Nucleus Flashcards
What is the nuclear envelope?
Membrane that is continuous with the ER and separates nuclear content from the cytoplasm
What is the nuclear lamina?
Meshwork of intermediate filaments underlying the inner nuclear membrane
What is the function of nuclear pores?
To control traffic between nucleus and cytoplasm
What is the function of the nuclear lamina?
Provides structural and functional support to the nucleus
Binds chromatin and other nuclear proteins
What are the three lamin proteins?
A
B
C
Describe laminA and C
Alternatively spliced products of single gene
Developmentally regulated
Disperse to the cytoplasm during mitosis
Describe the role of lamin B
Expressed in all cells
Modified by addition of isoprenyl group, which attaches protein to inner nuclear membrane
Binds inner nuclear membrane proteins such as emerin and lamin B receptor
How is lamin A modified and attached to the nuclear membrane?
A farnesyl group is added which attaches the protein to the nuclear membrane
This group is later removed
What is the role and function of the LINC complex?
Connects the nuclear lamina with the cytoskeleton
Can by any cytoskeletal protein
Plays a role in nuclear migration, nuclear integrity, and chromosome movement during cell division
Describe the nuclear pore complex.
Large complex that controls traffic between the nucleus and cytoplasm
Small molecules diffuse freely
Large molecules require a mechanism
Made up of nucleoporins
What is the role of structural nucleoporins?
Forms a basic structural scaffold on the inner and outer nuclear membrane
What are FG-nucleoporins?
NPs that line the central channel and form a semi-permeable channel
Named due to presence of hydrophobic FG-repeats
F-phenylalanine
G-glycine
What is the role of the nuclear localization signal?
Sequence on protein that is responsible for binding importin to be carried into the nucleus
Basic amino acid sequence (Lys-Arg)
Also lys-rich sequences
What is one way of regulating protein import into the nucleus?
Blocking and unblocking the NLS
What is the nuclear export signal?
AA sequence responsible for binding exportin so that cargo can be carried out of the nucleus
Rich in Leu
What is Ran?
Guanine nucleotide binding protein
Binds GTP or GDP
Has GTPase functionality
What is Ran guanine nucleotide exchange factor? (GEF)
Exchanges GDP for GTP in Ran
Found in nucleus
What is Ran GTPase activating protein? (GAP)
Facilitates the hydrolysis of GTP in Ran
Found in cytoplasm
Describe Ran-dependent import.
- Cargo/importin travels through NPC
- GEF converts RanGDP->RanGTP
- RanGTP binds importin, releasing the cargo
- RanGTP/importin travel through NPC to cytoplasm
- GAP makes Ran hydrolyze GTP to GDP and importin is free to bind again
Describe Ran-dependent export
- Cargo/Exportin/RanGTP travel through NPC to cytoplasm
- GAP hydrolyzes RanGTP->RanGDP causing the release of the cargo
- exportin and RanGDP travel through the NPC to the nucleus
- GEF recharged RanGDP->RanGTP
What is the role of NXF1/NXF2?
Binds to mRNA-protein complexes in order to transport mRNA out of the nucleus
What is Dbp5?
RNA helicase that removes NFX1 and NXT1 from mRNA as soon as it reaches the cytoplasmic side.
Utilizes ATP
What is the cause of Emery-Dreifuss muscular dystrophy?
Defect in emerin and lamin A/C that eventually affects the heart
What is the etiology and symptoms of Hutchinson-Gilford progeria?
Defect in lamin A/C
Farnesyl stays attached causing the protein to pile up at the nuclear envelope.
Causes premature again, children die of old age around age 13
