miRNA and RNA Interference — MCQs
Which discovery in gene regulation was awarded the Nobel Prize in Physiology or Medicine in 2006?
During eukaryotic protein synthesis, phosphorylation of which of the following is enhanced by insulin?
Which of the following statements best describes the mechanism of action of insulin on target cells?
Which of the following statements about gene therapy is false?
What is the gene fusion associated with Ewing's sarcoma?
All of the following are growth promoting proto-oncogenes except?
Which of the following is a primarily RNA based technique?
What is the primary function of the sigma subunit of prokaryotic RNA polymerase?
Which type of RNA is primarily involved in gene silencing?
Transcription is inhibited by which of the following agents?
miRNA and RNA Interference Indian Medical PG Practice Questions and MCQs
Question 1: Which discovery in gene regulation was awarded the Nobel Prize in Physiology or Medicine in 2006?
- A. Discovery of RNA interference (RNAi) (Correct Answer)
- B. Role of mitochondrial DNA in cellular functions
- C. Involvement of lipoxins in inflammation
- D. Function of transcription factors in gene regulation
Explanation: ***Discovery of RNA interference (RNAi)*** - The 2006 Nobel Prize in Physiology or Medicine was awarded to **Andrew Z. Fire** and **Craig C. Mello** for their discovery of **RNA interference (RNAi)** in the nematode *C. elegans*. - This seminal work revealed a fundamental mechanism for **controlling gene flow** in cells, involving double-stranded RNA molecules that silence gene expression. *Role of mitochondrial DNA in cellular functions* - While the role of **mitochondrial DNA** is crucial for cellular energy production and has been extensively studied, it was not the subject of the 2006 Nobel Prize in Physiology or Medicine. - The discovery and understanding of mitochondrial DNA's function emerged over several decades, with significant contributions from various researchers, predating 2006 for its fundamental elucidation. *Involvement of lipoxins in inflammation* - **Lipoxins** are important lipid mediators involved in the resolution of **inflammation**, and their discovery and characterization are significant. - However, the Nobel Prize in 2006 specifically recognized a discovery in **gene regulation**, not lipid mediators of inflammation. *Function of transcription factors in gene regulation* - **Transcription factors** play a critical role in regulating gene expression by binding to specific DNA sequences. - While vital to understanding gene regulation, the discovery and characterization of transcription factors was not the particular focus of the 2006 Nobel Prize, which centered on RNAi.
Question 2: During eukaryotic protein synthesis, phosphorylation of which of the following is enhanced by insulin?
- A. eIF2
- B. eIF4A
- C. eIF4G
- D. eIF4E (Correct Answer)
Explanation: ***eIF4E*** - Insulin activates the **mTOR pathway**, which leads to activation of **Mnk1/2 kinases** that phosphorylate eIF4E at **Ser209**. - This phosphorylation enhances eIF4E's **affinity for the 5' cap structure** and increases **cap-dependent translation initiation** efficiency. *eIF4G* - While eIF4G is essential for **eIF4F complex formation**, its phosphorylation is not the primary target enhanced by insulin signaling. - Insulin's effect on eIF4G is mainly **indirect through 4E-BP1 phosphorylation**, which releases eIF4E to bind eIF4G. *eIF2* - **eIF2 phosphorylation** by kinases like **PERK, PKR, and GCN2** inhibits translation initiation during stress conditions. - This is **opposite to insulin's anabolic effects**, as insulin signaling typically promotes conditions that reduce eIF2 phosphorylation. *eIF4A* - eIF4A functions as an **RNA helicase** in the eIF4F complex, unwinding mRNA secondary structures. - While important for translation, **direct phosphorylation enhancement by insulin** is not a primary mechanism for eIF4A regulation.
Question 3: Which of the following statements best describes the mechanism of action of insulin on target cells?
- A. Insulin binds to a receptor on the outer surface of the plasma membrane, activating adenylate cyclase through the Gs protein.
- B. Insulin binds to a cytoplasmic receptor and is transferred as a hormone receptor complex to the nucleus to modulate gene expression.
- C. Insulin enters the cell and causes the release of calcium ions from intracellular stores.
