Cell Communication and Cell Signaling MCQ Quiz - Objective Question with Answer for Cell Communication and Cell Signaling - Download Free PDF

The correct answer is P - i; Q - ii; R - iii; S - iv 

Explanation:

Viruses are microscopic infectious agents that require a host cell to replicate. They are classified based on the type of genetic material they possess, which can be DNA or RNA, and whether this genetic material is single-stranded (ss) or double-stranded (ds). The genetic material of viruses determines their replication mechanism and host specificity.

• Bacteriophage Lambda (P):
  • Bacteriophage lambda is a virus that infects bacteria, specifically E. coli. Its genetic material is double-stranded DNA (dsDNA).
• Bacteriophage M13 (Q):
  • Bacteriophage M13 is another bacterial virus, but it has single-stranded DNA (ssDNA) as its genetic material.
• Coronavirus (R):
  • Coronaviruses are a group of RNA viruses that infect animals and humans, causing respiratory illnesses like SARS, MERS, and COVID-19. Their genetic material is single-stranded RNA (ssRNA).
• Reovirus (S):
  • Reoviruses are non-enveloped viruses that infect a variety of organisms, including humans, where they cause gastrointestinal and respiratory symptoms. They are characterized by double-stranded RNA (dsRNA) as their genetic material.

The correct answer is Peak I - IgM; Peak II - IgG

Explanation:

• The adaptive immune system in animals responds to pathogens such as bacteria or viruses through the production of antibodies. These antibodies are specialized proteins that help neutralize or eliminate the invading pathogen.
• The two main classes of antibodies involved in the immune response are Immunoglobulin M (IgM) and Immunoglobulin G (IgG). These antibodies play distinct roles in the primary and secondary immune responses.
• The primary response occurs when the immune system encounters a pathogen for the first time. The secondary response occurs upon subsequent exposures to the same pathogen, which is faster and more robust due to the formation of immunological memory.
• Primary immune response (Peak I):
  • When the mammal is exposed to the pathogen for the first time, the immune system responds by producing IgM antibodies initially. IgM is the first antibody generated in response to an infection.
  • IgM antibodies are short-lived, and their levels peak early during the primary response.
• Secondary immune response (Peak II):
  • Upon a second exposure to the same pathogen, the immune system responds more rapidly and with greater intensity due to the activation of memory B cells.
  • In the secondary response, IgG antibodies dominate. IgG is more specific, longer-lasting, and more efficient at neutralizing the pathogen.
  • The levels of IgG are much higher in the secondary response compared to IgM in the primary response.
• Therefore, the graph showing Peak I (primary response) corresponds to IgM, while Peak II (secondary response) corresponds to IgG.

The correct answer is To grow disease-causing microorganisms.

Explanation:

• Robert Koch, a pioneering microbiologist, is renowned for his groundbreaking work in the field of bacteriology and his contributions to identifying specific pathogens as the cause of specific diseases. One of his significant innovations was the use of nutrient media to cultivate microorganisms in the laboratory, allowing them to grow and be studied in isolation.
• Robert Koch utilized nutrient media to cultivate and isolate microorganisms, such as the bacteria causing tuberculosis (Mycobacterium tuberculosis) and anthrax (Bacillus anthracis) 
• Before Koch, many scientists struggled to grow bacteria outside of the body in a controlled manner.
• Koch's innovation included using nutrient-rich substances like meat extracts (bouillons) and later solidifying them with gelatin and then agar to create a suitable environment for bacterial growth. This allowed him to obtain pure cultures of microorganisms, meaning a population of cells derived from a single cell, free from contamination by other microbial species.
• One of Koch's postulates states: "The microorganism must be isolated from a diseased organism and grown in pure culture." The meat-infused medium provided the necessary nutrients (carbon, nitrogen, vitamins, minerals) for various bacteria, especially pathogenic ones, to thrive in vitro.
•   

The correct answer is Guanosine tetraphosphate (ppGpp)

Explanation:

• The bacterial stringent response is a survival strategy triggered under nutrient deprivation or other environmental stress conditions. It helps bacteria adapt by altering gene expression, metabolism, and other cellular processes to conserve resources.
• A key molecule involved in the stringent response is Guanosine tetraphosphate (ppGpp), which is synthesized by the enzyme RelA or SpoT in bacteria.
• ppGpp acts as a signaling molecule and regulates various processes such as transcription, translation, and replication in response to stress.
• ppGpp is synthesized when bacteria experience amino acid starvation or other stress conditions. For example, RelA is activated on ribosomes when uncharged tRNA binds to the A site, leading to ppGpp synthesis.
• ppGpp regulates transcription by binding to RNA polymerase, altering its affinity for promoters. Genes related to ribosomal RNA synthesis are downregulated, while stress response genes are upregulated.
• This helps bacteria conserve energy and resources during unfavorable conditions, enhancing survival.

