Regulation of Gene Expression — MCQs
What is the primary function of the sigma subunit of prokaryotic RNA polymerase?
Which of the following is not associated with post-transcription modification?
Which of the following is considered a fundamental defense mechanism in psychology?
DNA Methylation is not related to?
Gene silencing refers to a gene that would be expressed under normal circumstances being switched off by cell machinery. Which one of the following cellular components is not involved in gene silencing?
Mutations are due to changes in:
What is the technique for accurate quantification of gene expression?
Which type of RNA is primarily involved in gene silencing?
Northern blotting used in separation and diagnosis of:
What is Northern blot used to detect?
Regulation of Gene Expression Indian Medical PG Practice Questions and MCQs
Question 1: 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 2: Which of the following is not associated with post-transcription modification?
- A. 5' capping
- B. Glycosylation (Correct Answer)
- C. Methylation
- D. Endonuclease cleavage
Explanation: ***Glycosylation*** - **Glycosylation** is a type of post-translational modification, which involves the enzymatic addition of carbohydrates to proteins or lipids, not RNA. - This process is crucial for protein folding, stability, and function in the cell, occurring after translation has been completed. *5' capping* - **5' capping** is a crucial post-transcriptional modification of eukaryotic pre-mRNA, involving the addition of a 7-methylguanosine cap to the 5' end. - This cap protects the mRNA from degradation, facilitates nuclear export, and is essential for translation initiation. *Methylation* - **Methylation** can occur as a post-transcriptional modification, affecting various RNA types including tRNA, rRNA, and mRNA. - For mRNA, internal methylation, particularly of adenosine residues (m6A), plays a role in mRNA stability, splicing, and translation regulation. *Endonuclease cleavage* - **Endonuclease cleavage** is a significant post-transcriptional modification, particularly in the maturation of rRNA and tRNA, where larger precursor molecules are cut into functional smaller units. - In mRNA processing, endonuclease cleavage is involved in the formation of the 3' end, signaling for the addition of the poly-A tail.
Question 3: Which of the following is considered a fundamental defense mechanism in psychology?
- A. Alienation
- B. Confabulation
- C. Repression (Correct Answer)
- D. Suppression
Explanation: ***Repression*** - **Repression** is the **fundamental unconscious defense mechanism** where unacceptable thoughts, feelings, or memories are pushed out of conscious awareness to protect the ego. - It is considered the foundational defense mechanism because it operates automatically and without conscious effort, forming the basis for many other defense mechanisms. *Alienation* - **Alienation** refers to a feeling of estrangement or disconnection from others, society, or oneself, often due to social or psychological factors, but it is not a defense mechanism. - It describes a state of being rather than an active psychological process used to cope with anxiety. *Confabulation* - **Confabulation** is the creation of false autobiographical memories without the intent to deceive, often seen in neurological conditions like **Korsakoff's syndrome**. - It is a symptom of memory impairment, not an active psychological defense mechanism. *Suppression* - **Suppression** is a defense mechanism but is considered a mature/conscious defense; it involves deliberately and consciously putting unwanted thoughts or feelings out of mind. - Unlike **repression**, **suppression** is an intentional and relatively aware act of avoiding disturbing thoughts.
Question 4: DNA Methylation is not related to?
- A. DNA Replication
- B. Gene silencing
- C. Capping (Correct Answer)
- D. Mismatch repair
Explanation: ***Capping*** - **Capping** is a modification of messenger RNA (mRNA) that occurs during **mRNA processing** in eukaryotes, involving the addition of a 7-methylguanosine cap to the 5' end of the mRNA molecule. - This process is crucial for mRNA stability, translation initiation, and nuclear export, and is entirely **independent of DNA modifications** like DNA methylation. *DNA Replication* - DNA methylation plays a role in **DNA replication** to distinguish newly synthesized strands from parental strands during **DNA repair**. - In bacteria, methylation at specific sites (**Dam methylase**) helps in **mismatch repair** by identifying the parental strand. *Gene silencing* - **DNA methylation** of CpG islands in promoter regions is a well-established mechanism for **gene silencing** by altering chromatin structure and preventing transcription factor binding. - This epigenetic modification leads to stable transcriptional repression and is critical for processes like X-chromosome inactivation and genomic imprinting. *Mismatch repair* - In prokaryotes, **DNA methylation** marks the parental strand, which is used by the **mismatch repair system** to correct errors on the newly synthesized, unmethylated strand. - In eukaryotes, while not directly marking strands, DNA methylation can influence the efficiency of mismatch repair pathways by altering chromatin accessibility.
Question 5: Gene silencing refers to a gene that would be expressed under normal circumstances being switched off by cell machinery. Which one of the following cellular components is not involved in gene silencing?
- A. Double stranded RNA
- B. siRNA
- C. Micro-RNA
- D. Ribosomal RNA (Correct Answer)
Explanation: ***Micro-RNA*** - **Micro-RNAs** play a crucial role in gene regulation by binding to complementary sequences in mRNA, leading to gene silencing or degradation [1]. - They are involved in post-transcriptional regulation, effectively controlling gene expression at the **mRNA level** [1]. *Si RNA* - While **small interfering RNA (siRNA)** is also involved in gene silencing, it operates through a slightly different mechanism, primarily within RNA interference pathways. - SiRNAs typically require specific machinery for their function and are not the primary agents of gene silencing described in the question. *Double stranded RNA* - **Double-stranded RNA (dsRNA)** can induce silencing but serves primarily as a trigger for the RNA interference pathway rather than being the active component in gene silencing itself. - It is often utilized in research and therapeutic contexts but does not directly engage in the gene silencing process. *Ribosomal RNA* - **Ribosomal RNA (rRNA)** is primarily involved in protein synthesis and the structural component of ribosomes, with no role in gene silencing mechanisms. - It serves as a scaffold for ribosome assembly and is not implicated in the regulation of gene expression. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. With Illustrations By, pp. 16-18.
