Cellular Organization MCQ Quiz - Objective Question with Answer for Cellular Organization - Download Free PDF

The correct answer is A and B only

Explanation:

• Post-translational modifications (PTMs) are chemical changes to proteins that occur after translation. These modifications play a crucial role in regulating protein function, localization, stability, and interactions.
• Phosphorylation (A):
  • Phosphorylation is the addition of a phosphate group to an amino acid residue, typically catalyzed by kinases.
  • The most commonly phosphorylated amino acids are serine, threonine, and tyrosine. However, histidine can also be phosphorylated, though it is less common and often overlooked in studies.
• Ubiquitination (B):
  • Ubiquitination involves the attachment of ubiquitin, a small protein, to lysine residues on target proteins. This modification regulates protein degradation, signaling, and trafficking.
  • Although lysine is the predominant target for ubiquitination, N-terminal methionine can also be modified under specific circumstances.
• O-linked glycosylation (C):
  • O-linked glycosylation is the attachment of sugar molecules to the hydroxyl group of serine or threonine residues.
  • The table incorrectly lists "Asparagine" as the target residue for O-linked glycosylation. Asparagine is involved in N-linked glycosylation, not O-linked glycosylation.
  • Thus, the match for "O-linked glycosylation" is incorrect.
• Hydroxylation (D):
  • Hydroxylation is the addition of a hydroxyl group (-OH) to amino acid residues, typically catalyzed by hydroxylases. It is commonly seen in proline and lysine residues, particularly in collagen proteins.
  • The table incorrectly lists "Cysteine" as a residue subject to hydroxylation. Cysteine is not typically hydroxylated..

The correct answer is B and C

Concept:

• Pancreatic duct cells play a crucial role in secreting bicarbonate-rich fluid into the pancreatic ducts, which helps neutralize acidic chyme from the stomach and provides an optimal pH for digestive enzyme activity.
• Ion transport proteins located on the basolateral and apical membranes of these cells facilitate the movement of ions, such as bicarbonate, chloride, potassium, and sodium, across the cell membrane.
• The basolateral membrane is the side of the cell facing the blood vessels, while the apical membrane faces the duct lumen.

Explanation:

• Sodium-bicarbonate cotransporter (NBC):
  • Located on the basolateral membrane of pancreatic duct cells.
  • Plays a key role in importing bicarbonate ions (HCO₃-) from the bloodstream into the cell, which is later secreted into the duct lumen.
  • Couples the transport of sodium ions (Na⁺) and bicarbonate ions to maintain ionic balance during bicarbonate secretion.
• K⁺ Channel:
  • Also located on the basolateral membrane of pancreatic duct cells.
  • Facilitates the efflux of potassium ions (K⁺) to maintain intracellular ionic balance and membrane potential during active ion transport.

Other Options

• The cystic fibrosis transmembrane conductance regulator (CFTR) is located on the apical membrane, not the basolateral membrane. CFTR primarily facilitates chloride ion (Cl-) secretion into the duct lumen and bicarbonate ion transport via secondary mechanisms.
• The chloride-bicarbonate exchanger (Cl-/HCO₃- exchanger) is located on the apical membrane, not the basolateral membrane. This exchanger is responsible for secreting bicarbonate ions into the duct lumen in exchange for chloride ions.

Fig: Ion transport model for a pancreatic duct cell expressing various H⁺ /HCO₃− transporters and ion channels (Cl⁻ and K⁺ ) necessary for vectorial transport (secretion) of NaHCO₃ into the pancreatic duct lumen. (Source)

The correct answer is A and B

Concept:

• The plasma membrane is composed of a bilayer of lipids, and the two monolayers have an asymmetric distribution of lipid molecules.
• This asymmetry is functionally important, especially in processes like membrane trafficking, apoptosis, and intracellular signaling.
• Certain phospholipids are restricted to the cytosolic face of the plasma membrane and play essential roles in cell signaling.
• Phosphatidylserine (A) and phosphatidylinositol 4-phosphate (B) are such lipids that are localized to the cytosolic face and involved in signaling pathways.

Explanation:

• Phosphatidylserine (A):
  • Primarily located on the cytosolic side of the plasma membrane.
  • Plays a critical role in cell signaling, including pathways related to apoptosis (programmed cell death).
  • Its translocation to the extracellular side serves as a signal for phagocytic cells to engulf apoptotic cells.
• Phosphatidylinositol 4-phosphate (B):
  • Found on the cytosolic leaflet of the plasma membrane.
  • Serves as a precursor for the synthesis of phosphatidylinositol 4,5-bisphosphate (PIP2), a key lipid in signaling pathways.
  • Involved in intracellular signaling cascades, such as those regulated by G-proteins and receptor tyrosine kinases.