- D. Insulin binds to a transmembrane receptor on the outer surface of the plasma membrane, activating the tyrosine kinase in the cytosolic domain of the receptor. (Correct Answer)
Explanation: ***Insulin binds to a transmembrane receptor on the outer surface of the plasma membrane, activating the tyrosine kinase in the cytosolic domain of the receptor.*** - **Insulin** is a **peptide hormone** and cannot freely pass through the lipid bilayer, thus it binds to a **transmembrane receptor** on the cell surface. - This binding leads to the activation of the receptor's intrinsic **tyrosine kinase activity** in the intracellular domain, initiating a signaling cascade. *Insulin binds to a cytoplasmic receptor and is transferred as a hormone receptor complex to the nucleus to modulate gene expression.* - This mechanism describes the action of **steroid hormones**, which are lipid-soluble and can cross the cell membrane, binding to **intracellular receptors**. - **Insulin** acts via a **cell surface receptor** and its downstream effects are mediated through signal transduction pathways, not direct nuclear translocation. *Insulin binds to a receptor on the outer surface of the plasma membrane, activating adenylate cyclase through the Gs protein.* - This mechanism is characteristic of **G-protein coupled receptors (GPCRs)**, which activate or inhibit enzymes like adenylate cyclase via G-proteins to produce second messengers like cyclic AMP. - The **insulin receptor** is a **receptor tyrosine kinase**, not a GPCR, and does not directly activate adenylate cyclase via Gs protein. *Insulin enters the cell and causes the release of calcium ions from intracellular stores.* - While some hormones and neurotransmitters can trigger the release of intracellular **calcium ions**, this is typically mediated by specific pathways (e.g., GPCRs linked to phospholipase C). - **Insulin** does not directly enter target cells to cause calcium release; its actions are primarily mediated through receptor tyrosine kinase signaling pathways.
Question 4: Which of the following statements about gene therapy is false?
- A. Gene also considered as drug
- B. Gene therapy can be used to treat some cancers.
- C. Has been tried in cystic fibrosis
- D. Gene therapy is only used for genetic disorders. (Correct Answer)
Explanation: ***Gene therapy is only used for genetic disorders.*** - This statement is **false** because gene therapy has applications beyond just genetic disorders. It is also being explored and used in the treatment of acquired diseases such as **cancer** and **infectious diseases**. - While it's a prominent approach for correcting genetic defects, its scope is much broader, involving the introduction or modification of genes to achieve a therapeutic effect in various conditions. *Gene also considered as drug* - This statement is **true**. Gene therapy products are often regulated as **drugs** or **biological products** by regulatory bodies like the FDA. - This is because they involve the delivery of genetic material that acts to modify gene expression or cell function to produce a therapeutic effect, similar to how traditional drugs work. *Has been tried in cystic fibrosis* - This statement is **true**. Gene therapy has been extensively investigated as a potential treatment for **cystic fibrosis (CF)**. - CF is caused by mutations in the **CFTR gene**, and researchers have attempted to deliver functional copies of this gene to the affected cells, particularly in the lungs, to correct the underlying defect. *Gene therapy can be used to treat some cancers.* - This statement is **true**. Gene therapy is an active area of research and treatment for various **cancers** [1]. - Approaches include introducing genes that make cancer cells more susceptible to chemotherapy, enhancing the immune system's ability to fight cancer, or directly killing cancer cells through gene delivery [1].
Question 5: What is the gene fusion associated with Ewing's sarcoma?
- A. EWS-FLI1 (Correct Answer)
- B. FUS-CHOP
- C. EWS-ATF1
- D. PAX3-FOXO1
Explanation: ***EWS-FLI1*** * This is the **most common and characteristic gene fusion** found in Ewing's sarcoma, occurring in about 85% of cases. * The fusion involves the **Ewing sarcoma RNA-binding protein 1 (EWSR1)** gene on chromosome 22 and the **Friend leukemia integration 1 transcription factor (FLI1)** gene on chromosome 11. *PAX3* * **PAX3** gene fusions, particularly **PAX3-FOXO1**, are associated with **alveolar rhabdomyosarcoma**, a different type of soft tissue sarcoma. * While both are pediatric tumors, their genetic drivers and typical histologies differ significantly from Ewing's sarcoma. *FUS-CHOP* * The **FUS-CHOP (DDIT3)** gene fusion is characteristic of **myxoid liposarcoma**, a distinct type of adipocytic tumor. * This fusion involves the **FUS RNA binding protein (FUS)** gene and the **DNA damage inducible transcript 3 (DDIT3)** gene. *EWS-ATF1* * The **EWS-ATF1** gene fusion is a molecular hallmark of **clear cell sarcoma** (also known as malignant melanoma of soft parts). * This fusion involves the **EWSR1** gene and the **activating transcription factor 1 (ATF1)** gene, leading to distinct biological and clinical features compared to Ewing's sarcoma.
