Cell Communication and Cell Signaling MCQ Quiz in मराठी - Objective Question with Answer for Cell Communication and Cell Signaling - मोफत PDF डाउनलोड करा

The correct answer is Option 4 i.e.Guanylyl cyclase

Concept:

• The second messenger is the component of the signal transduction cascade.
• A secondary messenger is a molecule that is involved in relaying the signals (message) from receptors to the target molecule inside the cell.
• They amplify the signal and increase their strength. 
• They cause some changes in the activity of the cells.
• Increase in the concentration of the second messenger lead to rapid change in the cells like proliferation, differentiation, apoptosis, survival, depolarization, etc.; while removal or degradation of the second messenger removes/terminates the cellular signals. 
• They are short-lived intracellular molecules.
• Four classes of second messengers are - cyclic nucleotides (cAMP), membrane lipid derivatives, Ca²⁺ and Nitric oxide/carbon monoxide.

Important Points

• Nitric oxide is generated in the cell by the nitric synthase enzyme that catalyzes the oxidation of the guanine nitrogen of the arginine which results in the releasing of nitric oxide.
• It is a small glass, second messenger.
• Nitric oxide activates the guanylyl cyclase enzyme.
• This enzyme converts GTP into cGMP, leading to an increased in the concentration of cGMP.
• cGMP mediates a number of physiological responses further like smooth muscle relaxation, platelet inhibition and change in gene expression. 
• Increases in the concentration of cGMP activate the protein kinase G, which results in decreases in the concentration of the Ca²⁺ and thus results in relaxation of the smooth muscle. 

Hence, the correct answer is Option 4.

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The Correct Answer is Carcinoma

Key PointsCarcinomas are cancers that start in the epithelial cells, which are the cells that make up the skin and the lining of organs. This makes them the most common type of cancer.

• Carcinomas account for 80 to 90% of all cancer cases. They are most commonly found in adults.
• Because epithelial cells are found throughout the body, carcinomas can occur in many different locations. Some of the most common sites include the breast, prostate, lung, and colon.
• Carcinomas are often named based on their specific location. For instance, a carcinoma in the breast is known as 'breast carcinoma', one in the lung is 'lung carcinoma', and so on.
• Squamous cell carcinoma and adenocarcinoma are two primary types of carcinoma. Squamous cell carcinomas originate from squamous epithelial cells that are flat and scale-like, often found in the skin and the linings of certain organs. Adenocarcinomas originate in glandular epithelial cells that produce mucus, and are common in organs such as the lungs, colon, and breast.
• The behavior and growth of carcinomas vary based on the type and location. Some may grow slowly and pose little threat, while others may be more aggressive and spread quickly.
• Carcinomas may spread or "metastasize" to other parts of the body via the lymphatic system and bloodstream.
• Treatment options for carcinomas include surgery, radiation therapy, chemotherapy, immunotherapy, targeted therapy, or a combination of these. The specific treatment plan will depend on the type, stage, and location of the carcinoma, as well as the patient's overall health.

The correct answer is apoptosis

Explanation:

• During normal embryonic development, the elimination of cells in specific regions is essential for proper tissue and organ formation.
• Apoptosis, or programmed cell death, is a highly regulated process that plays a critical role in shaping the developing tissues and removing unnecessary or damaged cells.
• In the development of the mouse paw, apoptosis is responsible for removing cells from the inter-digital space, allowing the formation of distinct digits (fingers or toes).

Other Options:

• Meiosis: This is a type of cell division that reduces the chromosome number by half, producing four haploid cells. It is essential for sexual reproduction but is not involved in the elimination of cells in the inter-digital space during embryonic development.
• Mutagenesis: This refers to the process by which the genetic information of an organism is changed, resulting in a mutation. While mutations can impact development, mutagenesis itself is not the process responsible for cell elimination in the inter-digital spaces.
• Necrosis: This is a form of cell injury that results in the premature death of cells in living tissue. Unlike apoptosis, necrosis is usually the result of acute damage or disease and is not a regulated process. Therefore, it does not play a role in normal embryonic development like apoptosis does.

The correct answer is It inactivates Gα protein.

Explanation:

GTPase Activating Proteins (GAPs) are involved in the regulation of heterotrimeric G proteins by promoting the hydrolysis of GTP to GDP on the Gα subunit. This hydrolysis inactivates the Gα protein and returns it to its GDP-bound, inactive state, allowing it to reassociate with the Gβ/Gγ subunits, thus turning off the signaling pathway.

• In the active state, Gα is bound to GTP and can transmit signals. When GTP is hydrolyzed to GDP (a process accelerated by GAP), Gα becomes inactive.
• This inactivation ensures that the G-protein signaling is tightly regulated and prevents prolonged or unwanted activation of downstream signaling pathways.

The correct answer is Quadrant 2

Explanation:

Flow cytometry is a technique used to analyze the physical and chemical characteristics of cells or particles. In this case, the question pertains to the analysis of T cell development using CD4 and CD8 markers.

