Question 1

Which of the following is a primary function of the smooth endoplasmic reticulum (SER) in liver cells?

Accepted Answer

Drug detoxification and lipid metabolism

Question 2

During protein synthesis at the rough endoplasmic reticulum (RER), what determines whether a protein will be secreted or become a transmembrane protein?

Accepted Answer

The sequence and position of the stop-transfer and signal sequences

Question 3

Which chaperone protein in the ER lumen assists in the proper folding of newly synthesized polypeptides?

Accepted Answer

BiP

Question 4

A mutation prevents the formation of disulfide bonds in the ER. Which amino acid is most likely affected?

Accepted Answer

Cysteine

Question 5

Which process in the Golgi apparatus is essential for targeting lysosomal enzymes?

Accepted Answer

Addition of mannose-6-phosphate to oligosaccharides

Question 6

A protein contains the KDEL sequence at its C-terminus. What is the fate of this protein?

Accepted Answer

It is retained or retrieved to the ER

Question 7

Which of the following best describes glycosylation in the ER?

Accepted Answer

Attachment of oligosaccharide chains to asparagine residues

Question 8

A cell is unable to export secretory proteins. Which step in the endomembrane system is most likely defective?

Accepted Answer

Vesicle formation at the Golgi for exocytosis

Question 9

Which equation best represents the formation of a disulfide bond between two cysteine residues?

Accepted Answer

$$2 \mathrm{Cys}-\mathrm{SH} \rightarrow \mathrm{Cys}-\mathrm{S}-\mathrm{S}-\mathrm{Cys} + 2 \mathrm{H}^+$$

Question 10

Which of the following tags is used to direct proteins to lysosomes?

Accepted Answer

Mannose-6-phosphate

Question 11

A patient has a genetic disorder affecting the transition vesicles between the ER and Golgi. Which cellular process is most likely impaired?

Accepted Answer

Shuttling of lipids and proteins for further modification

Question 12

Which of the following is NOT a function of the smooth endoplasmic reticulum?

Accepted Answer

Protein glycosylation

Question 13

Which step occurs first during the synthesis and export of a secretory protein?

Accepted Answer

Translation and translocation into the ER lumen

Question 14

Which of the following best describes the role of transition vesicles in the endomembrane system?

Accepted Answer

They shuttle lipids and proteins from the ER to the Golgi apparatus

Question 15

A protein is found in the ER lumen but lacks a KDEL tag. What is its most likely fate?

Accepted Answer

It will be exported to the Golgi apparatus for further modification

Question 16

Which of the following modifications occurs in the Golgi apparatus and is essential for sorting proteins to their correct destinations?

Accepted Answer

Phosphorylation of sugars

Question 17

Which equation represents the phosphorylation of a serine residue in a protein?

Accepted Answer

$$\mathrm{Ser}-\mathrm{OH} + \mathrm{ATP} \rightarrow \mathrm{Ser}-\mathrm{OPO}_3$$^{2-}$$ + \mathrm{ADP}$$

Question 18

Which of the following is a consequence of improper folding of proteins in the ER?

Accepted Answer

Proteins are destroyed and not exported

Question 19

Which of the following best explains the role of the endomembrane system in cellular transport?

Accepted Answer

It coordinates the modification, sorting, and export of proteins and lipids

Protein Modification and Sorting in the Endomembrane System: The Endoplasmic Reticulum

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