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

Key Points

• Statement I: Diffusion does not require any energy expenditure because it is a passive process where molecules move from a region of higher concentration to a region of lower concentration due to the concentration gradient.
• Statement III: In plants, the transport of materials over longer distances occurs through vascular tissues (xylem and phloem), which is referred to as translocation. This process is essential for the distribution of water, nutrients, and food throughout the plant.
• Both statements I and III are correct, making Option 3 the correct choice.

Additional Information

• Statement II: Facilitated diffusion involves the movement of substances across a membrane with the help of specific transport proteins, but it does not require ATP. It is still a passive process, as substances move along the concentration gradient.
• Statement IV: Facilitated diffusion is highly specific to the molecules being transported. The transport proteins involved are designed to recognize specific molecules or ions, ensuring selective transport.
• Diffusion: Diffusion is the movement of molecules from a region of higher concentration to a region of lower concentration without the involvement of energy or specific transport proteins.
• Translocation: The process of translocation in plants involves the movement of food (sugars), minerals, and water through xylem and phloem tissues. This is an active process that can occur over long distances.
• Facilitated Diffusion: Facilitated diffusion is a passive transport mechanism that uses transport proteins to move molecules across the cell membrane. It does not require energy expenditure (ATP) and is specific to certain molecules.

The correct answer is (A), (B), (C), and (D)

Key Points

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The correct answer is (A), (B) and (D) only

Explanation:

• Membrane transport refers to the movement of substances across the cell membrane, either into or out of the cell.
• There are different types of membrane transport mechanisms, including passive transport (such as diffusion and facilitated diffusion) and active transport.

Proteins play a crucial role in facilitating the transport of molecules that cannot freely diffuse through the lipid bilayer.

• (A). Channel proteins form open pores, through which suitably sized molecules/ions can cross the membrane: This statement is correct. Channel proteins provide a passageway for specific ions or molecules to pass through the membrane. They can open or close in response to certain stimuli, allowing selective permeability.
• (B). Carrier proteins selectively bind specific molecules, and transport them across the membrane by undergoing a conformation change: This statement is also correct. Carrier proteins bind to specific molecules on one side of the membrane, undergo a conformational change, and release the molecule on the other side. This can happen through facilitated diffusion or active transport.
• (D). Small uncharged molecules can diffuse freely, through the phospholipid bilayers: This statement is correct. Small, nonpolar, and uncharged molecules, such as oxygen and carbon dioxide, can diffuse directly through the phospholipid bilayer without the need for transport proteins.
• (C). Transport of molecules across membranes, through channel proteins and carrier proteins, always involves active transport: This statement is incorrect. Transport through channel proteins and carrier proteins can involve both passive (facilitated diffusion) and active transport. Facilitated diffusion does not require energy, while active transport does.

The correct answer is Golgi, smooth endoplasmic reticulum, rough endoplasmic reticulum.

Explanation:

Sucrose density gradient centrifugation is a technique used to separate cellular organelles based on their size and density. In this method, cellular components are placed in a tube with a gradient of sucrose concentrations, and then centrifuged. Organelles will sediment at different rates, allowing them to be separated from each other.

• When cell homogenates are subjected to centrifugation through a sucrose density gradient, the organelles sediment according to their buoyant densities.
• The Golgi apparatus, due to its less compact structure and larger vesicles, stays at higher (less dense) regions of the gradient.
• The smooth endoplasmic reticulum, having fewer ribosomes and a more tubular structure, sediments to the middle.
• The rough endoplasmic reticulum, with its associated ribosomes, exhibits the highest density among the three organelles given and thus migrates to the regions of the gradient with higher sucrose concentration.

Therefore, the correct order of organelle sedimentation from lower to higher concentration of sucrose is Golgi, smooth endoplasmic reticulum, rough endoplasmic reticulum. The Golgi apparatus has a lower density, followed by the smooth endoplasmic reticulum, and then the rough endoplasmic reticulum which has the highest density due to the presence of ribosomes on its surface.

The correct answer is microorganisms export the antibiotic, using efflux pumps, as soon as it exceeds a certain intracellular concentration.

Explanation:

Microorganisms that produce antibiotics have developed mechanisms to avoid self-destruction by their own antibiotics. One of the key mechanisms is the use of efflux pumps, which actively transport the antibiotic out of the cell, preventing it from reaching toxic concentrations within the microorganism. Efflux pumps are proteins located in the cell membrane that act as transporters, expelling unwanted toxic substances, including antibiotics.

Option 1: Active pharmacophore of the bactericidal antibiotic remains bound to antibodies while they are intracellular.

• This option is incorrect because antibiotics do not bind to antibodies inside the producing microorganisms. Antibodies are part of the immune system of higher organisms, not bacteria or fungi that produce antibiotics.

Option 2: Antibiotics are always produced in inactive forms, and get activated by the enzymatic action of the target cell.

• This option is incorrect because while some antibiotics may require activation, this is not a general mechanism for all antibiotics. Many antibiotics are produced in their active forms.

Option 3: Microorganisms export the antibiotic, using efflux pumps, as soon as it exceeds a certain intracellular concentration.

• This option is correct. Efflux pumps help the microorganism to expel the antibiotic, thereby preventing it from accumulating to toxic levels inside the cell. This mechanism is well-documented and effective in protecting the antibiotic-producing microorganism.

Option 4: Antibiotics are made in parts, and are assembled after being transported to the extracellular environment.

• This option is incorrect because antibiotics are synthesized as complete molecules within the cell and are not assembled extracellularly. The biosynthetic pathways for antibiotics take place within the producing microorganism.

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.