Question 1

What is the name sometimes given to a single Golgi stack in a plant cell?
A)endosome
B)dictyosome
C)flagosome
D)ribosome
E)plantosome

Accepted Answer

A single Golgi stack in a plant cell is sometimes referred to as a dictyosome.

Question 2

How does GT recognize incompletely folded or misfolded proteins that have been recently synthesized?
A)Such proteins display exposed hydrophilic residues that are absent from properly folded proteins.
B)Five histidine residues are exposed on the protein's surface when it is improperly folded.
C)Such proteins display exposed hydrophobic residues that are absent from properly folded proteins.
D)Six arginine residues are exposed on the protein's surface when it is improperly folded.
E)Such proteins display numerous carboxyl groups on their surfaces,which decreases their solubility.

Accepted Answer

Incompletely folded or misfolded proteins are recognized by GT based on the exposure of hydrophobic residues on their surfaces, which are normally buried in the interior of properly folded proteins. This is because GT contains chaperones such as Hsp70 and Hsp90 that have hydrophobic binding sites that can interact with the exposed hydrophobic patches on the misfolded proteins, leading to their refolding or degradation. Exposed hydrophilic residues (choice A) and carboxyl groups (choice E) are not specific features of misfolded proteins and do not play a significant role in their recognition by GT. Likewise, the exposure of five histidine residues (choice B) or six arginine residues (choice D) on the protein's surface is not a well-established mechanism for GT recognition of misfolded proteins.

Question 3

The movement of vesicular-tubular carriers (VTCs)farther away from the ER and toward the Golgi complex occurs along tracks composed of what material?
A)RNA
B)DNA
C)microtubules
D)microfilaments
E)intermediate filaments

Accepted Answer

The movement of vesicular-tubular carriers (VTCs) along tracks occurs along microtubules which serve as the "railway" for intracellular transport in the cell.

Question 4

CDG1b results from a deficiency in what enzyme?
A)phosphomannose phosphatase
B)phosphotungstate isomerase
C)phosphomannose isomerase
D)phosphatase
E)phosphoenol pyruvate carboxylase

Accepted Answer

CDG1b is caused by a deficiency in the enzyme phosphomannose isomerase, which leads to a deficiency in the synthesis of certain glycoproteins and glycolipids.

Question 5

Where are misfolded secretory proteins eventually destroyed?
A)in the RER
B)in the SER
C)in the Golgi complex
D)in the cytosol (cytoplasm)
E)in the nucleus

Accepted Answer

Misfolded secretory proteins are eventually destroyed in the cytosol by the proteasome, which is responsible for degrading misfolded or damaged proteins.

Question 6

What happens if the UPR is unsuccessful in relieving the stressful conditions in the cell?
A)The cell grows.
B)The cell divides.
C)The cell-death pathway is triggered and the cell is destroyed.
D)The cell shrinks.
E)The cell's temperature is raised.

Accepted Answer

If the UPR is not successful in resolving the stress in the cell, the cell-death pathway is triggered through apoptosis, which is a programmed cell death process that removes damaged or dysfunctional cells from the body.

Question 7

How do misfolded proteins get to the cytoplasm to be destroyed?
A)They diffuse freely through the lipid bilayer.
B)A process called reverse transcription takes proteins back through the translocons they passed through on their way into the ER lumen.
C)They diffuse through gap junctions.
D)An enzyme flips them through the hydrophobic part of the lipid bilayer.
E)Proteins are transported back to the cytosol through the translocon that brought them into the ER lumen or through a separate dislocation channel of uncertain identity.

Accepted Answer

Misfolded proteins are transported back to the cytosol through the same translocon that brought them into the ER lumen or through a separate dislocation channel of uncertain identity. This process is known as retrotranslocation. Once in the cytosol, the misfolded proteins either undergo degradation by the proteasome or are refolded by chaperone proteins.

Question 8

The accumulation of misfolded proteins in the ER is a potentially lethal situation and thus causes the triggering of what process?
A)the unfolded protein response (UPR)
B)the posttranscriptional response
C)the polysomal response
D)the proteasomal response
E)the intracellular protein response

Accepted Answer

The accumulation of misfolded proteins in the ER leads to the triggering of the unfolded protein response (UPR). This is a cellular process designed to reduce the load of protein folding in the ER and restore homeostasis. Failure of the UPR can lead to cell death. Therefore, the UPR is a critical response mechanism for dealing with misfolded proteins in the ER.

Question 9

The oligosaccharide block that is added to secretory proteins after they enter the ER lumen goes through a number of modifications after its attachment.What is the first modification that occurs?
A)addition of more sugars
B)addition of glucose
C)trimming of some sugars from the oligosaccharide block
D)chemical modification of the sugars on the oligosaccharide chain
E)both addition of more sugars and addition of glucose

Accepted Answer

The first modification that occurs to the oligosaccharide block is trimming of some sugars from the block. This is done by enzymes in the ER and is important for proper folding of the protein.

