The Nucleus Flashcards
What are the 4 main functions of the cell nucleus?
- Stores genomic DNA
- Replicates genomic DNA once every cell cycle
- Controls expression of the genome
- Communicates with the cytoplasm
Why does the eukaryotic cell have a more complex protein synthesis?
- As it involves splicing pre-mRNA to remove introns using splicing factors before exit through the nuclear pore
- Prokaryotic cells simply have transcription and translation
What is the importance of the cell nucleus in embryonic stem cells?
Allows cell to differentiate into different cell types, with interactions between the nuclear structure and the sub-nuclear domains being vital for correct and efficient gene expression
Name 3 human diseases linked to the cell nucleus
- Leukaemia
- CAG triplet diseases
- Laminopathies
What are 2 observed traits of chromosomes?
- Occupy distinct territories
- Different levels of chromatin condensation
What are the main functions of the nucleolus?
- Makes ribosomes
- Composed of the fibrillar centre where genes encoding for ribosomal RNA are found
What is the role of the dense fibrillar component?
rRNA processing
What is the role of the granular component?
assembly of ribosome subunits
What are nuclear speckles and what are their function?
- Contain protein splicing factors such as snRNP and non-snRNP
- Acts as storage site for splicing factors that proteins can move in and out of (shown by photobleaching)
What are nuclear bodies?
A variety of structures found in the nucleus that tend to be spherical and which have various roles in gene expression
Give 3 examples of nuclear bodies and their functions
- PML bodies are involved in transcriptional regulation
- Cleavage bodies are involved in the formation of the 3’ of mRNA
- Cajal bodies & gems are involved in the synthesis of snRNP and splicing factors
What is the nuclear pore complex?
Found on the nucleus side of the nuclear pores, with each one being formed of 8 subunits
What is the function of the nuclear lamina?
Provides support to the nuclear envelope by binding/anchoring to membrane proteins, lipids (by insertion and modification) and the nuclear pore complex
What are mutations in Lamin A associated with?
Hitchinson-Gilford progeria which causes premature aging
Name 5 things that travel in and out of the nucleus
- Protein
- RNA
- Glucose
- ATP
- Ions
What do the rates of nuclear passage depend on?
Protein complexity
What are the 2 categories of karyopherins?
importins and exportins
Where are RanGTP/RanGDP (Ras-related nuclear protein) usually found?
RanGDP - cytosol
RanGTP - nucleus
How does RanGTP/GDP control nuclear transport?
By a carefully maintained nuclear gradient
How is the RanGTP/GDP gradient maintained?
Ran-GAP protein in the cytosol dephosphorylates RanGTP to form RanGDP
Ran-GEF in the nucleus which is attached to chromatin phosphorylates RanGDP to form RanGTP
How is cargo exported from the cell nucleus?
- Cargo binds to an exportin and RanGTP in the nucleus
- Complex carried out by the nuclear pore complex
- RanGTP and cargo are released to the cytosol
- exportin travels back into the nucleus via the nuclear pore
How is cargo imported into the cell nucleus?
- Cargo binds directly to the importin and travels into the nucleus via the nuclear pore
- Importin then binds to RanGTP which then allows it to be carried back out of the cell via the nuclear pore complex
How do karyopherins allow cargo to enter and exit the nuclear pore?
Interact with FG repeats in the lumen of the nuclear pore
What do RNAs exist in the cell as?
ribonuclear protein complexes
How is correctly processed mRNA exported from the cell nucleus?
Assisted by the activity of RNA helicase Dbp5
