Membrane Transport Quiz

Membrane Transport

• Transport across membranes includes passive and active transport.
• Passive transport moves substances down their concentration or electrochemical gradient, without energy expenditure.
• Active transport moves substances against their concentration or electrochemical gradient, requiring energy.

Types of Transport

• Passive Transport:
  • Substances move down their concentration gradient.
  • No energy is required.
  • Examples include simple diffusion, facilitated diffusion, and osmosis.
• Active Transport:
  • Substances move against their concentration gradient.
  • Energy (ATP) is required.
  • Examples include primary active transport and secondary active transport.

Passive Transport Subtypes

• Simple diffusion:

  • Small, uncharged molecules (e.g., oxygen, carbon dioxide) can pass directly through the lipid bilayer.
  • The rate-limiting step is moving across the lipid bilayer from the aqueous environment.
  • Ions and charged molecules diffuse poorly across the lipid bilayer.

• Facilitated diffusion:

  • Molecules that are not lipid-soluble or too large to move through the lipid bilayer (e.g., glucose, amino acids) travel through protein channels or carrier proteins.
  • No energy expenditure is needed.
  • Examples include glucose transporters (GLUTs) and aquaporins.

• Osmosis:

  • The movement of water across a selectively permeable membrane from an area of high water concentration to an area of low water concentration.

Active Transport Subtypes

• Primary active transport:

  • Directly uses ATP for transport.
  • Example: sodium-potassium pump (Na+/K+ ATPase).

• Secondary active transport:

  • Uses the electrochemical gradient of one substance (e.g., Na+) to move another substance against its gradient.
  • Examples include SGLT-1 and SGLT-2 for glucose transport.
  • Subtypes include symport (both substances move in the same direction) and antiport (substances move in opposite directions).

Sodium-Potassium Pump (Na+/K+ ATPase)

• An important primary active transport protein maintaining ion gradients necessary for cell function.
• Transports 3 Na+ ions out and 2 K+ ions in per ATP molecule hydrolyzed.
• Contributes to resting membrane potential and drives secondary active transport.
• It's a crucial component of cell function in various tissues.
• The pump itself has 4 subunits (two alpha and two beta).

ABC Transporter Protein Family

• Transports diverse substrates, including drugs, and plays a major role in drug resistance.
• The transporter has 2 transmembrane and 2 ATP domains (casettes).
• Often found in tumor cells, resisting cytostatic drugs.

Proton Pump

• Transports protons (H+) across a membrane, usually actively.
• A critical component in cellular processes including respiration and stomach HCl secretion.
• Uses energy from ATP hydrolysis.

Gibbs-Donnan Equilibrium

• Ions, with opposite charges, distribute unequally across a membrane.
• When a semipermeable membrane separates two solutions containing diffusible and non-diffusible ions, the concentration difference creates a membrane potential.
• The imbalance in concentrations on both sides, of the membrane, results in an uneven distribution of ions.
• Unequal ion distribution creates a membrane potential across the membrane.

This quiz covers the fundamental concepts of membrane transport, including both passive and active transport mechanisms. You will explore key examples of each type, along with detailed subtypes of passive transport such as simple diffusion and osmosis.