What is the main function of the Nucleus?
Control gene expression within the cell
Describe the role of the nuclear envelope.
Separates the nucleoplasm from the cytoplasm
It is a two membrane structure with perinuclear space between: Inner membrane and the outer membrane
What is the role of the inner membrane?
Binds chromatin and other nuclear components
What is the role of the outer membrane?
Connects with the rough ER
What is the Nuclear Lamina and what is the role?
Network of protein filaments with supporting functions
Serve as scaffolding for chromatin, chromatin-associated proteins, nuclear pores and nuclear envelope membranes
What is Chromatin?
DNA and protein complex that keeps DNA organised
Non-dividing cells there are varying amounts of coiling including uncoiled chromatin- more access by proteins
What is the structure of Chromatin?
composed of nucleosides coiled around an axis, with 6 per turn, to create a chromatin fibril
What is the Nucleosome and describe it’s structure?
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
What is the role of the Nucleus?
Seperates translation and transcription allowing Eukaryotes levels of gene regulation not available to Prokaryotes
Controls the replication of DNA during the cell division process
Movement of molecules, ions, proteins and RNA in to and out of the nucleus is controlled by?
Nuclear Pore Complex
Label the structures.
What is Active Nuclear Import?
A process in which macromolecules (proteins and RNA) are transported out of cells using energy.
What is a nuclear localisation signal (NLS)?
It is a specific amino acid sequence in cargo proteins that notifies the cell its destination.
Describe the process of Active Nuclear Import.
Cargo proteins contain nuclear localisation signal, which notifies the cell its destination
Cytoplasmic receptor proteins (importins) recognise and bind to the NLS of proteins displaying them
Importin binda to the cargo proteins and transports the protein to the nuclear pore complex.
Through the sequential binding with various proteins, importin and cargo proteins are translocated into the nucleoplasm
GTP- binding protein (RAN) recognises and binds to the importin-cargo protein complex, releasing the cargo protein into the nucleoplasm
The importin-Ran complex is exported out the nucleus
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
Ran is then recycled back into the nucleus via the NPC using the nuclear transport factor two (NTF2)
Nuclear protein ran guanine nucleotide exchange factor (RAN- GEF) stimulates the release of GDP from Ran so it can pick up GTP.
Describe the process of Active Nuclear Export .
Proteins destined for the cytoplasm contain nuclear export signal (NES) which tells the cell it is destined for import.
Nuclear transport receptor proteins (exportins) binds to the NES of cargo proteins
Export in binds to cargo proteins and Ran-GTP (helps stabilise interactions) and is then transported to the NPC
The exportin, cargo protein and Ran-GTP complex are translocated through the NPC into the cytoplasm
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
Ran bound to GDP is unable to associate with exportin. It is therefore recycled back into the nucleus
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
What is the average size of the nucleus?
6 micrometers
Range= 2-10 micrometers
What evolutionary theory is based on a Progressive increase in complexity without the need for an endosymbiotic stage?
Last changed9 months ago