Smartwork chapter 15 - secretion

The outer membrane of the nucleus is continuous with the membrane of which other organelle?
A.  mitochondrion

B.  peroxisome

C.  Golgi apparatus

D.  endoplasmic reticulum

E.  endosome

D. endoplasmic reticulum

Which organelle is the major site of new membrane synthesis in a cell?

A. mitochondrion

B. endoplasmic reticulum

C. nucleus

D. Golgi

E. peroxisome

B. endoplasmic reticulum

The outer membrane of the nucleus is continuous with the membrane of which other organelle?
A.  mitochondrion

B.  peroxisome

C.  Golgi apparatus

D.  endoplasmic reticulum

E.  endosome

D. endoplasmic reticulum

Which organelle is the major site of new membrane synthesis in a cell?

A. mitochondrion

B. endoplasmic reticulum

C. nucleus

D. Golgi

E. peroxisome

B. endoplasmic reticulum

Which organelle receives proteins and lipids from the endoplasmic reticulum, modifies them, and then dispatches them to other destinations in the cell?

A. Golgi apparatus

B. nucleus

C. endosome

D. mitochondrion

E. peroxisome

A. Golgi apparatus

How do the interiors of the ER, Golgi apparatus, endosomes, and lysosomes communicate with each other?

A.  by excreting hormones and other small signaling molecules

B.  They do not communicate with one another.

C.  by open pores that allow ions to exit and enter the organelles

D.  by small vesicles that bud off of one organelle and fuse with another

E.  by fusing with one another

D. by small vesicles that bud off of one organelle and fuse with another

Which membrane-enclosed organelles most likely evolved in a similar manner?
A. mitochondria and the Golgi apparatus

B. chloroplasts and peroxisomes

C. mitochondria and the nucleus

D. mitochondria and the ER

E. the nucleus and the ER

E. the nucleus and the ER

In muscle cells, which organelle sequesters Ca²⁺ from the cytosol?
A. Smooth ER

B. lysosome

C. endosome

D. rough ER

E. mitochondrion

A. Smooth ER

In a typical human secretory cell, which of the following membranes has the largest surface area?
A. lysosome

B. nuclear inner membrane

C. plasma membrane

D. smooth ER

E. rough ER

E. rough ER

NFᴋB regulates cellular responses to stress and damage including regulating the immune response to infection. In the absence of stimulation, a second protein, IᴋB, binds to NFᴋB blocking the nuclear import signal of NFᴋB so NFᴋB remains inactive in the cytosol. After stimulation by signaling pathways that sense cellular stress or infection, IκB is ubiquitinated and degraded, releasing NFᴋB. The nuclear localization signal of NFᴋB is unmasked when IᴋB is degraded leading to nuclear import of NFᴋB. Nuclear NFᴋB regulates transcription of genes that respond to the cellular stress or infection. Eventually NFᴋB is transported back to the cytosol to await the next cellular stress signal.

The location of NFᴋB in cells under different conditions can be studied using immunofluorescence microscopy with an antibody that specifically binds NFᴋB. NFᴋB is mostly found in the cytosol in unstimulated cells and in the nucleus in cells stimulated with IL-1α.

Which of the following would lead to decreased nuclear localization of NFᴋB after IL-1α stimulation?
 

Choose one or more:

A. Ran is bound to a nonhydrolyzable analog of GTP.

B. The ubiquitination sites on IᴋB are altered so ubiquitination no longer occurs.

C.Ran-GEF is kept in an active form in the nucleus.

D.A large excess of a short peptide containing a nuclear localization signal is added to the cells.

A. Ran is bound to a nonhydrolyzable analog of GTP.

B. The ubiquitination sites on IᴋB are altered so ubiquitination no longer occurs.

D.A large excess of a short peptide containing a nuclear localization signal is added to the cells.

Proteins that lack a sorting signal remain as permanent residents of which part of a eukaryotic cell?

A. proteasome

B. Golgi apparatus

C. cytosol

D. ER

E. nucleus

C. cytosol

What would happen to a protein that is engineered to contain both a nuclear localization signal and a nuclear export signal?

