BIOL 200 Chapter Notes - Chapter 4: Photographic Emulsion, Signal Recognition Particle, Organelle
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These compartments are involved in the processing of. Proteins entering the cell from the cell surface. Once proteins enter the er, they never return to the cytosol compartment. They are carried by vesicle transport to the other compartments of the system (highly regulated). Proteins that are entering the endomembranes system can only enter at the (cid:858)sta(cid:396)t(cid:859) of each pathway (never enter in the middle). Protein destined for the secretory/lysosomal pathways always enter at the er. Proteins going through endocytosis always enter via plasma membrane. Note: p(cid:396)otei(cid:374)s that e(cid:374)te(cid:396) the e(cid:374)do(cid:373)e(cid:373)(cid:271)(cid:396)a(cid:374)e (cid:374)e(cid:448)e(cid:396) lea(cid:448)e the (cid:858)path(cid:449)ay(cid:859) they a(cid:396)e follo(cid:449)i(cid:374)g u(cid:374)til they reach the final destination for that pathway. Processing can include any number of events, including: Removal of the first methionine (i. e. carried by the start trna) Formation of disulfide bridges (most common in secreted proteins) Glycosylation (only proteins destined for the cell exterior) Protein folding spontaneous process (polypeptide takes on the lowest energy conformation possible)