BIOL 3450 Chapter 14: Chapter 14 – Vesicular Traffic, Secretion, and Endocytosis
28 January 2019
BIOL 3450
Chapter 14 – Vesicular Traffic, Secretion, and Endocytosis
o Secretory pathway ~ allow proteins to be secreted from ell or delivered to plasma
membrane and lysosomes; dedicated secretory cells tat produce and secrete large
quantities of proteins to outside of cell; allows proteins to be targeted to cell surface
o Endocytic pathway ~ used to take up substances from cell surface and move them into
interior of cell; can selectively remove proteins from plasma membrane and has part in
regulating protein composition of plasma membrane
o Transport vesicles ~ collect cargo proteins in buds arising from membrane of one
compartment and then deliver these cargo proteins to next compartment by fusing with
membrane of that compartment
▪ Cisterna ~ container for holding water or other liquid
▪ Trans Golgi network ~ major branch point in secretory pathway; proteins are
loaded into different kinds of vesicles and thereby trafficked to different
destinations
o Exocytosis ~ process by which vesicle moves to and fuses with plasma membrane and
releases its contents
o Late endosome ~ compartment in trans Golgi network
o Endocytosis ~ vesicles bud inward from plasma membrane, bringing membrane proteins
and their bound ligands into cell; some proteins are transported to lysosomes via late
endosome while some are recycled back to cell surface
14.1 Techniques for Studying Secretory Pathway
Key Concepts
o All assays for following trafficking of proteins through secretory pathways in lie cells
require way to label cohort of secretory proteins and way to identify compartments where
labeled proteins are subsequently located
o Pulse labeling with radioactive amino acids specifically label cohort of newly made
proteins in ER
▪ Alternatively, temperature sensitive mutant protein that is retained in ER due to
misfolding at nonpermissive temperature will be released as cohort for transport
when cells are shifted to permissive temperature
o Transport of fluorescently labeled protein along secretory pathway can be observed by
microscopy
▪ Transport of radiolabeled protein is commonly tracked by following
compartment specific covalent modifications to protein
o Many of components required for intracellular protein trafficking have been identified in
yeast by analysis of temperature sensitive sec mutans defective for secretion of proteins
at nonpermissive temperature
o Cell free assays for intercompartmental protein transport have allowed biochemical
dissection of individual steps of secretory pathway
▪ Such in vitro reactions can be used to produce pure transport vesicles and to test
biochemical function of individual transport proteins
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
14. 2 molecular mechanisms of vesicle bussing and fusion. Targeting sequences on cargo proteins make specific molecular contacts with coat proteins: sorting signals ~ specific sequences; in cytosolic portion of membrane cargo proteins. Snare proteins in target membrane, including fusion of two membranes: after fusion if completed, snare complex is disassembled in atp dependent reaction mediated by other cytosolic proteins. Golgi complex: soluble and membrane proteins advance through golgi complex by cisternal maturation, process of anterograde transport that depends on resident golgi enzymes moving by. 14. 4 later stages of secretory pathway: plasma membrane of polarized epithelial cells is divided into two domains apical and basolateral. In polarized epithelial cells, membrane proteins destined for apical and basolateral domains of plasma membrane are sorted in trans golgi network into different transport vesicles: gpi anchor is only apical basolateral sorting signal identified so far.
