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MCB 2050 Exam Questions and Answers
100% Solved
rough endoplasmic reticulum - ✔✔mostly cisternae w/bound ribosomes,
involved in protein and membrane phospholipid synthesis
smooth endoplasmic reticulum - ✔✔mostly curved tubules lacking
ribosomes, involved in Ca2+ storage and hormone synthesis
outer nuclear membrane - ✔✔continuous w/RER, contains nups and
attached ribosomes
2 concentric phospholipid bilayers arranged in parallel and separated by
nuclear envelope lumen, joined at NPCs
MAM and PAM - ✔✔mitochondria and plasma membrane-associated
membranes
regions of ER that make direct contact w/mitochondria or pm
involved in membrane lipid exchnage
ERES - ✔✔ER exit sites
ER subdomain located next to cisface of Golgi
, ©JOSHCLAY 2024/2025. YEAR PUBLISHED 2024.
responsible for packaging of vesicles w/correct proteins and lipids destined
for Golgi
reticuloplasmins - ✔✔chaperones that operate at the ER
bind to nascent soluble or membrane proteins and mediate their proper
folding and oligomeric assembly (prevent protein aggregation)
ex. BiP, calnexn, calreticulin
sec61 translocon - ✔✔hourglass-shaped pore containing a pore ring of 6
hydrophobic AAs located at the narrowest diamater of the pore
- AA side chains act as a gate
- alpha-helix prevents ion movement/small molecules movement b/w ER
lumen and cytoplasm - maintains ER organelle compartmentalization
N-linked glycosylation - ✔✔addition of sugar monomers to the terminal
amino group of an asparagine
2 stages: core glycosylation and core modification
core glycosylation - ✔✔step 1 of N-linked glycosylation
- a sugar is added to dolichol phsophate, a lipid carrier, then more sugar
are added one a time
- core is flipped across the ER membrane into the ER lumen during its
synthesis
, ©JOSHCLAY 2024/2025. YEAR PUBLISHED 2024.
- glycosyltransferase links the core oligosaccharide to the NXS/T
sequence on a soluble or integral membrane protein that's still being
synthesized in the Sec61 co-translational translocation pathway
- dolichol phosphate is recycled for another round of core oligosaccharide
synthesis
core modification - ✔✔step 2 of N-linked glycosylation
- two of the terminal glucose units are trimmed by glucosidase I and II
- nascent glycoprotein is folded by reticuloplasmins and undergoes protein
control during this process
ER protein quality control - ✔✔- nascent glycoprotein (w/1 remaining
terminal glucose) binds to calnexin, which mediates final folding steps
glucosidase II then trims the last glucose unit, releasing the protein from
calnexin
- if properly folded, protein goes and lives it's life
- if misfolded is recognized by the UGGT monitoring enzyme, which adds a
glucose residue back, at which point the protein binds to calnexin again
and the process repeats until the protein is properly folded or is destroyed
via the ERAD pathway
, ©JOSHCLAY 2024/2025. YEAR PUBLISHED 2024.
ERAD pathway - ✔✔- oligosaccharide chain is removed and protein is
poly-ubiquinated
- UB-protein binds to cap of proteasome, the UB is removed and recycled
and the protein is threaded into the proteasome and degraded
- AAs are reused for new protein synthesis
mono-UB - ✔✔serves as signal for membrane protein import into late
endosomal intralumenal vesicles
poly-UB - ✔✔serves as signal for ER protein degradation and for most
other cellular proteins destined for normal turnover
calnexin - ✔✔membrane-bound reticuloplasmin
UGGT monitoring enzyme - ✔✔glycosyltransferase that recognizes
hydrophobic residues that are usually masked by the attached
oligosaccharide core in a correctly folded protein
UPR pathway - ✔✔unfolded protein response
occurs under ER stress (misfolded proteins accumulate in ER to high levels
due to overload of ERAD pathway)
two types: PERK and ATF-6
MCB 2050 Exam Questions and Answers
100% Solved
rough endoplasmic reticulum - ✔✔mostly cisternae w/bound ribosomes,
involved in protein and membrane phospholipid synthesis
smooth endoplasmic reticulum - ✔✔mostly curved tubules lacking
ribosomes, involved in Ca2+ storage and hormone synthesis
outer nuclear membrane - ✔✔continuous w/RER, contains nups and
attached ribosomes
2 concentric phospholipid bilayers arranged in parallel and separated by
nuclear envelope lumen, joined at NPCs
MAM and PAM - ✔✔mitochondria and plasma membrane-associated
membranes
regions of ER that make direct contact w/mitochondria or pm
involved in membrane lipid exchnage
ERES - ✔✔ER exit sites
ER subdomain located next to cisface of Golgi
, ©JOSHCLAY 2024/2025. YEAR PUBLISHED 2024.