Fig: Distribution of common membrane lipids between the inner and outer leaflets of erythrocytes.

Other Options:

• Phosphatidylcholine (C) and sphingomyelin (D) are primarily located on the extracellular face of the plasma membrane. They are structural components of the membrane and are not primarily involved in intracellular signaling.

The correct answer is A, B, and D

Concept:

• Endocytosis is a cellular process through which cells internalize molecules, such as nutrients and signaling factors, from their external environment by engulfing them in vesicles.
• Vesicular transport is a critical mechanism for sorting, delivering, and recycling molecules within cells. Specific pathways, such as clathrin-mediated endocytosis and the multivesicular body pathway, regulate these processes.
• Early endosomes, late endosomes, and lysosomes are key compartments involved in endocytosis and vesicular trafficking.

Explanation:

Statement A: "Clathrin-mediated endocytosis requires the recruitment of adaptors to the cytosolic face of the plasma membrane."

• This statement is correct.
• Clathrin-mediated endocytosis is a well-characterized pathway where clathrin proteins form a coat around vesicles, aiding in their formation.
• Adaptor proteins, such as AP2, are recruited to the cytosolic face of the plasma membrane. These adaptors bind to specific cargo and clathrin, facilitating vesicle formation.

Statement B: "The low-pH environment of early endosomes leads to the dissociation of cargo from its receptor, allowing for the recycling of receptors to the plasma membrane."

• This statement is correct.
• Early endosomes are mildly acidic (pH ~6.0), which causes a conformational change in receptor-cargo complexes.
• This acidification leads to cargo dissociation from its receptor. The cargo is often sorted for degradation or further trafficking, while receptors are recycled back to the plasma membrane for reuse.

Statement C: "The late endosomes, which mature into the lysosomes, are directly involved in the recycling of synaptic vesicle proteins in neurons."

• This statement is incorrect.
• Late endosomes are primarily involved in sorting cargo for degradation in lysosomes. They mature into lysosomes, which are specialized organelles for degradation.
• Synaptic vesicle protein recycling in neurons typically occurs via specialized endocytic pathways at the synapse, not through late endosomes or lysosomes.

Statement D: "The multivesicular body pathway involves the formation of intraluminal vesicles, which sort cargo for degradation in the lysosomes."

• This statement is correct.
• Multivesicular bodies (MVBs) are intermediate endosomal compartments that contain intraluminal vesicles (ILVs).
• ILVs sort and sequester specific cargo, such as ubiquitinated membrane proteins, for eventual degradation in lysosomes.
• This pathway is crucial for downregulating receptor signaling and degrading unwanted proteins.

The correct answer is Protein synthesis will begin but terminate prematurely, leading to shorter products.

Concept:

• Protein translation is a fundamental biological process where ribosomes synthesize proteins using mRNA templates. In eukaryotes, secretory proteins are specifically targeted to the endoplasmic reticulum (ER) for processing and secretion.
• Secretory proteins contain a signal sequence at their N-terminal, which directs them to the ER during synthesis. This process requires the signal recognition particle (SRP), SRP receptor, and the intact ER membrane for successful targeting and incorporation.
• Triton X-100 is a detergent that disrupts lipid bilayers, effectively destroying the functional structure of the ER membrane.

Explanation:

• When mRNA encoding a secretory protein is translated in a cell-free system, the process begins as usual, producing a nascent polypeptide chain.
• If a signal recognition particle (SRP) is present, it binds to the signal sequence of the nascent polypeptide, pausing translation temporarily.
• The paused ribosome-SRP complex requires an intact ER membrane with SRP receptors to resume translation and translocate the growing polypeptide chain into the ER lumen.
• In the scenario described, the ER has been treated with Triton X-100, which disrupts the membrane structure and functionality, rendering the ER incapable of supporting protein translocation.
• As a result, the SRP-bound ribosome cannot interact with the ER membrane, and translation cannot proceed beyond the initial stages. This leads to premature termination of protein synthesis, producing shorter products.

