BICD 110 Lecture Notes - Lecture 9: Nuclear Lamina, Nuclear Membrane, Nuclear Pore
The Nucleus
NUCLEUS STRUCTURE AND FUNCITON
• structure
o Nuclear envelope: 2 nuclear membranes, 1 nuclear lamina, 1000s nuclear pores
o inside nucleus: chromatin (DNA packaged in nucleosomes using histones),
nucleolus (site of ribosomal RNA synthesis and assembly), hnRNA (=mRNA
precursors), ribosomal RNA precursors
o absence of cytoplasmic organelles and proteins >40kDa
• functions
1. DNA replication
2. DNA recombination and repair
3. RNA transcription (mRNA, rRNA, tRNA precursors)
4. RNA splicing and modifications (mRNA, rRNA, tRNA)
5. nuclear transport (import and export)
6. mitosis (disassembly and reassembly of nuclear envelope)
NUCLEAR ENVELOPE AND LAMINS AND DISEASE
• nuclear envelope consists of outer nuclear membrane (contiguous with ER and has
ribosomes- appears like RER), inner nuclear membrane (contains proteins that are
binding sites for nuclear lamina) and nuclear lamina (70 kDa,provides structural
support/strength of nuclear envelope, gene Lamin A! B C)
o laminopathies = many diseases are caused by Lamin A gene mutations (ex:
certain muscular dystrophies, progeria)
▪ progeria: described by john hutchison, rare (1 in 4 million), accelerates
aging; clues to normal aging and atherosclerotic disease? mapped to point
mutation in Lamin A gene
▪ broken down lamin rather than circular membrane
NUCLEAR PORES
• outside: cytoplasmic filament, transport region, spoke; inside: nuclear basket (nuclear
ring, basket filament, terminal ring
• contains 30 different proteins,each present in multiple copies
• 1/3 of proteins contain FG repeats (Phe/Gly – hydrophobic), act as binding sites for
importin, transportin, snurportin
o spokes don’t have FG but everywhere else on nuclear pore does
• Passive diffusion
o small molecules like ions, small ions (<40kDa)
• Receptor mediated transport
o nuclear proteins
o newly assembled ribosomes
o mRNA, tRNA
o in: any protein that regulates a gene (histones, DNA/RNA pol, transcription
factors)
o out: tRNA, mRNA, mature ribosomes
NUCLEAR IMPORT
• different import receptors recognize Nuclear Localization Sequences (NLS)
