Nucleus Flashcards
Perinuclear space
Space within the outer nuclear membrane that is continuous with the ER lumen
Nuclear pore complex structure
Eight outer subunits, nuclear basket, cytoplasmic filaments reaching out, FG-Repeat plug.
Nuclear lamina
Just below the envelope. Intermediate filaments - lamins A, B, and C
Nuclear lamin B
Lipid-anchored protein (via an isoprenyl group)
Phosphorylation of the nuclear lamina
Causes disassembly.
Via kinases and CDC2.
Occurs during prophase.
Dephosphorylation of the nuclear lamina.
Causes assembly.
Via phosphatases.
Once the chromosomes have been segregated.
Euchromatin
Loosely packed chromatin that is available to be transcribed.
Heterochromatin
In clumps around the nuclear envelope, densely packed and repressed DNA.
Nucleolus function
Several per nucleus. Site of rDNA transcription into rRNA and subsequent assembly.
Nucleolus structure from the centre out
Fibrillar center
Dense fibrillar component
Granular component
Granular component function
Ribosome in various stages of assembly
Dense fibrillar compartment function
Where transcription from rDNA to rRNA occurs
Fibrillar center function
Stores mostly rRNA
Ribosome structure
Total 80S
Large subunit (60S)
Small subunit (40S)
+ 82 proteins
One “branch” of transcribed rRNA can provide:
ALL the rRNE required to form one ribosome.
Nuclear pore complex size and mass
100nm, 120 million daltons
FG Nucleoporins (FG repeats)
Phenylalanine and glycine rich domain that acts as a mesh to block diffusion of random particles. Highly disordered and hydrophobic.
Nuclear localisation signal (NLS) overview
8-10 amino acid chain with a strong positive charge near the center of a protein.
Binds to importin for import.
Process of import through the nuclear pore complex
- importin binds the NLS on a cargo protein
- importin binds the cytoplasmic filaments of the NPC
- complex moves through into nucleus
- Ran-GTP binds importin, triggering cargo release.
- Ran-GTP + importin exit the nucleus
- Ran is hydrolysed, releasing the importin
GTPase on/off mechanism
ON - bound to GTP (through exchange)
OFF - bound to GDP (though GTP hydrolysis)
GEFs
Guanine exchange factors
- put a GTP on GTPases
GAPs
GTPase Activating Proteins
- Aid in the hydrolysis of GTP to GDP
RCC1
GEF for Ran, resides in the nucleus.
RanGAP1
GAP for Ran, resides in the cytoplasm
