Chapter 11 Diagnostic Quiz

Which statement about transmembrane proteins is true?

A) They cross the membrane only once.

B) They are always inserted with the amino terminus on the lumenal side and the carboxyl terminus in the cytosol.

C) The signal sequences are always cleaved off.

D) They usually have one or more helices spanning the membrane bilayer.

D) They usually have one or more helices spanning the membrane bilayer.

Explanation: The transmembrane portions are usually helices of approximately 20-25 amino acids. Helices are especially stable in the nonpolar environment of the lipid bilayer.

The lumen of the ER is equivalent topologically to the

A) nucleoplasm

B) cytoplasm.

C) extracellular space.

D) cytoplasmic face of the plasma membrane.

C) extracellular space

Explanation: The lumen of the ER is topologically equivalent to the extracellular space, and hence the inner leaflet of the ER membrane is topologically equivalent to the cell surface.

The major site at which membrane lipids are synthesized is the

A) cytosolic side of the Golgi membrane
B) lumenal side of the ER membrane
C) cytosol
D) cytosolic side of the ER membrane

D) cytosolic side of the ER membrane

Explanation: Because lipids are hydrophobic in nature, they are synthesized in association with already existing membranes, and the synthetic enzymes are located in the cytosol

Which is not a destination for vesicles leaving the Golgi apparatus?

A) Mitochondria

B) The exterior of the cell

C) Lysosomes

D) The plasma membrane

A) Mitochondria

Explanation: Proteins destined for the mitochondria are transported via a mechanism that does not involve vesicular transport or the Golgi apparatus.

The trans-Golgi network is the

A) intermediate compartment between the ER and the Golgi.

B) part of the Golgi where fusion of vesicles from the ER occurs.

C) exit part of the Golgi where sorting of proteins to the lysosomes, plasma membrane, and cell exterior occurs.

D) network of vesicles that transport resident Golgi proteins between cisternae.

C) exit part of the Golgi where sorting of proteins to the lysosomes, plasma membrane, and cell exterior occurs.

Explanation: The trans-Golgi network is the last part of the Golgi through which proteins pass. It serves as a distribution center.

Which lipid(s) is(are) synthesized in the Golgi apparatus?

A) Ceramide

B) Glycolipids

C) Cholesterol

D) Phospholipids

B) Glycolipids

Explanation: Glycolipids are synthesized from ceramide in the Golgi.

Clathrin-coated vesicles are involved in

A) retrieval of ER resident proteins from the cis Golgi or the ER-Golgi intermediate compartment.

B) transport from the ER to the Golgi.

C) recycling of Golgi resident proteins during cisternal maturation.

D) uptake of extracellular molecules by endocytosis and the transport of molecules from the trans-Golgi network to the lysosomes.

D) uptake of extracellular molecules by endocytosis and the transport of molecules from the trans-Golgi network to the lysosomes.

Explanation: Clathrin-coated vesicles mediate both of these processes.

The major model of vesicle fusion holds that actual fusion of a vesicle with its target membrane is driven by the interaction of pairs of proteins called vesicle and target

A) SNAREs.

B) COPs.

C) Rab proteins.

D) tethers. 

A) SNAREs

Explanation: According to the hypothesis, SNAREs on vesicles bind to corresponding SNAREs on the target membrane and initiate fusion of the two.

Which would you expect to find at high concentrations in lysosomes?

A) Recycling endosomes

B) Proteins destined for secretion

C) Degradative enzymes

D) Glycosylation enzymes

C) Degradative enzymes

Explanation: The function of lysosomes is to degrade, at an acidic pH, substances taken up from outside the cell and components within the cell that have outlived their usefulness.

The process by which cells degrade their own components by enclosing them in ER membrane is

A) phagocytosis.

B) ER-mediated endocytosis.

C) autophagy.

D) pinocytosis.

C) autophagy

Explanation: Autophagy involves the degradation of the cell’s own components by enclosing them in an autophagosome formed from the ER membrane. This autophagosome then fuses with a lysosome for degradation and recycling.

A cell is exposed to conditions that result in an overload of misfolded proteins within the ER. What mechanism is most likely to be triggered in response to this situation?

A) Initiation of the unfolded protein response.

B) Increased synthesis of lipids in the smooth ER.

C) Augmentation of translocon activity.

D) Activation of the signal recognition particle (SRP).

A) Initiation of the unfolded protein response.

Explanation: The unfolded protein response is activated under stress conditions, such as when there is an accumulation of misfolded proteins in the ER.

