The Nucleus Flashcards
(38 cards)
What are the 2 main functions of the nucleus ?
- replication
- transcription
What is replication ?
The constant formation of genetic material for information transfer
What is transcription ?
Copying genetic material for expression of genetic instructions
Describe the structure of the nucleus in a neutrophil
- it is bilobed and the 2 lobes are connected by a piece of chromatin
- there is a greater amount of cytoplasm compared to nucleus
Describe the structure of the nucleus in a lymphocyte
- it is spherical and the cytoplasm is crescent shaped
- there is very little cytoplasm compared to nucleus
Describe the structure of the nucleus in a myeloma (blood tumour cell)
- nucleus is quite round
- there is an equal ratio of cytoplasm to nucleus
What is the evidence for the complete genome ?
1) an unfertilised frog egg was exposed to UV light causing the nucleus to be destroyed
2) the skin cells of another frog were scraped off its back
3) ex vivo skin cells were regrown in vitro
4) micro-dissection of random skin cells to isolate its nucleus
5) the nucleus was transplanted into the cytoplasmic shell of the egg cell
6) this egg is developed into an embryo
7) the embryo developed into a tadpole and matured into an adult frog
What did the frog experiment show ?
- showed the relationship of the nucleus and the cytoplasm
- cells have specialised functions and express genes required for their functions
- the remaining genes in the nucleus are switched off (repressed)
- repression is controlled by the cytoplasm
What is the role of the inner face of the nuclear envelope ?
Binds chromatin to regulate DNA replication and transcription
What is the role of the outer face of the nuclear envelope ?
Binds the cytoskeleton to position the nucleus
What is the diameter of the nucleus ?
7 - 10 micrometers
What is the role of the nuclear envelope ?
Acts as a barrier that keeps ions, solutes and macromolecules from passing between the nucleus and the cytoplasm
What are the nuclear components ?
- lamina
- pores
- matrix
- nucleolus
- nucleolar organising region (NOR)
- chromatin
Describe the structure of the nuclear lamina
- made of intermediate filaments
- 10 nm thick
- embedded under the nuclear envelope
What is the function of the nuclear lamina ?
- used for strength
- acts as a anchor for chromatin
What are nuclear pores ?
They are little breaks in the nuclear envelope which act as gateways across the barrier
What are the components that make up a nuclear pore channel ?
• cytoplasmic filaments
• central transporter
• proximal filaments
• spoke ring
• nuclear basket
How many nuclear pores are there in a cell ?
~ 6000
What is the role of the central transporter in the nuclear pore channel ?
It is the route through which proteins cross the nuclear envelope
It is 40 nm in diameter
What is the role of the spoke channels in the nuclear pore channel ?
It is a 10 nm aqueous channel for small uncharged molecules
Briefly summarise how import and export takes place in the nucleus
- nuclear localisation signals are needed for import
- nuclear export signals are needed for export
How are molecules imported into the nucleus ?
They move through the nuclear pore channel in a linear array (one by one)
What are the 2 types of import in the nucleus ?
- passive import for small and water soluble molecules (this happens in the spoke channels)
- active import for proteins used in replication and transcription
Describe the process of import into the nucleus
- a transport protein known as importin is used
- the localisation signal binds to the importin protein
- this complex binds to the nuclear pore channel
- energy from GTP is used