Other Options:

• The protein will be fully synthesized and incorporated into ER: This is incorrect because the ER membrane has been disrupted by Triton X-100. Without an intact ER, the ribosome-SRP complex cannot dock onto the ER, and translocation into the ER lumen is impossible.
• The protein will be fully synthesized, and its signal sequence will be removed without being incorporated into the ER: This is incorrect because the signal sequence is cleaved by signal peptidase only during translocation into the ER. With the ER membrane destroyed, translocation and subsequent signal sequence removal cannot occur.
• The protein will be fully synthesized but not incorporated into ER: This is incorrect because the presence of SRP interrupts translation until the ribosome docks onto the ER membrane. Without an intact ER, translation cannot proceed to completion, and the protein remains incomplete.

Concept:

• Chromatin condensation is a process by which chromatin gets densely packaged and reduced in volume for the broader purpose of gene regulation.
• Subsets of chromatins are:
  1. Heterochromatin - transcriptionally inactive part due to dense chromatin condensation.
  2. Euchromatin - transcriptionally active part due to comparatively loose chromatin condensation or presence of expanded DNA regions for transcription.

Explanation:

HP1 - 

• HP1 is a family of non-histone chromosomal proteins found in mammals.
• HP1 has three paralogs: HP1alpha, HP1 beta and HP1 gamma.
• HP1 belongs to the heterochromatin protein 1 family, which binds to methylated histone H3 at the lysine 9 position and represses DNA transcription of the region.

SIR Complex- 

• SIR (silent information regulator) proteins are nuclear proteins found in budding yeast (Saccharomyces cerevisiae).
• These proteins form specialized chromatin structures that resemble heterochromatin of higher eukaryotes.
• SIR-3 is known to be the primary structural component of SIR proteins of heterochromatin condensation.
• SIR 2-4 complex helps in the recruitment of other SIR proteins.

Su(var) - 

• The role of Su(var) heterochromatin protein is seen in Drosophila only.
• It controls position effect variegation in Drosophila by methylation at H3-K9 position.

Hence, the correct option is option 2.

The correct answer is Cdk2/Cyclin E

Concept:

• Cell cycle is a highly regulated and ordered series of events. The engines that derive the progression from one step of the cell cycle to the next are cyclin-CDK complexes.
• These complexes are composed of two subunits- cyclin and cyclin-dependent protein kinase. Cyclin is a regulatory protein whereas CDK is a catalytic protein and acts as serine/threonine protein kinase.
• Cyclins are so named as they undergo a cycle of synthesis and degradation in each cycle.   
• Humans contain four cyclins- G1 cyclins, G1/S cyclins, S cyclins, and M cyclins.

Explanation:

• Cyclin-CDK complexes trigger the transition from G1 to the S phase and from G2 to the M phase by phosphorylating a distinct set of substrates.
• According to the classical model of cell cycle control, D cyclins and CDK4/CDK6 regulate events in the early G1 phase. Cyclin E-CDK2 regulates the completion of the S-phase.
• The transition from G2 to M is driven by sequential activity of cyclin A-CDK1 and cyclin B-CDK1 complexes.

So, the correct answer is Option 2.

Concept:

• Transmembrane proteins are characterized by having transmembrane-spanning segments.
• They contain a stretch of 21 to 26 hydrophobic amino acid residues coiled into an alpha-helix that is believed to facilitate the spanning of a lipid bilayer.
• In a few membrane proteins, transmembrane portions comprise beta-barrel made up of antiparallel beta strands.

Explanation:

• Membrane proteins are covalently bound to lipids molecules and are called lipid-linked or lipid-anchored proteins.
• They form covalent attachments with three classes of lipids- compounds formed from isoprene units such as farnesyl and geranylgeranyl residues, fatty acids such as myristic acid and palmitic acid, and glycosylated phospholipid.
• Proteins that are covalently attached with isoprenoid compounds such as farnesyl (15-carbon compound) and geranylgeranyl (20-carbon compound) are termed prenylated proteins. In these proteins, isoprenoid compounds are covalently linked to a cysteine residue at C-terminal via thioether linkage.
• Proteins covalently attached with fatty acids such as palmitic acid and myristic acid are termed fatty acylated proteins. Myristic acid is a 14-carbon molecule that is attached to a protein through an amide linkage to the alpha-amino group of an N-terminus Glycine residue (myristoylation).
• Palmitic acid is attached to cysteine residue close to N or C-terminus via amide linkage (palmitoylation).
• A glycophosphatidylinositol molecule (GPI) attaches at the C terminal amino acid via an amide linkage.

So, the correct answer is option 1. 

The correct answer is "synthesis in the cytosol, import by TOM complex and insertion from the inter-mitochondrial membrane space".

