Golgi Apparatus & Vesicular Traffic (14) Flashcards
location of golgi
b/w the ER & cell surface
structure of golgi
membrane-bound stacks called cisternae
function of golgi
modify & sort PROs for export or for other organelles, tag PROs ensuring they go to the correct location
how are the stacks of the Golgi named?
their proximity to the ER
trans-Golgi network
vesicles that bud off of Golgi & move to diff places in the cell
how do the cisternae layers differ among each other?
each department has unique enzymes
how can the Golgi be studied?
electron microscope
staining the layers based on their diffs in enzyme composition
Cis region
sugars & PROs are phosphorylated
medial region
have enzymes that remove carbs that were added in the ER & then add new carbs
trans region
area where lysosomes are sorted
what enzyme is the trans region rich of?
acid phosphatase`
enzyme found in lysosomes
N linked glycoPROs
sugars attached at the N of the asparagine
Begins in ER & continues in Golgi Glycosyltransferases facilitate the attachments
Glycosyltransferase
add sugars to the N of aspargine in N linked glycoPROs
found in the Golgi
act in a rigidly determine sequence
O-linked glycoPROs
sugars attached to the O of serine of threonine
occurs only in the Golgi
what is the diff b/w O-linked & N-linked glycoPROs?
attachment of the sugar: N –> N of asparagine & O –> O of serine or threonine
Location of attachment: N –> Golgi & ER & O –> Golgi only
how does glycosylation of PROs effect their solubility?
more hydrophilic & therefore, increases solubility
Glycosylating PROs allows them to bind where?
extracellular matrix
what is a way for PROs to have more specific interactions?
through glycoPROs
why glycosylate PROs?
Increases their solubility by making them hydrophilic
Enables binding to the extracellular matrix
Reduces susceptibility to proteases, carbs act as a physical barrier protecting the PRO core
Protects cell surface
Structural complexity to the PRO
New function
Provides more specific interactions with other PROs
where do we see an abundance of glycosylated PROs?
cell’s surface where cell-to-cell interactions occur
what creates diversity of AAs?
phosphorylation & glycosylation
what contents move through the Golgi?
membranes including PROs, phosphoglycerides & other membrane lipids
vesicles including PROs being processed & enzymes doing the processing
transient/anterograde movement
forward
cis to trans
retrograde movement
trans to cis
reverse
cisternal maturation model. When does this occur? & how?
each cisternae is physical moved up the stack & changes composition
Enzymes seem localized to departments but vesicles can come & go Maturation process New vesicles form causing upwards movements Done when macromolecules require transport (can’t fit in vesicles)
vesicular transport model
materials in the interior & in the membrane are brought up to next cisternae by vesicle transport
vesicles bud off cis & then fuse with medial etc.
what evidence is provided for the vesicular transport model?
vesicles were found to move both forward & backwards so they could maintain enzymes diffs
what evidence is provided for the cisternal maturation model?
there are some materials that are never seen in vesicles
including large molecules
how do vesicles travel?
along microtubules, anchored by PROs including dynactin
how do vesicles move?
travel along microtubules
dyenin can grab dynactin & pull the vesicle with it
Kinesin use other adaptor PROs recognizing PROs in the membrane
when does the Golgi break up?
onset of mitosis during nuclear membrane degradation (prophase)
when does the Golgi reappear in mitosis? & How?
telophase
Still UK but, growing microtubules may collect & algin small vesicles which later fuse together creating cisternae
what is the role of coat PROs in vesicle formation?
mechanical force
what is the role of integral PROs in vesicle formation?
selection of cargo
what are the PROs found in a vesicle?
integral PROs binding cargo & other PROs to connect with the coat
what are the 3 functions of the vesicles integral & peripheral PROs?
vesicle formation/budding
selection of vesicle contents by receptor sys
recognition & fusing target membrane
COP II coated vesicles
forward movement from ER & b/w cisternae
o Anterograde movement
o Cis – medial – trans – OT
COP I coated vesicles
retrograde movement from TGN to Golgi to RER
Trans – medial – cis … maybe back to ER
clathrin-coated vesicles
TGN to lysosomes & endocytosis
Assoc with movement of vesicles from trans Golgi to other places
bulk flow
non-specific contents are captured during vesicle formation
ex: water
what types of contents are found in vesicles?
bulk flow
specific materials
vesicle formation process
Receptor PRO with specificity to specific cargo
Will recruit PROs to help build coat
Coat will build vesicle
Vesicle will bud off
Vesicle will move to Golgi via motor PROs
what are the requirements of vesicular transport?
selection of contents (receptor-mediated)
production of vesicles (PRO coat)
movement of vesicle (tethering/docking & membrane fusion)
how do vesicle select their cargo?
Receptors select & carry contents High specificity & affinity for cargo & its target molecule Integral PROs (ligand with cargo)
The target molecule is at low concentrations in the mixture, the receptor picks it out
For every cargo molecule there is a receptor holding it in place (1:1)
How do vesicles bud off?
Coat PROs assemble at the membrane forcing the bilayer to bend
Coat PROs help gather the receptors that will carry the cargo
Shortly after the vesicle pinches off, the coat falls off & the vesicle is ready to travel to its destination
steps in COP II coated vesicles
- Receptors bind selected PROs (cargo) within the lumen of the RER & assembles 2 PROs: coat PRO & GTPase Sar1
PROs destined for secretion
ER resident PROs such as BiP are left behind - Sar1, a GTP binding PRO, if active promotes assembly of the coat
- Coat PROs bind to cytosol side of specific receptor in RER membrane, vesicle form determined by steric hindrance of coat PROs
- Coated bud forms & leaves the RER
Taking along receptor/cargo complexes
Also some membrane PROs (ex: Golgi glycosyltransferases)
Also membrane PROs involved in docking/fusion: destination tags Rab & SNARES (not shown) - Sar1 hydrolyzes the GTP GDP becoming inactive
- Disassembly of the coat (Sar1)
Things in the lumen of the vesicle & in the membrane stay there
Membrane-bound PRO but not integral
Leaves the membrane
Has a branch that pokes outside the membrane, GTP hydrolyzes occurs & causes it to change shape - The vesicle is now able to fuse with the cis Golgi (vesicles are no longer coated)
What activates Sar1?
attachment to GTP
what inactivates Sar1?
GTP –> GDP
what does a budded vesicle contain in COP II vesicles?
Taking along receptor/cargo complexes
Also some membrane PROs (ex: Golgi glycosyltransferases)
Also membrane PROs involved in docking/fusion: destination tags Rab & SNARES (not shown)
what causes the coat PRO to fall off in COP II vesicles?
GTP –> GDP causing a change in shape
What components required for the formation of COP II vesicles?
Receptors to bind cargo
Coat PRO
GTPase Sar1 promoting the assembly & disassembly of the coat PRO
Destination tags for docking/fusion (Rab & SNARES)
what is required for a coat PRO to recognize a receptor?
ligand bound to a receptor
What determines which PROs enter COP I vesicles?
PROs contain retrieval signals which are recognized by the receptor in the COP I membranes
what signal is recognized by COP I receptors on soluble PROs?
KDEL
what signal is recognized by COP I receptors on membrane PROs?
KKXX
How does COP I look for KDEL receptors?
looks for KKXX sequence
