Q.24 Nucleosome is basically composed of:
- Histone core
- Linker histone
- Core DNA
- Linker DNA
Choose the correct answer:
- (A), (B) and (D) only
- (A), (B) and (C) only
- (A), (C) and (D) only
- (A) and (C) only
Answer: Option 4 ((A) and (C) only).
A nucleosome is fundamentally composed of histone core (H2A, H2B, H3, H4 octamer) + core DNA (146 bp wrapped 1.65 turns around histone spool). Linker histone (H1) and linker DNA connect adjacent nucleosomes but aren’t part of the basic nucleosome unit.
Option Analysis
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(A) Histone core: Correct. Octamer = 2×(H2A+H2B+H3+H4); positively charged spool for DNA wrapping.
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(B) Linker histone: Incorrect. H1 binds linker DNA, stabilizes chromatin fiber (30 nm solenoid), not nucleosome core.
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(C) Core DNA: Correct. ~147 bp DNA wrapped left-handed around histone octamer (11 nm diameter × 5.5 nm height).
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(D) Linker DNA: Incorrect. 10-80 bp stretches connecting nucleosomes (“beads-on-a-string”); variable length by species.
Component Comparison Table
Component Part of Nucleosome? Function bp/Proteins (A) Histone core Yes DNA spool 8 proteins (B) Linker histone No 30 nm fiber H1 (C) Core DNA Yes Genetic info 147 bp (D) Linker DNA No Spacer 20-80 bp Nucleosome composition histone core DNA defines the fundamental chromatin subunit for GATE Life Sciences exams. Basic nucleosome = histone core (octamer) + core DNA (147 bp)—excludes linker components.
Nucleosome Core Particle Structure
textDNA (147 bp) ← 1.65 left-handed superhelical turns →
↓
Histone octamer: 2×(H2A + H2B + H3 + H4)
↓
"Beads-on-a-string" with linker DNA between beads
Dimensions: 11 nm diameter × 5.5 nm height cylinder.
Complete Chromatin Hierarchy
Level Components Compaction Nucleosome Histone core + Core DNA 7-fold Chromatosome Nucleosome + H1 6-fold more 30 nm fiber 6 nucleosomes/turn 40-fold Chromosome Loops + scaffold 10,000-fold GATE Life Sciences Pattern Recognition
Question trap: Includes linker components to test core vs extended nucleosome knowledge. “Basically composed” = core particle only (A+C).
Memory aid: “Core = Core” (histone core + core DNA). Links to your Arabidopsis genetics (n=5 chromosomes packaged by 30 million nucleosomes).
Jaipur lab tip: MNase digestion isolates nucleosome cores (146 bp ladder on agarose gel). Master nucleosome composition for guaranteed molecular biology scores.
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