Cellular Organization part 2 test

1.

Which of the following is correct about microtubule organizing centers (MTOCs)?

A. They are rich in γ-tubulin ring complexes that nucleate microtubules.
B. They are composed mainly of actin and myosin.
C. They nucleate actin filaments at barbed ends.
D. They are absent in animal cells.

2.

A scientist mutated the KDEL sequence of a soluble ER-resident protein. What would be the fate of this protein?

A. It would still stay in ER
B. It would be secreted outside the cell
C. It would accumulate in nucleus
D. It would go to lysosomes

3.

Which of the following is NOT a feature of peroxisomes?

A. Contain catalase and urate oxidase
B. Involved in β-oxidation of very long-chain fatty acids
C. Have their own genome and ribosomes
D. Generate hydrogen peroxide during metabolism

4.

The inner membrane of mitochondria is rich in which unique phospholipid that stabilizes ETC complexes?

A. Sphingomyelin
B. Phosphatidylcholine
C. Cardiolipin
D. Phosphatidylserine

5.

Which of the following proteins directly powers vesicle transport along microtubules?

A. Dynein and kinesin
B. Dynamin and dynein
C. Myosin and kinesin
D. Rab and SNARE

6.

Which of the following is TRUE regarding nuclear pore complex (NPC)?

A. Only small ions (<40 kDa) can diffuse freely; larger molecules require active transport.
B. Nuclear import requires Ran-GTP in the cytoplasm.
C. Exportins bind to cargo in the nucleus in presence of Ran-GDP.
D. NPC is composed of actin filaments.

7.

Which one of the following cytoskeletal drugs correctly matches its action?

A. Nocodazole – stabilizes microtubules
B. Taxol – depolymerizes actin filaments
C. Latrunculin – sequesters actin monomers
D. Cytochalasin – enhances microtubule polymerization

8.

Brefeldin A treatment disrupts which process?

A. Translation in ER
B. Protein glycosylation in ER lumen
C. Transport from ER to Golgi
D. Protein degradation in lysosomes

9.

Which of the following organelles shows a dual genetic origin for its proteins (encoded by both organelle DNA and nuclear DNA)?

A. Peroxisome
B. Lysosome
C. Mitochondria
D. ER

10.

A protein destined for lysosome has a specific signal modification in the Golgi apparatus. What is that signal?

A. Ubiquitination of lysine residues
B. Addition of mannose-6-phosphate
C. Acetylation of N-terminal residues
D. Prenylation at C-terminal cysteine

11.

Signal peptide–containing proteins are synthesized:

A. In the nucleus
B. On free cytosolic ribosomes
C. On ER-bound ribosomes
D. Inside lysosomes

12.

In microtubules, dynamic instability is due to:

A. GTP cap hydrolysis
B. ATP hydrolysis on tubulin
C. GDP to GTP exchange on actin
D. Phosphorylation of MAPs

13.

The correct order of protein secretion pathway is:

A. Nucleus → Golgi → ER → Plasma membrane
B. ER → Golgi → Plasma membrane
C. ER → Lysosome → Golgi → Plasma membrane
D. Plasma membrane → ER → Golgi

14.

During apoptosis, which organelle releases cytochrome c?

A. ER
B. Mitochondria
C. Lysosome
D. Peroxisome

15.

Protein disulfide isomerase (PDI) is localized in which organelle?

A. Cytoplasm
B. Mitochondria
C. Endoplasmic reticulum
D. Lysosome

16.

Which of the following statements about mitochondria is TRUE?

A. Outer membrane contains ATP synthase.
B. Inner membrane is highly impermeable and forms cristae.
C. Mitochondria lack their own ribosomes.
D. Mitochondria are part of the endomembrane system.

17.

Which cytoskeletal element provides structural support to the nuclear envelope?

A. Actin filaments
B. Microtubules
C. Intermediate filaments (Lamins)
D. Septins

18.

Which protein is responsible for pinching off clathrin-coated vesicles during endocytosis?

A. Kinesin
B. Dynein
C. Dynamin
D. Myosin

19.

Which of the following is NOT considered a part of the endomembrane system?

A. Endoplasmic reticulum
B. Golgi apparatus
C. Peroxisomes
D. Lysosomes

20.

The nuclear localization signal (NLS) is generally composed of which type of amino acids?