Explanation-

Porins are present in the outer mitochondrial membrane, and their synthesis typically occurs in the cytosol. The TOM complex, located in the outer mitochondrial membrane, facilitates the import of precursor proteins into the mitochondria. After entering the inter-membrane space of mitochondria, the precursor proteins are translocated across the outer mitochondrial membrane.

Synthesis in the Cytosol: Like most other proteins in the cell, mitochondrial porins, also known as Voltage Dependent Anion Channels (VDACs), are synthesized in the cytosol from mRNA translated by free ribosomes—not by the endoplasmic reticulum (ER) or by mitochondrial ribosomes.

Import by TOM Complex: The Translocase of the Outer Membrane (TOM) complex facilitates the transport of these porins from the cytosol across the outer mitochondrial membrane. The TOM complex forms a general entry gate for almost all mitochondrial precursor proteins that are synthesized in the cytosol.

Insertion in the Membrane & Folding: Once in the intermembrane space (the space between the inner and outer mitochondrial membranes), the proteins have to be inserted into the outer mitochondrial membrane. This task is accomplished by the SAM (sorting and assembly machinery) complex. The SAM complex inserts the precursor proteins into the outer membrane and assists in their folding and assembly to form functional porin channels.

The TIM (translocase of the inner mitochondrial membrane) complex is not involved in this process. This complex targets proteins to the inner mitochondrial membrane, the intermembrane space, or the matrix of mitochondria but does not affect proteins destined for the outer mitochondrial membrane like the porins.

Concept:

• Transporters are membrane proteins or carrier proteins that span the membrane and assist in the movement of ions, molecules, small peptides, and certain macromolecules.
• Transport across the membrane can occur via simple diffusion, facilitated diffusion, osmosis, or active transport.
• Two distinct translocation complexes that mediate translocation are situated in the outer and inner mitochondrial membrane.

Important Points

Sec 61 - 

• Nearly every newly synthesized polypeptide translocation to the endoplasmic reticulum occurs via a translocon protein.
• This protein is present in the ER membrane of all nucleated cells.
• Translocon contains sec 61 channel protein along with other protein complexes.
• Sec 61 transports proteins to the endoplasmic reticulum in eukaryotes and out of the cell in prokaryotes.

TOM - 

• TOM complex (translocase of outer membrane) consists of receptor proteins (Tom20, Tom22, and Tom70), channel-forming proteins (Tom40), and three small Tom proteins (Tom5, Tom6, and Tom7).
• TOM 20 is a mitochondrial import receptor.
• It is the translocase in the outer mitochondrial membrane.

Importin - 

• Importin is a type of karyopherin (protein transporter for transporting molecules between cytoplasm and nucleus).
• It is found in eukaryotic cells. Importin beta specifically transports proteins inside the nucleus.
• Importin beta must associate with the nuclear pore complexes to deliver cargo protein into the nucleus.
• This is accomplished by binding with the nuclear pore complex.
• It transports proteins bigger than 50 kDa across the nuclear membrane.

Tim 44 - 

• Tim 44 (translocase inner membrane 44) is located in the mitochondrial matrix and is also peripherally attached to the inner membrane.

So, the correct answer is option 3. 

So, the correct answer is option 3.

The correct answer is Chlamydomonas.Key Points

• Chlamydomonas is a type of haploid unicellular eukaryote cell that has a diameter of approximately 10 μm.
• Half of its volume is occupied by cup-shaped chloroplasts, which are responsible for photosynthesis.
• Chlamydomonas is found in freshwater environments and is capable of both sexual and asexual reproduction.
• It is commonly used as a model organism in genetic and biochemical research.

Additional Information

• Hydrodictyon is a genus of green algae that forms a net-like structure.
  • It is commonly known as the water net.
• Ulva is a genus of green algae that is commonly known as sea lettuce.
  • It is often found in marine environments.
•  Oedogonium is a genus of filamentous green algae.
  • It is commonly found in freshwater environments.

The correct answer is Phospholipid metabolism

Concept:

Mitochondria-associated ER membranes (MAM) are specialized regions where the endoplasmic reticulum (ER) is closely associated with mitochondria. This association facilitates various important cellular functions, particularly related to lipid metabolism, calcium signaling, and communication between the ER and mitochondria.

• Phospholipid metabolism: MAM plays a critical role in the synthesis and metabolism of phospholipids. The close proximity of the ER and mitochondria at MAM allows for the transfer of lipids and coordination of lipid synthesis, which is essential for maintaining membrane integrity and function.

