Gene Expression and Regulation — MCQs
Which of the following statements is NOT applicable to bacterial genomes?
Which of the following is considered a fundamental defense mechanism in psychology?
If the percentage of thymine residues in DNA is 28%. What is the percentage of cytosine?
Which type of mutation can act as a suppressor to restore the wild-type phenotype in organisms carrying a mutant gene?
Which type of RNA is primarily involved in gene silencing?
Assertion: DNA methylation leads to gene silencing. Reason: Methylation prevents binding of transcription factors to promoter regions.
What is the technique for accurate quantification of gene expression?
Recombinant human insulin is made by -
What is Northern blot used to detect?
Effect of environment on genes is called?
Gene Expression and Regulation Indian Medical PG Practice Questions and MCQs
Question 1: Which of the following statements is NOT applicable to bacterial genomes?
- A. It is composed of DNA
- B. It does not contain histones
- C. It is circular
- D. Its DNA has both introns and exons (Correct Answer)
Explanation: ***Its DNA has both introns and exons*** - **Bacterial genomes** are typically organized as continuous coding sequences and **lack introns** (non-coding regions) that are characteristic of eukaryotic genes. - The presence of introns and their subsequent splicing is a hallmark of **eukaryotic gene expression**, not prokaryotic. *It is composed of DNA* - The genetic material of bacteria, like all cellular life forms, is primarily composed of **DNA (deoxyribonucleic acid)**. - DNA serves as the blueprint for all cellular processes and hereditary information. *It does not contain histones* - **Bacterial DNA** is typically compacted by various DNA-binding proteins, but these are not the **histone proteins** found in eukaryotes. - Histones are fundamental for packaging DNA into **chromatin** in eukaryotic cells. *It is circular* - The main chromosome in most bacteria is **covalently closed** and **circular**, unlike the linear chromosomes found in eukaryotes. - This circular structure aids in replication and stability within the bacterial cell.
Question 2: 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 3: If the percentage of thymine residues in DNA is 28%. What is the percentage of cytosine?
- A. 36%
- B. 44%
- C. 22% (Correct Answer)
- D. 28%
Explanation: ***22%*** - According to **Chargaff's rules**, in a DNA molecule, the amount of **adenine (A) is equal to the amount of thymine (T)**, and the amount of **guanine (G) is equal to the amount of cytosine (C)**. - If thymine (T) is 28%, then adenine (A) is also 28%, making a total of 56% for A+T. The remaining 44% (100% - 56%) is split equally between guanine and cytosine, so cytosine (C) is 22%. *36%* - This percentage would be plausible if the sum of adenine and thymine were 28%, which is incorrect as A and T are equal and their sum would thus be 56%. - This value does not adhere to the principle of **base pairing complementarity** and the total percentage of all bases summing to 100%. *44%* - This would be the combined percentage of guanine and cytosine, not the percentage of cytosine alone. - If cytosine were 44%, then guanine would also be 44%, leading to a total of 88% for G+C, which is inconsistent with T being 28%. *28%* - This is the percentage of thymine, and by **Chargaff's rules**, it would also be the percentage of adenine, not cytosine. - Cytosine percentages are derived from the remaining proportion of bases after accounting for adenine and thymine.
Question 4: Which type of mutation can act as a suppressor to restore the wild-type phenotype in organisms carrying a mutant gene?
- A. Frameshift mutation of coding gene
- B. Mutation of tRNA (Correct Answer)
- C. Deletion of mutant gene
- D. Addition of another normal gene
Explanation: ***Mutation of tRNA*** - A **tRNA suppressor mutation** can alter its anticodon, allowing it to recognize a **stop codon** (nonsense suppressor) or a missense codon, and insert an amino acid, thereby suppressing the original mutation. - This is a classic example of an **intergenic suppressor mutation** that acts at a different genetic locus from the original mutation. - These suppressors are particularly effective for **nonsense mutations** (premature stop codons) and certain missense mutations by correcting the decoding error during translation. *Frameshift mutation of coding gene* - A single frameshift mutation causes a shift in the **reading frame**, leading to a completely different protein sequence downstream and often a premature stop codon, which would worsen the phenotype. - While a **second compensating frameshift** mutation in the same gene could theoretically restore the reading frame (acting as an intragenic suppressor), this is context-dependent and less reliable than tRNA suppressors. - The question asks for mutations that "can act as a suppressor," and **tRNA mutations are the more universally recognized and reliable suppressor mechanism** in classical genetics. *Deletion of mutant gene* - **Deleting the mutant gene** removes the genetic information entirely but does not restore wild-type function; instead, it typically results in **loss of function** or complete absence of the protein. - This would lead to a **null phenotype** rather than restoration of wild-type phenotype, especially if the gene is essential. *Addition of another normal gene* - The **addition of another normal (wild-type) gene copy** provides a functional protein that can compensate for the mutant gene's deficiency. - While this can restore a wild-type phenotype, it represents **gene complementation** or gene therapy, not a true suppressor mutation that modifies the interpretation or expression of the existing mutant allele.