A. Acidic residues (Asp, Glu)
B. Basic residues (Lys, Arg)
C. Hydrophobic residues (Leu, Ile)
D. Aromatic residues (Phe, Tyr)

21.

The following schematic shows the topology of a protein spanning the plasma membrane.

🟦 = extracellular domain
🟥 = transmembrane helix
🟩 = cytoplasmic domain

If the protein has a single N-terminal signal peptide which is cleaved off, what will be the orientation of the protein in the membrane?

A. N-terminus in cytosol, C-terminus extracellular
B. N-terminus extracellular, C-terminus cytosolic
C. Both termini in cytosol
D. Both termini extracellular

22.

Which cytoskeletal filament is most important for phagocytosis in macrophages?

A. Microtubules
B. Actin filaments
C. Intermediate filaments
D. Septins

23.

Nuclear import of proteins requires:

A. Nuclear localization signal and importin
B. Mannose-6-phosphate tag
C. KDEL sequence
D. TOM/TIM complexes

24.

Which of the following correctly describes microtubule dynamics?

A. Tubulin polymerization requires GTP hydrolysis
B. Tubulin dimers polymerize using GDP-bound tubulin
C. Dynamic instability is due to GTP cap loss
D. Microtubules grow from minus end in cells

25.

A yeast mutant lacks the gene encoding phosphotransferase that adds mannose-6-phosphate to lysosomal enzymes. What will be the consequence?

A. Lysosomal enzymes secreted outside the cell
B. Lysosomal enzymes accumulate in ER
C. Proteins degraded in proteasome
D. No effect on lysosomal targeting

26.

In mitochondria, most of the ATP is synthesized at which location?

A. Outer membrane
B. Intermembrane space
C. Inner membrane (cristae)
D. Matrix

27.

Dynein motor proteins in cilia and flagella function by:

A. Sliding of adjacent microtubule doublets using ATP hydrolysis
B. Polymerization of actin filaments
C. Hydrolysis of GTP on tubulin dimers
D. Breaking down ATP in the basal body

28.

Which of the following organelles shares a double membrane and has its own DNA and ribosomes?

A. Mitochondria and chloroplast
B. Lysosome and ER
C. Golgi and peroxisome
D. ER and vacuole

29.

During cell division, nuclear lamina disassembles at the onset of mitosis. This process is triggered by:

A. Dephosphorylation of lamins
B. Phosphorylation of lamins by CDK1
C. Acetylation of histones
D. Proteolysis of lamins

30.

Which of the following is NOT a component of the endomembrane system?

A. Endoplasmic reticulum
B. Golgi apparatus
C. Lysosomes
D. Mitochondria

31.

In eukaryotic cells, secretory proteins are synthesized and transported through different organelles. A mutation in the SRP (signal recognition particle) receptor would most likely block which step?

A. Transport of proteins from ER to Golgi
B. Binding of ribosome–nascent chain complex to ER membrane
C. Glycosylation of proteins in Golgi
D. Packaging of proteins into secretory vesicles

32.

A researcher investigated the nuclear lamina in mammalian cells. A mutation in lamins caused disassembly of the nuclear lamina even during interphase. Which of the following consequences are expected?

1. Abnormal nuclear shape.

2. Impaired chromatin organization.

3. Block in vesicle transport between ER and Golgi.

4. Premature aging syndromes (e.g., progeria).

Options:

A. 1 and 2 only
B. 1, 2, and 4 only
C. 1 and 3 only
D. 2 and 3 only

33.

A mutant yeast strain lacks functional Sec61 translocon complex. Which of the following cellular processes would be disrupted?

1. Co-translational translocation of secretory proteins into ER lumen.

2. Insertion of ER membrane proteins into lipid bilayer.

3. Glycosylation of proteins in Golgi.

4. Protein targeting to mitochondria.

Options:

A. 1 and 2 only
B. 1, 2, and 3 only
C. 2 and 4 only
D. 1 and 4 only

34.

Chloroplast and mitochondria share several common features, but also key differences. Which of the following statements are TRUE?

1. Both have circular DNA and prokaryotic-type ribosomes.

2. Both generate ATP by chemiosmosis.

3. Chloroplast proton gradient is across thylakoid membrane, while mitochondria use inner mitochondrial membrane.

4. In chloroplasts, protons accumulate inside the stroma.

Options:

A. 1, 2, and 3 only
B. 1 and 3 only
C. 1, 2, 3, and 4
D. 1 and 2 only

35.