Question 6: All of the following are growth promoting proto-oncogenes except?
- A. Fibroblast Growth Factor (FGF)
- B. TGF alpha
- C. TGF beta (Correct Answer)
- D. Platelet-Derived Growth Factor (PDGF)
Explanation: ***TGF beta*** - **TGF-β (Transforming Growth Factor-beta)** is primarily a **growth inhibitory cytokine** and a **tumor suppressor**, rather than a growth-promoting proto-oncogene [3]. - While it can have complex roles, its main function in the context of cancer is to **inhibit cell proliferation** and promote differentiation or apoptosis, unless its signaling pathway is disrupted. *Fibroblast Growth Factor (FGF)* - **FGFs** are a family of **growth factors** that play crucial roles in cell proliferation, differentiation, and tissue repair [1]. - **Overexpression** or aberrant signaling of FGF receptors can lead to uncontrolled cell growth and is associated with various cancers, making them **growth-promoting proto-oncogenes** [1]. *TGF alpha* - **TGF-α (Transforming Growth Factor-alpha)** is a **growth factor** that binds to the **epidermal growth factor receptor (EGFR)**, stimulating cell proliferation and differentiation [1]. - Its mechanism of action is distinctly different from TGF-β, and its involvement in **promoting cell growth** classifies it as a growth-promoting proto-oncogene [1]. *Platelet-Derived Growth Factor (PDGF)* - **PDGF** is a potent **mitogen** that stimulates cell division in various cell types, particularly fibroblasts and smooth muscle cells [2]. - **Dysregulation** of PDGF signaling can contribute to tumor growth and angiogenesis, confirming its role as a **growth-promoting proto-oncogene** [1], [2]. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Neoplasia, p. 292. [2] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. With Illustrations By, pp. 31-32. [3] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. The Lung, pp. 706-707.
Question 7: Which of the following is a primarily RNA based technique?
- A. Next generation sequencing
- B. RT-PCR (Correct Answer)
- C. Sanger's technique
- D. Western blotting
Explanation: ***RT-PCR (Reverse Transcriptase PCR)*** - RT-PCR is a **primarily RNA-based technique** that uses **RNA as the initial template** - The enzyme **reverse transcriptase** converts RNA into complementary DNA (cDNA) in the first step - This technique is essential for studying **gene expression**, detecting **RNA viruses**, and analyzing **mRNA levels** - Unlike standard PCR which amplifies DNA, RT-PCR **begins with RNA** as the starting material *Next generation sequencing* - NGS is primarily used for **sequencing DNA fragments** - While RNA-seq exists, it requires **conversion of RNA to cDNA** first, and the actual sequencing chemistry reads DNA - The core technology is **DNA-based** *Sanger's technique* - **Sanger sequencing** is a method for determining the **nucleotide sequence of DNA** - It directly uses **DNA as a template** and does not involve RNA - This is a classical **DNA sequencing method** *Western blotting* - This technique is used for the **detection and quantification of specific proteins** - It involves protein separation by electrophoresis, membrane transfer, and antibody detection - This is a **protein-based technique**, not nucleic acid-based
Question 8: What is the primary function of the sigma subunit of prokaryotic RNA polymerase?
