Molecular Techniques in Physiology — MCQs

10 questions

Techniques used for protein expression proteomics study include:

Which of the following is used to detect abnormal gene sequences EXCEPT?

Which one of the following enzymes is obtained from Thermus aquaticus bacterium that is heat stable and used in PCR at high temperature?

All are examples of negative feedback except

A research team is developing a gene therapy approach using CRISPR-Cas9 to correct a point mutation causing sickle cell disease. They must decide between two strategies: (A) correcting the mutation in hematopoietic stem cells ex vivo, or (B) in vivo correction in bone marrow. Considering molecular physiology principles, what is the most significant advantage of strategy A over strategy B?

A novel drug is designed to treat a genetic disorder caused by a nonsense mutation in the dystrophin gene. The drug works by allowing the ribosome to skip over the premature stop codon and continue translation. Evaluation of this therapeutic strategy reveals partial restoration of dystrophin protein with 60% of normal length but sufficient function. What is the most critical molecular consideration in determining if this approach will be clinically beneficial?

A genetic study identifies a family with multiple members having early-onset colorectal cancer. DNA mismatch repair gene testing reveals a mutation in MLH1 gene. Which molecular phenomenon would be most prominently observed in tumor cells from these patients?

A 45-year-old woman with breast cancer is being treated with trastuzumab (Herceptin). Laboratory analysis of her tumor cells shows 100-fold amplification of a specific gene. Analysis of the signal transduction pathway reveals constitutive activation of PI3K/AKT pathway. Which receptor is most likely overexpressed?

A researcher is studying a cell line that shows resistance to apoptosis despite DNA damage. Analysis reveals overexpression of a protein that normally prevents p53 from inducing cell cycle arrest. Which protein is most likely overexpressed?

Q10

A 6-month-old infant presents with severe anemia, jaundice, and hepatosplenomegaly. Hemoglobin electrophoresis shows predominantly HbF (fetal hemoglobin) with absent HbA. Which molecular defect best explains this clinical picture?

Molecular Techniques in Physiology Indian Medical PG Practice Questions and MCQs

Question 1: Techniques used for protein expression proteomics study include:

A. PolyAcrylamide Gel Electrophoresis (PAGE)
B. Gene Expression Analysis (indirectly related to proteomics)
C. Mass Spectrometry
D. All of the options (Correct Answer)

Explanation: ***All of the options*** - All listed techniques—**Polyacrylamide Gel Electrophoresis (PAGE)**, **Gene Expression Analysis**, and **Mass Spectrometry**—are used in protein expression proteomics studies, either directly or indirectly, to analyze and quantify proteins. - The integration of these various techniques provides a comprehensive approach to understanding protein expression profiles. *PolyAcrylamide Gel Electrophoresis (PAGE)* - **PAGE** (including 1D and 2D-PAGE) is a fundamental technique for separating proteins based on their **molecular weight** and **isoelectric point**, which is crucial for visualizing and quantifying expressed proteins. - It often serves as an initial separation step before more detailed analysis, such as **mass spectrometry**. *Gene Expression Analysis (indirectly related to proteomics)* - Although **gene expression analysis** (e.g., using **RT-PCR** or **microarrays**) measures mRNA levels, it is indirectly related to proteomics because mRNA levels often **correlate with protein levels**. - It provides insights into the **transcriptional regulation** that influences protein expression, complementing direct protein analysis. *Mass Spectrometry* - **Mass spectrometry** is a powerful and widely used technique in proteomics for **identifying, quantifying, and characterizing proteins** and peptides by measuring their **mass-to-charge ratio**. - It can be used for both **discovery proteomics** (identifying novel proteins) and **targeted proteomics** (quantifying specific proteins).

Question 2: Which of the following is used to detect abnormal gene sequences EXCEPT?

A. RFLP analysis
B. Pyrosequencing
C. Flow cytometry (Correct Answer)
D. FISH

Explanation: ***Flow cytometry*** - **Flow cytometry** is primarily used to analyze **cell populations** based on their physical and biochemical characteristics (e.g., size, granularity, and protein expression) by passing them single file through a laser beam, not for direct gene sequencing. - It detects and quantifies cells labeled with **fluorescent antibodies**, making it useful for immunophenotyping, cell sorting, and DNA content analysis, but not for identifying specific gene sequences or mutations. *RFLP analysis* - **Restriction fragment length polymorphism (RFLP) analysis** detects variations in **DNA sequences** by using **restriction enzymes** to cut DNA at specific sites. - Differences in fragment lengths indicate **polymorphisms** or **mutations** within the recognition sites, thereby identifying abnormal gene sequences. *Pyrosequencing* - **Pyrosequencing** is a method of **DNA sequencing** that determines the sequence of nucleotides by detecting the release of pyrophosphate during DNA synthesis. - It is used to identify **single nucleotide polymorphisms (SNPs)** and **short genetic variations**, making it suitable for detecting abnormal gene sequences. *FISH* - **Fluorescence in situ hybridization (FISH)** uses **fluorescently labeled DNA probes** that bind to specific complementary **DNA sequences** on chromosomes. - It is a powerful cytogenetic technique for detecting **chromosomal abnormalities**, such as deletions, translocations, and amplifications, thereby identifying abnormal gene sequences.

