processed-EE6F3B8C-2911-4389-A917-50FF8F9EAF14.jpeg

# Membrane Transport **Channels** * **Leakage Channels (Passive Channels):** Always allow ions to pass through their concentration gradient. * **Gated Channels:** Open under certain conditions. 1. **Ligand-gated:** Receptor and channel are in one, hormones or neurotransmitters open them. 2...

# Membrane Transport **Channels** * **Leakage Channels (Passive Channels):** Always allow ions to pass through their concentration gradient. * **Gated Channels:** Open under certain conditions. 1. **Ligand-gated:** Receptor and channel are in one, hormones or neurotransmitters open them. 2. **Mechanically-gated:** Open in response to mechanical deformation of the membrane (e.g., blood pressure). 3. **Voltage-gated:** Open due to a change in charge (e.g., neurons and muscle tissue). * **Selectively Permeable Membranes:** Allow some things through while preventing others. **Mechanisms Used** * **Passive:** Requires no ATP (filtration, diffusion, osmosis). Small molecules can pass readily, but larger ones cannot. * **Active:** Uses ATP. * **Carrier-mediated:** Uses membrane proteins to transport substances across. **Concentration Gradients** * **Difference in concentration:** Substance moves from high concentration to low concentration * **Factors determining membrane permeability:** * Size of molecule * Properties of molecule (polar vs. nonpolar, charged vs. uncharged, hydrophobic vs. hydrophilic). **Passive vs. Active Transport** * **Passive:** No energy required; molecules move down their concentration gradient. * **Active:** Uses energy; molecules move up (against) their concentration gradient. Transport proteins are required.