- A. Is inhibited by α-amanitin
- B. Specifically recognizes the promoter site (Correct Answer)
- C. Is part of the core enzyme
- D. Inhibits the activity of RNA polymerase
Explanation: ***Specifically recognizes the promoter site*** - The **sigma subunit** is crucial for **transcription initiation** in prokaryotes, enabling the RNA polymerase holoenzyme to specifically bind to **promoter sequences** on the DNA. - This specific recognition ensures that transcription begins at the correct start site, making it a key component for accurate gene expression. *Inhibits the activity of RNA polymerase* - The sigma subunit does not inhibit RNA polymerase; rather, it **facilitates** its activity by guiding it to the correct transcription start sites. - After initiation, the sigma subunit often **dissociates** from the core enzyme, allowing the core polymerase to proceed with elongation. *Is inhibited by α-amanitin* - **α-amanitin** is a toxin that primarily inhibits **eukaryotic RNA polymerases**, particularly RNA polymerase II, and is not known to inhibit prokaryotic RNA polymerase or its sigma subunit. - Prokaryotic RNA polymerase has a different structure and mechanism, rendering it **insensitive** to α-amanitin. *Is part of the core enzyme* - The sigma subunit is **not considered part of the core enzyme**; the core enzyme consists of the α, β, β', and ω subunits. - Together with the core enzyme, the sigma subunit forms the **RNA polymerase holoenzyme**, which is responsible for initiating transcription.
Question 9: Which type of RNA is primarily involved in gene silencing?
- A. rRNA
- B. tRNA
- C. miRNA (Correct Answer)
- D. mRNA
Explanation: ***miRNA*** - **miRNA** (microRNA) is a small non-coding RNA molecule that plays a crucial role in **post-transcriptional regulation of gene expression**. - It functions by binding to complementary messenger RNA (mRNA) molecules, leading to **mRNA degradation** or **inhibition of translation**, thereby silencing genes. - miRNA is the primary RNA type involved in **gene silencing** through the RNA interference (RNAi) pathway. *rRNA* - **rRNA** (ribosomal RNA) is a primary component of **ribosomes**, the cellular machinery responsible for protein synthesis. - Its main function is to **catalyze peptide bond formation** and provide structural integrity to the ribosome, not gene silencing. *tRNA* - **tRNA** (transfer RNA) is responsible for carrying specific **amino acids** to the ribosome during protein synthesis. - It acts as an adapter molecule, translating the **genetic code** in mRNA into an amino acid sequence. *mRNA* - **mRNA** (messenger RNA) carries genetic information from **DNA to ribosomes** for protein synthesis. - While mRNA can be targeted by gene silencing mechanisms (like miRNA), it is not the RNA type that performs the silencing function itself.
Question 10: Transcription is inhibited by which of the following agents?
- A. Actinomycin D (Correct Answer)
- B. Amanitin
- C. Chloramphenicol
- D. Streptomycin
Explanation: **Explanation:** Transcription is the process of synthesizing RNA from a DNA template. **Actinomycin D (Dactinomycin)** is a potent inhibitor of transcription in both prokaryotes and eukaryotes. It works by **intercalating between cytosine-guanine (C-G) base pairs** of the DNA template, creating a stable complex that physically blocks the movement of RNA polymerase, thereby preventing RNA chain elongation. **Analysis of Options:** * **A. Actinomycin D (Correct):** As described, it inhibits transcription by DNA intercalation. Clinically, it is used as a chemotherapy agent (e.g., for Wilms tumor and Ewing sarcoma). * **B. Amanitin (α-Amanitin):** While this also inhibits transcription (specifically **RNA Polymerase II** in eukaryotes), it is derived from the *Amanita phalloides* mushroom. In many MCQ contexts, if both are present, Actinomycin D is the classic general inhibitor cited for its action on the DNA template itself. (Note: Some sources consider both correct; however, Actinomycin D is the universal inhibitor for both cell types). * **C. Chloramphenicol:** This is a **translation (protein synthesis) inhibitor**. It binds to the **50S ribosomal subunit** of bacteria, inhibiting peptidyl transferase. * **D. Streptomycin:** This is an aminoglycoside that inhibits **translation** by binding to the **30S ribosomal subunit**, causing misreading of mRNA and inhibiting the initiation of protein synthesis. **High-Yield Clinical Pearls for NEET-PG:** * **Rifampicin:** Inhibits bacterial transcription by binding to the **beta-subunit of DNA-dependent RNA polymerase**. * **α-Amanitin:** Found in "Death Cap" mushrooms; causes severe hepatotoxicity by halting mRNA synthesis. * **Prokaryotic vs. Eukaryotic Inhibition:** Always distinguish if a drug acts on the 30S/50S (Prokaryotic translation) or 40S/60S (Eukaryotic translation) subunits.
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