PNB 2264 Chapter Notes - Chapter 3: Lipid Bilayer, Cell Adhesion Molecule, Signal Transduction

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Biological membranes - selective barriers that separate the inner contents of the cell from the interstitial fluid, and the contents of an organelle from the cytoplasm. Semipermeable barrier maintains homeostasis by only permitting entrance or exit of specific molecules. Membrane bound organelles compartmentalize various cellular processes. Ex) energy production in the mitochondria, biomolecule degradation in the lysosome and genomic dna protection in the nucleus. Plasma membranes are composed of a phospholipid bilayer. Phospholipids are composed of a glycerol backbone (with two fatty acid tails on one side) and a phosphate head group. Amphipathic - molecules with both polar (hydrophilic) regions and nonpolar (hydrophobic) regions. Phospholipids arrange themselves into two inverted sheets with the polar head groups exposed to aqueous extracellular and cytoplasmic environments and the nonpolar tails sandwiched in the center forming hydrophobic interactions. Proteins in the membrane help with signal transduction, enzymatic activity, cell adhesion, etc. Transmembrane (integral) proteins span the entire bilayer.

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