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MCB 2050 Exam Questions and Answers 100% Solved
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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 oute...

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  • October 12, 2024
  • 32
  • 2024/2025
  • Exam (elaborations)
  • Questions & answers

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  • mcb 2050

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  • MCB 2050
  • MCB 2050

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©JOSHCLAY 2024/2025. YEAR PUBLISHED 2024.

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

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