Other Options (Incorrect):

• Cyclic di-GMP (c-di-GMP): c-di-GMP is a bacterial second messenger that regulates biofilm formation, motility, and virulence. It is not directly involved in the stringent response but plays a role in bacterial lifestyle transitions.
• Cyclic-AMP (cAMP): cAMP is another second messenger in bacteria that mediates catabolite repression, a process where the presence of a preferred carbon source (like glucose) inhibits the utilization of other carbon sources.
• Cyclic-GMP (cGMP): cGMP is a signaling molecule found in eukaryotes that regulates processes like vision and vasodilation. 

The correct answer is P−5 ; Q−4 ; R−2 ; S−1

Explanation:

• The immune system consists of various molecules and proteins that play distinct roles in defending the body against pathogens. These molecules include immunoglobulins (antibodies) such as IgM, IgE, IgA, and others like Major Histocompatibility Complex (MHC).
• Each type of antibody has unique properties and functions, including participating in immune responses, providing protection, and facilitating communication between immune cells.
• MHC proteins are essential for presenting antigens to T cells and initiating adaptive immune responses.
  • IgM - Contains ten heavy and light chains: IgM is the largest antibody and is the first to be produced during an immune response. It forms a pentamer structure, consisting of five antibody units, resulting in ten heavy and light chains. This structural feature enables IgM to efficiently agglutinate antigens.
  • IgE - Associated with allergic reactions: IgE is involved in allergic responses. It binds to allergens and triggers the release of histamine and other chemicals from mast cells and basophils, leading to symptoms such as itching, swelling, and inflammation.
  • IgA - Predominant antibody type in various body secretions: IgA is the primary antibody found in mucosal areas, including saliva, tears, breast milk, and respiratory and intestinal secretions. It plays a vital role in protecting mucosal surfaces by neutralizing pathogens and preventing their adhesion to epithelial cells.
  • MHC - Involved in antigen presentation: Major Histocompatibility Complex (MHC) molecules are critical for the immune system. They present processed antigens to T cells, enabling recognition of foreign substances and initiation of adaptive immune responses.

The correct answer is  Pseudopodia.

Key Points

• The change in shape in amoeba which facilitates movement is due to Pseudopodia.
• The pseudopodia extends from the two sides of the food molecule and surrounds it and finally engulfs the food.
• Pseudopodia is used in movement and as a tool to capture prey or obtain required nutrition.

Structure of Amoeba:

Additional Information 

The correct answer is Option 4 i.e. Asialoglycoprotein

Concept:

Cytoplasmic domains of any receptor bind with different proteins and signals cell for specific functions accordingly.

A cell has two types of receptors:

1. Cytoplasmic receptors -
   • These are found in the cytoplasm of a cell and respond to hydrophobic ligands.
   • They are also known as internal or intracellular receptors.
2. Transmembrane receptors -
   • These are membrane-anchored receptors that are also known as integral membrane proteins.
   • Transmembrane receptors bind to extracellular signals and transmit them into the intracellular environment.

Tyrosine kinase receptors (RTK) - 

• They belong to the high-affinity cell surface receptor category and aid in the binding of many growth factors, cytokines and hormones.
• RTKs possess intrinsic cytoplasmic enzymatic activity which catalyzes the transfer of phosphate from ATP to a tyrosine residue in protein substrates.
• Epidermal growth factor, platelet-derived growth factor, and insulin function as a protein that binds to tyrosine kinase receptors.

Explanation:

Option 1: Epidermal growth factor (EGF)

• EGF receptor (EGFR) is a transmembrane protein that binds to EGF.
• EGFR contains a cytoplasmic tyrosine kinase active site.
• It is expressed in the human body at multiple locations like gums, placenta, vulva, superficial temporal artery, human penis, urethra, mouth cavity, etc.
• Hence, this option is incorrect.