Question 3: Which one of the following enzymes is obtained from Thermus aquaticus bacterium that is heat stable and used in PCR at high temperature?

A. DNA gyrase
B. DNA polymerase III
C. Taq polymerase (Correct Answer)
D. Endonuclease

Explanation: ***Taq polymerase*** - This **heat-stable DNA polymerase** is isolated from the thermophilic bacterium *Thermus aquaticus*. - Its ability to withstand high temperatures makes it ideal for the **polymerase chain reaction (PCR)**, where DNA denaturation steps occur at elevated temperatures. *DNA gyrase* - **DNA gyrase** is a type II topoisomerase that introduces negative supercoils into DNA, which is important for DNA replication and transcription. - It is not heat-stable and is not directly used for DNA amplification in PCR. *DNA polymerase III* - **DNA polymerase III** is the primary enzyme responsible for DNA replication in *E. coli* and other bacteria. - It rapidly synthesizes DNA but is **not heat-stable** and would denature at the temperatures required for PCR. *Endonuclease* - **Endonucleases** are enzymes that cleave phosphodiester bonds within a polynucleotide chain. - While essential for processes like DNA repair and restriction mapping, they are not primarily involved in and are not heat-stable for DNA synthesis in PCR.

Question 4: All are examples of negative feedback except

A. Regulation of blood CO2 level
B. Regulation of pituitary hormones
C. Regulation of blood pressure
D. Coagulation of the blood (Correct Answer)

Explanation: ***Coagulation of the blood*** - **Blood coagulation** is a classic example of **positive feedback**, where the initial clotting process amplifies itself until bleeding stops - Platelets aggregate and release factors that promote further platelet aggregation and activation of the clotting cascade, thereby **accelerating the response** rather than diminishing it - This is the exception among the options, as it represents positive feedback while all others are negative feedback *Regulation of blood CO2 level* - The regulation of **blood CO2 levels** is a vital example of **negative feedback**, where an increase in CO2 stimulates breathing to expel excess CO2 - This mechanism works to return the blood CO2 concentration to its homeostatic set point, thus **counteracting the initial stimulus** - Central and peripheral chemoreceptors detect elevated CO2 and trigger increased ventilation *Regulation of pituitary hormones* - The regulation of **pituitary hormones** involves **negative feedback loops**, where high levels of target gland hormones inhibit the release of stimulating hormones from the pituitary and hypothalamus - For example, high thyroid hormone levels inhibit TSH release from the pituitary and TRH from the hypothalamus - This effectively **reduces the initial stimulus** and maintains hormonal balance *Regulation of blood pressure* - The regulation of **blood pressure** is primarily controlled by **negative feedback mechanisms** involving baroreceptors, which detect changes in pressure - If blood pressure rises, baroreceptors in the carotid sinus and aortic arch signal the medulla to reduce heart rate and dilate blood vessels - This response **lowers the pressure back to the set point**, maintaining cardiovascular homeostasis

Question 5: A research team is developing a gene therapy approach using CRISPR-Cas9 to correct a point mutation causing sickle cell disease. They must decide between two strategies: (A) correcting the mutation in hematopoietic stem cells ex vivo, or (B) in vivo correction in bone marrow. Considering molecular physiology principles, what is the most significant advantage of strategy A over strategy B?

A. Strategy A allows for screening and selection of successfully edited cells before transplantation, minimizing off-target effects (Correct Answer)
B. Strategy A requires lower doses of viral vectors
C. Strategy A produces faster clinical improvement
D. Strategy A is less expensive to implement

Explanation: ***Strategy A allows for screening and selection of successfully edited cells before transplantation, minimizing off-target effects*** - **Ex vivo** correction allows scientists to perform **quality control** by screening the patient's cells for the desired **on-target** modification and ensuring no harmful **off-target** mutations exist. - This selection process ensures that only **genetically verified** hematopoietic stem cells are re-infused, providing a significant safety and efficacy profile compared to blind **in vivo** delivery. *Strategy A requires lower doses of viral vectors* - While the total volume might be smaller, the primary advantage is the **precision** and **safety** of editing, not merely the quantity of the vector used. - **In vivo** methods actually face greater challenges with **vector distribution** and immune clearance, but this is less critical than the ability to screen cells. *Strategy A produces faster clinical improvement* - The **ex vivo** process is time-consuming, involving **cell harvesting**, laboratory editing, and **myeloablative conditioning** before re-infusion. - Clinical improvement depends on the **engraftment** of edited cells and the turnover of red blood cells, which is not necessarily faster than **in vivo** methods. *Strategy A is less expensive to implement* - **Ex vivo** gene therapy is highly expensive due to the need for **specialized laboratory facilities**, intensive cell culture protocols, and prolonged patient **hospitalization**. - **In vivo** strategies are conceptually cheaper and easier to scale, but currently lack the **safety oversight** provided by laboratory screening.

