BABS1201 Lecture Notes - Lecture 8: Lipid Bilayer, Facilitated Diffusion, Membrane Transport
Document Summary
The phospholipid bilayer is impermeable to most molecules. But the cell needs energy, building blocks for its components, cofactors, etc. , which are outside of the cell. In facilitated diffusion, transport proteins assist movement of molecules down a concentration gradient; requires no energy input. Channels: conduits allow direct passage from one side of the membrane to the other. Carriers: binding of solute on one side of membrane produces conformational change in protein moving solute through. Channels: integral membrane proteins, which allow diffusion across membrane down a concentration gradient. Channel proteins provide a corridor for specific molecules or ions to cross the membrane. Water can diffuse across the membrane - but only very slowly because it is polar. Aquaporins are the specific channel proteins for water. Allows the cell to take up and retain the molecules it needs and exclude what is unwanted.