Option 2: Platelet-derived growth factor (PDGF)

• The receptors of PDGF belongs to family of cell surface tyrosine kinase receptors.
• These function for cell proliferation, cellular growth and differentiation.
• Hence, this option is incorrect.

Option 3: Insulin

• The insulin receptors are heterotetrameric transmembrane glycoproteins.
• It contains 2 α-subunits and 2 β-subunits.
• They have one transmembrane domain and one tyrosine-kinase cytoplasmic domain.
• Hence, this option is incorrect.

Option 4: Asialoglycoprotein

• Asialogycoprotein and glycoprotein binds to asialoglycoprotein receptors (ASGPR).
• ASGPR are transmembrane receptors which are specifically present on hepatocytes (liver cells) and thus also called as hepatic lectin.
• The human ASGPR has 4 functional domains:
  • Cytoplasmic domain
  • Transmembrane domain
  • Stalk
  • Carbohydrate recognition domain (CRD)
• The cytoplasmic or cytosolic domain does not act as a tyrosine kinase here.
• Hence, this option is correct. 

Thus, the correct answer is Asialoglycoprotein.

The correct answer is Option 3 i.e.Differential RNA processing.

Concept:

Differential RNA Processing- 

• Differential RNA processing plays a crucial role in determining whether the Ig(immunoglobulin) will be expressed as a membrane bound receptor or a secreted antibody.
• The determination of whether the Ig will be receptor bound or secreted is primarily controlled by the process of alternative RNA splicing during m-RNA maturation.
• This process involves several steps, including transcription, splicing and translation.
• The splicing process involves the removal of certain exon and the joining of others, resulting in different protein products. 
• For membrane-bound immunoglobulins, exons encoding a hydrophobic transmembrane domain are retained, anchoring the immunoglobulin to the B-cell membrane.
• In contrast, for secretory Ig, these transmembrane domain-encoding exons are spliced out, leading to the transmembrane domain, allowing the Ig to be secreted and circulate in body fluids.
• This differential RNA processing enables B-cells to produce both membrane bound and secretory forms of immunoglobulins, allowing them to function effectively in different immune responses, such as on the cell surface for antigen recognition or as soluble antibodies to combat pathogen in body fluids.

Additional Information

Allelic exclusion -​

• The function of allelic exclusion mechanism is to assure that each antibody forming cell will produce antibodies of only a single specificity.

Class switch recombination-

• The function of class switch recombination is to replaces the Immunoglobulin constant region for the isotype which can protect again the pathogen.

Codominant expression-

• In genetic inheritance when two alleles of the same gene are expressed separately to yield different traits in an individual, is known as codominant expression.

Conclusion:-Hence, Option 3 is correct.

The correct answer is Innate immunity has only a narrow range of specificity.

Explanation:

• Innate immunity is the body's first line of defense against pathogens and is present from birth. It is non-specific, meaning it responds to a wide range of pathogens using general mechanisms rather than highly specific responses like the adaptive immune system. It provides an immediate, response to a wide variety of pathogens, including bacteria, viruses, fungi, and parasites. Unlike adaptive immunity, which is highly specific to particular pathogens and involves memory, innate immunity is generic but broad in its target range.

• Pattern recognition receptors (PRRs) are indeed a key component of innate immunity. They recognize pathogen-associated molecular patterns (PAMPs) found on a broad range of pathogens, which triggers an immune response. These receptors can detect many types of invaders, making innate immunity broad in its action.

• Serum complement proteins are part of innate immunity. These proteins help identify and clear pathogens by marking them for destruction and aiding in their removal through processes like phagocytosis.

• The outcome of innate immunity is rapid recognition and destruction of pathogens. This involves processes like phagocytosis, where immune cells engulf and destroy invaders, and inflammatory responses to contain and eliminate threats.

Thus, the statement about "narrow specificity" is incorrect because innate immunity is actually broad and non-specific in its recognition of pathogens.

The correct answer is Option 4 i.e. For HAT selection of hybridoma, the antibody producing B‐cells are pre‐treated with 8‐azaguanine to block salvage pathway of DNA synthesis.

