Non-Vesicular Transport

What is simple diffusion

Passive movement of molecules across lipid bilayer down their concentration gradient

Which substances move by simple diffusion

Small, nonpolar, uncharged molecules (O2, CO2 steroid hormones)

What factors influence the rate of diffusion

concentration gradient, surface area, membrane permeability, temperature, and diffusion distance

What is osmosis

Net movement of water across a semipermeable membrane from low solute to high solute concentration

What are aquaporins

Membrane water channels that facilitate osmosis

What is facilitated diffusion

Passive transport via carrier or channel proteins; no energy required

Example of a facilities diffusion carrier

GLUT transporter for glucose

What are gated ion channels and what types exist?

Channels that open or close in response to stimuli: voltage-gated, ligand-gated, or mechanically-gated

What is active transport

Energy-dependent transport of molecules against their gradient

What is the main difference between primary and secondary active transport?

Primary uses ATP directly (eg Na+/K+ pump); secondary couples to another ion’s gradient (eg glucose cotransporter)

Describe Na+/K+ pump

Moves 3 Na+ out and 2 K+ in per ATP hydrolyzed; maintains gradients and membrane potential

What is transport saturation

In mediated transport, the rate plateaus once all protein binding sites are occupied