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MCB complete unit Terms in this set (559) The secretory and endocytic pathways o Cells need to eat, communicate, and respond to changes in their environment o Material is secreted through exocytosis and internalised through endocytosis o Mater€8,34
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MCB complete unit Terms in this set (559) The secretory and endocytic pathways o Cells need to eat, communicate, and respond to changes in their environment o Material is secreted through exocytosis and internalised through endocytosis o Mater
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MCB complete unit
Terms in this set (559)
The secretory and endocytic pathways o Cells need to eat, communicate, and respond to changes in their environment
o Material is secreted through exocytosis and internalised through endocytosis
o Material is sorted and modified t...
MCB complete unit
Jeremiah
Terms in this set (559)
o Cells need to eat, communicate, and respond to
changes in their environment
o Material is secreted through exocytosis and
internalised through endocytosis
The secretory and endocytic pathways
o Material is sorted and modified through many
cellular compartments using transport vesicles
Red - secretory pathway
Green - endocytic pathway
Blue - retrieval pathways
A roadmap of the secretory and endocytic
pathways
Visualising the secretory pathway using
cryo-electron tomography
1. Budding
-Select cargo (in membrane or lumen)
-Generate membrane curvature
2. transport
Transport the vesicle on microtubules and/or actin
Moving material from one compartment to
filaments
another
3. fusion
MCB complete unit
Capture vesicle
Fusion
1/20
,8/12/24, 12:31 PM
Membrane coat proteins are important for
cargo selection and curvature generation
COPI and COPII coats operate in OPPOSITE
DIRECTIONS in transport between the ER
and Golgi
Activation of Sar1
Sec 12 catalyses guanine nucleotide exchange on
Sar1, recruiting Sar1 to the ER membrane. Membrane
deformation initiates.
Selecting cargo and building a COPII coat:
Activation of Sar1 Sec12 is the Sar1-GEF
Activates Sar1 promoting exchange of GDP for GTP
Amphipathic helix of Sar1 exposed and inserts into
membrane
Curvature formation is initiated
Selecting cargo and building a COPII coat:
Sar1 activation and amphipathic helix
insertion
Sar 1 at the membrane recruits the inner coat
proteins : the Sec23-Sec24 heterodimer
The Sec24 subunit binds to cargo proteins that need
to be transported out of the ER. This group (Sar1,
Sec23, Sec24 and cargo) is termed a pre budding
complex
Soluble cargo in the lumen of the ER can be
Selecting cargo and building a COPII coat: captured by transport adaptors. The formation of
Recruitment of the inner coat components pre-budding complexes is concentrated at ER exit
Sec23-Sec24 sites.
The Sec23 component binds to Sar1
The Sec24 component binds to membrane cargo
proteins
Soluble cargo captured by transport adaptors
Pre-budding complex
2/20
, 8/12/24, 12:31 PM
The outer COPII coat, the Sec13-Sec31
heterotetramer, binds and collects pre-budding
Selecting cargo and building a COPII coat complexes
Collection pf pre-budding complexes by
the Sec13-Sec31 heterotetramer Full COPII assembly leads to fission of a vesicle from
the donor ER membrane. Soluble 'bulk flow' cargo
can be trapped inside a vesicle
Visualising the inner coat using cryo-
electron tomography
The hydrolysis of GTP bound to Sar1 leads to COPII
Selecting cargo and building a COPII coat
coat disassembly
The hydrolysis of GTP bound to Sar1
triggers COPII coat disassembly
Sorting motifs are a ubiquitous feature of the
intracellular transport network
Note ‘di-acidic’ DxE motifs and link to the SARS-
COPII, like other coat proteins recognises
Cov2 post task
sorting motifs in cytosolic domains of
membrane proteins
Allow specific cargo selection
May co-operate with other protein- protein or
protein-lipid interactions
Coatamer complex
GTPase directing recruitment
Composition and assembly of the COPI coat
GEF and GAP regulators of the GTPase
Some similarities to COPII, but some important
differences
Whilst Sar1 (COPII) inserts an amphipathic helix into
Arf1 activation is the first step of COPI the membrane, Arf1 is attached via a Myristoyl
recuitment anchor
Arf1-GTP recruits the coatamer complex
3/20
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