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Diagrammatic representation of the rough ER branch of protein sorting. Newly synthesized proteins are inserted into the ER membrane or lumen from
membrane-bound polyribosomes (small black circles studding the cytosolic face of the ER). Proteins that are transported out of the ER are carried in
COPII vesicles to the cis-Golgi (anterograde transport). Movement of proteins through the Golgi appears to be mainly by cisternal maturation. In the TGN,
the exit side of the Golgi, proteins are segregated and sorted. Secretory proteins accumulate in secretory vesicles (regulated secretion), from which they
are expelled at the plasma membrane. Proteins destined for the plasma membrane or those that are secreted in a constitutive manner are carried out to
the cell surface in transport vesicles (constitutive secretion). Clathrin-coated vesicles are involved in endocytosis, carrying cargo to late endosomes and to
Source: Chapter 46. Intracellular Traffic & Sorting of Proteins, Harper's Illustrated Biochemistry, 29e
lysosomes. Mannose 6-phosphate (not shown; see Chapter 47) acts as a signal for transporting enzymes to lysosomes. COPI vesicles are involved in
Citation:
Murray
RK, Bender
Botham KM,transport)
Kennelly PJ,
Weil P.
Illustratedtransport.
Biochemistry,
2012 Available
at: in
retrieving proteins
from
the Golgi
to the DA,
ER (retrograde
andRodwell
may beVW,
involved
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some intra-Golgi
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II vesicles
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Accessed:
August
10,
2017
concentrating cargo for export from the ER to the GA. Cargo normally passes through the ERGIC compartment to the GA. (TGN, trans-Golgi network;
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© 2017 McGraw-Hill
Education.
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ERGIC, ER-Golgi
intermediate
complex.) (Courtesy
of EAllDegen.)