Nucleus

Control gene expression within the cell

• Separates the nucleoplasm from the cytoplasm

• It is a two membrane structure with perinuclear space between: Inner membrane and the outer membrane

Binds chromatin and other nuclear components

Connects with the rough ER

• Network of protein filaments with supporting functions

• Serve as scaffolding for chromatin, chromatin-associated proteins, nuclear pores and nuclear envelope membranes

• DNA and protein complex that keeps DNA organised

• Non-dividing cells there are varying amounts of coiling including uncoiled chromatin- more access by proteins

• composed of nucleosides coiled around an axis, with 6 per turn, to create a chromatin fibril

The nucleosome is a condensed area of chromatin.

Structure:

• Granules- rRNA molecules being packaged with cytoplasmic proteins

• 1-4 nucleoli

• Fibrils- DNA that is being actively transcribed into rRNA.

• Chromatin- condensed DNA

• Seperates translation and transcription allowing Eukaryotes levels of gene regulation not available to Prokaryotes

• Controls the replication of DNA during the cell division process

Nuclear Pore Complex

A process in which macromolecules (proteins and RNA) are transported out of cells using energy.

It is a specific amino acid sequence in cargo proteins that notifies the cell its destination.

1. Cargo proteins contain nuclear localisation signal, which notifies the cell its destination

2. Cytoplasmic receptor proteins (importins) recognise and bind to the NLS of proteins displaying them

3. Importin binda to the cargo proteins and transports the protein to the nuclear pore complex.

4. Through the sequential binding with various proteins, importin and cargo proteins are translocated into the nucleoplasm

5. GTP- binding protein (RAN) recognises and binds to the importin-cargo protein complex, releasing the cargo protein into the nucleoplasm

6. The importin-Ran complex is exported out the nucleus

7. Once in the cytoplasm, Ran GTPase Activating Protein (Ran-GAP) hydrolyses the GTP attached to Ran in GDP and an inorganic phosphate. This releases the importin into the cytoplasm

8. Ran is then recycled back into the nucleus via the NPC using the nuclear transport factor two (NTF2)

9. Nuclear protein ran guanine nucleotide exchange factor (RAN- GEF) stimulates the release of GDP from Ran so it can pick up GTP.

1. Proteins destined for the cytoplasm contain nuclear export signal (NES) which tells the cell it is destined for import.

2. Nuclear transport receptor proteins (exportins) binds to the NES of cargo proteins

3. Export in binds to cargo proteins and Ran-GTP (helps stabilise interactions) and is then transported to the NPC

4. The exportin, cargo protein and Ran-GTP complex are translocated through the NPC into the cytoplasm

5. Ran-GAP hydrolyses the GTP attached to Ran, into GDP and inorganic phosphate, triggering the dissociation of the three components and they are release into the cytoplasm

6. Ran bound to GDP is unable to associate with exportin. It is therefore recycled back into the nucleus

7. Ran-GDP is brought to the nucleus by NTF2. NTF2 dissociates from Ran-GDP. Ran-GEF stimulates the release of GDP from Ran so that it can pick up GTP

6 micrometers

Range= 2-10 micrometers