypertonic  –  water  flows  out  of  the  cell  /  area  of  lower  solute   concentration     o Ex  –  RBC  –  hemolysis     o Plant  cells  –  plasmolysis  and  deplasmolysis   • Facilitated  Diffusion   o Solute  binds  specifically  to  membrane  protein  carrier   o Michaelis  menton  Kinetics     ▯ Specificity  –  D  glucose  not  L  glucose   ▯ Saturation  kinetics   ▯ Competitive  inhibition   o Glucose  facilitated  diffusion  GluTa-­‐GluT5   • Partition  Coefficients  –  solubility  in  lipids,  measure  of  hydrophobicity,  how   non  polar  a  substance  is.   o More  nonpolar  means  LARGER  partition  coefficient.     Cycstic  Fibrosis   • Defect  in  Cl-­‐  secretion   • Isolation  of  a  gene   • CFTR  protein   • Problem  in  membrane  localization   • Gene  Therapy   • Mutations  can  occur  throughout  the  CFTR  gene  causing  defects  in  multiple   amino  acids  of  the  protein.    


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