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Membrane Transport
Types of Transport
Passive Transport Active Transport
Passive Transport
Process by which membrane proteins allow molecules to cross the membrane
No energy required
Membrane Proteins
Allow polar molecules, such as ions, sugars, and amino acids to pass through the lipid bilayer
Types: Carrier Channel
Use passive transport
Carrier Proteins
A binding-site binds the molecule, which allows for a conformational change and thus passage through the membrane
The binding site is the complementary shape for the molecule
Channel Proteins
Forms a pore that allows a specific molecule (correct size and charge) to cross the membrane
Active Transport
Ions are actively pumped across the membrane – against their concentration gradient
Ways of Driving Active Transport
Coupled Transporters ATP-Driven Pumps Light-Driven Pumps
Coupled Transporters
Uphill transport of one molecule across the membrane as another moves down
Types: Symporters Antiporters
Symporters
Needs two molecules moving through the protein at the same time
Antiporters
One molecule comes in as the other moves out
ATP-Driven Pumps
Uphill transport with ATP hydrolysis Types:
P-Type Pumps F-Type Pumps ABC Transporters
P-Type Pumps
Pass ions across the membrane and phosphorylate themselves
F-Type Pumps
Called ATP synthases – make ATP instead of use it Pumps H+ across the membrane to drive this
ABC Transporters
Pump small molecules across the membrane, not just ions
Two ATP-binding sites
Light-Driven Pumps
Uphill transport coupled with light activation
Ion Channels
Contain water Allow ions to diffuse down 4 types:
Voltage-gated Ligand-gated (extracellular) Ligand-gated (intracellular) Mechanically gated
Voltage-Gated
Activated by changes in electrical potential Important in neurons
Ligand-Gated (Extracellular)
Stimuli from outside the cell opens the channel
Ligand-Gated (Intracellular)
Stimuli from inside the cell opens the channel
Mechanically Gated
Responds to mechanical pressure or vibration, includes stress