what is the nucleus surrounded by ?
nuclear envelope
The nuclear envelope consists of how many membrane bilayers?what seperates the two?
include membrane bilayer property
two bilayers seperated by a perinuclear space , each membrane with its own proteins
what is the perinuclear space continuous with?what is the outer membrane continuous with?
perinuclear space is continues with the er lumen
the outer membrane is continuous with the er membrane(can be studded as well)
where do the two membranes meet? define the region of fusion
the two membranes meet at the nuclear pore
the nuclear pore is a protien complex that serves as entry and exit pores
what is the nuclear lamina ?
include function , structure
the nuclear lamina acts as structural support for the nucleus specially the envelope
it is made up of thin meshwork filaments(protien known as lamin)found on the internal surface of animal cell envelopes
what is the nucleolus ?what is its function ?
irregularly shaped ,electron dense region functioning in rRNA and ribosome synthesis
what does the nucleoplasam fluid contain ?
1)ions
2)nucleotides,phosphates,dna/rna components
3)RNA transcripts, rRNA and proteins that make ribosomes
4)protiens that do the nucleus work
5)chromatin
how does 2m of DNA fit into a 10mm nucleus diameter?
what allows them to fold ?what are they like in interphase vs mitosis
by being folded ten thousand times
the proteins found on the dna allow them to condense during interphase
the chromasomes in mitosis is more condensed than in interphase
what does eukaryotic chromatin include ?
include importance of histones and class
contains dna ,histone and non histone protein segments
histones allow dna to condendse into the nucleus
histone has five major classes(small protiens lots of positive charged residue )
what are nucleosomes?
include dna and histone properties
nucleosome is the basic chromatin packaging unit
DNA wraps around histones twice(150 base pairs , 50 act as spacers and H1 attaches here)
coiling of dna allows for compaction
histones interaction makes octamer core
what is the beads on string model?
nucleosomes make the beads (histones) on string(dna coiled ) model
this model is 10nm long and the histones have long n temrinal tails that interact with one another
what is selenoid ?
the selenoid is the further compaction of the nucleosomes ,it is 30 nm thick
how does chromatin compact even more?
chromatin that is already in selenoid form gets gathered into large loops anchored to protien scaffold
the protien scaffold is made of non histone protiens
what does nuclear pore complex move in and out ?why
dna transcription requires protiens made in the cytoplasam so they move into the nucleus
mRNA ,tRNA and ribosomal subunits made in the nucleus are needed in the cytosol so they exit via the pores
pore can transport 1000 macromlcls per second in both ways at the same t
properties of the pore
1)travel in a linear array
2)pores contain a nuclear pore complex that projects into the nucleus and cytoplasam
what does the nuclear pore complex contain?
1)complex of 30 different protiens called nucleoporins (displays octagonal symmetry )
2)30 times bigger than ribosomes
3)central channel (large and expandable) that allows small polar mlcls to diffuse through and fully folded protiens
what are FG REPEAT DOMAINS
FG repeat domains are nucleoporins that line the inner channel projecting the disordered protiens into regions of the pore
what do the FG repeat domains form ?
the FG repeat domains form a hydrophobic seive that blocks free diffusion of large mlcls through the channel
what are cytoplasmic filaments?
what they include and functiom
they extend into the cytoplasam from the rim of the nucleoporins , also contain FG repeat domains
Function in guiding cytosolic cargo into the central channel
what directs protiens to enter the nucleus ?
protiens that have to go to the nucleus have to get a Nuclear localized signal
proteins need specific amino acid sequences (like address tags) to be sent to the correct place in the cell.
what are importins ?
NLS protiens tell the protien where to go
importins are protien families that recognize the protien ,attach to it and then takes the protien to its exact location
what actually carries the importin to its exact location ?
importin protiens have binding sites for FG repeat domains
the FG repeat domains attach to the importin and help pull it and the protien its carrying through the nuclear pore
what are the first three steps of importin protiens ?
1)importin interacts with the FG domains on the cytosolic fibriles that extend out of the NPC
2)importin then binds to the FG domains of the nucleoporins ,passes through the sieve into the nucleus as it binds to one FG repeat and then to the next
3)once the importin passes through the sieve into the nucleuse , the importin leaves the protien it was carrying
what is RAN and why is it needed?
for a importin to deattach from the protien it was carrying we need the help of the protien RAN
RAN is a monomeric GTpase, can bind and hydrolize GTP (ATP but guanine as the base)