T Cell Development Stages:

• Initial Stage: Cells are CD4+ CD8+ (Double Positive).
• Differentiation: Cells differentiate into either CD4+ CD8- (Helper T cells) or CD4- CD8+ (Cytotoxic T cells)

Some cells may become CD4- CD8- (Double Negative), although this is less common in mature cells.

Flow Cytometry Quadrants:

In a flow cytometry graph with CD4 on one axis and CD8 on the other, the quadrants represent the following:

• Quadrant 1 (Top Left): CD4+ CD8-
• Quadrant 2 (Top Right): CD4+ CD8+
• Quadrant 3 (Bottom Left): CD4- CD8-
• Quadrant 4 (Bottom Right): CD4- CD8+

Defect in Development: If there is a defect in the development of T cells, the cells may not differentiate properly. This can result in a higher density of cells remaining in the double positive (CD4+ CD8+) stage.

Therefore, the correct answer is Quadrant 2

The correct answer is Option 4 

Explanation:

Receptor Tyrosine Kinases (RTKs) are a key class of cell surface receptors critical for mediating the cellular response to a wide array of external signals, including growth factors, hormones, and cytokines. Their activity regulates essential processes such as cell growth, differentiation, metabolism, and apoptosis. 

Structure of RTKs
RTKs are composed of an extracellular ligand-binding domain, a single transmembrane helix, and an intracellular domain that possesses tyrosine kinase activity. The existence of multiple RTK families and subtypes allows cells to respond to a wide range of ligands with high specificity.

Activation Mechanism:

• Ligand Binding: The process begins when a specific ligand (such as a growth factor) binds to the extracellular domain of an RTK. This specificity ensures that cells can respond appropriately to various external signals.
• Dimerization: Ligand binding induces a conformational change in the RTK that promotes dimerization – either homodimerization (two identical RTKs) or heterodimerization (two different RTKs). This dimerization is essential for the activation of the RTK's kinase activity.
• Autophosphorylation: Once dimerized, the intracellular tyrosine kinase domains of RTKs become activated. The activation allows the kinase domain of one RTK molecule in the dimer to phosphorylate tyrosine residues on its partner and vice versa. This process is known as autophosphorylation. The phosphorylation of specific tyrosine residues creates binding sites for a variety of intracellular signaling proteins.

Downstream Signaling:
The autophosphorylation of tyrosine residues serves as docking sites for signaling molecules that contain Src Homology 2 (SH2) domains. These SH2 domain-containing proteins can directly bind to the phosphorylated tyrosines, initiating a cascade of downstream signaling events. Several major pathways are typically activated downstream of RTKs:

• Ras/MAPK Pathway: Often involved in controlling gene expression and cell cycle progression. It is initiated when the adaptor protein GRB2 and the guanine nucleotide exchange factor SOS are recruited to the RTK. They facilitate the conversion of Ras from its inactive GDP-bound form to its active GTP-bound form, leading to the activation of a kinase cascade involving RAF, MEK, and ERK.
• PI3K/Akt Pathway: Plays a vital role in cell survival and proliferation. Activated RTKs recruit PI3K (phosphoinositide 3-kinase), leading to the production of PIP3 (phosphatidylinositol (3,4,5)-trisphosphate) and the subsequent activation of Akt. Activated Akt can mediate multiple cellular responses, including promoting cell survival and growth.
• PLCγ/PKC Pathway: Involved in controlling various cellular functions, including gene expression and migration. RTK activation leads to the recruitment of phospholipase Cγ (PLCγ), which hydrolyzes PIP2 to generate diacylglycerol (DAG) and inositol trisphosphate (IP3), triggering calcium mobilization and the activation of protein kinase C (PKC).

Conclusion:

The activity of RTKs is tightly regulated. Mechanisms such as dephosphorylation by phosphatases, endocytosis, and degradation of RTKs ensure that their signaling is transient and appropriately modulated. Dysregulation of RTK signaling is implicated in numerous diseases, including many types of cancer

- Correct Answer: Epithelial tissues
- Explanation: Carcinoma refers to a type of cancer that originates in the epithelial tissue, which is the tissue that lines the inner and outer surfaces of the body, including the skin, blood vessels, organs, and glands. It is the most common type of cancer.

- Incorrect Options:
- Bone Tissues: Cancers originating in the bone tissues are referred to as sarcomas, not carcinomas. Sarcomas are relatively rare and affect the connective tissues of the body.
- Muscle Tissues: Similar to bone tissues, cancers that begin in the muscle tissues are also classified under sarcomas. These include cancers that grow in the smooth, skeletal, or cardiac muscles.
- Bone Marrow Cells: Malignancies that start in the bone marrow cells are known as leukemias or lymphomas, depending on the specific type of blood cell that becomes cancerous. Leukemia affects the blood and bone marrow, while lymphoma affects the lymphatic system.

The correct answer is A - iii, B - i, C - iv, D - ii

Explanation-

The correct pairings are as follows:-

A. Anchoring junction - iii. Desmoglein

B. Occluding junction - i. Claudins

C. Channel-forming junction - iv. Connexin

D. Signal-relaying junction - ii. Delta-Notch

Additional InformationAnchoring junction: These junctions provide mechanical stability to tissues and help form strong sheets of cells. Desmoglein is a type of cadherin protein that is involved in the formation of desmosomes, a type of anchoring junction.

