Nucleus Flashcards
What is the nuclear lamina made out of?
A mesh of long filament-like proteins called ABC nuclear lamins.
Where is the nuclear lamina located?
It is bound to the inner surface of the nuclear envelope
What is the name given to nuclei that have mutations in the nuclear lamina?
Progeria
What are nuclear speckles?
Subdomains where mRNA slicing factors are highly concentrated.
True or False: each cell has about 10 speckles that are stationary.
False. Speckles are numerous (about 50) and can move, grow and shrink depending on cell needs.
True or False: the nucleolus is not membrane bound
True.
Where does ribosomal assembly occur?
The early stages begin in the nucleolus before being transported to the cytosol for final assembly.
What is the purpose of the nuclear matrix?
It is a mesh that serves a structural role for the nucleus, and as a scaffold for anchoring protein factors.
What “filament-like” protein lines the inside of the Nuclear Pore Complex?
The FG nucleoporins, made of numerous FG repeats.
True or False: only the cytoplasmic side of the NPC has filaments.
True. The nucleoplasm side has a basket instead.
How small do molecules have to be to freely pass through the NPC?
Less than 40 kDa. RNA and most proteins have to be selectively imported.
Where is nucleoplasmin synthesized?
In the cytosol
Explain the difference between a classic NLS and a bipartite NLS.
The classic NLS is a short stretch of basic amino acids, while the bipartite NLS is two short sequences with a 7-10 amino acid spacer.
Name the two types of karyopherins (transport receptors)
Importin (into nucleus) and exportin (out of nucleus)
How do G-proteins work?
A GTP (3 Ps) holds the protein closed in its active state. When a P is released to become GDP (2 Ps), the protein opens up into its non-active state.
True or False: there is a high amount of Ran-GTP in the cytosol.
False. Ran-GTP flows a gradient to accumulate in the nucleus. It is low in the cytosol.
What is the role of GTPase Activating Protein (GAP) in the cytosol?
It hydrolyses Ran-GTP into Ran-GDP so it can translocate back into the nucleus.
What is the role of Guanine nucleotide Exchange Factor in the nucleus?
It exchanges Ran-GDP for Ran-GTP in the nucleus.
True or False: Importin a attaches to the cargo protein to transport it into the nucleus.
True. However, Importin B needs to bind to Importin a in order to transport. It does this by binding to the cytoplasmic filament to open the NPC.
What is the role of Ran-GTP?
Once the cargo receptor complex passes into the NCP, it attaches to Importin B in order to release the cargo from the NCP and disassemble it.
Name the two proteins involved in regulating the Ran-GTP gradient.
RCC1 and Ran-GAP1
How does exportin and Ran-GTP work together to transport proteins?
Exportin targets proteins in the nucleus with NES sequences, and the Ran-GTP binds to this complex in order to move it down the Ran-GTP gradient out of the nucleus.