Explanation:

• 1) Protein glycosylation: This process primarily occurs in the ER, where proteins are modified (glycosylated) as they are synthesized. While MAM may have some role in protein processing, it is not specifically known for glycosylation.

• 2) ATP synthesis: This is a primary function of mitochondria themselves, specifically in the inner mitochondrial membrane, where ATP synthase operates to produce ATP during oxidative phosphorylation.

• 4) Iron-sulfur cluster assembly: This process primarily occurs in mitochondria and involves specific mitochondrial proteins. While there may be some interactions related to iron-sulfur clusters at the MAM, it is not the main associated activity.

Therefore, phospholipid metabolism is the key activity associated with Mitochondria-associated ER membranes (MAM).

The correct answer is A, B, C only

Explanation:

A. Synaptonemal complex formation between homologous chromosomes.

• Correct. The synaptonemal complex is a protein structure that forms between homologous chromosomes during prophase I of meiosis. It facilitates the pairing (synapsis) of homologs, allowing for crossover events, which are critical for genetic recombination and proper segregation.

B. Degradation of cohesins at the chromosome arms.

• Correct. During meiosis I, cohesins, which hold sister chromatids together, are degraded at the arms of the chromosomes. This degradation allows homologous chromosomes to separate while sister chromatids remain connected at the centromeres, ensuring proper segregation.

C. Retention of cohesins at the centromeres.

• Correct. While cohesins are degraded along the arms of the chromosomes, they are retained at the centromeres. This retention is crucial because it keeps the sister chromatids together until anaphase II, ensuring that they are properly segregated in the second meiotic division.

D. Bi-orientation of kinetochores of sister chromatids.

• Incorrect. Bi-orientation refers to the alignment of kinetochores of sister chromatids in opposite directions (one facing each pole).
• In meiosis I, the kinetochores of sister chromatids do not bi-orient as they do in mitosis or meiosis II.
• Instead, the kinetochores of homologous chromosomes are oriented toward opposite poles, ensuring the separation of the homologs.

Thus, the correct option that includes all correct features is A, B, C only.

The correct answer is Protein-RNA

Concept:

UV Absorbance Characteristics:

• Proteins primarily absorb at 280 nm due to the presence of aromatic amino acids (such as tryptophan, tyrosine, and phenylalanine). The strong absorbance at 280 nm indicates the presence of proteins.
• Nucleic acids (RNA/DNA) absorb strongly at 260 nm due to the presence of nucleotide bases. If the spectrum shows significant absorbance at 260 nm, it suggests the presence of nucleic acids (RNA or DNA).

Explanation:

• The two spectra shown likely correspond to absorbance at 260 nm and 280 nm (one for each filter).
• If one of the spectra shows a peak at 260 nm, it strongly suggests the presence of RNA (or DNA), as nucleic acids absorb more at this wavelength.
• If another peak appears at 280 nm, it indicates the presence of protein.
• The combination of peaks at 260 nm and 280 nm suggests a complex of protein and RNA. This could be a riboprotein complex or a protein that interacts with RNA, leading to the combined absorbance pattern.

Concept:

• Aquaporins are the membrane water channels that play an important role in regulating the water content of the cell.
• They allow the passive movement of water across the membrane. 
• They are widely distributed and are found in various kingdoms like bacteria, plants, and animals. 
• Aquaporins are required because water is a polar molecule with a slightly +ve and slightly -ve charge. 
• The polar nature of the water molecules makes diffusion of the water molecules across the hydrophobic membrane a very slow process which is not fast enough to keep cell alive and to carry out essential cellular functions. 
• Hence, for faster transport of water, channels are required.

Explanation: 

• Aquaporins is a family of integral membrane protein that has a central pore through it. 
• It belongs to MIP i.e., major intrinsic protein family. 
• MIP is a super-family that contains three subfamilies namely aquaporins, aquaglyceroporins and S-aquaporins.
• Hence, option 1 is characteristics of aquaporins
• Aquaporins are present in all kingdoms of life including bacteria, plants and animals. 
• Hence, option 2 is not a characteristics of aquaporins
• All aquaporins are integral membrane proteins with six membrane-spanning alpha helices. The N and C terminal of the protein faces the cytosol of the cell
• At N-terminal and C-terminal, the high conserved identical sequence is found. 
• The sequence is Asn-Pro-Ala (NPA) motif. In this Two Asn residues form the aquaporin channel. 
• Hence, options 3 and 4 are characteristics of aquaporins

Hence, the correct answer is option 2.