Transcription Factors and Gene Regulation Indian Medical PG Practice Questions and MCQs
Practice Indian Medical PG questions for Transcription Factors and Gene Regulation. These multiple choice questions (MCQs) cover important concepts and help you prepare for your exams.
Transcription Factors and Gene Regulation Indian Medical PG Question 1: miRNA binds to which part of the mRNA to inhibit translation?
- A. Gene promoter
- B. 3'UTR (Correct Answer)
- C. Gene body
- D. 5'UTR
Transcription Factors and Gene Regulation Explanation: ***3'UTR***
- MicroRNAs (miRNAs) are small non-coding RNA molecules that regulate gene expression.
- They primarily bind to the **3' untranslated region (3'UTR)** of messenger RNA (mRNA) molecules, leading to translational repression or mRNA degradation.
*Gene promoter*
- The **gene promoter** is a region of DNA located upstream of a gene, where regulatory proteins bind to initiate transcription.
- miRNAs do not directly bind to gene promoters to inhibit translation.
*Gene body*
- The **gene body** refers to the entire transcribed region of a gene, including exons and introns.
- While some regulatory elements can be found within the gene body, the primary binding site for miRNAs to exert translational control is the 3'UTR.
*5'UTR*
- The **5' untranslated region (5'UTR)** is located at the 5' end of an mRNA molecule, upstream of the start codon.
- While the 5'UTR can play a role in regulating translation initiation, it is not the primary target for miRNA binding to inhibit translation.
Transcription Factors and Gene Regulation Indian Medical PG Question 2: Steroid hormone receptors have attachment site for all except:
- A. Hormone responsive element
- B. Steroid hormone
- C. Transcription activators (Correct Answer)
- D. Transcription repressors
Transcription Factors and Gene Regulation Explanation: ***Transcription activators***
- **Steroid hormone receptors** bind directly to **steroid hormones** and **hormone response elements (HREs)** on DNA, as well as to **transcription repressors** in their inactive state.
- They do not have a direct attachment site for **transcription activators**; rather, activated steroid receptors can *act* as transcription activators or co-activators through protein-protein interactions.
*Hormone responsive element*
- This is a specific **DNA sequence** in the promoter region of target genes where the **steroid hormone-receptor complex** binds to regulate gene transcription.
- It defines the genomic target for the activated steroid receptor, ensuring **gene-specific responses**.
*Steroid hormone*
- The **steroid hormone** itself binds to its specific receptor, inducing a conformational change that allows the receptor to translocate to the nucleus and bind to DNA.
- This binding is essential for the **receptor's activation** and subsequent gene regulation.
*Transcription repressors*
- In the absence of a steroid hormone, **transcription repressors** (e.g., heat shock proteins) are often bound to the **steroid hormone receptor**, preventing its activation and binding to DNA.
- Upon hormone binding, these repressors dissociate, allowing the receptor to become active and modulate **gene expression**.
Transcription Factors and Gene Regulation Indian Medical PG Question 3: Which of the following statements regarding Huntington’s chorea is true?
- A. It is a trinucleotide repeat expansion type of disorder (Correct Answer)
- B. There is a loss of function type of mutation.
- C. It is an autosomal recessive disorder.
- D. Increased number of CAA repeats.
Transcription Factors and Gene Regulation Explanation: ***It is a trinucleotide repeat expansion type of disorder***
- Huntington's chorea is caused by an expansion of a **CAG trinucleotide repeat** in the **huntingtin gene (HTT)**.
- This expansion leads to a misfolded protein and an **autosomal dominant** neurodegenerative disorder [1].
*There is a loss of function type of mutation.*
- Huntington's chorea is primarily a **gain-of-function** mutation, where the expanded polyglutamine tract in the huntingtin protein leads to **toxic protein aggregation** and neuronal dysfunction.
- While there might be some aspects of altered protein function, the core pathology is attributed to the **toxic effects** of the abnormal protein rather than a simple loss of its original function [1].
*It is an autosomal recessive disorder.*
- Huntington's chorea is an **autosomal dominant** disorder, meaning only one copy of the mutated gene is sufficient to cause the disease.
- Each child of an affected parent has a **50% chance** of inheriting the disease.
*Increased number of CAA repeats.*
- Huntington's chorea is characterized by an increased number of **CAG trinucleotide repeats**, not CAA repeats.
