BIO130 Section Two Guide (3B)

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Department
Biology
Course
BIO130H1
Professor
Kenneth Yip
Semester
Winter

Description
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 o The cell makes many polysaccharides in the Golgi o Lies 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 o Chaperones 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 o Foreign peptides are loaded onto MHC in the ER lumen and proteins transported to the cell surface o T lymphocytes recognizes the peptides as non-self antigens and kill infected cells www.notesolution.com
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