membranes+membrane transport

• Who is the professor associated with the lecture on membranes and membrane transport?

  Professor Christer Hogstrand
• What are the learning outcomes of the lecture on membranes and membrane transport?


  • Outline functional properties and biological roles of cellular membranes
  • Explain differential concentrations of ions and charges across the plasma membrane
  • Understand concepts like $K_{ow}$, transport kinetics, uniport, symport, antiport
  • Exemplify ways solutes can cross biomembranes
  • Describe principles of solute transporters
  • Explain advantages of multiple transporters for the same substrate
  • Explain cholera toxin effects and electrolyte replacement therapy
• What is the Fluid Mosaic Model of membrane structure?


  It describes membranes as 'proteins floating in a sea of lipids'
• What is the role of biological membranes?


  They act as selective permeability barriers
• Which types of molecules can freely traverse the lipid bilayer?


  Small uncharged or hydrophobic molecules
• What do charged polar molecules require to cross the membrane?


  Specialist proteins like pumps, transporters, or pores
• What are examples of hydrophobic molecules that can permeate the lipid bilayer?


  • O₂
  • N₂
  • Benzene
  • Short chain fatty acids
• What are examples of small uncharged polar molecules that can permeate the lipid bilayer?


  • H₂O
  • CO₂
  • Urea
  • Glycerol
• What are examples of ions that cannot freely cross the lipid bilayer?


  • H⁺
  • Na⁺
  • Mg²⁺
  • Ca²⁺
  • Cl^-
• What is the permeability of the lipid bilayer higher for?


  Uncharged, non-polar, and small molecules
• What are the typical intracellular and extracellular concentrations of Na⁺ and K⁺ ions?

  • Na⁺: [IN] = 10 mM, [OUT] = 140 mM
  • K⁺: [IN] = 140 mM, [OUT] = 4 mM
• What is the role of glucose transporters (GLUT)?


  They facilitate the transport of glucose across cell membranes
• What are the types of transport mechanisms mentioned?


  • Simple diffusion
  • Facilitated diffusion
  • Primary active transport
  • Secondary active transport
• What is simple diffusion?


  It is the movement of solute along its concentration gradient
• What does the octanol-water partitioning coefficient (K_ow) indicate?


  It indicates the lipid solubility of a molecule
• How does a higher K_ow value affect a molecule's permeability?


  A higher K_ow value means the molecule is more lipid soluble
• What is the significance of the Na⁺/K⁺-ATPase?


  It maintains the electrochemical gradient across the plasma membrane
• What are the steps in the functioning of the Na⁺/K⁺-ATPase?


  1. Na⁺ binds to the intracellular site
  2. Autophosphorylation occurs
  3. Conformational change releases Na⁺ outside
  4. K⁺ binds, triggering dephosphorylation
  5. K⁺ is discharged into the cell
• What is the role of insulin in GLUT4 regulation?


  Insulin signals for GLUT4 translocation to the membrane
• What is the function of secondary active transport?


  It utilizes an electrochemical gradient to move solutes
• What are the roles of SGLT1 and SGLT2 transporters?


  • SGLT1: Absorption of dietary glucose in intestinal epithelial cells
  • SGLT2: Reabsorption of glucose in proximal tubules of the kidney
• How does cholera toxin affect electrolyte and fluid loss?


  It causes large Cl^- secretion, leading to fluid loss
• What is the mechanism of action of cholera toxin?


  1. Binds to GM1 ganglioside receptor
  2. Internalized and transported to the ER
  3. A1 subunit activates Adenylyl Cyclase
  4. Increases cAMP levels
  5. Activates CFTR Cl^- channel
• What is the role of the Na⁺/glucose cotransporter in electrolyte replacement therapy?


  It drives Na⁺ and Cl^- back into the intestine