In a lab experiment, the activity of flippases is inhibited in a certain cell line. What cellular process would be directly affected by this?

A) Cleavage of signal sequences in the ER.

B) Protein translocation into the ER.

C) Modification of proteins by N-linked glycosylation.

D) Lipid synthesis and distribution in membranes.

D) Lipid synthesis and distribution in membranes.

Explanation: Flippases are enzymes that help distribute lipids between membrane leaflets.

If a mutation occurred that disrupted the retrieval process of proteins from the Golgi to the ER, what would be the most likely consequence?

A) Proteins would not be synthesized.

B) ER-resident proteins would be mistakenly sent to the cell surface.

C) Misfolded proteins would accumulate in the Golgi.

D) Proteins destined for secretion would accumulate in the ER.

B) ER-resident proteins would be mistakenly sent to the cell surface.

Explanation: Without the retrieval process, proteins that are supposed to reside in the ER could be mistakenly sent forward to other destinations, such as the cell surface.

While both N-linked and O-linked glycosylation occur in the Golgi apparatus, what primarily differentiates the two processes?

A) The specific carbohydrate groups they add to proteins.

B) The location within the Golgi where they take place.

C) The type of amino acid residue they modify.

D) Their respective roles in protein sorting.

C) The type of amino acid residue they modify.

Explanation: N-linked glycosylation modifies the amide nitrogen of asparagine residues, while O-linked glycosylation occurs on the hydroxyl group of serine or threonine.

In a genetically modified cell line, proteins meant for the plasma membrane are instead secreted outside the cell. Which stage of protein sorting in the Golgi apparatus is most likely malfunctioning?

A) Protein modification in the medial-Golgi.

B) Protein reception at the cis-Golgi.

C) Protein sorting in the trans-Golgi network.

D) O-linked glycosylation.

C) Protein sorting in the trans-Golgi network.

Explanation: If proteins are being secreted instead of being sent to the plasma membrane, there’s a malfunction in the sorting mechanism of the trans-Golgi network.

A cell needs to transport specific molecules to the cell surface. Which process best describes how this is achieved?

A) Passive diffusion from the cell’s nucleus.

B) Formation of transport vesicles that fuse with the plasma membrane.

C) Osmosis through the cell membrane.

B) Formation of transport vesicles that fuse with the plasma membrane.

Explanation: This process accurately describes how specific molecules are delivered to the cell surface.

Which proteins play a critical role in the selection of molecules to be transported in vesicles?

A) Small GTP-binding proteins and adaptor proteins

B) Clathrin and dynamin

C) v-SNAREs and t-SNAREs

D) Rab proteins

A) Small GTP-binding proteins and adaptor proteins

Explanation: These complexes play a role in selecting specific molecules for vesicle transport.

If a scientist discovers a cell line where vesicles continually accumulate near but don’t fuse with their target membranes, which proteins might be malfunctioning?

A) Small GTP-binding proteins.

B) v-SNAREs and t-SNAREs.

C) Rab proteins.

D) Clathrin and dynamin.

B) v-SNAREs and t-SNAREs.

Explanation: These proteins are responsible for ensuring vesicles bind and fuse with target membranes.

How are lysosomes primarily formed?

A) From the smooth endoplasmic reticulum.

B) Directly from the trans-Golgi network.

C) By the fusion of early endosomes with vesicles from the Golgi.

D) As a result of cellular division and replication. 

C) By the fusion of early endosomes with vesicles from the Golgi.

Explanation: Lysosomes are formed when late endosomes fuse with vesicles carrying acid hydrolases from the Golgi.

If a mutation occurred in the signal peptidase enzyme, making it non-functional, how would protein processing in the endoplasmic reticulum be affected?

A) Polypeptide chains would remain attached to their signal sequences.

B) Proteins would not be correctly targeted to the ER.

C) Lipid synthesis would be significantly enhanced.

D) Protein translocation into the ER would be uninterrupted

A) Polypeptide chains would remain attached to their signal sequences.

Explanation: Signal peptidase cleaves the signal sequence, allowing the polypeptide to be released into the ER lumen.

A researcher disrupts the function of the cis-Golgi in a group of cells. Which of the following would most likely be affected first?

A) Reception of proteins from the endoplasmic reticulum.

B) Protein secretion to the extracellular environment.

C) Protein glycosylation in the medial-Golgi.

D) Sorting of proteins in the trans-Golgi network.

A) Reception of proteins from the endoplasmic reticulum.