Question 6: Mutations are due to changes in:
- A. DNA nucleotide sequence (Correct Answer)
- B. RNA nucleotide sequence
- C. Amino acid sequence of ribonuclease
- D. Cell membrane
Explanation: ***DNA nucleotide sequence*** - **Mutations** are defined as changes in the **genetic material**, which is primarily composed of **DNA**. - These changes in the **nucleotide sequence** of DNA can alter the genetic code, leading to changes in **protein structure and function**. *RNA nucleotide sequence* - While RNA can have its nucleotide sequence altered, these changes are generally not considered true **mutations** in the heritable sense for most organisms. - RNA is typically a temporary molecule, and changes to its sequence are usually not passed down to subsequent generations. *Amino acid sequence of ribonuclease* - An altered **amino acid sequence** in a protein like ribonuclease is a consequence of a **mutation in the DNA**, not the mutation itself. - **Ribonucleases** are enzymes that catalyze the degradation of RNA, and their structure is determined by the **DNA sequence**. *Cell membrane* - The cell membrane is a **lipid bilayer** with embedded proteins that regulates cellular transport and communication. - While its components can be affected by genetic mutations, alterations in the cell membrane itself do not constitute the primary definition of a **mutation**.
Question 7: What is the technique for accurate quantification of gene expression?
- A. PCR
- B. Real-Time Reverse Transcriptase PCR (Correct Answer)
- C. Reverse Transcriptase PCR
- D. Northern blot
Explanation: ***Real-Time Reverse Transcriptase PCR*** - This technique allows for the **quantification of gene expression** by concurrently reverse-transcribing RNA to cDNA and amplifying it while monitoring the accumulation of DNA in real-time using fluorescent reporters. - The ** threshold cycle (Ct) value** is inversely proportional to the initial amount of target mRNA, enabling precise quantification. *Northern blot* - This method is used to detect **RNA sequences** and can provide semi-quantitative data about gene expression levels based on band intensity. - However, it is generally **less sensitive** and provides less precise quantification compared to real-time PCR. *PCR* - **Standard PCR** amplifies DNA, but it is not directly used for gene expression quantification as it starts with DNA templates. - While it can be used to detect the presence of a gene, it does not quantify its expression without further modifications or additional steps like reverse transcription and real-time monitoring. *Reverse Transcriptase PCR* - This technique involves **reverse transcribing RNA into cDNA** and then performing standard PCR to amplify the cDNA. - While it confirms the presence of mRNA and allows for cDNA amplification, it is a **qualitative or semi-quantitative** method for expression, as the endpoint detection does not accurately reflect initial mRNA concentration due to plateau effects.
Question 8: 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 9: Northern blotting used in separation and diagnosis of:
- A. DNA
- B. RNA (Correct Answer)
- C. Histones
- D. Proteins
Explanation: ***RNA*** - **Northern blotting** is a molecular biology technique used to detect specific **RNA sequences** in a sample. - It involves separating RNA fragments by size using gel electrophoresis, transferring them to a membrane, and then probing with a labeled complementary DNA or RNA sequence. *DNA* - **Southern blotting** is the technique specifically designed for the detection and analysis of specific **DNA sequences**. - While RNA can be used as a probe in Southern blotting, the primary target molecule for separation and diagnosis is DNA. *Histones* - **Histones** are proteins and are not typically targeted by Northern blotting, which is for nucleic acids. - Techniques like **Western blotting** or specific chromatin immunoprecipitation (ChIP) assays are used to study histones. *Proteins* - **Western blotting** is the technique used for the separation and detection of specific **proteins** in a sample. - Proteins are separated by size via SDS-PAGE, transferred to a membrane, and detected using specific antibodies.
Question 10: What is Northern blot used to detect?
- A. Protein
- B. Immunoglobulin
- C. RNA (Correct Answer)
- D. DNA
Explanation: ***RNA*** - **Northern blot** is a laboratory technique used to detect specific **RNA** molecules among a mixture of RNA. - It involves separating RNA fragments by **gel electrophoresis**, transferring them to a membrane, and then probing with a labeled complementary sequence. *Protein* - **Proteins** are typically detected using a **Western blot**, which involves similar separation and transfer techniques but uses **antibodies** as probes. - While RNA codes for proteins, Northern blot *directly* detects RNA transcripts, not the resulting protein products. *Immunoglobulin* - **Immunoglobulins** (antibodies) are a type of protein, and their detection usually falls under **Western blot** or specific immunological assays like **ELISA**. - Northern blot is specifically designed for nucleic acid analysis, not protein detection. *DNA* - **DNA** is detected using a **Southern blot** technique, which also involves electrophoresis, transfer to a membrane, and hybridization with a complementary probe. - The name "Northern blot" was coined as a play on "Southern blot" because it uses similar methodology but for RNA instead of DNA.
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