responsible for packaging of vesicles w/correct proteins and lipids destined
for Golgi
reticuloplasmins - ✔✔chaperones that operate at the ER
bind to nascent soluble or membrane proteins and mediate their proper
folding and oligomeric assembly (prevent protein aggregation)
ex. BiP, calnexn, calreticulin
sec61 translocon - ✔✔hourglass-shaped pore containing a pore ring of 6
hydrophobic AAs located at the narrowest diamater of the pore
- AA side chains act as a gate
- alpha-helix prevents ion movement/small molecules movement b/w ER
lumen and cytoplasm - maintains ER organelle compartmentalization
N-linked glycosylation - ✔✔addition of sugar monomers to the terminal
amino group of an asparagine
2 stages: core glycosylation and core modification
core glycosylation - ✔✔step 1 of N-linked glycosylation
- a sugar is added to dolichol phsophate, a lipid carrier, then more sugar
are added one a time
- core is flipped across the ER membrane into the ER lumen during its
synthesis
, ©JOSHCLAY 2024/2025. YEAR PUBLISHED 2024.
- glycosyltransferase links the core oligosaccharide to the NXS/T
sequence on a soluble or integral membrane protein that's still being
synthesized in the Sec61 co-translational translocation pathway
- dolichol phosphate is recycled for another round of core oligosaccharide
synthesis
core modification - ✔✔step 2 of N-linked glycosylation
- two of the terminal glucose units are trimmed by glucosidase I and II
- nascent glycoprotein is folded by reticuloplasmins and undergoes protein
control during this process
ER protein quality control - ✔✔- nascent glycoprotein (w/1 remaining
terminal glucose) binds to calnexin, which mediates final folding steps
glucosidase II then trims the last glucose unit, releasing the protein from
calnexin
- if properly folded, protein goes and lives it's life
- if misfolded is recognized by the UGGT monitoring enzyme, which adds a
glucose residue back, at which point the protein binds to calnexin again
and the process repeats until the protein is properly folded or is destroyed
via the ERAD pathway
, ©JOSHCLAY 2024/2025. YEAR PUBLISHED 2024.
ERAD pathway - ✔✔- oligosaccharide chain is removed and protein is
poly-ubiquinated
- UB-protein binds to cap of proteasome, the UB is removed and recycled
and the protein is threaded into the proteasome and degraded
- AAs are reused for new protein synthesis
mono-UB - ✔✔serves as signal for membrane protein import into late
endosomal intralumenal vesicles
poly-UB - ✔✔serves as signal for ER protein degradation and for most
other cellular proteins destined for normal turnover
calnexin - ✔✔membrane-bound reticuloplasmin
UGGT monitoring enzyme - ✔✔glycosyltransferase that recognizes
hydrophobic residues that are usually masked by the attached
oligosaccharide core in a correctly folded protein
UPR pathway - ✔✔unfolded protein response
occurs under ER stress (misfolded proteins accumulate in ER to high levels
due to overload of ERAD pathway)
two types: PERK and ATF-6