Question 10

What happens to a newly synthesized glycoprotein after the binding of calnexin or calreticulin to help the protein correctly complete its folding?
A)When the glycoprotein's folding is correctly completed,the remaining glucose on its oligosaccharide chain is eventually reduced and the glycoprotein is released from the chaperone.
B)The oligosaccharide chain is totally degraded.
C)Nothing happens.
D)When the glycoprotein's folding is correctly completed,the remaining glucose on its oligosaccharide chain is eventually removed enzymatically and the glycoprotein is released from the chaperone.
E)The oligosaccharide chain is totally degraded

Accepted Answer

After the binding of calnexin or calreticulin to a newly synthesized glycoprotein, the protein is helped to correctly complete its folding. Once the glycoprotein's folding is correctly completed, the remaining glucose on its oligosaccharide chain is eventually removed enzymatically (by the ER glucosidases) and the glycoprotein is released from the chaperone. Therefore, the best choice is answer D.

Question 11

What do studies suggest governs the "decision" to destroy a defective protein that has been unable to fold correctly and has been in the ER for an extended period of time?
A)a fast-acting ER enzyme that trims a mannose residue from an exposed end of the oligosaccharide of a protein
B)a slow-acting ER enzyme that trims a mannose residue from an exposed end of the oligosaccharide of a protein
C)a fast-acting cytoplasmic enzyme that trims a mannose residue from an exposed end of the oligosaccharide of a protein
D)a slow-acting nuclear enzyme that trims a mannose residue from an exposed end of the oligosaccharide of a protein
E)a slow-acting cytoplasmic enzyme that trims a mannose residue from an exposed end of the oligosaccharide of a protein

Accepted Answer

Studies suggest that a slow-acting ER enzyme trims a mannose residue from an exposed end of the oligosaccharide of a protein, marking it for destruction by the proteasome. This process is known as ER-associated degradation (ERAD). A fast-acting ER enzyme trims a glucose residue from an exposed end of the oligosaccharide of a protein, allowing it to fold correctly and continue along the secretory pathway.

Question 12

What is responsible for degrading misfolded proteins in the cytoplasm?
A)polysomes
B)polyribosomes
C)peroxisomes
D)proteasomes
E)spliceosome

Accepted Answer

Proteasomes are responsible for degrading misfolded proteins in the cytoplasm. Polysomes and polyribosomes are complexes of ribosomes that are involved in protein synthesis. Peroxisomes are involved in lipid metabolism and detoxification. The spliceosome is responsible for removing introns from mRNA molecules during post-transcriptional processing.

Question 13

What is the effect of CDG1b on cell physiology and what is the treatment that has shown some promise of being effective?
A)Mannose is unavailable for incorporation into oligosaccharides;oral supplements of mannose are the treatment.
B)Mannose is available for incorporation into oligosaccharides;oral supplements of mannose are the treatment.
C)Mannose is unavailable for incorporation into oligosaccharides;a diet free of mannose is the treatment.
D)Mannose is available for incorporation into oligosaccharides;a diet free of mannose is the treatment.
E)Fructose is unavailable for incorporation into oligosaccharides;oral supplements of fructose are the treatment.

Accepted Answer

The answer of What is the effect of CDG1b on...

Question 14

What is responsible for adding sugars to dolichol phosphate?
A)membrane-bound glycosyltransferases
B)membrane-bound oligosaccharyltransferase
C)membrane-bound gangliosidase
D)glycosylsynthetase
E)peptidyltransferase

Accepted Answer

Membrane-bound glycosyltransferases are responsible for adding sugars to dolichol phosphate in the process of N-linked glycosylation. Oligosaccharyltransferase transfers the whole oligosaccharide to the protein, while gangliosidase is responsible for breaking down gangliosides. Glycosylsynthetase is not a known enzyme, and peptidyltransferase catalyzes the formation of peptide bonds during protein synthesis.

Question 15

TB 8.066 The ER reportedly contains sensors that monitor the concentration of unfolded or misfolded proteins in the lumen.One proposal suggests that the sensors are normally kept in an inactive state by ______,particularly ______.
A)molecular chaperones,ribosomes
B)proteasomes,BiP
C)molecular chaperones,BiP
D)enzymes,ER
E)molecular chaperones,Rubisco

Accepted Answer

The sentence indicates that the sensors are kept inactive by something, and the options include molecular chaperones, proteasomes, enzymes or Rubisco. However, option C is the only one that provides a plausible answer because BiP is a molecular chaperone that is known to interact with unfolded or misfolded proteins in the endoplasmic reticulum lumen. Therefore, option C is the best choice.

