BIOL 150 Lecture Notes - Lecture 11: Facilitated Diffusion, Cell Membrane, Nuclear Membrane
Document Summary
Biol 150 principles of molecular & cellular biology. We again considered why eukaryotes cannot couple transcription and translation, and realized that the nuclear membrane prevents these two processes from occurring simultaneously. We discussed the role of membranes in cell stability and structure. We looked at typical membranes made up in many bacteria of saturated diglycerides and triglycerides, then looked at the more fluid nature of membranes with unsaturated lipids. The addition of cholesterol allows animal cells to regulate the degree of membrane fluidity through control of the amount of cholesterol in the membrane. Membranes are a barrier to movement of molecules into and out of the cell. Molecules in solution diffuse randomly to come to equilibrium concentrations. A few molecules: gases, ethanol, can move across membranes freely, called passive diffusion. Water diffuses slowly across lipid membranes, but flow can be speeded up through transport through aquaporin proteins.
