BIOL 3510 1st Edition Lecture 17 Outline of Last Lecture I Organelles II Mechanisms of Protein Transport into Organelles III Peroxisomes Outline of Current Lecture I Secondary Pathways II Osteogensis imperfecta III Golgi networks IV Exocytosis V Endocytosis Current Lecture Transport by vesicles moves proteins and lipids between membrane compartments Secretory pathway pink ER to the GA to the plasma membrane ER to the GA to endosone to the lysome Coated vesicles bud from membrane surfaces Cargo receptors recognize transport signals on cargo molecules and bind Adaptins mediate the connection between coat proteins and cargo receptors Dynamin binds GTP pinches off the vesicle Protein protein interactions mediate fusion of transport vesicles with appropriate membranes Proteins are modified by enzymes in the ER 1 Disulfide bond formation 2 Glycosylation addition of oligosaccharide side chains protein protection keep the protein in the ER act as transport signal cell cell recognition These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute Pre formed oligosaccharides are transferred to asparagines by oligosaccharide protein transferase Oligosaccharides are further modified in both the ER and Golgi apparatus Exit from the ER is selective Proteins remain in the ER if they Have an ER retention signal 4 aa Are incorrectly folded o Retained by chaperones Are incorrectly assembled multimeric proteins retained by chaperones Osteogensis imperfecta brittle bones disease Defects in type 1 collagen Collection of symptoms including weak bones that often fracture Genetic causes of brittle bone disease include Mutations that disrupt collagen protein function Mutations that disrupt collagen protein folding o Abnormal collagen is retained in the ER and degraded Mutation of ER proteins that post translationally modify collagen to promote protein folding o Abnormal collagen is retained in the ER and degraded Proteins are further modified and sorted in the Golgi apparatus Cis golgi network faces the ER Buds vesicles that return to the ER or continue through the Golgi apparatus Trans golgi network faces the plasma membrane Buds vesicle destined for the plasma membrane or other compartments Exocytosis is the fusion of a vesicle transport or secretory with the plasma membrane Proteins and lipids move to the plasma membrane via two distinct types of exocytosis Unregulated exocytosis default pathway Transport vesicles are continuously fusing Regulated exocytosis only in some cells Secretory vesicles do not fuse until a signal is received Endosomes are sorting compartments 1 Recycling receptors return to the plasma membrane 2 Degradation receptors cargo and contents of the lumen move to lysosomes 3 Transcytosis receptors cargo move to a new plasma membrane area Lysosomes digest extracellular materials and old organelles Acidic contains H group Transporters that export metabolites Membrane proteins are glycosylated for protection Signal sequence mannose 6 phosphate Endocytosis is the uptake of material into a cell by membrane invagination and internalization of the resulting vesicle 1 Phagocytosis uptake of particles into large vesicles called phagosomes Occurs in phagocytic cells Phagosomes fuse with lysosomes 2 Pinocytosis the uptake of fluids and molecules in small vesicles o Indiscriminate o Occurs via clathrin coated pits and vesicles o Balanced with the rate of exocytosis o Vesicles fuse with endosomes ATP H pumps keep endosomes acidic Promotes separation of receptors and cargo Early and late endosomes 3 Receptor mediated endocytosis is the selective endocytosis of specific macromolecules Autophagy enclosure of an old organelle in a double membrane creating an autophagosome
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