The Question is from neet-botany cell-biology chromosomes-and-nucleosomes, and it was created by the author K SURESH KUMAR

Question

Certain histone modifications are associated with actively transcribed genes. Which of the following combinations is MOST likely to be found in the nucleosomes of such genes?

K SURESH KUMAR · Accepted Answer

## CORE INFORMATION
✓ **Answer**: C
## CONCEPT FRAMEWORK
 **Primary Concept**: Histone modifications and gene expression
 **Related Topics**: Chromatin structure, epigenetics, gene regulation
 **Prerequisites**: Understanding of histone proteins, their modifications (acetylation, methylation, phosphorylation, ubiquitination), and the relationship between chromatin structure and gene transcription.
## SOLUTION PATHWAY
**Given Information**:
  Actively transcribed genes are associated with specific histone modifications.
  Four options presenting different histone modification combinations are given.
**Method & Steps**:
 1. Identify histone modifications associated with active transcription.
  Reasoning: Acetylation of histone tails (H3 and H4) generally loosens chromatin structure, making DNA more accessible to transcriptional machinery.  Trimethylation of H3K4 (lysine 4 on histone H3) is another mark strongly associated with active promoters.
  Formula/Rule: No specific formula, but understanding of the correlation between histone modifications and gene expression is crucial.
 2. Evaluate each option based on the known associations.
  Working: 
        * Option A: Methylation of H3K9 and H3K27, and deacetylation of H3 and H4 are repressive marks, associated with gene silencing.
        * Option B: Phosphorylation of H2AX is involved in DNA damage repair, not directly related to active transcription. Trimethylation of H3K9 is a repressive mark.
        * Option C: Acetylation of H3 and H4, and trimethylation of H3K4 are both activating marks, strongly associated with active transcription.
        * Option D: Ubiquitination of H2A can have both activating and repressive roles, depending on the context. Trimethylation of H3K27 is a repressive mark.
 3. Select the option with the combination most likely to be found in actively transcribed genes.
  Result: Option C (Acetylation of H3 and H4; Trimethylation of H3K4)
  Verification: The chosen option aligns with established knowledge about histone modifications and their role in gene regulation.  The other options contain modifications associated with gene repression.
 ## OPTION ANALYSIS
A :x: Repressive marks indicate inactive genes.
B :x:  Contains repressive marks and a mark related to DNA damage repair.
C ✓: Activating marks are consistent with active transcription.
D :x: Contains a repressive mark and a modification with context-dependent effects.
 ## LEARNING AIDS
 **Common Mistakes**:
  1.Confusing activating and repressive histone modifications:  Memorizing the association between specific modifications (e.g., H3K4me3, H3K9me3, H3K27me3) and their impact on gene expression is key.
  2.Overlooking the context-dependency of some modifications: Some modifications, like H2A ubiquitination, can have different effects depending on the specific location and other epigenetic factors.
 **Quick Tips**:
  1.Remember the “activation” marks (H3K4me3, H3/H4 acetylation) and the “repression” marks (H3K9me3, H3K27me3).
  2.Create a table summarizing the common histone modifications and their association with gene activity.

K SURESH KUMAR · Answer

Methylation of H3K9 and H3K27; Deacetylation of H3 and H4

K SURESH KUMAR · Answer

Phosphorylation of H2AX; Trimethylation of H3K9

K SURESH KUMAR · Answer

The correct Option is "Acetylation of H3 and H4; Trimethylation of H3K4"

K SURESH KUMAR · Answer

Ubiquitination of H2A; Trimethylation of H3K27

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