Occluding junction (also known as tight junctions): These occur where a seal is required between cells to prevent the leakage of molecules across a layer of cells instead of passing through them. Claudins are the key proteins that form the backbone of these tight junctions.

Channel-forming junction (also known as gap junctions): These allow the passage of ions and small molecules between cells, thus facilitating communication. Connexin proteins create a pore for these ions and small molecules to move directly from one cell to another.

Signal-relaying junction (also known as communicating junctions): Delta-Notch signaling is a primary example of this, where the Delta protein on one cell interacts with the Notch protein on a neighboring cell to relay signals. Notch signaling is critical for cell differentiation and development.

Fig- Types of cell junction.

Concept:

• MHC or major histocompatibility complex contains a group of cell surface proteins essential for the adaptive immune system. 
• There are 3 major kinds of MHC groups in humans. 
• MHC-I is a heterodimer formed of two proteins, viz, alpha (alpha 1, 2, and 3) and beta microglobulin. 
• Only the alpha subunit spans the plasma membrane. 
• The MHC-I is present in all nucleated cells, hence they are absent in erythrocytes or RBCs.
• The MHC I alpha and beta chains associate within the lumen of the endoplasmic reticulum. 
• The MHC-I binds to peptides that originate in the cytoplasm.
• This includes foreign peptides that originate in the cytoplasm, intracellular pathogenic viruses, or cancerous transformations. 
• They present antigens on CD8 molecules.

Explanation:

• The transporter associated with antigen processing (TAP) and tapasin, the endoplasmic reticulum (ER) oxidoreductases ERp57 and protein disulfide isomerase (PDI), the lectin chaperones calnexin and calreticulin, and the ER aminopeptidase coordinate the assembly of major histocompatibility complex (MHC) class I molecules with peptides (ERAAP).
• Chaperone molecules facilitate the binding of peptide antigens with class I MHC (major histocompatibility complex) molecules.
• Proteins are known as chaperone molecules that aid in the folding and construction of other proteins.
• Chaperone molecules support the correct folding and stabilization of the complex in the case of class I MHC molecules by directing the binding of the peptide antigen to the MHC molecule.
• When the class I MHC molecule binds to the peptide antigen, the complex is displayed on the cell's surface where CD8+ T cells with receptors specific to the complex can identify it.
• The start of an immune reaction against infected or abnormal cells depends on this recognition.
• There is no direct interaction between immunoglobulins and cytokines and class I MHC molecules during the synthesis of peptide antigens.
• While cytokines are signaling molecules that are involved in controlling immune reactions, immunoglobulins, also known as antibodies, are secreted by B cells and are involved in recognizing and binding to antigens outside of cells.

Therefore, the correct answer is option 1.

The correct answer is A-3, B-2, C-1, D-4.

Explanation:

1. Caspase-3:

   • Caspase-3, also known as an executioner caspase, plays a critical role in the dismantling of cellular structures during apoptosis by cleaving key proteins. It is activated downstream in the apoptotic pathway by other caspases and components such as APAF-1 and cytochrome c.
   • Its activation leads to the cleavage of cellular proteins and DNA, culminating in the characteristic morphological changes observed during apoptosis including cell shrinkage, chromatin condensation, and DNA fragmentation.

2. Bcl-2:

   • Bcl-2 is an anti-apoptotic protein that plays a vital role in regulating mitochondrial outer membrane permeabilization (MOMP). By binding to and inhibiting pro-apoptotic proteins like Bax and Bak, Bcl-2 prevents the release of cytochrome c from the mitochondria, thus inhibiting the downstream apoptotic signaling.
   • The overexpression of Bcl-2 is often associated with increased cell survival and is implicated in the resistance of cancer cells to chemotherapy and radiation therapy.

3. Cytochrome c:

   • Cytochrome c is a mitochondrial protein involved in the electron transport chain under normal conditions. However, during apoptosis, it is released into the cytoplasm where it binds to APAF-1.
   • This binding facilitates the formation of the apoptosome, a multi-protein complex that activates initiator caspases such as caspase-9, leading to the activation of executioner caspases like caspase-3.
   • The release of cytochrome c from mitochondria is a pivotal step in the intrinsic (mitochondrial) pathway of apoptosis and is tightly regulated by the Bcl-2 family of proteins.

4. APAF-1 (Apoptotic protease activating factor-1):

   • APAF-1 is an essential component of the apoptotic machinery involved in the intrinsic pathway of apoptosis. Upon release of cytochrome c from the mitochondria, APAF-1 undergoes a conformational change and interacts with cytochrome c and dATP (or ATP) to form the apoptosome.
   • The apoptosome serves as a platform for the activation of initiator caspase-9, which subsequently activates executioner caspases like caspase-3, culminating in the execution phase of apoptosis.
   • The proper functioning of APAF-1 is crucial for the apoptotic response to various cellular stresses and damage, and defects in this pathway can contribute to the development of cancer.