A. It would be unable to fold properly and would be targeted for destruction.

B. It would bind to nuclear import receptors and nuclear export receptors, forming a nonfunctional complex.

C. It would shuttle in and out of the nucleus.

D. It would spend most of its time in the nucleus.

E. It would spend most of its time in the cytoso

C. It would shuttle in and out of the nucleus.

Which proteins bind to nuclear localization signals on newly synthesized proteins?
A. nuclear export receptors

B. nuclear import receptors

C. nuclear pore proteins

D. cytosolic fibrils

E. signal-recognition particles (SRPs)

B. nuclear import receptors

Which of these actions occur(s) commonly at a nuclear pore complex?
Choose one or more:

A. mRNA molecules are exported to the cytosol.

B. Protein complexes diffuse into the nucleus.

C. Nuclear import receptors enter from the cytosol.

D. Proteins with a nuclear localization signal enter at the same time that proteins with a nuclear export signal exit.

E. Small water-soluble molecules are selectively transported into the nucleus.

F. Nuclear import receptors are exported to the cytosol.

A. mRNA molecules are exported to the cytosol.

C. Nuclear import receptors enter from the cytosol.

D. Proteins with a nuclear localization signal enter at the same time that proteins with a nuclear export signal exit.

F. Nuclear import receptors are exported to the cytosol

Proteins destined for the Golgi apparatus, endosomes, lysosomes, and even the cell surface must pass through which organelle?

A. ER

B. nucleus

C. mitochondrion

D. peroxisome

A. ER

Which is true of ribosomes?
A. Polyribosomes translate only those proteins that have an ER signal sequence.

B. A common pool of ribosomes is used to synthesize both cytosolic proteins and proteins destined for the ER.

C. Polyribosomes translate only cytosolic proteins.

D. A special class of ribosomes attached to the ER membrane translates the proteins destined for that organelle.
E.All ribosomes are attached to the ER when they begin synthesizing a protein.

B. A common pool of ribosomes is used to synthesize both cytosolic proteins and proteins destined for the ER.

As a polypeptide is being translocated across the membrane of the endoplasmic reticulum, a stop-transfer sequence can halt the process. What eventually becomes of this stop-transfer sequence?

A. It forms an α-helical membrane-spanning segment of the protein.

B. It remains in the cytosol.

C. It stops protein synthesis and causes the ribosome to be released back to the cytosol.

D. It is cleaved from the protein.

E. It is translocated into the lumen of the endoplasmic reticulum.

A. It forms an α-helical membrane-spanning segment of the protein.

The ER signal sequence on a growing polypeptide chain is recognized by a signal-recognition particle (SRP) in the cytosol.  What does this interaction accomplish?

A. It cleaves the ER signal sequence from the polypeptide chain.

B. It returns the ribosome to the pool of free ribosomes in the cytosol.

C. It speeds the synthesis of the polypeptide chain.

D. It releases the polypeptide chain from the ribosome.

E. It guides the ribosome and its polypeptide to the ER.

E. It guides the ribosome and its polypeptide to the ER.

Which of these statements is true?

A. The N-terminus of a protein translocated into the ER will always remain in the ER lumen.

B. The signal sequence that directs a growing polypeptide chain to enter the ER membrane is always removed by a transmembrane signal peptidase.

C. Membrane-bound ribosomes and free ribosomes are structurally and functionally identical; they differ only in the proteins they are making at a particular time.

D. Only those proteins that are destined to remain inserted in the membrane are made on the rough ER; soluble proteins are made in the cytosol.

E. Attachment to a polyribosome prevents a growing polypeptide chain from being translocated into the ER.

C. Membrane-bound ribosomes and free ribosomes are structurally and functionally identical; they differ only in the proteins they are making at a particular time.

Which organelle cannot receive proteins directly from the cytosol?

A. mitochondrion

B. chloroplast

C. peroxisome

D. nucleus

E. Golgi apparatus

E. Golgi apparatus

What is the source of energy for protein translocation into the ER?

A. hydrolysis of ATP by the translocator

B. synthesis of the protein

C. hydrolysis of ATP by the SRP receptor

D. the action of chaperones

E. hydrolysis of GTP by the translocator

B. synthesis of the protein

Nuclear import is driven by the hydrolysis of GTP, which is triggered by an accessory protein called Ran-GAP (GTPase-activating protein). Which is true of this process?

A. Nuclear receptors carry Ran-GTP from the nucleus to the cytosol

B. Nuclear import receptors have the ability to catalyze hydrolysis of GTP.

C. Ran-GAP is present exclusively in the nucleus.

D. Ran-GDP displaces proteins from nuclear import receptors inside the nucleus.

E. Ran-GTP is present in high concentrations in the cytosol.

A. Nuclear receptors carry Ran-GTP from the nucleus to the cytosol

What enables proteins destined for nuclear import to pass through the nuclear pore?

A. Their nuclear localization signal interacts with the cytosolic fibrils that extend from the pore. 

B. They are recognized by receptors that interact with repeated amino acid sequences in proteins lining the nuclear pore.

