The basic structure of a membrane is a phospholipid bilayer with hydrophilic heads facing out and hydrophobic tails facing in, separating an inner and outer hydrophobic region. Transmembrane proteins like receptors and channels span the membrane. Lipids do not require channels as their hydrophobic tails allow diffusion through the membrane, while hydrophilic signaling molecules require receptors located in the membrane to interact with them from outside the cell.

1. Draw the basic structure of a membrane (a phoshphalpid bilayer). Label the phospholipid heads
and tails, the region of the membrane that is hydrophobic, and add-in a couple transmembrane
proteins (a receptor, and a channel). Would a lipid require a channel to pass through the
membrane? Why or why not? Receptor signaling - If a signaling molecule is hydrophilic, where
must its receptor be located? Why must it be there?