Cellular communication MCQ Quiz in தமிழ் - Objective Question with Answer for Cellular communication - இலவச PDF ஐப் பதிவிறக்கவும்

The correct answer is Option 3

Explanation:

• Removal of some cells by the controlled induction of cell death is not directly involved in the steady state regulation of hematopoiesis.
• Hematopoiesis is the process of blood cell production, development, and differentiation in the bone marrow. This process is tightly regulated to ensure a balanced production of different blood cells.
• While the removal of cells through apoptosis or programmed cell death is a component of maintaining overall cell balance within the body, it is not a direct regulator of the steady-state hematopoiesis.
• Controlled cell death is more about maintaining homeostasis and preventing the accumulation of damaged or unnecessary cells rather than directly influencing the steady production rates or types of blood cells generated in the bone marrow.

Overview of Other Options:

• Control of the levels and types of cytokines produced by stromal cells in bone marrow: This is a critical component of hematopoiesis regulation. Stromal cells in the bone marrow produce cytokines that directly influence the survival, proliferation, and differentiation of hematopoietic stem cells and progenitor cells into various blood cell lineages.
• Production of cytokines with hematopoietic activity by cells such as activated T cells and macrophages: This is also a significant factor in hematopoiesis. Cytokines produced by these cells can act in an autocrine or paracrine manner to support the production and regulation of blood cells, indicating their involvement in the steady-state regulation of hematopoiesis.
• Mesangial cells: These cells are primarily found in the kidney and are involved in the regulation of blood flow and filtration in the glomeruli. They do not play a direct role in the regulation of hematopoiesis. However, the question identifies them as not being involved in hematopoiesis, which might seem confusing because they are indeed not involved, but the context of the question suggests looking for an option that is generally considered a part of the process but is not involved in the steady-state regulation specifically.

The correct answer is Option 1 i.e.causing formation of ADP-EF2 complex

Explanation:

• Diphtheria toxin, produced by the bacterium Corynebacterium diphtheriae, is a potent inhibitor of protein synthesis in eukaryotic cells. Its mechanism of action involves the inactivation of elongation factor 2 (EF2), a vital component of the protein synthesis machinery in the cell.
• EF2 is essential for the translocation step during protein synthesis, where it facilitates the movement of the ribosome along the mRNA, allowing for the addition of new amino acids to the growing polypeptide chain.
• Diphtheria toxin catalyzes the ADP-ribosylation of EF2.
• This process involves the transfer of an ADP-ribose moiety from nicotinamide adenine dinucleotide (NAD⁺) to a specific diphthamide residue on EF2.
• The ADP-ribosylated EF2 (ADP-EF2 complex) is unable to participate in protein synthesis, effectively halting the elongation of nascent polypeptide chains and leading to cell death.
• This mode of action is specific and potent, making diphtheria toxin one of the classic examples of a bacterial toxin that targets the eukaryotic protein synthesis machinery.
• The specificity of the toxin for EF2 and the critical role of EF2 in protein synthesis underscore the vulnerability of the translation process to targeted disruption by bacterial virulence factors.

Conclusion: Diphtheria toxin inhibits protein synthesis by 1) causing formation of ADP-EF2 complex.

The correct answer is Option 4 i.e., Transferrin. 

Explanation:

Proteins with cytoplasmic domains having tyrosine kinase activity typically act as receptors for various signaling molecules. However, transferrin receptors do not possess tyrosine kinase activity in their cytoplasmic domains. Therefore, the correct option is Transferrin​

Key Points Here are key points regarding receptors with cytoplasmic domains having tyrosine kinase activity and their respective ligands:

