BIOL 141 Lecture Notes - Lecture 4: Ion Channel, Protein Structure, Glut1
Wednesday, October 4, 2017
BIOL 141
•Plasma membrane is a fluid mosaic - all the individual pieces are moving/dynamic"
•Polar group would be unstable inside the hydrophobic middle of the bilayer"
•Diffusion - random movement of molecules from high concentration to low
concentration - driven by entropy"
•Concentration gradient - driving force, drives the movement of permeable molecules
to become equally spaced"
•Diffusion is spontaneous - low entropy to high entropy, no energy required - passive
transport"
•Osmosis - diffusion of water"
•To observe osmosis, we need to have a selectively permeable membrane, [gradient]
- driving force that drives water"
•Osmosis only occurs across a selectively permeable membrane"
•Osmolarity - measure of total [solute]"
•Tonicity is relative"
•Hypo, hyper, iso"
•Regulate permeability by regulating the expression of proteins (expression of central
dogma)"
•What protein? How much protein? Where is it in the cell? (cell membrane or not)"
•Aquaporins - rapidly transports water, found in many types of cells, expression
tightly regulated, critical for maintaining osmolarity"
•Charged amino acid side groups help polar water molecules go through extremely
hydrophobic middle part of the bilayer."
•Protein is coupling ATP hydrolysis to facilitate transport"
•Three main transport mechanisms:"
•Diffusion through the membrane"
•Facilitated diffusion:"
•Via carrier proteins"
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