Q.72 Match List I with List II
| LIST I | LIST II |
|---|---|
| A. DNA methylation B. Histone acetylation C. ATP-dependent chromatin remodelling D. Nucleosome |
I. Increase accessibility of DNA sequence II. Gene silencing III. Occurs on lysine residues of histones IV. Barrier for transcription |
Choose the correct answer from the options given below:
- (A)–(I); (B)–(II); (C)–(IV); (D)–(III)
- (A)–(I); (B)–(II); (C)–(III); (D)–(IV)
- (A)–(III); (B)–(II); (C)–(I); (D)–(IV)
- (A)–(II); (B)–(III); (C)–(I); (D)–(IV)
DNA methylation primarily causes gene silencing, while histone acetylation and ATP-dependent chromatin remodelling increase DNA accessibility, and nucleosomes act as transcription barriers. The correct answer is (A)–(II); (B)–(III); (C)–(I); (D)–(IV).
Option Analysis
Correct matching: A-II, B-III, C-I, D-IV
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A. DNA methylation → II. Gene silencing: DNA methylation adds methyl groups to cytosine (typically at CpG islands), recruiting silencing proteins like MeCP2 that compact chromatin and block transcription factors, leading to stable gene repression.
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B. Histone acetylation → III. Occurs on lysine residues of histones: Acetyltransferases (HATs) add acetyl groups to lysine residues (e.g., H3K9, H3K27) on histone tails, reducing positive charge, loosening chromatin, and promoting transcription.
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C. ATP-dependent chromatin remodelling → I. Increase accessibility of DNA sequence: SWI/SNF complexes use ATP to reposition nucleosomes, exposing promoter regions and enhancer sequences to transcription machinery.
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D. Nucleosome → IV. Barrier for transcription: Core nucleosomes (histone octamer + DNA) package DNA, sterically blocking RNA polymerase access unless remodelled or modified.
Incorrect options explained:
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(A)–(I); (B)–(II); (C)–(IV); (D)–(III): Wrong—A (methylation) doesn’t increase accessibility; B (acetylation) doesn’t silence.
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(A)–(I); (B)–(II); (C)–(III); (D)–(IV): Wrong—A mismatches; B mismatches.
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(A)–(III); (B)–(II); (C)–(I); (D)–(IV): Wrong—A (methylation) doesn’t occur on histones; B (acetylation) doesn’t silence genes.
Introduction to Epigenetic Regulation Matching
DNA methylation histone acetylation chromatin remodelling nucleosome mechanisms control gene expression without altering DNA sequence. This List I List II matching tests core epigenetic concepts crucial for molecular biology exams like GATE Life Sciences.
DNA Methylation: Gene Silencing Master
DNA methylation silences genes by methylating CpG islands, recruiting MBD proteins and HDACs that deacetylate histones, forming heterochromatin. Persistent through cell divisions, it’s key in X-inactivation and imprinting.
Histone Acetylation on Lysine Residues
Histone acetylation targets lysine residues (H3K9ac, H4K16ac), neutralizing charges to open chromatin. HATs like p300 activate, while HDACs repress; common in active promoters with H3K27ac marks.
ATP-Dependent Chromatin Remodelling
ATP-powered complexes (SWI/SNF, ISWI) slide/evict nucleosomes, increasing DNA accessibility at enhancers. Essential for inducible genes like stress responses.
Nucleosome as Transcription Barrier
Nucleosomes wrap ~147 bp DNA around histone octamers, occluding transcription factor binding sites. Remodelling or histone variants (H2A.Z) overcome this barrier.
Exam Strategy for Epigenetics MCQs
For “Match List I with List II” questions, recall: methylation=II (silencing), acetylation=III (lysine), remodelling=I (accessibility), nucleosome=IV (barrier). Perfect for competitive biology prep.
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