Nuclear Structure
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COMPONENTS OF NUCLEUS
• Nucleolus
• Chromatin
• Nucleoplasm
• Nuclear envelope: compartmentalizes nucleus and its contents
NUCLEAR ENVELOPE
• Outer and inner nuclear membranes (perinuclear space between them)
• Porous with nuclear pore complexes
• Continuous with endoplasmic reticulum
• Ribosomes on the surface
• Nuclear lamina: comprises lamins, provides structural support to nucleus and organizes heterochromatin
NUCLEOPLASM
• Medium within the nucleus (mostly water)
• Suspends nucleolus and chromatin
NUCLEOLUS
• Lacks a membrane
• Functions in rRNA synthesis and assembly of ribosomal subunit precursors
CHROMATIN
• Comprises DNA and associated proteins
• Functions in DNA compaction and protection
• Regulates and controls transcription
• Heterochromatin: gene-poor, rich in histone modifications, densely packed, tethered to nuclear lamina at periphery of nucleus
• Euchromatin (the rest): transcriptionally active and loosely packed; distributed throughout the nucleus
CLINICAL CORRELATION
Laminopathies
- Mutations in nuclear lamins; diverse group of disorders ranging from myopathies to progeria