BIO130H1 Study Guide - Autophagy, Autophagosome, Mitochondrion

39 views5 pages
26 Apr 2011
School
Department
Course
Professor

For unlimited access to Study Guides, a Grade+ subscription is required.

Chapter 13 Intracellular Vesicular Traffic
Lecture 5+6: (Pg. 766-769, 779-783)
Transport From the ER Through the Golgi Apparatus
-Golgi apparatus major site for carbohydrate synthesis, sorting & dispatching
station for products of the ER
oThe cell makes many polysaccharides in the Golgi
oLies on the exit route from the ER many carbohydrates it makes are
attached as oligosaccharide side chains to many proteins and lipids that the
ER sends to it
Proteins Leave the ER in COPII-Coated Transport Vesicles
-Proteins that enter the ER and are destined for the Golgi or beyond are first
packaged into small COPII-coated transport vesicles these bud from ER exit
sites, whose membrane lacks bound ribosomes
-Entry into vesicles leaving the ER is selective; cargo proteins display exit signals on
their cytosolic surface that COPII can recognize (these coat components act as cargo
receptors and are recycled back to the ER after they deliver to the Golgi
-Soluble cargo proteins in the ER lumen have exit signals that attach them to
transmembrane cargo receptors, which in turn bind through exit signals in their
cytoplasmic tails to components of the COPII coat
-At a lower rate, proteins without exit signals enter transport vesicles (ER resident
proteins) and leak out of the ER and are delivered to the Golgi
-Secretory proteins made in high concentrations can leave the ER without signals
Only Proteins That Are Properly Folded and Assembled Can Leave the ER
- Misfolded proteins remain in the ER, bound to chaperone proteins like BiP or
calnexin
oChaperones cover up exit signals or somehow anchor the protein in the ER
-Failed proteins are transported to the
cytosol, and degraded by proteasomes
-90% of newly synthesized subunits of T
cell receptors are destroyed without ever
reaching the cell surface, where they
function
-Continual degradation of these proteins
provide an early warning system to alter
the immune system of a virus infection
Using specialized ABC-type
transporters, the ER imports peptide
fragments of viral proteins produced by
proteases in the proteasome
oForeign peptides are loaded onto MHC in the ER lumen and proteins
transported to the cell surface
oT lymphocytes recognizes the peptides as non-self antigens and kill infected
cells
www.notesolution.com
Unlock document

This preview shows pages 1-2 of the document.
Unlock all 5 pages and 3 million more documents.

Already have an account? Log in
- Mutations that cause cystic fibrosis result in the production of a misfolded form of a
plasma membrane protein important for Cl- transport. Although the mutant protein
would function perfectly normally if it reached the plasma membrane, it remains in
the ER.
oThe disease thus results not because the mutation inactivates the protein but
because the active protein is discarded before it reaches the plasma
membrane.
Vesicular Tubular Clusters Mediate Transport from the ER to the Golgi
Apparatus
-Once transport vesicles bud off, and shed their coat, they fuse with one another
oHomotypic/heterotypic fusion (similar/different membranes)
-In both types of fusion, a set of matching SNAREs is required
oSNARE proteins catalyze the membrane fusion reactions in vesicular
transport
oThe interaction is symmetrical (both membranes contribute v- and t-
SNAREs
-Vesicular tubular clusters - Structures formed when vesicles fuse
oclusters are separate from the ER and lack many proteins that function in
the ER
oFunction as
transport
containers from the
ER to the Golgi
oMove along
microtubules to the
Golgi, then fuse to
deliver contents
-As soon as these clusters form, they begin to bud off transport vesicles of their own
oThese vesicles are COPI-coated and they carry ER resident proteins that
have escaped back to the ER, as well as proteins like cargo receptors
-The retrieval (retrograde) transport continues as the vesicular tubular clusters
move towards the Golgi
Transport From the Trans Golgi Network to Lysosomes
-The trans Golgi network sorts proteins that pass through the Golgi apparatus
according to their final destination (except resident proteins)
Lysosomes Are the Principal Sites of Intracellular Digestion
-Lysosomes membrane-enclosed compartments filled with soluble hydrolytic
enzymes that control intracellular digestion of macromolecules
oContain 40 types of hydrolytic enzymes that are all acid hydrolases
ofor optimal activity, they need to be activated by proteolytic cleavage and
require acidic environments (4.5-5.0)
www.notesolution.com
Unlock document

This preview shows pages 1-2 of the document.
Unlock all 5 pages and 3 million more documents.

Already have an account? Log in

Get access

Grade+
$10 USD/m
Billed $120 USD annually
Homework Help
Class Notes
Textbook Notes
40 Verified Answers
Study Guides
1 Booster Class