1. Epidermal Growth Factor (EGF) Receptor:
   1. EGF receptors (EGFRs), also known as ErbB receptors, belong to the receptor tyrosine kinase (RTK) family.
   2. They consist of an extracellular ligand-binding domain, a single transmembrane domain, and an intracellular domain with tyrosine kinase activity.
   3. Binding of EGF or related ligands (e.g., TGF-alpha) to the extracellular domain induces receptor dimerization and activation of the tyrosine kinase activity.
   4. Activation of EGFR initiates downstream signaling pathways involved in cell proliferation, survival, differentiation, and migration.
2. Platelet-Derived Growth Factor (PDGF) Receptor:
   1. PDGF receptors (PDGFRs) are also members of the receptor tyrosine kinase (RTK) family.
   2. Similar to EGFRs, PDGFRs have extracellular ligand-binding domains, single transmembrane domains, and intracellular domains with tyrosine kinase activity.
   3. Binding of PDGF ligands (e.g., PDGF-A, PDGF-B) to the extracellular domain leads to receptor dimerization and activation of tyrosine kinase activity.
   4. Activated PDGFRs trigger signaling pathways that regulate cell growth, proliferation, migration, and differentiation, particularly in the context of wound healing, tissue repair, and embryonic development.
3. Insulin Receptor:
   1. The insulin receptor (IR) is a receptor tyrosine kinase (RTK) involved in insulin signaling.
   2. It consists of two extracellular α subunits and two transmembrane β subunits, each containing a tyrosine kinase domain.
   3. Insulin binding induces conformational changes in the receptor, leading to autophosphorylation of tyrosine residues in the β subunits and activation of the receptor's tyrosine kinase activity.
   4. Activated IRs initiate downstream signaling cascades that regulate glucose uptake, metabolism, protein synthesis, and cell growth.
4. Transferrin Receptor:
   1. Transferrin receptors are not receptor tyrosine kinases (RTKs).
   2. They are transmembrane proteins involved in the cellular uptake of iron-bound transferrin.
   3. Transferrin receptors lack intrinsic tyrosine kinase activity in their cytoplasmic domains.
   4. Instead of initiating signaling through tyrosine phosphorylation, transferrin receptors facilitate the endocytosis of transferrin-bound iron into the cell via clathrin-coated pits.

Conclusion:

Proteins with cytoplasmic domains having tyrosine kinase activity do NOT act as receptors for Transferrin.

The correct answer is Option 4 i.e. A, B and D

Explanation-
The activated PLC- cleaves phosphatidylinositol 4,5-bisphosphate (PIP₂) to generate two second messengers:-
Inositol 1,4,5-trisphosphate (IP₃) and diacylglycerol (DAG). The membrane phospholipid PIP₂ is a minor component of the plasma membrane, localized to the inner leaflet of the phospholipid bilayer. One second messenger DAG remains associated with the plasma membrane, the other second messenger produced by PIP₂ cleavage, IP₃, is a small polar molecule that is released into the cytosol, where it acts to signal the release of calcium ion from the endoplasmic reticulum. IP₃ acts to release calcium ion from the endoplasmic reticulum by binding to receptors that are ligand-gated calcium ion channels (IP₃-gated calcium-release channels, also called IP₃ receptors).

As a result, cytosolic calcium ion levels increase, which affects the activities of a variety of target proteins, including protein
kinases and phosphatases. DAG together with calcium ion, helps activate the enzyme protein kinase C (PKC), which is recruited from the cytosol to the cytosolic face of the plasma membrane. When activated, PKC phosphorylates specific serine or threonine residues on target proteins that vary depending on the cell type.

The correct answer is Option 3 i.e. only D.

Explanation-
An inactivating mutation in the PKA phosphorylation site of GREB leads to the activation of gene expression, which is incorrect.

• Inactivation of the phosphorylation site would usually result in a loss of the ability to be phosphorylated, and phosphorylation is often associated with activation rather than inactivation.

The pathway proceeds as follows: the Gs protein activates adenylyl cyclase, leading to the production of cAMP. cAMP then binds to the regulatory subunits of PKA, triggering the release of the active catalytic subunits of PKA. The catalytic subunits can then phosphorylate CREB, leading to gene transcription.

A: A loss of function mutation in the cAMP binding site of the PKA regulatory subunit would lead to a lack of activation of PKA, and thereby prevent gene expression. So Statement A is correct.

B: An activating mutation in the GTP-binding domain of the α subunit of Gs would lead to an increased production of cAMP by activating adenylyl cyclase. This would, in turn, activate PKA, resulting in the activation of gene expression by CREB. So Statement B is correct.

C: An inactivating mutation that prevents the regulatory subunit of PKA from binding to the catalytic subunit would lead to an excess of free, active catalytic subunits that can phosphorylate CREB and lead to gene expression. So Statement C is correct.

D: An inactivating mutation in the PKA phosphorylation site of CREB would result in CREB not getting phosphorylated, thus, it can’t activate gene expression. So Statement D is incorrect.

Conclusion-Therefore, the incorrect statement is D.

The correct answer is Option 1 i.e. PI3-Kinase.

Explanation-

The activation of PI3K leads to the phosphorylation of phosphatidylinositol 4,5-bisphosphate (PIP2) to generate phosphatidylinositol 3,4,5-trisphosphate (PIP3). PIP3 serves as a second messenger that activates downstream signaling pathways.

