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Endoplasmic Reticulum and Golgi Questions and Answers

21.

A secretory protein spends 5 minutes in the endoplasmic reticulum, 20 minutes in the Golgi and 5 minutes in a vesicle. What fraction of its journey is spent in the Golgi?

Answer: A

The total journey is 30 minutes and 20 of them are spent in the Golgi, which is two thirds. Modifying and sorting take considerably longer than either synthesis or transport. Most of a secretory protein's life before release is spent being modified.

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22.

Cotranslational import means that a protein enters the endoplasmic reticulum

Answer: B

The ribosome docks on the membrane and threads the growing chain straight through a channel into the lumen. Import into mitochondria works the other way, after the protein is finished. The two import routes are quite distinct and use different targeting signals.

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23.

Consider the following statements about the endomembrane system.
1. The nuclear envelope is continuous with the endoplasmic reticulum.
2. Vesicles carry material between its compartments.
3. Mitochondria are part of the endomembrane system.

Answer: C

The first two are correct. Mitochondria are excluded because they import their proteins directly from the cytosol and exchange no vesicles with the rest of the system. Their double membrane and own DNA point to a separate endosymbiotic origin.

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24.

Misfolded proteins in the endoplasmic reticulum are

Answer: D

Quality control retains them, and persistent failures are pushed back out and destroyed by the proteasome. An accumulation of such proteins triggers the unfolded protein response. That response is the cell's attempt to clear the backlog before damage spreads.

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25.

The unfolded protein response is triggered when

Answer: A

The cell slows translation, makes more chaperones and increases degradation until the backlog clears. If the stress persists too long, the same pathway can instead trigger programmed cell death. A cell that cannot restore order is safer removed than left to misfold indefinitely.

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26.

Molecular chaperones in the endoplasmic reticulum assist proteins by

Answer: B

They bind exposed hydrophobic patches that would otherwise stick to one another, giving the chain time to find its correct shape. They supply no information about the final structure, which is written in the sequence itself.

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27.

State whether the following is true or false.
A molecular chaperone determines the final three-dimensional shape of a protein.

Answer: C

The shape is dictated by the amino acid sequence; the chaperone merely prevents wrong associations while folding proceeds. Calling it a template rather than a minder is the usual misunderstanding. All the information needed for folding is contained in the sequence itself.

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28.

Vesicles budding from the endoplasmic reticulum towards the Golgi are coated with

Answer: D

Correct answer: COPII protein

COPII coats vesicles moving forward from the endoplasmic reticulum to the Golgi. COPI coats the retrograde traffic returning from the Golgi to the reticulum, and clathrin coats vesicles budding from the trans Golgi network and from the plasma membrane in endocytosis. The three coats therefore mark the three legs of the secretory and retrieval pathway.

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29.

Clathrin-coated vesicles are characteristically involved in

Answer: A

The coat assembles into a basket that deforms the membrane into a pit and then a vesicle. It also operates at the trans Golgi network, sending material towards the lysosome. The same coat protein therefore serves two quite different departure points.

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30.

Assertion (A): A cell must retrieve certain proteins from the Golgi and return them to the endoplasmic reticulum.
Reason (R): Resident reticulum proteins are constantly swept forward by the flow of vesicles.

Answer: B

Both are true and the reason gives the necessity: bulk forward flow carries residents along with the cargo, so a retrieval signal and a retrograde COPI route are needed to bring them back and keep each compartment's identity.

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