L37- Membrane Transport

• What are the two main types of membrane transport discussed?

  • Diffusion
  • Facilitated diffusion
• What is passive transport?

  Movement of molecules without energy input
• What is the difference between uniport and coupled transport?

  Uniport moves one molecule, coupled moves two
• What type of molecules can cross protein-free lipid bilayers?

  Small hydrophobic molecules
• What influences the rate and direction of diffusion?

  The concentration gradient
• What is the dynamic equilibrium in diffusion?

  Equal concentration on both sides
• What role do transporters play in cellular membranes?

  Facilitate import/export of metabolites and ions
• What is a channel in membrane transport?

  A pore for specific solutes to diffuse
• How do transporters differ from channels?

  Transporters bind solutes and change shape
• What is the electrochemical gradient?

  Combination of concentration and electrical potential
• How does membrane potential affect transport of charged molecules?

  It enhances or reduces transport based on charge
• What happens to transport rate at low solute concentrations?

  Transport is fast and can be saturated
• What is GLUT-1 responsible for?

  Basic glucose uptake in all tissues
• Which GLUT transporter is insulin regulated?

  GLUT-4
• What is the K_M for D-glucose?

  1.5 mM
• What does IC₅₀ represent in transporter kinetics?

  Concentration that inhibits half of transporters
• How do active transporters differ from passive transporters?

  Active transporters require energy to move cargo
• What is the role of coupled transporters?

  They use gradients to transport solutes uphill
• What is the energy source for primary active transporters?

  ATP hydrolysis
• What is the function of symporters?

  They transport two solutes in the same direction
• What is the function of antiporters?

  They exchange one solute for another
• How does Na⁺ function in coupled transport?

  It provides a driving force for active transport
• What are the types of active transport mechanisms?

  • Primary active transport
  • Secondary active transport
  • Coupled transport
• What do active transport processes require for energy input?

  Electrochemical gradient
• What is the direction of cargo movement in active transport?

  Against the concentration gradient
• What are the types of transporters mentioned?

  • Symporters (co-transporters)
  • Antiporters (exchangers)
  • Uniporers
• How do coupled transporters utilize energy?

  They harness energy from concentration gradients
• What is a common co-transported ion in coupled transporters?

  Na⁺
• What is the role of Na⁺ in active transport?

  It provides a driving force for transport
• What happens to Na⁺ ions in the cell during active transport?

  They are pumped out by ATP-driven pumps
• How does glucose leave the intestines?

  Through transcellular transport mechanisms
• What are the steps involved in glucose transport from the intestinal lumen to extracellular fluid?

  1. Na+ -driven glucose symporter
  2. Passive glucose transporter
  3. Na+ - K+ pump antiporter
• What type of transporters use ATP for active transport?

  Primary active transporters
• What do P-type pumps do during the transport cycle?

  They phosphorylate themselves
• What ions can P-type pumps move?

  H+, K+, Na+, Ca2+
• What is the function of the SERCA pump?

  Pumps Ca²⁺ ions into the sarcoplasmic reticulum
• How do V-type ATPases function?

  They acidify endosomes and lysosomes
• What is the optimal pH for lysosomal enzymes?

  ~pH 4.5 - 5.0
• How is low lysosomal pH maintained?

  By pumping protons into the lysosome lumen
• What is the role of counterions in maintaining transmembrane voltage during proton pumping?

  They help dissipate voltage for continued pumping