SFP: nucleus Flashcards
what are the components of the nuclear envelope?
- inner and outer membrane
- nuclear lamina
- nuclear pores
what are the components of the nuclear matrix
- intermediate filaments
- nuclear matrix proteins
describe the components of the nuclear membrane
- outer membrane: continuous with the ER
- inner: closely associated with the nuclear lamina
-perinuclear space: continuous with the lumen of the ER
what proteins are associated with the structure of the membrane?
lamins that underlie the membrane; they get farnesylated into the membrane
Lamin A: produced by alternative splicing of a single gene
Lamin B: products of separate genes
Lamins bind to ____ to connect the nuclear envelope to chromatin
histones 2A and 2B
describe the role of lamins in the breaking and forming of the nuclear envelope in mitosis
they can facilitate these processes by being phosphorylated or dephosphorylated
what are the main components of a nuclear pore
cytoplasmic ring, spoke-ring, nuclear ring, and transporter
describe the cytoplasmic ring
element of the nuclear pore that binds to spoke proteins and attach to the outer membrane. they anchor cytoplasmic filaments that couple the pore to the cytoskeleton
describe the nuclear ring
binds to spoke proteins and attached to the inner membrane. they form a nuclear basket
describe the spoke ring
form a central channel that connect the nuclear and cytoplasmic rings
describe the transporter
subunits that are freely permeable to ions and small proteins, but nothing large
what processes are associated with selective transport in the nucleus
import of proteins, export of proteins, export of RNA
what is the nuclear association sequence
a sequence in the amino acid of a target protein that functions as a binding site for transport proteins
which amino acids re common in nuclear localization sequences
lysine and arginine
describe the main steps of importing proteins into the nucleus
- importin binds to a cargo protein containing an NLS
- importin-cargo protien binds to filaments in the nuclear pore
- importin-cargo protein traverses the pore
- importin-cargo protein binds to Ran GTP in the nucleus, releasing the cargo protein
- importin-RanGTP is exported to the cytoplasm
- GTP is hydrolyzed to GDP by GAP
describe the main steps in exporting proteins from the nucleus
- exportin binds to cargo proteins with an NLS
- RanGTP binds to the exportin-cargo protein
- exportin-cargo protein-RanGTP traverses the nuclear pore
- GTP is hydrolyzed to GDP by ran GAP, releasing the cargo protein and exportin
- exportin is transported back into the nucleus
- ranGDP is transported back into the nucleus
what is NTF2
it is an import receptor specific to RanGDP; when RanGTP in the cytoplasm is hydrolyzed to RanGDP, NTF2 brings it right back into the nucleus to be re-activated and reused
what are the export receptors of mRNA and tRNA
mRNA: Crm1
tRNA: exportin-t
all mRNAs are exported as ___
mRNP
what is NXF1
they bind to mRNP to bring it out of the cell; this is used instead of ranGTP
where are rRNAs transcribed
the nucleolus
where do ribosomes assemble
the nucleolus
does the nucleolus have a membrane?
no
what are nucleolar organizing regions
rRNA is processed by ___ after being transcribed
snoRNPs
what are the structural correlates of ribosome production
- fibrillar centers: site of rRNA transcription. contain euchromatin. show up as light centers
- dense fibrillar component: site of processing into mature rRNA. very dark stained regions
- granular component: site of ribosome assembly. look grainy/dotted