In an experiment, fibroblast cells were treated with a drug that specifically inhibits dynein activity. Which of the following cellular processes would be most affected?

1. Retrograde transport of vesicles from the plasma membrane to Golgi.

2. Anterograde transport of vesicles from ER to Golgi.

3. Movement of lysosomes towards the nucleus.

4. Separation of chromosomes during anaphase.

Options:

A. 1, 3, and 4 only
B. 1 and 3 only
C. 2 and 4 only
D. 1, 2, and 3 only

36.

A scientist engineered a GFP-tagged membrane protein and expressed it in mammalian cells. Under confocal microscopy, the protein was found localized in the endoplasmic reticulum (ER) but not in the plasma membrane.

Possible reasons could be:

1. The protein lacks a signal peptide.

2. The protein contains a KDEL sequence at its C-terminal.

3. The protein has a hydrophobic transmembrane domain.

4. The protein contains a nuclear localization signal (NLS).

Which options are correct?

A. 2 and 3 only
B. 1 and 4 only
C. 2 only
D. 2 and 4 only

37.

A mutation in actin-binding proteins of epithelial cells leads to disorganization of microvilli. Which consequences would most likely occur?

1. Reduced surface area for absorption.

2. Impaired anchoring of terminal web to plasma membrane.

3. Defective phagocytosis of pathogens.

4. Increased mitochondrial ATP production.

Which of the following options is correct?

A. 1, 2, and 3 only
B. 2 and 4 only
C. 1 and 3 only
D. 1, 2, 3, and 4

38.

In eukaryotic cells, nuclear import and export are tightly regulated. Consider the following statements:

1. Proteins destined for the nucleus contain nuclear localization signals (NLS) rich in lysine and arginine.

2. Nuclear export signals (NES) are often rich in leucine residues.

3. Importins mediate transport of proteins into the nucleus, while exportins mediate transport out.

4. Both import and export require energy in the form of GTP, hydrolyzed by Ran GTPase.

Which of the following combinations is correct?

A. 1, 2, and 3 only
B. 2 and 4 only
C. 1, 2, 3, and 4
D. 1 and 4 only

39.

A researcher isolated mitochondria from liver cells and measured oxygen consumption in the presence of substrates and ADP. The following results were obtained:

• Normal mitochondria: Increased O₂ consumption after ADP addition.

• Mitochondria treated with uncoupler (e.g., DNP): High O₂ consumption even without ADP.

• Mitochondria treated with oligomycin: No increase in O₂ consumption after ADP.

Which interpretation is correct?

A. Uncouplers allow electron transport without ATP synthesis, while oligomycin blocks ATP synthase.
B. Oligomycin increases ATP synthesis, while uncouplers block electron transport.
C. Both uncouplers and oligomycin inhibit electron transport.
D. Uncouplers inhibit ATP synthase and oligomycin stimulates oxidative phosphorylation.

40.

During protein targeting, a mutant yeast strain was discovered where lysosomal enzymes were secreted outside the cell instead of being delivered to lysosomes. Genetic analysis showed a defect in a Golgi enzyme responsible for a specific modification.

Which of the following defects explains the observation?

A. Failure to attach mannose-6-phosphate to lysosomal enzymes.
B. Failure to attach ubiquitin to lysosomal enzymes.
C. Improper glycosylation of plasma membrane proteins.
D. Absence of SRP (Signal Recognition Particle) during protein synthesis.

41.

In an experiment, a researcher treated mammalian cells with a drug that selectively disrupts microtubules but does not affect actin or intermediate filaments. After treatment, the researcher observed the following:

1. The Golgi complex was fragmented and dispersed in the cytoplasm.

2. The movement of secretory vesicles towards the plasma membrane was blocked.

3. The shape of the nucleus remained intact.

4. Phagocytosis of bacteria was unaffected.

Which of the following best explains these observations?

A. Microtubules are essential for maintaining Golgi organization and long-distance vesicle transport.
B. Intermediate filaments control Golgi structure and vesicle transport.
C. Actin filaments regulate Golgi and vesicle transport, hence phagocytosis was affected.
D. Golgi fragmentation is independent of cytoskeletal components.