Nucleus and Nucleolus Flashcards
What are factors of the nucleolus?
Biggest single organelle
Contains DNA in the form of chromatin
Site of RNA transcription
How many membranes lie in between the nucleoplasm and Cytoplasm?
2
What lies in between the inner and outer membrane?
The perinuclear space
How big is the nuclear pore complex?
Extremely large
What do the nuclear pore complexes connect?
The nucleoplasm to the cytosol
What are the NPC’s consisting of?
Cytosilic fibrils, Channel nucleoporins and nuclear basket
How many nucleoporins in a mammalian cell
Between 3k and 25k
How many macromolecules a second can be transported through an NPC
1000, in both directions at the same time
How do different molecules of differing size go through the NPC’s
5 KDa, freely diffuse
60 KDa, diffuse through, but takes lonfer
>60KDa, requires energy input to allow movement through
What are NLS’s recognised by?
Nuclear import receptors (importins)
How do large proteins move through the nucleoporins after being detected and binded to by the importin?
Binding and unbinding the FG repeats
Once the protein has moved through the NPC, what happens to the importer?
Binds to Ran GTP and moves through the FG repeats
What happens when the Importer + Ran GTP complex reaches the Cytosol
Ran GTP dissaciates from importin, becoming Ran GDP + Pi.
Importin is recycled
How does nuclear export work?
Protein binds to nuclear exporter (which is already binded to a RAN GTP molecule), allowing for it to pass thropugh the FG repeats. From there the exporter moves out of the nucleus into the cytosol through a nuclear porin, and then RAN GTP (now RAN GDP) and protein are dissociated from exporter
In what form is DNA stored in the nucleolus?
Chromatin
What are the two different types of chromatin and how are they represented?
Dense inactive Heterochromatin (dark region)
Loose active Euchromatin (Lightly packed)
What is present in large quantities in the nucleolus?
What is synthesized in there?
RNA’s and Proteins
Ribosomes are generated (Ribosomal biogenesis
How heavy are ribosomes (in S)
How is that mass constituted
80S ->60S+40S
What is the 60S subunit of the ribosome constituted of?
5S rRNA, 5.8S rRNA, 28S rRNA +49 proteins
What is the 40S subunit of the ribosome constituted of?
18S rRNA + 33 proteins
What are tandem repeats?
The rRNA genes clustered together on a DNA sequence
How big is the pre rRNA gene, how many spacers and coding elements?
45S, 3 coding elements and 4 spacers
These coding elements are (18S, 5.8S and 28S)
How are 90S pre ribosomes formed?
Ribosomal proteins move into the nucleoporin, needing the Ran cycle to move into the nucleus
What modifies the 90S pre ribosomes to form two sections? (Cleaves them)
SnoRNP’s
What happens to the 5.8S and 28S rRNA molecules after being cleaved and having the non-coding RNA removed?
Binds with 5S rRNA to form the (large) 60S subunit
What happens to the 40S and 60S subunit once finished being formed in the nucleus
Exported through the Ran cycle