Question 6: A novel drug is designed to treat a genetic disorder caused by a nonsense mutation in the dystrophin gene. The drug works by allowing the ribosome to skip over the premature stop codon and continue translation. Evaluation of this therapeutic strategy reveals partial restoration of dystrophin protein with 60% of normal length but sufficient function. What is the most critical molecular consideration in determining if this approach will be clinically beneficial?

A. Whether the drug prevents degradation of dystrophin mRNA
B. Whether the drug enhances ribosomal binding to the start codon
C. Whether the drug increases transcription of the dystrophin gene
D. Whether the truncated protein retains the actin-binding domain and maintains membrane stability (Correct Answer)

Explanation: ***Whether the truncated protein retains the actin-binding domain and maintains membrane stability*** - For a truncated **dystrophin** protein to be clinically effective, it must preserve the functional linkage between the **actin cytoskeleton** and the **extracellular matrix**. - This is the fundamental mechanism behind converting a severe **Duchenne** phenotype into a milder **Becker** muscular dystrophy phenotype through **read-through** or exon-skipping therapies. *Whether the drug prevents degradation of dystrophin mRNA* - While **nonsense-mediated decay (NMD)** can reduce mRNA levels in nonsense mutations, preventing degradation is useless if the resulting translation still produces a non-functional protein. - The primary goal of read-through therapy is the quality and **functional domains** of the protein produced, rather than just the quantity of mRNA present. *Whether the drug enhances ribosomal binding to the start codon* - Enhancing **ribosomal binding** to the **start codon** (AUG) might increase the initiation of translation but does not address the premature stop codon issue. - Clinical benefit depends on the ribosome's ability to bypass the **premature termination codon (PTC)**, not the efficiency of initial binding. *Whether the drug increases transcription of the dystrophin gene* - Increasing **transcription** would only result in more mutated mRNA transcripts, which would still terminate at the **premature stop codon**. - Without a mechanism to ensure a functional protein product, simply increasing **gene expression** does not mitigate the mechanical instability of the muscle cell membrane.

Question 7: A genetic study identifies a family with multiple members having early-onset colorectal cancer. DNA mismatch repair gene testing reveals a mutation in MLH1 gene. Which molecular phenomenon would be most prominently observed in tumor cells from these patients?

A. Chromosomal translocations
B. Telomere shortening
C. DNA methylation
D. Microsatellite instability (MSI) (Correct Answer)

Explanation: ***Microsatellite instability (MSI)*** - Mutations in **MLH1** lead to defective **DNA mismatch repair (MMR)**, which is the hallmark of **Lynch syndrome** (HNPCC). - Failure to repair errors in repetitive DNA sequences results in **microsatellite instability**, characterized by the expansion or contraction of short tandem repeats in tumor cells. *Chromosomal translocations* - These are typical of **hematologic malignancies** (e.g., Philadelphia chromosome in CML) or certain sarcomas, rather than MMR defects. - Lynch syndrome tumors usually exhibit **diploidy** and stable karyotypes compared to tumors following the **chromosomal instability (CIN)** pathway. *Telomere shortening* - This is a feature of **cellular senescence** and aging, where repeating sequences at the end of chromosomes are lost over time. - Cancer cells generally find ways to **maintain telomere length** (via telomerase) rather than experiencing shortening, which would limit their proliferative capacity. *DNA methylation* - While **hypermethylation** of the MLH1 promoter can cause sporadic MSI, this case specifies a **germline mutation** in a genetic study context. - Methylation is an **epigenetic modification** that affects gene expression but is not the primary molecular consequence arising directly from the loss of DNA repair enzyme function.

Question 8: A 45-year-old woman with breast cancer is being treated with trastuzumab (Herceptin). Laboratory analysis of her tumor cells shows 100-fold amplification of a specific gene. Analysis of the signal transduction pathway reveals constitutive activation of PI3K/AKT pathway. Which receptor is most likely overexpressed?

