Channel Proteins Facilitate Diffusion by Forming Hydrophilic Transmembrane Channels Flashcards
What do hydrophilic transmembrane segments do?
allow specific solutes to move across the membrane directly
What are the three kinds of transmembrane protein channels
- ion channels
- porins
- aquaporins
What are ion channels?
transmembrane proteins that allow rapid passage of specific ions. They are tiny pores lined with hydrophilic amino acid side chains - remarkably selective
Ion channels are solute specific meaning they…
separate proteins needed to transport Na+, K+, Ca2+, Cl-, etc…)
ion channels are selectively based on…
both binding sites involving amino acid side chains, and a size filter
Most ion channels are gated, meaning
they open and close in response to stimuli
Voltage gated ion channels…
open and close in response to changes in membrane potential
Ligand-gated ion channels…
triggered by the binding of specific substances to the channel protein
Mechanosensitive ion channels…
respond to mechanical forces that act on the membrane
regulation of ion movement across membranes plays an important role in many types of cellular communication. Examples include..?
Ion channels are also necessary for…?
- muscle contraction and electrical signaling of nerve cells
- maintaining proper salt balance in the cells and the airways linking the lungs
What are porins? Where are they?
transmembrane proteins that allow rapid passage of various solutes - pores on outer membranes of bacteria, mitochondria, and chloroplasts
porins compared to ion channels?
porins are larger and less specific than ion channels
How are porins formed?
formed by multipass transmembrane proteins (porins)
Porins cross the membranes as..?
B barrels
Porins and B barrels…(3)
- B barrel has a water filled porin at its center
- polar side chains line the inside of the pore
- outside of the barrel contains many nonpolar side chains that interact with the hydrophobic interior of the membrane
