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BIOL 3096
Joel Sheffield

Sheffield Week 8 Wednesday 10/16/13 Lecture 21 – Coated Vesicles, Endocytosis, Begin Nucleus Endocytosis – Transport of materials into a cell through a membrane modification • Types of Endocytosis ◦ Phagocytosis ◦ Pinocytosis - “Drinking” one can see vesicles forming that are taking in extracellular liquid. • In looking at the vesicles involved in endocytosis, there was noticed a network of fibers around the vesicles. • This network, or “coating” was found to be composed of a single protein, called clathrin, which forms a trimer, called a triskelion. Many triskelions come together to form a regular lattice, or clathrin cage. • The clathrin binds to a membrane receptor protein, which in turn binds to the plasma membrane. Because Clathrin is curved, it also curves the plasma membrane, creating a greater and greater curve (eventually a sphere) as more and more triskelions join the lattice-work. • To finally separate the forming vesicle from the plasma membrane, a protein called dynamin forms a ring around the neck of the vesicle, and when GTP is hydrolyzed, the dynamin contracts, pulling the vesicle off of the membrane. • To determine if GTP was truly necessary for correct dynamin formation, GTPγS was substituted, but it caused dynamin to form a spiral, and only elongated the vesicle neck, instead of severing it. Vesicle Movement in Cell • Vesicle loses Clathrin Coat, forms a sorting component (early peripheral endosome), lowers its pH with a Proton Pump, divides receptors from proteins (in late endosome) using a lysozome to lower pH, which causes receptors to release proteins. Protein Synthesis • Starts in Nucleus ◦ Contains a mixture of DNAand Proteins: ◦ Histones, Polyme
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