ch 7 endomembrane system Flashcards
nuclear envelope is part of the endomembrane system
includes nucleus, nuclear envelope, smooth er, rough er, golgi apparatus, plasma membrane; a manufacturing and shipping complex
endomembrane system is a collection of
interrelated membranous sacs and tubules that divide the cell into functional and structural compartments
the endomembrane system has many functions
1) synthesis, transport, modification and secretion of proteins 2) transport and breakdown (digestion) of large biomolecule containing particles 3) synthesis of lipids and detoxification of toxins
evolution of endomembrane system
membranes of organelles are so similar; directly connected or fuse portions of membrane; hypothesis is that all related membranes derive from the plasma membrane; ancestor of euk (plasma membrane and chromosomes); infoldings of plasma membrane that surround chromosomes form the nuclear envelope of euk cells arisen
different parts of the endomembrane system require specific proteins
proteins transported from 1 compartment to another by vesicles; vesicles are membrane enclosed sacs that transport proteins from er to golgi, golgi to plasma membrane or lysosomes, plasma membrane to lysosomes; vesicles are key to cargo transport; if transport steps depended on random movement of diffusion, cargos may never reach intended destinations; instead they have defined tracks that direct the movement of vesicles
secretory pathway
synthesis, modification, transport, secretion of proteins; protein synthesis-folding-modification at ribosomes of er; transport exit er packaged in vesicles to cis surface of golgi; modification enter golgi processed from cis to trans; transport packaged in vesicles exit golgi to plasma membrane; secretion protein is secreted from cell
targeting protein to the er
protein synthesis in free ribosomes of cytosol (peptide of 20 a.a. sequences translated on protein); er signal sequence in mRNA; er signal sequence binds to signal recognition partical srp; stops translation and binds to srp receptor on er membrane; srp is key activated by er signal, srp receptor is lock
translation continues at the translocon
srp associates with protein translocator translocon in er membrane; srp sequence releases; translation continues; er signal is removed; peptide moves to er lumen for secreted or internal proteins, peptide moves to er membrane for membrane proteins
rough er is involved in protein production, modification and export
have associated ribosomes, not attached; proteins destined for other parts of endomembrane system are synthesized, folded into 3d shape, partly processed on and in er; carbohydrates/sugars added to form glycoproteins
golgi processes proteins and other molecules
have system of flattened membranous sacs, cisternae; products of er are sorted and modified as they move through cisternae, golgi is polar, cis and trans surfaces; vesicles bud off from er, move and fuse only w cis surface of golgi, new cisternae form at cis and replace broken at trans
proteins sorted to plasma membrane or other parts of endomembrane system, sortment
sortment; 1. to lysosome have mannose-6-phosphate tags, postal codes that bind to receptor protein in trans surface of golgi 2. to er, retrieval pathway; accidentally sent to golgi, sent back 3. stay in golgi, synthesized into enzymes that stay in golgi 4. constitutive secretory pathway; default, no tag required 5. regulated secretory pathway; exports material; leave through trans side of golgi, pause on way to plasma membrane
proteins sorted to plasma membrane or other parts of endomembrane system, shipment
shipment; proteins of endomembrane system have distinct tags, postal codes for destinations; proteins are sorted in golgi by binding to receptors, transport vesicles bud off trans surface, attach + fuse at destinations; vesicles deliver contents by exocytosis
exocytosis
proteins to be secreted from the cell are transported to membrane in secretory vesicles; release contents to exterior by exocytosis; 2 membranes fuse; vesicle contents diffuse into space outside of cell
endocytosis
vesicles bring molecules from outside of cell; 2 membranes fuse; vesicle contents diffuse into space inside of cell
transportation and breakdown/digestion of large biomolecule containing particles
cell import small mc’s across lipid bilayer, cannot for large mc’s; lysosomes are cell’s recycling centres; contain enzymes to breakdown mc’s; lower pH than cytoplasm for enzymes to function; can digest other organelles or material from outside of cell; enzymes come from golgi
3 pathways to lysosome: receptor mediated endocytosis
use receptors to bind to macromc’s outside of cell; plasma membrane pinches to form vesicle that delivers cargo to early endosome; early endosome is acidified by proton pumps. cargo released from receptors; early endosome matures into late endosome, the lysosome
3 pathways to lysosome receptor mediated endocytosis
use receptors to bind to macromc’s outside of cell; plasma membrane pinches in to form vesicle that delivers cargo to early endosome; proton pumps acidify early endosome, cargo released from receptors; early endosome matures into late endosome, the lysosome
3 pathways to lysosome phagocytosis
brings smaller cell or food particle into cell, phagosome; phagosome is delivered to lysosome, fuse and digested
3 pathways to lysosome autophagy
encloses damaged organelle within a membrane, autophagosome; autophagosome is delivered to lysosome, digested; lysosome releases small mc’s from digested material into cytoskeleton
3 pathways to lysosome results
all pathways lead to same result; mc’s are hydrolyzed, digested products released to cytosol for recycling
synthesis of lipids, detoxification of toxins
smooth er synthesizes lipids, contains important detox enzymes; no associated ribosomes; synthesizes lipids that become part of cell membrane; e.g. in liver, converts drugs, poisons into safer substances to be easily removed from body; in reproductive organs, makes steroid sex hormones; stores calcium for cell signaling