- The expansion of these CAG repeats beyond a certain threshold (typically >35-40 repeats) in the huntingtin gene is directly responsible for the disease.
Transcription Factors and Gene Regulation Indian Medical PG Question 4: Identify the gene commonly involved in the condition shown in the image?
- A. RAS
- B. RET
- C. BRAF V600E (Correct Answer)
- D. P53
Transcription Factors and Gene Regulation Explanation: ***BRAF V600E***
- The image displays cells with **Langerhans cell morphology**, including folded nuclei and abundant pale cytoplasm, which are characteristic of **Langerhans cell histiocytosis (LCH)** [1].
- The **BRAF V600E mutation** is the most common genetic alteration found in LCH, present in about 50-60% of cases and activating the MAPK pathway [1].
*RAS*
- **RAS mutations** are frequently seen in various cancers, including colorectal adenocarcinoma, pancreatic adenocarcinoma, and non-small cell lung cancer.
- While RAS pathway activation can occur in LCH, a direct RAS mutation is not the most common genetic driver; rather, downstream effectors like BRAF V600E are more prominent [1].
*RET*
- **RET mutations** are primarily associated with **medullary thyroid carcinoma** (in both sporadic and inherited forms like MEN 2A and MEN 2B) and can also be found in certain types of lung cancer.
- They are not a characteristic genetic alteration for Langerhans cell histiocytosis.
*P53*
- The **TP53 gene** encodes the tumor suppressor protein p53, and mutations in this gene are among the most frequent genetic alterations across a wide spectrum of human cancers.
- Although p53 plays a critical role in cell cycle regulation and apoptosis, it is not a primary or common driver mutation specifically associated with Langerhans cell histiocytosis [1].
**References:**
[1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Diseases of White Blood Cells, Lymph Nodes, Spleen, and Thymus, pp. 629-630.
Transcription Factors and Gene Regulation Indian Medical PG Question 5: 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
Transcription Factors and Gene Regulation 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.
Transcription Factors and Gene Regulation Indian Medical PG Question 6: Which of the following is an X-linked dominant disorder?
- A. Vitamin D resistant rickets (Correct Answer)
- B. Red green color blindness
- C. Achondroplasia
- D. Familial hypercholesterolemia
Transcription Factors and Gene Regulation Explanation: ***Vitamin D resistant rickets***
- This is an **X-linked dominant** disorder characterized by impaired renal phosphate reabsorption and defective vitamin D metabolism, leading to **rickets-like symptoms** despite adequate vitamin D intake.
- Affected individuals show **hypophosphatemia** and bone defects, with sons and daughters of affected fathers being affected.
*Red-green color blindness*
- This is an **X-linked recessive** disorder, meaning it primarily affects males and is passed from carrier mothers to their sons.
- Affected individuals have difficulty distinguishing **red and green hues** due to defects in cone photoreceptors.
*Achondroplasia*
- This is an **autosomal dominant** disorder caused by a mutation in the **FGFR3 gene**, leading to dwarfism.
- It is not X-linked and affects both sexes equally, with an affected individual having a 50% chance of passing it to each child.
*Familial hypercholesterolemia*
- This is an **autosomal dominant** metabolic disorder characterized by extremely high levels of **LDL cholesterol** due to defects in the LDL receptor.
- It is not X-linked and can lead to premature cardiovascular disease, affecting both males and females.
Transcription Factors and Gene Regulation Indian Medical PG Question 7: Which one of the following is an autosomal dominant disorder?
- A. Cystic fibrosis
- B. Hereditary spherocytosis (Correct Answer)
- C. Sickle cell anemia
- D. G-6PD deficiency
Transcription Factors and Gene Regulation Explanation: ***Hereditary spherocytosis***
- It is characterized by **autosomal dominant inheritance** [1], leading to the destruction of red blood cells.
- Mutations in proteins that maintain the **red blood cell membrane** integrity result in spherocyte formation [1].
*Cystic fibrosis*
- This condition follows a **autosomal recessive inheritance pattern**, requiring two copies of the mutated gene for disease manifestation.
- It is caused by mutations in the **CFTR gene**, affecting chloride transport and leading to thick secretions.
*G-6PD deficiency*
- This disorder is inherited in an **X-linked recessive manner** [2], primarily affecting males and transmitted through carrier females.