Concept:

• Monoclonal antibodies (mAb) are crucial tools used in biomedical research, disease detection, and cancer and other types of disease treatment.
• These antibodies are created by cell lines or clones derived from animals that have received vaccinations against the research chemical.
• B cells from the immunized animal are fused with myeloma cells to create the cell lines.
• The cells must be cultivated in one of two methods in order to create the necessary mAb.
• in vitro tissue culture or injection into the peritoneal cavity of an appropriately prepped mouse (the in vivo, or mouse ascites, approach). 
• To get mAb with the desired purity and concentration, additional processing of the tissue-culture supernatant and mouse ascitic fluid may be necessary.

Explanation:

Option A:- CORRECT

• Monoclonal antibodies are made from B cell clones that each produce a single antibody with a well-defined specificity.
• Without an antibody, B cells won't typically divide.

Option B:- CORRECT

• When mammalian cells that make a particular antibody combine with tumor cells that can multiply indefinitely, the outcome is a fusion known as a hybridoma that continuously produces antibodies. Because they originate from a single type of cell, the hybridoma cell, those antibodies are referred to as monoclonal.

Option C:- CORRECT

• Aminopterin, a medication that inhibits dihydrofolate reductase to act as a potent inhibitor of folate metabolism, is combined with hypoxanthine, a purine derivative, and thymidine, a deoxynucleoside, which are intermediates in DNA synthesis, to create HAT Medium, a selection medium for mammalian cell culture.

Option D:- INCORRECT

• The ability of mammalian cells to manufacture nucleotides using either the salvage pathway or the de novo pathway is what makes HAT selection possible. Aminopterin, a folic acid analog, blocks the de novo process by which a methyl or formyl group is transferred from an active form of tetrahydrofolate.

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 A - i, B - iii, C - ii, D - i

Explanation:

1. SH2 domain (Src homology 2)

• Binding specificity: SH2 domains recognize and bind to phosphorylated tyrosine residues on receptor proteins, particularly in receptor tyrosine kinases (RTKs).
• Correct match: A – i (Phosphorylated tyrosine residue on receptors)

2. SH3 domain (Src homology 3)

• Binding specificity: SH3 domains typically bind to proline-rich sequences on target proteins. These sequences are often found in signaling proteins and cytoskeletal components.
• Correct match: B – iii (Short proline-rich amino acid sequence on proteins)

3. PH domain (Pleckstrin homology domain)

• Binding specificity: PH domains bind to charged head groups of phosphoinositides, specifically phosphatidylinositol lipids like PIP2 and PIP3, on the plasma membrane. These interactions are important in membrane-associated signaling pathways.
• Correct match: C – ii (Charged head groups of specific phosphoinositides on plasma membrane)

4. PTB domain (Phosphotyrosine-binding domain)

• Binding specificity: PTB domains bind to phosphorylated tyrosine residues as well, but often in a specific sequence context, such as NPXY motifs, which are different from the typical SH2 domain-binding sites.

Thus, the correct answer contains A – i, B – iii, C – ii, D-i.

The correct answer is Option 1 i.e. A and C

Concept:-

Cancer stem cells

• A subgroup of tumor cells known as cancer stem cells (CSCs) is capable of initiating tumors and triggering relapses. CSCs come from differentiated cells or adult tissue resident stem cells at the stage of tumor genesis.
• Due to their significance, a number of CSC-specific biomarkers have been discovered and linked to prognosis, treatment, and diagnosis.
• However, it has been demonstrated that CSCs exhibit significant plasticity, which modifies their phenotypic and functional characteristics.
• Senescent tumor cells and chemo- and radiotherapy agents can also trigger these changes by altering the tumor microenvironment.
• Senescence induction reduces tumor size by altering an anti-tumorigenic environment, which attracts immune cells and forces tumor cells to stop growing.

Cancer cells

• Grow in the absence of signals telling them to grow. 
• Ignore signals that normally tell cells to stop dividing or to die (a process known as programmed cell death, or apoptosis).
  invade into nearby areas and spread to other areas of the body.
• Tell blood vessels to grow toward tumors. These blood vessels supply tumors with oxygen and nutrients and remove waste products from tumors.
• Hide from the immune system. The immune system normally eliminates damaged or abnormal cells. 
• Trick the immune system into helping cancer cells stay alive and grow.
• For instance, some cancer cells convince immune cells to protect the tumor instead of attacking it.

