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Biology 2382B Study Guide - Midterm Guide: Protein Folding, Signal Peptide, Detergent

Course Code
BIOL 2382B
Sashko Damjanovski
Study Guide

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10000 proteins
Must be localized correctly
Typical mammalian cell:
Newly made peptides must be directed to the correct destination
Direct proteins to the right destinations (organelles)
During or after synthesis
Protein Sorting/Targeting
Those which remain in the cytosol
Many proteins are synthesized just by cytosolic ribosomes:
Other proteins are synthesized by ribosomes attached to the ER (the
rough ER)
Accordingly, two major protein-sorting pathways are known: nonscretory
and secretory.
General principles of protein synthesis, targeting and sorting
Signal sequence
Receptor for the signal sequence
Translocation channel
Source of energy
Basic Mechanism of Protein Targeting to the Membranes of Organelles
are Common:
Newly synthesized proteins stay in the cytosol
3 options:
Section 4: Protein Synthesis
Tuesday, January 26, 2016
4:41 PM
Midterm 1 Page 1

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Polypeptide sequence is beginning to peal off ribosomes. Proteins
that recognize this bring the protein to the ER where it continues to
be made and the newly synthesized protein is in the lumen of the
ER Structure
Uninterrupted membranous tubules and vesicles seperated from
Cisterna are stacked
RER is coated by ribosomes on the tubules (cisterna)
ER extend from the nuclear membrane
It's like being outside the cell
Can also end up in lysosome; doesn't necessarily have to leave
Lumen is continuous with the golgi lumen --> secretory vesicles
which fuse with the outside of the cell (secretory pathway known as
There are ribosomes in the cytosol but there aren't any inside the ER
Identify cellular features by microscopy, isolate and homogenize them to
free organelles
Sucrose density-gradient centrifugation of homogenate allows to isolation
of microsomes and ribosomes
SDS-page is used to identify newly translated proteins.
Stringing Concepts Together!
Add radioactive amino acids to the cell.
Any protein that it'll make Is going to be radioactive.
Identifying Proteins
Should also contain collagen if ER has collagen
To confirm: isolate the ER
Collagen in ER?
Midterm 1 Page 2
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