the nucleus Flashcards
What is the nucleus?
-Principle defining characteristic of eukaryotic cells
why have a nucleus
-The nucleus separates the process of transcription and translation
-allows organisms to make decisions like when the gene product would like to be made
-Enables alternative splicing
-associated complexity- aggregation of cells together to form something that resembles an organism
Where (evolutionarily ) did the nucleus come from: hypothesis I
-Invagination of membrane around DNA and then Formation of primitive nucleus
-start with ancient prokaryotic cell and end with ancient eukaryotic cell
Where (evolutionarily ) did the nucleus come from: hypothesis II
-the idea that mitochondria were descendants of ancient prokaryotes which got engulfed by a other cell type which then evolved to be specific energy generators - called endosymbiosis
how can we ensure the hypothesises about where the nucleus came from are true
- compare with archaea, as this is more similar to genes found in the nucleus than bacteria might be
what effects do both hypotheses have on topology
-implications
-two membranes formed- double unit membrane
what’s in the nucleus content
-DNA in the nucleus is packaged into chromosomes
-DNA is wrapped around histones for effective packaging.
-In non-dividing cells, DNA is loosely packed forming a tangle of strands – chromatin.
-Just before cell division, packaging tightens up and chromosomes become visible.
-long lengthen chromosomes can fit into the small nucleus
whats heterochromatin
-Dense staining of interphase DNA
-around periphery of chromosomes
whats euchromatin
-Less-dense staining interphase DNA
whats the nucleolus
-Highly dense staining of RNA
whats Fluorescent In Situ Hybridisation
-fluorecse when the right wavelength of light is shone at it
- these small sequences of DNA, which we carefully arranged the sequence to be complimentary to a particular region on a chromosome- We can find that chromosome looking at a microscope at a particular cell
-hybridised a small DNA molecule that’s fluorescent, Two DNA inside the nucleus of a cell.
-also stained all the chromosomes in that cell with a non-specific dye that’s blue - condensed mitotic chromosomes
how is The nucleus compartmentalised
-Chromosomes occupy specific territories within the nucleus
-territories are inherited but can change following differentiation or disease
how is The nucleus dynamic
-The location of a gene within the nucleus changes depending on its transcriptional status
-CD4 =HIV receptor (CD4- and + which are T lymphocytes)
-Co-localisation of CD4 gene with heterochromatin
-Red: Stain for Centromeric heterochromatin
Green: Stain for CD4
-CD4 is quite a long way away from the Central American hetero progress.
-it’s actually in the euchromatin space, whereas it localises with heavy recognition when it’s switched off.
-So it literally moves away from heterochromin and into euchromatic space when it’s switched on.
whats gene tagging revealed
-revealed the existence and function of multiple sub-nuclear organelles in inter-chromatin space
-Nucleolus: ribosome synthesis
-Speckles: pre-mRNA processing
-Cajal bodies: splicing
-PML bodies: storage depot
-lots of sub organelles
whats the nucleolus
-As with other nuclear organelles, it is not membrane bound
-Site for processing ribosomal RNA to produce ribosomes
-It is a collection of macromolecules including:
=rRNA genes
=precursor rRNA - manufacture of RNA genes
=mature rRNA
=rRNA processing enzymes
=snoRNPs
=ribosomal protein subunits
=partly assembled ribosomes
-The nucleolus also processes other types of RNA:
=mRNA – messenger RNA
=tRNA – transfer RNA
what can Sub-nuclear organelles be
-dynamic and move in non-random ways in an ATP-dependent manner
-energy dependent
whats the nuclear envelope
-double unit membrane perforated with pores (perforated) and supported by a fibrous meshwork called the lamina
whats the lamina responsible for
-in part, for ensuring the asymmetric nature of the double unit membrane
-proteins ache to membrane and attach to the lamina
-outer and inner nuclear membrane present
-the protein composition of the inner nuclear membrane is different from the outer
-part of the way that’s maintained is that quite a lot of the proteins in the inner nuclear membrane are actually anchored onto the lamina
-inside membrane does different things than the outside does
what plays a large role in gene regulation
-HGPS and other laminopathies
-Hutchinson–Gilford progeria syndrome- Caused by mutation in the LMNA gene that encodes Lamin A
-lamin assembly= pro-lamin A -> laminate A
what do laminopathies cause
-diverse range of inheried diseases
-with lamins you get completely different tissue specific diseases depending on exactly where the mutation
whats the Nuclear pore structure provided by
-scanning electron mic
-we can determine where individual proteins are using this technique known as cryo electron microscopy in the nuclear pore- high resolution
whats the The signal for entry
-a specific peptide sequence
-Particles MW>50,000 CANNOT enter nucleus by diffusion
-but CAN by active signal-dependent transport
-On signal, pore can open up to 26nm in diameter
-Nuclear access is controlled by the pore in a size-dependent manner
what do nuclear pores do
-regulate the movement of substances into and out of the nucleus