Question 5: 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 6: Assertion: DNA methylation leads to gene silencing. Reason: Methylation prevents binding of transcription factors to promoter regions.
- A. Assertion is true but reason is false.
- B. Both assertion and reason are true and reason is the correct explanation. (Correct Answer)
- C. Both assertion and reason are true but reason is not the correct explanation.
- D. Both assertion and reason are false.
Explanation: ***Both assertion and reason are true and reason is the correct explanation.*** - **DNA methylation** at **CpG islands** in promoter regions is a well-established **epigenetic mechanism for gene silencing** - The reason directly explains HOW methylation causes silencing: **methylation prevents transcription factor binding** to promoter regions, blocking transcriptional machinery - Both statements are factually correct AND the reason provides the mechanistic explanation for the assertion *Assertion is true but reason is false.* - While the assertion is correct (DNA methylation does lead to gene silencing), the reason is also TRUE, not false - Methylation preventing transcription factor binding is indeed a **primary mechanism** of gene silencing - This option would only be correct if the reason statement were factually incorrect *Both assertion and reason are true but reason is not the correct explanation.* - Both statements are individually true, but this option is incorrect because the reason IS the correct explanation - The prevention of transcription factor binding **directly explains** how methylation silences genes - If this were correct, the reason would describe an unrelated consequence of methylation, not the causal mechanism *Both assertion and reason are false.* - Both statements are well-established biological facts - DNA methylation-mediated gene silencing is a fundamental epigenetic mechanism - Prevention of transcription factor binding is a validated mechanism of this silencing
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: Recombinant human insulin is made by -
- A. cDNA of pancreatic cell (Correct Answer)
- B. cDNA from any eukaryote cell
- C. Genome of pancreatic cell
- D. Genome of any eukaryote
Explanation: ***CDNA of pancreatic cell*** - **Recombinant human insulin** is produced using **cDNA** (complementary DNA) synthesized from the **mRNA** of human pancreatic cells, as these cells naturally produce insulin. - This cDNA ensures that only the **coding sequences** for insulin are used, without introns, making it suitable for expression in prokaryotic hosts like *E. coli*. *CDNA from any eukaryote cell* - While insulin is a eukaryotic protein, using cDNA from "any eukaryote cell" would not be specific enough, as only **pancreatic islet beta cells** produce insulin. - Other eukaryotic cells do not express the insulin gene, so their cDNA would not contain the necessary genetic information. *Genome of pancreatic cell* - Although the **genome of a pancreatic cell** contains the insulin gene, it also includes **introns** (non-coding regions) that must be removed through splicing in eukaryotic cells. - If directly used in prokaryotic systems (like *E. coli*), which lack the machinery to remove introns, it would lead to an incorrect or non-functional protein. *Genome of any eukaryote* - Similar to "genome of pancreatic cell," using the **genome of any eukaryote** would be problematic due to the presence of introns and the general lack of the insulin gene in most eukaryotic cells. - This option combines the disadvantages of non-specificity and the presence of introns that are incompatible with prokaryotic expression systems.
Question 9: 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.
Question 10: Effect of environment on genes is called?
- A. Euthenics
- B. Positive Eugenics
- C. Negative Eugenics
- D. Epigenetics (Correct Answer)
Explanation: ***Epigenetics*** - **Epigenetics** refers to heritable changes in **gene expression** that do not involve alterations to the underlying **DNA sequence**. - These changes are often influenced by **environmental factors**, such as diet, stress, and exposure to toxins, which can affect how genes are turned on or off. *Positive Eugenics* - **Positive eugenics** aims to improve the human population by encouraging the reproduction of individuals deemed to have "desirable" traits. - This concept is ethically controversial and focuses on directed breeding rather than environmental gene influence. *Negative Eugenics* - **Negative eugenics** aims to reduce the prevalence of "undesirable" traits in the human population by discouraging or preventing the reproduction of individuals deemed to possess them. - Like positive eugenics, this is a highly controversial concept focused on limiting reproduction based on perceived genetic quality. *Euthenics* - **Euthenics** is a movement focused on improving human well-being and development by improving living conditions and the environment. - While it acknowledges the impact of the environment, it focuses on societal and lifestyle improvements rather than the direct molecular changes in gene expression.
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