C. Their nuclear localization signal interacts with the unstructured meshwork of proteins lining the pore.

D. They promote the hydrolysis of GTP, which provides the energy needed for their transport.

E. They are unfolded to allow them to snake through the meshlike network of proteins lining the nuclear pore.

B. They are recognized by receptors that interact with repeated amino acid sequences in proteins lining the nuclear pore.

You join a lab studying a receptor protein thought to facilitate infection of human intestinal cells by a new virus. You are interested in understanding how the receptor was inserted into the plasma membrane of the host cells. The protein has the following general structure across the plasma membrane. Glycosylation is shown by the blue hexagons. You notice that the previous student forgot to label the cytosolic and extracellular sides of the plasma membrane on the diagram. Given the diagram, where are the N and C termini of the protein?

A.  The N terminus is on the extracellular side and the C terminus is on the cytosolic side, since the C terminus is on the same side of the membrane as the glycosylation.

B.  The N terminus is on the extracellular side and the C terminus is on the cytosolic side, since the N terminus is inserted into the ER and therefore is always on the extracellular side.

C.  It is impossible to tell, so you decide to repeat the experiment.

D.  The N terminus is on the cytosolic side and the C terminus is on the extracellular side, since the C terminus is on the same side of the membrane as the glycosylation.

D.  The N terminus is on the cytosolic side and the C terminus is on the extracellular side, since the C terminus is on the same side of the membrane as the glycosylation.

Where in the cell are some proteins initially decorated with an oligosaccharide tree on asparagine residues?
A. ER

B. nucleus

C. Golgi apparatus

D. peroxisome

E. cytosol

A. ER

You have attached green fluorescent protein (GFP) to the carboxy terminal end of a secreted yeast protein. You express this protein in normal yeast cells, secretory mutant A cells, and secretory mutant B cells (see image).

Using fluorescent microscopy, you observe the expected results, with protein secretion in normal cells, ER accumulation in mutant A, and Golgi apparatus accumulation in mutant B. You also express the GFP-fusion protein in double-mutant yeast cells containing mutations in both the gene underlying mutant A and the gene underlying mutant B. What is the correct location and explanation for where the GFP-fusion protein will accumulate in these A and B double-mutant yeast cells?

A. The protein will accumulate in the ER because that is an earlier step in the secretory pathway.

B.  The protein will accumulate in the Golgi apparatus because that is a later step in the secretory pathway.

C.  The protein will accumulate in the Golgi apparatus because that is an earlier step in the secretory pathway.

D.  The protein will be secreted because the two different mutants will cancel each other out.

A. The protein will accumulate in the ER because that is an earlier step in the secretory pathway.

Which best describes a pathway that a protein might follow from synthesis to secretion?

A. ER → Golgi apparatus → secretory vesicle → plasma membrane

B. ER → Golgi apparatus → transport vesicle → endosome → secretory vesicle → plasma membrane

C. Cytosol → ER → secretory vesicle → plasma membrane

D. Cytosol → ER → Golgi apparatus → transport vesicle → endosome → secretory vesicle → plasma membrane

E. Cytosol → ER → transport vesicle → Golgi apparatus → transport vesicle → plasma membrane

E. Cytosol → ER → transport vesicle → Golgi apparatus → transport vesicle → plasma membrane

How are newly made lipids supplied to the plasma membrane?
A. via vesicles that bud from the ER and fuse with the plasma membrane

B. via secretory vesicles produced by the regulated exocytosis pathway

C. via enzymes that synthesize phospholipids, which are attached to the plasma membrane

D. via the constitutive pathway of exocytosis

E. via lysosomes

D. via the constitutive pathway of exocytosis

How are proteins destined to function in the ER retained there?

A. They are anchored to dolichol in the ER membrane.

B. They are embedded in the ER membrane by a transmembrane α helix.

C. They contain a C-terminal ER retention signal.

D. They bind to chaperones within the ER.
E. They retain their N-terminal ER signal sequence.

C. They contain a C-terminal ER retention signal.

Which of the following accurately describes a step in GTP-driven nuclear transport?
A.  Binding of Ran-GTP to the receptor releases the cargo protein.

B.  GTP-bound cargo interacts specifically with the protein fibrils of the pore.

C.  GTP hydrolysis powers a membrane-bound transporter protein.

D.  Ran-GDP escorts the nuclear receptor back to the cytosol.

A.  Binding of Ran-GTP to the receptor releases the cargo protein.