- Characterized by **hemolytic anemia** triggered by certain medications or infections, it does not follow dominant inheritance [2].
*Sickle cell anemia*
- Sickle cell anemia is also an **autosomal recessive disorder** [3], meaning affected individuals must inherit two copies of the sickle cell gene.
- It results in a mutation in the **HBB gene**, leading to the production of abnormal hemoglobin (HbS) [3].
Transcription Factors and Gene Regulation Indian Medical PG Question 8: Which one of the following statements about chromatin is not true?
- A. DNA winds approximately 1.75 times around the nucleosomes
- B. Covalent modification of histones influence chromatin compaction
- C. Non-histone proteins are part of mitotic chromosomes
- D. H2A-H2B bind to both the entry and exit ends of DNA in nucleosomes (Correct Answer)
Transcription Factors and Gene Regulation Explanation: ***H2A-H2B bind to both the entry and exit ends of DNA in nucleosomes***
- This statement is **not entirely true** as presented because while **H2A-H2B dimers** do make contacts with DNA near entry/exit regions, they do not bind **exclusively** at these ends.
- In the nucleosome structure, two H2A-H2B dimers flank the central **(H3-H4)₂ tetramer** and interact with DNA throughout approximately **30 base pairs on each side**.
- The **entry and exit points** of nucleosomal DNA are primarily stabilized by **linker histones (H1)**, which bind to the dyad axis and linker DNA regions.
- The statement oversimplifies the complex three-dimensional interactions within the nucleosome core particle.
*DNA winds approximately 1.75 times around the nucleosomes*
- This statement is **true**; approximately **1.65 to 1.75 turns** of DNA (about 146-147 base pairs) wrap around the **histone octamer** to form the core nucleosome particle.
- This precise winding is crucial for the compaction of DNA into eukaryotic chromatin and represents the fundamental repeating unit of chromatin structure.
*Covalent modification of histones influence chromatin compaction*
- This statement is **true**; **post-translational modifications** (PTMs) such as acetylation, methylation, phosphorylation, and ubiquitination on histone tails significantly impact **chromatin structure and accessibility**.
- For example, **histone acetylation** generally leads to a more open chromatin conformation (euchromatin) by neutralizing positive charges, facilitating gene expression.
- **Histone methylation** can lead to either open or compact chromatin depending on the specific residue modified (e.g., H3K4me3 for activation, H3K9me3 for repression).
*Non-histone proteins are part of mitotic chromosomes*
- This statement is **true**; mitotic chromosomes contain numerous **non-histone proteins** essential for chromosome structure and function.
- Examples include **structural maintenance of chromosomes (SMC) proteins** like condensin and cohesin, topoisomerases (DNA topoisomerase II), and kinetochore proteins.
- These non-histone proteins are crucial for chromosome condensation, sister chromatid cohesion, segregation, and proper mitotic progression.
Transcription Factors and Gene Regulation Indian Medical PG Question 9: 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.
Transcription Factors and Gene Regulation 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
Transcription Factors and Gene Regulation Indian Medical PG Question 10: Phenotypic expression of a gene depending on the parent of origin is referred to as:
- A. Genomic imprinting (parent-of-origin gene expression) (Correct Answer)
- B. Mosaic genetic variation
- C. Nonpenetrance of genotype
- D. Genetic anticipation
Transcription Factors and Gene Regulation Explanation: ***Genomic imprinting (parent-of-origin gene expression)***
- **Genomic imprinting** is an epigenetic phenomenon where gene expression is dependent on whether the gene was inherited from the mother or the father.
- This results in monoallelic expression of specific genes, with only one copy (maternal or paternal) being active.
*Mosaic genetic variation*
- **Mosaicism** refers to the presence of two or more populations of genetically different cells in one individual, all derived from a single zygote.
- This typically arises from a somatic mutation during development, not from differential expression based on parental origin.
*Nonpenetrance of genotype*
- **Nonpenetrance** occurs when individuals carrying a disease-causing genotype do not express the associated phenotype.
- This concept relates to the presence or absence of a phenotype, not the differential expression based on parental origin.
*Genetic anticipation*
- **Genetic anticipation** is the phenomenon where the symptoms of a genetic disorder become more severe and/or appear at an earlier age in successive generations.
- This is commonly observed in disorders caused by expansions of trinucleotide repeats, such as Huntington's disease, and is distinct from parent-of-origin gene expression.
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