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Flashcards in Chapter Fifteen Deck (18):

membrane enclosed organelles import proteins by

(1) selective transport of specific cytosolic folded proteins into nucleus via nuclear pores (2) unfolded proteins move from cytosol to ER mitochondria, chloroplasts, peroxisomes via translocators in memb. (3) unfolded proteins move from ER via transport vesicles to ferry proteins from 1 component to another in vesicle


signal sequences

direct proteins to correct membrane enclosed organelle; demonstrated by recombinant DNA techniques; altering signal seq can change location of 2 proteins protein redirected to abnormal location in cell


signal sequence configuration

rather than AA is sequence is recognized by specific receptor proteins that initiate protein translocation


nuclear entry

nuclear transport signal w/i or at end of protein sequence


nuclear pore complex

makes gate where selected macromols/larger complexes enter/exit nucleus


proteins in the nuclear pore complex

30 diff proteins; 1-2 water filled channels for water sol mols to pass non selectively in each pore; nuc basket of fibrils/polypep chains that selectively allow other mol/macromol to pass (e.g. ribosome are too big to pass)


vesicular transport

budding from one membrane and fusing w another


clathrin-coated vesicles

transport selected cargo mols via receptor mediated endocytosis


steps for clathrin coated vesicles transport

(1) cargo receptors w bound cargo (e.g. LDL)bind adaptins (2) adaptins also bind clathrin mols on cytosolic side of budding vesicle (3) clathrin itself plays no part in capturing specific mols for transport (4) adaptins secure clathrin coat to form vesicle membrane; help select cargo for transport (5) dymain (GTP bound motor protein) assembles around neck of budding vesicles; hydrolyze bound GTP and pinch off vesicle (6) coat proteins (adaptins, clathrin) removed; transport vesicle docks to target membrane



a mol that can hydrolyze its GTP for GDP to release E


rab, tethering proteins and SNAREs

help direct transport vesicles to their target membranes


vesicle (containing cargo) w transmembrane v-SNARE and attached rab protein

bind a tethering protein on target membrane


tethering protein (on target cell membrane)

binds rab protein (on vesicle) rab is hydrolyzed and vesicle is pulled toward target for docking


V-SNARE (on vesicle)

fuses w T-SNARE (on target membrane) facilitating membrane fusion


SNARE proteins

play central role in membrane fusion of transport vesicle at its destination; wind around each other and help squeeze any water lying between membranes so lipids in membrane can coalesce as cont bilayer; either degraded or reused



contains large variety of hydrolytic enzymes which are only active under acidic conditions


lumen of lysosome

maintained at acidic pH by H+ ATPase pump in membrane that helps pump H+ into lumen (against concentration gradient)


lumenal facing membrane proteins (e.g. H+ATPase pump)

have to be highly glucosylated to protect them from lysosomal proteases etc the sit in the lysosomal lumen