Membrane bound protiens

Study Notes

Membrane proteins have various functions, including transport of molecules and ions across the cell membrane
There are three mechanisms of membrane transport: passive, active, and secondary active transport
Ion channels and pumps are involved in membrane transport and generate ion gradients that power secondary active transport
Water can also move across membranes through osmosis

Have alpha helices that span the membrane with hydrophilic residues facing the inside of the protein and hydrophobic residues facing the lipid bilayer
Involved in various functions such as cell adhesions and cancer metastasis

Permeability through the lipid bilayer: some molecules can pass freely, but many biologically important molecules cannot pass through at rates required by cells
Proteins have evolved to allow cells to move these molecules in a fast and controlled manner
Three mechanisms of membrane transport:
- Passive transport: molecules move down their concentration gradient; spontaneous and requires no energy input
- Active transport: ions move against their concentration/charge gradients; non-spontaneous and requires energy input
- Secondary active transport: uses ion gradients generated by active transport to energize the transport of another ion/solute

Two types:
- Simple diffusion: molecules move through the bilayer itself
- Facilitated diffusion: molecules move through transport proteins (channels/carriers)
Osmosis: movement of water down its concentration gradient
Aquaporins: proteins that facilitate water transport across the cell membrane

Uses ion gradients generated by active transport to energize the transport of another ion/solute
Example: Na+/glucose symporter in the kidney, which can move glucose against a 30,000-fold concentration gradient

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