Question 1

Your friend works in a biotechnology company and has discovered a drug that blocks the ability of Ran to exchange GDP for GTP.What is the most likely effect of this drug on nuclear transport?

Accepted Answer

Blocking the ability of Ran to exchange GDP for GTP would prevent Ran-GTP from forming, which is necessary for the release of cargo from nuclear transport receptors in the nucleus. Without Ran-GTP, the receptors would be unable to release their cargo once inside the nucleus.

Question 2

Signal sequences that direct proteins to the correct compartment are

Accepted Answer

Signal sequences are typically encoded in the amino acid sequence of a protein, and they are sufficient for directing the protein to its correct destination. These sequences may be recognized by specific receptors or transporters that move the protein to the appropriate compartment within the cell. In some cases, the signal sequence may be cleaved or modified after the protein reaches its destination, but it is still required for initial targeting. Choice A is incorrect because signal sequences are usually part of the primary amino acid sequence and not added post-translationally. Choice B is partially true, as some signal sequences may be recognized and bound by protein translocators, but this is not the only mechanism involved in protein targeting. Choice D is also incorrect because not all signal sequences are removed after a protein reaches its correct destination.

Question 3

Which of the following statements about the endoplasmic reticulum (ER) is FALSE?

Accepted Answer

Proteins to be delivered to the ER lumen are actually synthesized on the rough ER, not the smooth ER. The rough ER has ribosomes attached to its surface, which are responsible for protein synthesis.

Question 4

Which of the following statements about nuclear transport is TRUE?

Accepted Answer

Nuclear pores contain proteins with disordered segments that fill the channel, allowing small water-soluble molecules to pass through in a non-selective fashion.

Question 5

Which of the following organelles is not part of the endomembrane system?

Accepted Answer

Mitochondria are not part of the endomembrane system. They are membrane-bound organelles responsible for producing energy in the form of ATP through cellular respiration, and their own DNA is involved in making their own proteins.

Question 6

What is the role of the nuclear localization sequence in a nuclear protein?

Accepted Answer

The nuclear localization sequence (NLS) is recognized and bound by cytoplasmic proteins, specifically importins, which then direct the nuclear protein to the nuclear pore complex for import into the nucleus. This sequence is crucial for the targeting and transport of proteins into the nucleus.

Question 7

Which of the following statements about transport into mitochondria and chloroplasts is FALSE?

Accepted Answer

Proteins destined for mitochondria and chloroplasts are unfolded as they are transported, but they do not diffuse in the lumen until they encounter a protein translocator in the inner membrane. Rather, they are threaded directly through protein translocators in both the outer and inner membranes simultaneously. The statement that proteins diffuse in the lumen is false.

Question 8

In which cellular location would you expect to find ribosomes translating mRNAs that encode ribosomal proteins?

Accepted Answer

Ribosomes are responsible for translating mRNA into proteins, and ribosomal proteins are part of the structure of ribosomes. Ribosomes are found in the cytosol, where most protein synthesis occurs. They can also be found on the rough endoplasmic reticulum (ER) when the proteins they are synthesizing are destined for a membrane or secretion outside the cell. However, in this case, the ribosomal proteins are being translated by existing ribosomes, which are found in the cytosol. The nucleus contains the DNA but not the ribosomes necessary for translation. The lumen of the ER is where proteins are folded and modified but not where translation occurs.

Question 9

You are interested in Fuzzy, a soluble protein that functions within the ER lumen.Given that information, which of the following statements must be TRUE?

Accepted Answer

The signal sequence of a protein destined for the ER lumen, like Fuzzy, is cleaved off by signal peptidase once the protein is translocated into the ER. This cleaved signal peptide is then ejected into the ER membrane and subsequently degraded, which is a standard process for proteins entering the secretory pathway.

Question 10

Which of the following statements about a protein in the lumen of the ER is FALSE?

Accepted Answer

Proteins in the lumen of the ER can indeed be synthesized by ribosomes on the ER membrane (A), can end up in the extracellular space (B), and can be transported to the lumen of an organelle in the endomembrane system (C). However, proteins that end up in the plasma membrane are typically integrated into or associated with the membrane itself, not located within the lumen of the ER. Thus, statement D is false because it inaccurately suggests that luminal proteins can directly integrate into the plasma membrane, overlooking the fact that membrane proteins and luminal proteins have different pathways and destinations.

Question 11

Which of the following statements is TRUE?

Accepted Answer

The nuclear membrane is indeed thought to have arisen from the invagination of the plasma membrane around the cell's DNA, a process that compartmentalized the DNA and led to the formation of a distinct nucleus. This is part of the endosymbiotic theory, which explains the origin of eukaryotic cells from prokaryotic organisms.