Explanation:

Statement A:-  Cancer cells mostly have mutations whereas cancer stem cells do not.

• Cancer stem cells are the cells that can give rise to tumors, which means they are not mutated yet but they can give rise to cancer cells that will have mutations.
• Hence, statement A is correct

Statement B:-  Cancer cells divide to form two different populations of cells whereas cancer stem cells do not divide.

• Cancer cells arose from cancer stem cells only which states that cancer stem cells have the property to divide.
• Due to the division property of cancer stem cells, it gives rise to tumors.
• Hence, statement B is incorrect

statement C:-  Cancer stem cells can undergo self‐renewal whereas cancer cells cannot.

• Cancer Stem Cells (CSCs) are a small subpopulation of cells within tumors with capabilities of self-renewal, differentiation, and tumorigenicity when transplanted into an animal host.
• A number of cell surface markers such as CD44, CD24, and CD133 are often used to identify and enrich CSCs.
• While the cancer cells can only proliferate but do not have the property of self-renewal.
• Hence, statement C is correct

Statement D:- Cancer cells are predominantly resistant to chemotherapy and radiation.

• Resistance can occur when cancer cells—even a small group of cells within a tumor—contain molecular changes that make them insensitive to a particular drug before treatment even begins, and this is possible in cancer stem cells, not cancer cells.
• Hence, statement D is incorrect.

Therefore, Option 1 (A and C) is correct.

The correct answer is A and D

Explanation:

Class Switching in B cells: B cells can undergo class switch recombination (CSR) to change the antibody isotype they produce without altering the antigen specificity. This switch is typically unidirectional due to the loss of intervening DNA sequences in the constant region of the immunoglobulin gene.

Possible Isotype Switching Pathways:

• IgM → IgG1
• IgG1 → IgA (Class switching from IgG1 to IgA is possible)
• IgM → IgA
   

Statement Analysis:

• Statement A: Cells that have switched to IgG1 may undergo further switching to IgA.
  • True: IgG1 B cells can switch to IgA because class switching can continue to downstream isotypes.
• Statement B: Cells that have switched to IgA may undergo further switching to IgG1.
  • False: Once a B cell switches to IgA, it cannot revert back to IgG1 because the DNA segment for IgG1 has been deleted.
• Statement C: A single cell can simultaneously secrete IgG1 and IgA.
  • False: A single B cell secretes only one class of antibody at a time. The presence of both IgG1 and IgA in wells indicates independent events from different cells.
• Statement D: The progeny of proliferating cells may undergo independent switching events.
  • True: This is consistent with the observed data where proliferating B cells can switch individually to different isotypes. Thus, progeny can independently switch to IgG1 or IgA from IgM.

Key Points

• Class switching in B cells is a unidirectional process.
• IgG1 can switch to IgA, but IgA cannot revert to IgG1.
• A single B cell cannot simultaneously secrete two isotypes.
• Independent progeny cells from the proliferation can undergo separate class switching events.
   

Conclusion:

• Statement A is correct because IgG1 B cells can switch to IgA.
• Statement D is correct because progeny cells from proliferating B cells can independently switch to different isotypes.

The correct answer is  αβγ₂.

Explanation:
In retinal rod cells, cGMP-phosphodiesterase (PDE6) is a crucial enzyme in the photo-transduction pathway, and its subunit structure is actually αβγ₂. This enzyme is responsible for breaking down cyclic GMP (cGMP), a molecule that keeps ion channels open in the dark, allowing the rod cells to respond to light.

• The α and β subunits are catalytic and provide the enzyme's activity for cGMP hydrolysis.
• The γ subunits (γ₂) are regulatory and act as inhibitors of the enzyme. There are two γ subunits that bind to the α and β catalytic subunits, regulating their activity.

Upon light activation, the protein transducin activates PDE6 by removing the inhibitory effect of the γ subunits, allowing the α and β subunits to hydrolyze cGMP.

Thus, the correct subunit structure for retinal rod cell cGMP-phosphodiesterase (PDE6) is αβγ₂, with two regulatory γ subunits controlling the enzyme's activity.