Question 1

Which of the following best describes the primary function of the rough endoplasmic reticulum (RER) in eukaryotic cells?

Accepted Answer

Protein synthesis, folding, and initial glycosylation for secreted and membrane proteins

Question 2

A patient with familial hypercholesterolemia has a defect in the processing of a membrane protein in the ER. Which ER function is most directly implicated in this disease?

Accepted Answer

Protein folding and quality control mechanisms

Question 3

Which of the following statements about N-linked glycosylation is TRUE?

Accepted Answer

The core oligosaccharide is assembled on dolichol phosphate and transferred to asparagine residues in the ER.

Question 4

During cotranslational import, which sequence of events correctly describes how a secreted protein enters the ER lumen?

Accepted Answer

Translation begins on a free ribosome, SRP binds signal sequence, ribosome docks at translocon, polypeptide enters ER lumen, signal peptidase cleaves signal sequence.

Question 5

Which of the following vesicle coat proteins is responsible for anterograde transport from the ER to the Golgi?

Accepted Answer

COPII

Question 6

A mutation prevents the addition of mannose-6-phosphate (M6P) to lysosomal enzymes. What is the most likely cellular consequence?

Accepted Answer

Lysosomal enzymes are secreted outside the cell instead of being delivered to lysosomes.

Question 7

Which of the following best explains why glycoprotein carbohydrate chains are found on the extracellular surface of the plasma membrane?

Accepted Answer

Carbohydrate chains are added on the lumenal side of the ER and Golgi, which is topologically equivalent to the outside of the cell.

Question 8

Which of the following is a function of the smooth ER in liver cells that contributes to drug tolerance?

Accepted Answer

Hydroxylation of hydrophobic drugs by cytochrome P450 enzymes, increasing their solubility for excretion

Question 9

A cell is exposed to colchicine, which disrupts microtubules. Which process is most likely to be directly affected?

Accepted Answer

Vesicle movement during exocytosis

Question 10

Which of the following best describes the role of SNARE proteins in vesicle trafficking?

Accepted Answer

SNAREs provide fusion specificity by pairing v-SNAREs on vesicles with t-SNAREs on target membranes.

Question 11

Which of the following equations correctly represents the ATP-dependent pumping of calcium ions back into the sarcoplasmic reticulum after muscle contraction?

Accepted Answer

$$\mathrm{Ca$$^{2+}$$_{cytosol}} + \mathrm{ATP} \rightarrow \mathrm{Ca$$^{2+}$$_{SR}} + \mathrm{ADP} + \mathrm{P_i}$$

Question 12

Which of the following is TRUE regarding the cisternal maturation model of Golgi transport?

Accepted Answer

Cis cisternae mature into medial and then trans cisternae, with enzymes transported backward by vesicles.

Question 13

A protein destined for the lysosome is synthesized in the ER and receives a specific tag in the Golgi. Which tag is responsible for its targeting to the lysosome?

Accepted Answer

Mannose-6-phosphate (M6P)

Question 14

Which of the following best describes the process of receptor-mediated endocytosis?

Accepted Answer

Specific uptake of macromolecules using plasma membrane receptors, clathrin-coated pits, and dynamin-mediated vesicle formation

Question 15

Which of the following is a key feature of lysosomal storage diseases such as Tay-Sachs?

Accepted Answer

Defective lysosomal enzymes lead to accumulation of undigested substrates, causing cell damage.

Question 16

Which of the following best explains the mechanism by which botulinum toxin causes paralysis?

Accepted Answer

Botulinum toxin cleaves SNARE proteins, preventing vesicle fusion and neurotransmitter release.

Question 17

Which of the following equations represents the hydrolysis of GTP by dynamin during clathrin-mediated endocytosis?

Accepted Answer

$$\mathrm{GTP} \rightarrow \mathrm{GDP} + \mathrm{P_i}$$

Question 18

Which of the following is a major function of plant vacuoles that distinguishes them from animal lysosomes?

Accepted Answer

Storage of pigments, toxins, and nutrients, as well as maintenance of turgor pressure and cell volume

Question 19

Which of the following best describes the role of flippases in membrane biosynthesis?

Accepted Answer

Flippases move phospholipids between the cytosolic and lumenal leaflets of the ER membrane to build bilayers.

Endomembrane System: ER, Golgi, Vesicular Transport, and Lysosomes

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