Question 12

After isolating the rough endoplasmic reticulum from the rest of the cytoplasm, you purify the RNAs attached to it.Which of the following proteins do you expect the RNA from the rough endoplasmic reticulum to encode?

Accepted Answer

The rough endoplasmic reticulum is involved in the synthesis and processing of all types of secretory and membrane proteins, including soluble secreted proteins, ER membrane proteins, and plasma membrane proteins. Therefore, the RNA from the rough endoplasmic reticulum is expected to encode all of these protein types.

Question 13

Proteins that are fully translated in the cytosol and lack a sorting signal will end up in the

Accepted Answer

Proteins that are fully translated in the cytosol and lack a sorting signal remain in the cytosol because they do not have the necessary information to be transported to specific cellular compartments.

Question 14

Which of the following statements about membrane-enclosed organelles is TRUE?

Accepted Answer

The endoplasmic reticulum (ER) is a network of membranes within the cell, and its surface area is indeed much larger than that of the plasma membrane, allowing for extensive areas for protein and lipid synthesis.

Question 15

Most proteins destined to enter the endoplasmic reticulum

Accepted Answer

Most proteins destined for the endoplasmic reticulum contain a signal peptide that directs the ribosome synthesizing the protein to the ER membrane. As the protein is being synthesized, it begins to be threaded through a protein translocator in the membrane, such that the N-terminus of the protein ends up on the lumenal side of the membrane. Once the protein is completely synthesized, it is free to fold into its final conformation in the lumen of the ER.

Question 16

Which of the following statements about peroxisomes is FALSE?

Accepted Answer

Most peroxisomal proteins are synthesized in the cytosol and imported into peroxisomes post-translationally, not in the ER.

Question 17

Which of the following statements is TRUE?

Accepted Answer

Chaperone proteins are required to help move proteins across the outer and inner mitochondrial membranes. The signal sequences on mitochondrial proteins are usually at the N-terminus, not the C-terminus. Most mitochondrial proteins are actually imported from the cytosol, not synthesized inside the mitochondria. Mitochondrial proteins cross the membrane in an unfolded state and must refold after crossing.

Question 18

Proteins that are fully translated in the cytosol do not end up in

Accepted Answer

Proteins that are fully translated in the cytosol typically remain in the cytosol or are transported to organelles like the mitochondria or nucleus. They do not end up in transport vesicles, as these are involved in the secretory pathway, which requires translation on the rough ER.

Question 19

Where are chloroplast proteins translated?

Accepted Answer

Chloroplast proteins are initially translated in the cytosol and then transported to the chloroplast. Therefore, their translation occurs in both the cytosol and the chloroplast.

Question 20

A large protein that passes through the nuclear pore must have an appropriate

Accepted Answer

The correct answer is A because large proteins require a nuclear localization signal (NLS) to pass through the nuclear pore complex, and this signal often contains positively charged amino acids like lysine and arginine. This sorting sequence enables the protein to be recognized and transported into the nucleus.

Quiz 15: Intracellular Compartments and Protein Transport

Your friend works in a biotechnology company and has discovered a drug that blocks the ability of Ran to exchange GDP for GTP.What is the most likely effect of this drug on nuclear transport?

Signal sequences that direct proteins to the correct compartment are

Which of the following statements about the endoplasmic reticulum (ER) is FALSE?

Which of the following statements about nuclear transport is TRUE?

Which of the following organelles is not part of the endomembrane system?

What is the role of the nuclear localization sequence in a nuclear protein?

Which of the following statements about transport into mitochondria and chloroplasts is FALSE?

In which cellular location would you expect to find ribosomes translating mRNAs that encode ribosomal proteins?

You are interested in Fuzzy, a soluble protein that functions within the ER lumen.Given that information, which of the following statements must be TRUE?

Which of the following statements about a protein in the lumen of the ER is FALSE?

Which of the following statements is TRUE?

After isolating the rough endoplasmic reticulum from the rest of the cytoplasm, you purify the RNAs attached to it.Which of the following proteins do you expect the RNA from the rough endoplasmic reticulum to encode?

Proteins that are fully translated in the cytosol and lack a sorting signal will end up in the

Which of the following statements about membrane-enclosed organelles is TRUE?

Most proteins destined to enter the endoplasmic reticulum

Which of the following statements about peroxisomes is FALSE?

Which of the following statements is TRUE?

Proteins that are fully translated in the cytosol do not end up in

Where are chloroplast proteins translated?

A large protein that passes through the nuclear pore must have an appropriate