A. Human epidermal growth factor receptor 2 (HER2) (Correct Answer)
B. Vascular endothelial growth factor receptor (VEGFR)
C. Progesterone receptor (PR)
D. Estrogen receptor (ER)

Explanation: ***Human epidermal growth factor receptor 2 (HER2)*** - **Trastuzumab** is a monoclonal antibody specifically designed to target the **HER2/neu (ERBB2)** receptor, which is overexpressed in approximately 20-30% of breast cancers. - **HER2** is a receptor tyrosine kinase that, when amplified, leads to constitutive activation of the **PI3K/AKT** and **MAPK** pathways, driving uncontrolled cell proliferation. *Vascular endothelial growth factor receptor (VEGFR)* - **VEGFR** is primarily involved in **angiogenesis** (the formation of new blood vessels) and is the target of drugs like **bevacizumab**, not trastuzumab. - While important in many cancers, its signaling pathway is not the primary target in the standard clinical use of trastuzumab for breast cancer. *Progesterone receptor (PR)* - **PR** is a **nuclear receptor** that functions as a transcription factor, not a cell surface receptor tyrosine kinase that activates the **PI3K/AKT** pathway directly. - Overexpression of PR is managed with **hormonal therapies** (like aromatase inhibitors), but it is not the target of the antibody **trastuzumab**. *Estrogen receptor (ER)* - Similar to the progesterone receptor, the **ER** is an intracellular receptor used to guide treatment with drugs like **Tamoxifen**. - Genes for ER are not typically subject to the **100-fold amplification** described, as ER status is usually determined by ligand-dependent signaling rather than massive gene duplication.

Question 9: A researcher is studying a cell line that shows resistance to apoptosis despite DNA damage. Analysis reveals overexpression of a protein that normally prevents p53 from inducing cell cycle arrest. Which protein is most likely overexpressed?

A. MDM2 (Correct Answer)
B. Caspase-3
C. Cytochrome C
D. Bcl-2

Explanation: ***MDM2*** - **MDM2** functions as an **E3 ubiquitin ligase** that directly binds to **p53**, promoting its degradation and inhibiting its transcriptional activity. - Overexpression leads to the loss of **p53-mediated cell cycle arrest** (via p21) and apoptosis, allowing cells with **DNA damage** to survive and proliferate. *Caspase-3* - **Caspase-3** is an **executioner caspase** that plays a central role in the final stages of the apoptotic cascade, not the regulation of p53. - Overexpression would typically **promote apoptosis** rather than providing resistance to it after DNA damage. *Cytochrome C* - **Cytochrome C** is released from the **mitochondria** into the cytosol to activate the **apoptosome** during the intrinsic pathway of apoptosis. - Its release occurs **downstream** of p53 activation and is not a protein that inhibits p53-induced cell cycle arrest. *Bcl-2* - **Bcl-2** is an **anti-apoptotic** protein that prevents the release of Cytochrome C, but it does not directly regulate p53-mediated **cell cycle arrest**. - While its overexpression prevents apoptosis, the specific mechanism of inhibiting **p53's ability to induce arrest** points towards MDM2.

Question 10: A 6-month-old infant presents with severe anemia, jaundice, and hepatosplenomegaly. Hemoglobin electrophoresis shows predominantly HbF (fetal hemoglobin) with absent HbA. Which molecular defect best explains this clinical picture?

A. Deletion in alpha-globin gene causing alpha-thalassemia
B. Point mutation in beta-globin gene causing sickle cell disease
C. Deletion or mutation in beta-globin gene causing beta-thalassemia major (Correct Answer)
D. Mutation in gamma-globin gene

Explanation: ***Deletion or mutation in beta-globin gene causing beta-thalassemia major*** - This condition, also known as **Cooley's anemia**, results in a total or near-total absence of **beta-globin chain** production, leading to an **absence of HbA** (α2β2). - Symptoms manifest at approximately 6 months of age as **HbF** (α2γ2) production normally declines, resulting in **severe microcytic anemia**, **jaundice**, and compensatory **extramedullary hematopoiesis** (hepatosplenomegaly). *Deletion in alpha-globin gene causing alpha-thalassemia* - **Alpha-thalassemia** typically involves deletions of the alpha-globin genes; if severe (Hydrops Fetalis), it presents at birth with **Hb Barts** (γ4), not HbF. - Since alpha chains are required for HbF (α2γ2), a total absence of alpha-globin would prevent the formation of **fetal hemoglobin** entirely. *Point mutation in beta-globin gene causing sickle cell disease* - **Sickle cell disease** is caused by a specific **missense mutation** (glutamate to valine) and would show **HbS** on electrophoresis rather than a predominance of HbF with absent HbA. - While patients with sickle cell may have elevated HbF, it is the presence of **HbS** and characteristic **vaso-occlusive crises** that differentiate it from beta-thalassemia major. *Mutation in gamma-globin gene* - Mutations in the **gamma-globin gene** would affect fetal development and the production of **HbF**, which is the predominant hemoglobin shown in this infant. - A defect here would not cause the **absence of HbA**, as HbA production is dependent on the beta-globin gene, which occurs later in development.

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