Secretory Pathways and Exocytosis

three ways to leave trans-golgi

1. endo-lysosomal pathway

2. regulated secretory pathway

3. constitutive secretory pathway

- proteins are sorted into the endo-lysosomal pathway

M6P-tagged

in the regulated secretory pathway, a small group or single type of small molecules or proteins - to form dense granules that are packaged into -

aggregate, secretory vesicles

proteins that lack - (two things) or fail to - default to the constitutive secretory,

M6P tag, ER retrieval signals, aggregate into secretory vesicles

secretory vesicles are destined for the - and -

plasma membrane, exocytosis

all cells use the constitutive secretory pathway to - or - the plasma membrane with new - and -

replenish, load, lipids, membrane proteins

constitutive secretory vesicles bud from the - and proceed to the -

trans-golgi, PM

specialized cells bud - carrying large amounts of - cargo

regulated secretory vesicles, concentrated

soluble cargo is only one or few types of small molecules or proteins which aggregate into - and segregate into regulated secretory vesicles

dense granules

immature secretory vesicles bud-off - retrieval vesicles that recycle membrane proteins back to the -, reducing vesicle - and - cargo in the mature secretory vesicle

clathrin coated, trans golgi, size, concentrating

pancreatic beta cells form regulated secretory vesicles that are highly concentrated with - cargo

insulin

How are insulin secretory vesicles regulated by glucose concentration?

1. blood [glucose] rises → glucose transport - (into/out of) beta cells → increase in [-]

2. high [ATP] closes - channels → accumulation of - → membrane - (depolarization/repolarization)

3. voltage-gated Ca2+ channels in PM - (open/close) → Ca2+ - (enter/exit) → Ca2+ primes -

4. secretory vesicles and PM fuse → -

into, ATP, ligand gated K+, K+, depolarization, open, enter, v-snares, insulin released

polarized cells direct exocytic vesicles to the - domain

appropriate plasma membrane

most epithelial cells in tissues are polarized and have two or more - or -

distinct membrane faces - domains

domains perform specialized functions and are thus composed of different types of - and -

membrane proteins, lipids