Q: Which equation best represents the acidification of lysosomes required for activation of acid hydrolases?

$$ \text{H}^+_{\text{cytosol}} \xrightarrow{\text{proton pump}} \text{H}^+_{\text{lysosome}} $$

Question 1

Which of the following statements best describes the difference between N-linked and O-linked glycosylation in eukaryotic cells?

Accepted Answer

N-linked glycosylation starts in the ER and continues in the Golgi, attaching oligosaccharides to the nitrogen atom of asparagine residues; O-linked glycosylation occurs entirely in the Golgi, attaching oligosaccharides to the oxygen atom of serine, threonine, or tyrosine residues.

Question 2

During the initial steps of N-linked glycosylation, which molecule acts as the oligosaccharide carrier inserted into the ER membrane?

Accepted Answer

Dolichol phosphate

Question 3

A mutation impairs the function of protein disulfide isomerase (PDI) in the ER. Which process would be most directly affected?

Accepted Answer

Proper formation of disulfide bonds during protein folding

Question 4

Which of the following best explains the role of the unfolded protein response (UPR) in the ER?

Accepted Answer

UPR uses sensor molecules to shut down translation when unfolded proteins accumulate.

Question 5

Which of the following is TRUE regarding the structure and function of clathrin coats during vesicle formation?

Accepted Answer

Clathrin coats induce membrane curvature by assembling into a mixture of pentagons and hexagons, forming spherical vesicles.

Question 6

A patient is diagnosed with a lysosomal storage disease characterized by the accumulation of glycosaminoglycans. Which process is most likely defective?

Accepted Answer

Targeting of lysosomal enzymes by mannose-6-phosphate

Question 7

Which equation best represents the acidification of lysosomes required for activation of acid hydrolases?

Accepted Answer

$$ 	ext{H}^+_{	ext{cytosol}} \xrightarrow{	ext{proton pump}} 	ext{H}^+_{	ext{lysosome}} $$

Question 8

Which of the following best describes the SNARE hypothesis for vesicle targeting and fusion?

Accepted Answer

v-SNAREs on vesicles and t-SNAREs on target membranes interact to ensure specific recognition and membrane fusion.

Question 9

A researcher blocks the function of Rab GTPases in a cell. What is the most likely consequence?

Accepted Answer

Vesicles will fail to fuse with their correct target membranes due to lack of SNARE complex stabilization.

Question 10

Which of the following steps is required for the removal of the clathrin coat from a newly formed vesicle?

Accepted Answer

Action of Hsc70 chaperone and auxilin, using ATP to uncoat clathrin

Question 11

Which of the following is a function of COPI-coated vesicles in eukaryotic cells?

Accepted Answer

Retrograde transport from the Golgi back to the ER

Question 12

A cell is unable to recycle its plasma membrane receptors after endocytosis. Which process is most likely disrupted?

Accepted Answer

Decrease in endosomal pH causing dissociation of ligand and receptor

Question 13

Which of the following best explains why lysosomal membranes are coated with glycoproteins?

Accepted Answer

To protect the membrane from degradation by lysosomal hydrolases

Question 14

Which of the following is the correct sequence for the targeting of lysosomal enzymes from the trans-Golgi network (TGN) to lysosomes?

Accepted Answer

Enzymes are tagged with mannose-6-phosphate, bind to M6P receptors, are packaged into vesicles, delivered to endosomes, and finally to lysosomes.

Question 15

Which of the following equations best represents the hydrolysis of GTP by ARF during COPI coat disassembly?

Accepted Answer

$$ 	ext{ARF-GTP} ightarrow 	ext{ARF-GDP} + 	ext{P}_i $$

Question 16

A mutation in SNAP-25B impairs SNARE C-terminal assembly. Which cellular process would be most directly affected?

Accepted Answer

Synaptic exocytosis and neurotransmitter release

Question 17

Which of the following is a consequence of a defect in ER-associated degradation (ERAD)?

Accepted Answer

Accumulation of misfolded or unassembled proteins in the ER

Question 18

Which of the following best describes the role of dynamin during clathrin-mediated endocytosis?

Accepted Answer

Dynamin hydrolyzes GTP to constrict and sever the neck of the budding vesicle from the plasma membrane.

Question 19

Which of the following is a key function of the Golgi apparatus in protein processing?

Accepted Answer

Terminal glycosylation and sorting of proteins for their final destinations

Protein Processing, Glycosylation, and Membrane Trafficking in the ER and Golgi

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