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