water diffuses through cell membranes, how exactly does this happen? below is short question on facilitated d:
cell membranes usually consist of phospholipid bilayer. the phospholipid heads (glycerol & phosphate) are hydrophilic and the phospholipid tails (fatty acid hydrocarbons) are hydrophobic. thus the lipids, in aqueous solution (as in cell membranes), arrange themselves into a double layer (bilayer) with the hydrophobic tails packing inside the layer and hydrophilic heads facing out.
BUT… water moves through the cell membrane via diffusion (called osmosis), but how can this be as the hydrophobic interior of cell membranes repel water?
also, can anyone tell me how ———- neurotransmitter released from presynaptic membrane, then binding to receptor in postsynaptic membrane, which then opens channels in the postmembrane ——– is an example of facilitated diffusion?
Thanks a lot, reaaaaally appreciate it.
The previous anwer is totally wrong…
Water moves by osmosis because of concentration differences. “Pure” water will flow through the membrane to the “unpure” side. Or the purer water will flow to the less pure side. Solids, like Na and K also move by way of concentration gradients. More concentrated to less concentrated.
Facilitated diffusion is where molecules need to bind to protiens on the cell surface and be channeled into the cell through a channel protein, or be “carried” into the cell by carrier protiens. They can’t pass through themselves. In your example, if the neurotrasmitter is binding to the receptor and the receptor itself is a channel protein, then yes, this is facilitated diffusion.
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