Explanation: The cis-Golgi compartment is responsible for receiving proteins from the ER

In a situation where the enzyme responsible for N-linked glycosylation is inhibited, what would be the expected change in protein processing within the Golgi?

A) Proteins would bypass the Golgi without modification.

B) Proteins would accumulate unmodified N-linked glycosylation sites.

C) Proteins would be improperly folded.

D) Proteins would receive additional O-linked glycosylation to compensate.

B) Proteins would accumulate unmodified N-linked glycosylation sites

Explanation: With inhibited N-linked glycosylation, proteins would accumulate without these modifications.

If a researcher observes an unusual accumulation of glycolipids within a cell, and suspects a problem within a cellular organelle, which step in the Golgi’s function might be compromised?

A) Synthesis of membrane lipids.

B) Protein translocation into the ER.

C) Reception of proteins from the ER.

D) Phosphorylation on mannose residues.

A)  Synthesis of membrane lipids.

Explanation: Accumulation of glycolipids suggests a malfunction in their synthesis or further processing.

Which statement best describes the function of the trans-Golgi network?

A) Sorting proteins to their final destinations, like secretion, plasma membrane, or lysosomes.

B) Receiving proteins from the apical domain.

C) Synthesizing membrane lipids.

D) Initial glycosylation of proteins coming directly from the ER.

A) Sorting proteins to their final destinations, like secretion, plasma membrane, or lysosomes

Explanation: The trans-Golgi network sorts proteins for their final destinations.

Given the critical role vesicles play in cellular processes, why might it be advantageous for a cell to utilize vesicular transport for specific molecules rather than allowing free diffusion of these molecules in the cytoplasm?

A) To allow for larger molecules to move through the plasma membrane passively.

B) To increase the rate of diffusion of these molecules.

C) To save energy by avoiding active transport mechanisms.

D) To concentrate specific molecules in particular cellular locations.

D) To concentrate specific molecules in particular cellular locations.

Explanation: By isolating molecules within vesicles, the cell can direct their transport and release in specific locations, ensuring efficient and targeted delivery.

Consider a scenario where a defect results in the incorrect assembly of COPII coat proteins. What would be the most likely cellular outcome?

A) Impaired endocytosis from the plasma membrane.

B) Enhanced lysosomal enzyme transport.

C) Hindered vesicle formation from the ER to the Golgi.

D) Reduced vesicle formation from the Golgi to the ER.

C) Hindered vesicle formation from the ER to the Golgi.

Explanation: COPII proteins are critical for transporting vesicles from the ER to the Golgi

Analyzing the involvement of small GTP-binding proteins in vesicle formation, which process could be significantly disrupted if these proteins fail to hydrolyze GTP efficiently?

A) Initial tethering of vesicles to their target membranes.

B) Fusion of vesicles with target membranes.

C) Lysis of vesicles after delivering their content.

D) Selective recruitment of cargo proteins into vesicles.

D) Selective recruitment of cargo proteins into vesicles.

Explanation: The function of small GTP-binding proteins, especially their ability to hydrolyze GTP, is crucial for the selective recruitment of cargo.

Given that Gaucher disease is a lysosomal storage disorder, what would you infer about the enzymes associated with this condition?

A) They are rendered non-functional, leading to accumulation of undegraded substances.

B) They are overactive and degrade cellular components excessively.

C) They promote the transformation of lysosomes into peroxisomes.

D) They induce the fusion of lysosomes with the plasma membrane.

A) They are rendered non-functional, leading to accumulation of undegraded substances.

Explanation: Gaucher disease results from a deficiency in a specific enzyme, leading to substance accumulation.

Considering the relationship between endosomes and lysosomes, what would likely happen if the delivery of lysosomal acid hydrolases from the Golgi was disrupted?

A) Early endosomes would transform directly into lysosomes.

B) The endocytic vesicles would become acidic.

C) Autophagosomes would directly fuse with the plasma membrane.

D) Late endosomes would not mature into functional lysosomes.

D) Late endosomes would not mature into functional lysosomes.

Explanation: Without acid hydrolases, maturation to functional lysosomes is compromised.

Autophagy involves the degradation of the cell’s own components. Which scenario would most likely induce autophagy in cells?

A) Prolonged exposure to growth factors.

B) Cellular stress or nutrient starvation.

C) Exposure to external pathogens.

D) Abundant nutrient supply and optimal growth conditions.

B) Cellular stress or nutrient starvation.

Explanation: Cells induce autophagy to recycle components and provide energy during stress or starvation.