Question 16

What enzyme transfers a block of sugars to asparagine residues of a polypeptide as it enters the RER?
A)glycosyltransferase
B)acid phosphatase
C)oligosaccharyltransferase
D)cellulose
E)glycolase

Accepted Answer

Oligosaccharyltransferase is the enzyme responsible for transferring a block of sugars to asparagine residues of a polypeptide as it enters the endoplasmic reticulum (ER). This process is known as N-linked glycosylation.

Question 17

What happens if misfolded proteins are generated in the ER at a faster rate than they can be exported to the cytoplasm?
A)They are degraded in the ER.
B)They are inserted into the ER membrane.
C)They are resynthesized in the ER.
D)They accumulate in the ER.
E)They accumulate in the Golgi complex.

Accepted Answer

If misfolded proteins are generated in the ER at a faster rate than they can be exported to the cytoplasm, they will accumulate in the ER. This can lead to ER stress, which triggers a pathway called the unfolded protein response (UPR). The UPR tries to restore normal function to the ER by increasing the folding capacity and reducing the influx of new proteins. If the UPR is unable to restore ER homeostasis, cell death may occur.

Question 18

To what residue of a polypeptide are N-linked oligosaccharide chains attached as that poypeptide enters the RER lumen through the translocon?
A)arginine
B)asparagine
C)serine
D)threonine
E)ninhydrin

Accepted Answer

N-linked oligosaccharide chains are attached to asparagine residues in the polypeptide as it enters the RER lumen through the translocon. This occurs via an enzymatic process called N-linked glycosylation.

Question 19

What does the conformation-sensing enzyme GT do if it binds to a misfolded or incompletely folded glycoprotein?
A)It degrades the oligosaccharide chain.
B)It adds a single mannose back to one of the glucose residues at the exposed end of the recently trimmed oligosaccharide.
C)It adds a single glucose back to one of the mannose residues at the exposed end of the recently trimmed oligosaccharide.
D)It degrades the protein.
E)It refolds the protein on its own.

Accepted Answer

The conformation-sensing enzyme GT (glucosyltransferase) adds a single glucose back to one of the mannose residues at the exposed end of the recently trimmed oligosaccharide, allowing the glycoprotein to re-enter the folding cycle.

Question 20

Why does the cell use proteasomes to destroy misfolded proteins?
A)Destruction of misfolded proteins assures that aberrant proteins are not sent to other parts of the cell.
B)These proteins can be degraded into components that can be used to make polynucleotides.
C)These proteins are degraded into components that can be used to make polysaccharides.
D)These proteins are degraded into components that are used to make lipids.
E)Destruction of misfolded proteins prevents the dissolution of the plasma membrane.

Accepted Answer

Misfolded proteins can have toxic effects on the cell and can potentially disrupt normal cellular functions. By using proteasomes to destroy misfolded proteins, the cell ensures that these aberrant proteins are not sent to other parts of the cell where they could cause harm. This helps to maintain the overall health and integrity of the cell.

Quiz 8: Cytoplasmic Membrane Systems: Structure, Function, and Membrane Trafficking

What is the name sometimes given to a single Golgi stack in a plant cell?

How does GT recognize incompletely folded or misfolded proteins that have been recently synthesized?

The movement of vesicular-tubular carriers (VTCs) farther away from the ER and toward the Golgi complex occurs along tracks composed of what material?

CDG1b results from a deficiency in what enzyme?

Where are misfolded secretory proteins eventually destroyed?

What happens if the UPR is unsuccessful in relieving the stressful conditions in the cell?

How do misfolded proteins get to the cytoplasm to be destroyed?

The accumulation of misfolded proteins in the ER is a potentially lethal situation and thus causes the triggering of what process?

The oligosaccharide block that is added to secretory proteins after they enter the ER lumen goes through a number of modifications after its attachment.What is the first modification that occurs?

What happens to a newly synthesized glycoprotein after the binding of calnexin or calreticulin to help the protein correctly complete its folding?

What do studies suggest governs the "decision" to destroy a defective protein that has been unable to fold correctly and has been in the ER for an extended period of time?

What is responsible for degrading misfolded proteins in the cytoplasm?

What is the effect of CDG1b on cell physiology and what is the treatment that has shown some promise of being effective?

What is responsible for adding sugars to dolichol phosphate?

TB 8.066 The ER reportedly contains sensors that monitor the concentration of unfolded or misfolded proteins in the lumen.One proposal suggests that the sensors are normally kept in an inactive state by ,particularly .

What enzyme transfers a block of sugars to asparagine residues of a polypeptide as it enters the RER?

What happens if misfolded proteins are generated in the ER at a faster rate than they can be exported to the cytoplasm?

To what residue of a polypeptide are N-linked oligosaccharide chains attached as that poypeptide enters the RER lumen through the translocon?

What does the conformation-sensing enzyme GT do if it binds to a misfolded or incompletely folded glycoprotein?

Why does the cell use proteasomes to destroy misfolded proteins?