Q.105 Among the following molecular process-biological effect pairs, identify the mismatched pair.
(A) Histone deacetylation – activation of gene expression
(B) Protein phosphorylation – signal transduction
(C) DNA methylation – sex-specific control of gene expression
(D)Proteolytic cleavage – activation of signaling by peptide hormones
Histone deacetylation represses gene expression by condensing chromatin, making (A) the mismatched pair.
The correct answer is (A).
Molecular Process Analysis
Histone deacetylation: HDACs remove acetyl groups → positive charge on lysines → tighter DNA-histone binding → compact chromatin → transcription factor exclusion → gene silencing.
Other options correctly matched: Phosphorylation activates kinase cascades; DNA methylation (imprinting) silences sex-specific alleles; proteolytic cleavage activates insulin/glucagon signaling.
Option Breakdown
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(A) Histone deacetylation – activation: Mismatched—opposite effect. Acetylation (HATs) loosens chromatin for activation; deacetylation (HDACs) compacts for repression.
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(B) Protein phosphorylation – signal transduction: Matched—RTKs autophosphorylate → recruit effectors (Grb2/Sos) → Ras-MAPK cascade.
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(C) DNA methylation – sex-specific control: Matched—genomic imprinting (e.g., Igf2/H19); maternal/paternal methylation silences one allele.
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(D) Proteolytic cleavage – peptide hormone activation: Matched—pro-insulin → insulin (signal peptide removal); furin cleaves pro-proteins.
Introduction to Histone Deacetylation Gene Expression
Histone deacetylation gene expression repression via chromatin condensation contrasts acetylation activation—GATE Life Sciences epigenetics cornerstone. Q.105 identifies (A) mismatch: HDACs silence, don’t activate genes.
Epigenetic Mechanism
Unacetylated (repressed): DNA–(+H3K9)–tight binding → no transcription
↓ HDAC
Acetylated (active): DNA–(neutral H3K9ac)–loose chromatin → TF access
Deacetylation = gene OFF; acetylation = gene ON.
Correct vs Mismatched Pairs
| Process | Effect | Status |
|---|---|---|
| Histone deacetylation | Activation | ❌ Mismatched (actually repression) |
| Phosphorylation | Signal transduction | ✅ Matched |
| DNA methylation | Sex-specific control | ✅ Genomic imprinting |
| Proteolytic cleavage | Hormone activation | ✅ Insulin processing |
GATE Strategy
Histone deacetylation gene expression = repression (compact chromatin). Mnemonic: “D”eacetylation = “D”ense/”D”ormant DNA. PYQs test epigenetic opposites. Answer: (A). Distinguish HAT (open) vs HDAC (close).