Phosphoinositide 3-kinase (PI3-Kinase) is known to phosphorylate the 3-position of the inositol ring of phosphatidylinositol 4,5-bisphosphate to form phosphatidylinositol 3,4,5-trisphosphate (PIP3). This action plays crucial roles in cell survival, growth, and proliferation. The generated PIP3 acts as a second messenger, recruiting and activating several downstream effector proteins, including Protein Kinase B (PKB/Akt), which then regulate various cellular processes.

One of the significant aspects of PI3Ks is their ability to phosphorylate phosphoinositides (PIs) at the 3 position of the inositol ring. In particular, PI3Ks are responsible for the direct conversion of phosphatidylinositol 4,5-bisphosphate (PI(4,5)P2) to phosphatidylinositol 3,4,5-trisphosphate (PI(3,4,5)P3, PIP3.

Detailed view of that process:-

• A specific extracellular signal, such as a growth factor, binds to a receptor tyrosine kinase (RTK) in the plasma membrane of a cell.
• This binding activates the RTK, which then phosphorylates and activates the PI3K enzyme.
• Activated PI3K phosphorylates the inositol lipid PI(4,5)P2 (phosphatidylinositol 4,5-bisphosphate) at the 3-position on the inositol ring, converting it into PI(3,4,5)P3 (phosphatidylinositol 3,4,5-trisphosphate).
• PI(3,4,5)P3 then serves as a docking site on the membrane for intracellular proteins with a specific domain, known as a pleckstrin homology (PH) domain. Recruitment of these proteins to the cell membrane results in their activation and a cascade of downstream signaling that promotes cell survival and growth.

While PI3K promotes the formation of PI(3,4,5)P3, the enzyme PTEN (Phosphatase and tensin homolog) dephosphorylates PI(3,4,5)P3, converting it back to PI(4,5)P2. This balances the level of PI(3,4,5)P3 in the cell, acting as a crucial regulator of cell signaling. Consequently, mutations leading to a loss of PTEN are commonly seen in cancer, due to the increased cell survival and proliferation promoted by high levels of PI(3,4,5)P3.

Fig-Interconversion of the phosphoinositides PI(3,4,5)P3 and PI(4,5)P2 by phosphorylation/dephosphorylation at the 3 position of the inositol ring 

The correct answer is Calcitonin.

Explanation-

The principal mechanism of action of calcitonin it due to the ability of its receptor to couple at least two signal transduction pathways. One of the most important pathways is coupled with the cAMP signal transduction. Calcitonin receptor is a member of a subfamily of the seven-transmembrane domain G protein-coupled receptor superfamily.

Key Points

• Calcitonin: This hormone is produced in the human thyroid gland by the parafollicular cells (also called C cells). It participates in calcium and phosphate metabolism. When it binds to its receptor, it stimulates the G protein adenylate cyclase system, leading to an increase in the production of cAMP (cyclic AMP), which acts as a second messenger to mediate the hormone's effects.
• Oxytocin: Oxytocin does not primarily use the cAMP second messenger pathway. Instead, it exerts its action mainly by the phosphoinositide pathway. Oxytocin receptor belongs to the Gq protein-coupled receptor family that usually uses the phospholipase C-IP3-DAG (inositol trisphosphate-diacylglycerol) pathway, resulting in intracellular calcium ion release that eventually leads to its effects.
• Prolactin: Prolactin is synthesized and released by the anterior pituitary gland and does not primarily act via cAMP. It primarily exerts its effects by binding to prolactin receptors, which are associated with the JAK-STAT pathway. Upon binding, it activates the JAK-STAT signaling pathway, which leads to various cellular responses, including the proliferation, differentiation, and survival of target cells.
• Leptin: Leptin is a hormone that is produced and released mainly by the adipose cells, and its role is in the regulation of energy balance and appetite control. Leptin primarily acts through the JAK-STAT pathway similar to prolactin. It binds to leptin receptors and activates the JAK-STAT signaling pathway which leads to transcription and expression of genes that control hunger and energy expenditure.

Conclusion-Calcitonin elicits its cellular response primarily by producing cAMP as a second messenger.

The correct answer is Option 1

Concept-

The processes involve molecular switches:-

• Regulation of Ras during cell proliferation: Ras is a GTPase protein that functions as a molecular switch by cycling between an active GTP-bound form and an inactive GDP-bound form.
• Regulation of AKT in response to growth signals: AKT is a kinase that undergoes activation by phosphorylation in response to growth signals.
• Growth cone collapse regulation by RhoA: RhoA is a small GTPase that acts as a molecular switch to regulate various cellular processes.

