Question 1

Which of the following best explains why larger or denser macromolecules sediment more quickly during centrifugation?

Accepted Answer

They are less affected by the solution's resistance and overcome the centripetal force more readily.

Question 2

During differential centrifugation, which of the following sequences correctly describes the order in which cellular components are typically pelleted as centrifugation speed increases?

Accepted Answer

Nuclei → mitochondria → ribosomes

Question 3

A researcher uses density gradient centrifugation to separate organelles. Which property of the organelles primarily determines their final position in the gradient?

Accepted Answer

Their density

Question 4

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

Accepted Answer

Drug detoxification via hydroxylation reactions

Question 5

The hydroxylation of phenylalanine to tyrosine in the smooth ER requires which of the following cofactors?

Accepted Answer

$\mathrm{NADPH}$ and $\mathrm{O_2}$

Question 6

Which enzyme is the committed step in cholesterol biosynthesis and is targeted by statin drugs?

Accepted Answer

Hydroxymethylglutaryl-CoA reductase (HMG-CoA reductase)

Question 7

What is the primary function of flippase enzymes in the endoplasmic reticulum?

Accepted Answer

To transfer phospholipids from the cytosolic to the lumenal leaflet of the ER membrane

Question 8

A mutation in the RXR (Arg-X-Arg) retention tag of a protein would most likely result in which of the following?

Accepted Answer

The protein escapes the ER and is mislocalized to another organelle.

Question 9

Which of the following best describes the process of anterograde transport in the endomembrane system?

Accepted Answer

Movement of material from the ER toward the plasma membrane

Question 10

A protein destined for the lysosome is tagged with which of the following modifications in the Golgi apparatus?

Accepted Answer

Phosphorylation of mannose residues to form mannose-6-phosphate

Question 11

Which of the following statements about SNARE proteins is correct?

Accepted Answer

v-SNAREs and t-SNAREs interact to ensure vesicle fusion with the correct target membrane.

Question 12

Which of the following is NOT a function of lysosomes?

Accepted Answer

Synthesis of steroid hormones

Question 13

A plant cell's vacuole is analogous to which animal cell organelle in terms of its degradative function?

Accepted Answer

Lysosome

Question 14

Which of the following best describes the role of peroxisomes in the metabolism of fatty acids in animal cells?

Accepted Answer

They oxidize long-chain fatty acids, which are then further processed in mitochondria.

Question 15

Which enzyme in peroxisomes is responsible for converting superoxide radicals ($\mathrm{O_2^-}$) to hydrogen peroxide ($\mathrm{H_2O_2}$)?

Accepted Answer

Superoxide dismutase

Question 16

A patient is found to have a defect in the KDEL retrieval tag. Which of the following is the most likely consequence?

Accepted Answer

ER-resident proteins are not efficiently returned from the Golgi to the ER.

Question 17

Which of the following best explains why the pH inside lysosomes is maintained at around 4.5?

Accepted Answer

To activate hydrolytic enzymes and prevent their activity in the cytosol

Question 18

Which of the following is a function of the plant cell vacuole that is NOT shared with animal cell lysosomes?

Accepted Answer

Storage of anthocyanins and other secondary metabolites

Question 19

Which of the following best describes the role of phospholipid transfer proteins in membrane biosynthesis?

Accepted Answer

They convey specific phospholipids from the ER to mitochondria, chloroplasts, or peroxisomes.

Question 20

A scientist is studying a protein that is only found in the trans-Golgi network (TGN). Which of the following features is most likely responsible for its localization?

Accepted Answer

A short hydrophobic domain that matches the membrane thickness of the TGN

Eukaryotic Organelle Structure and Function: Isolation, Endomembrane System, and Protein Sorting

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