Explanation-

Regulation of Ras during cell proliferation: Ras is a small G protein that acts as a molecular switch in numerous signaling pathways. When it binds to GDP, it is off, while when it binds to GTP, it effectively switches on and can interact with and activate downstream signal transduction molecules. GTPase-activating proteins (GAPs) enhance the intrinsic GTPase activity of Ras, converting it back to the inactive GDP-bound state, while guanine nucleotide exchange factors (GEFs) catalyze the exchange of GDP for GTP, activating Ras.

Regulation of Akt in response to growth signals: Akt, also known as protein kinase B (PKB), plays a crucial role in the PI3K/Akt/mTOR signaling pathway, which is critical for cell growth and proliferation. Akt is switched on when it is translocated to the plasma membrane upon receiving a growth signal and is then phosphorylated and activated by other enzymes at the membrane. The active Akt can then phosphorylate a host of other proteins to elicit the cell's response.

Growth cone collapse regulation by RhoA: RhoA is another small G protein acting as a molecular switch, similar to Ras, and it has roles in actin cytoskeleton organization, cell adhesion, and cell cycle progression. In the context of growth cone activity in neurons, RhoA is involved in growth cone collapse when activated. It's switched on when it is bound to GTP and off when bound to GDP, similar to other G proteins.

Conclusion- So, while the regulation of Ras, Akt, and RhoA involves active-inactive (GTP-bound and GDP-bound) molecular switch mechanisms, the proteasome degradation of HIF1α during normoxia is not considered a molecular switch because it results in the destruction of the protein rather than simply altering its activity state.

The correct answer is Option 2 i.e.A – ii, B – iii, C – i

Explanation-

A. Entry receptor:Extracellular LysM domains and the cytoplasmic kinase domain's 

•  This receptor contains extracellular LysM domains, which are known for their ability to bind to peptidoglycan and related molecules in bacterial cell walls.
• This feature suggests a role in recognizing and interacting with bacterial components.
• Additionally, the cytoplasmic portion of the receptor contains kinase domains, indicating its involvement in signal transduction pathways. Together, these domains allow the entry receptor to recognize bacterial signals and initiate intracellular signaling cascades.

B. Signalling receptor:Extracellular LysM domains but lacks the kinase features in the cytoplasmic portion 

• The signaling receptor also possesses extracellular LysM domains, similar to the entry receptor, indicating a potential role in binding to bacterial ligands.
• However, unlike the entry receptor, the signaling receptor lacks kinase features in its cytoplasmic portion.
• This suggests that while the receptor can recognize bacterial signals, it may not directly initiate downstream signaling events through kinase activity. Instead, it may interact with other proteins or participate in alternative signaling mechanisms.

C. Symbiosis receptor kinase:Extracellular leucine-rich repeat domains in a large N-terminal segment and the cytoplasmic portion having kinase domains. 

• In contrast to the entry and signaling receptors, the symbiosis receptor kinase contains extracellular leucine-rich repeat (LRR) domains in a large N-terminal segment.
• These LRR domains are often involved in protein-protein interactions and are well-suited for ligand recognition and binding.
• Additionally, the cytoplasmic portion of the receptor harbors kinase domains, indicating its capability to initiate intracellular signaling pathways upon ligand binding. This combination of domains suggests that the symbiosis receptor kinase plays a role in recognizing symbiotic signals and transducing them into intracellular responses through kinase-mediated signaling cascades.

In summary, each receptor type exhibits specific domain characteristics that reflect its function in recognizing and responding to bacterial or symbiotic signals. The presence or absence of kinase domains in the cytoplasmic portion of the receptors influences their roles in initiating downstream signaling events and orchestrating cellular responses to external stimuli.

The correct answer is Option 3 i.e. Lamin

Explanation-

• Lamin: Lamins are structural proteins of the cell nucleus. They form a mesh-like structure called the nuclear lamina, providing mechanical support to the nucleus. Lamins are not part of the extracellular matrix; instead, they contribute to the structural integrity of the nuclear envelope
• Cadherin: Cadherins are a type of cell adhesion molecule that plays a crucial role in cell-cell adhesion. They are involved in the formation of adherens junctions, which are important in maintaining tissue integrity.
• Vitronectin: Vitronectin is an extracellular matrix glycoprotein that interacts with integrins on the cell surface. It plays a role in cell adhesion, spreading, and migration.
• Selectin: Selectins are a family of cell adhesion molecules that mediate the initial attachment of leukocytes to endothelial cells during inflammation. They are involved in the immune response but are not directly associated with the extracellular matrix.

Conclusion-In summary, while Cadherin, Vitronectin, and Selectin are related to cell adhesion and the extracellular matrix, Lamin is a nuclear protein involved in maintaining the structure of the cell nucleus.