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21 Cards in this Set
- Front
- Back
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Properties of nucleus |
-Segregated genome -Separates transcriptional vs translational machinery -Usually one per cell but varies -Matrix: organizes chromatin/regulates genes |
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Nuclear matrix |
What remains after all DNA is taken from nucleus --Transcription factors, polymerases, non histone proteins
Three parts: 1. Nuclear envelope/pore/lamina 2. Nucleolus 3. Internal matrix (98%) |
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Structure of nuclear envelope |
Double membrane
Outer: faces cytoplasm, with ribosomes and continuous with ER
Inner: Next to nuclear lamina and marginal heterochromatin |
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Nuclear pore complex |
Contains nucleoporins stacked in 3 rings of octamers, which bind to a nuclear cargo protein with an NLS "zipcode" that is in turn bound to its NLS receptor protein (basic lysine/argenine residues)
Marginal heterochromatin between pores |
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Rules of active/passive transport through nuclear pores |
Proteins less than 40 kD fuse right through passively (i.e. histones)
If bigger, need active transport (polymerases and transcription factors) |
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Nuclear import properties |
-Only allows proteins through -Energy dependent (discovered by testing proteins at pores at 0 degrees vs 37 degrees) -Energy=Ran-GTP; high concentration in nucleus, low in cytoplasm
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Steps of nuclear import |
1. Cargo with NLS "zip code" binds to NLS receptor on alpha unit of importin (an NLS heterodimer receptor protein)
2. Beta unit of importin binds to nuceloporin 3. Goes through pore |
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Phosphorylation of NLSs |
Another way to regulate nuclear importation phosphorylized NLSs can't go in nucleus |
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Nuclear export |
Can let out tRNAs, mRNAs, ribosome subunits and proteins
Exportins: proteins with nuclear export sequences (NES) that leave nucleus, though it is not necessary to have an NES to leave |
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Nuclear import and Ran-GTP steps |
1. Protein with NLS binds to NLS receptor, diffuses into nucleus 2. Drops cargo 3. Receptor drops off cargo 4. Empty receptor picks up Ran-GTP 5. Carries it out to cytosol where it hydrolyzes it to let go of it |
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Nuclear export and Ran-GTP steps |
1. Empty export receptor diffuses into nucleus 2. Binds to cargo and Ran-GTP 3. Goes to cytosol 4. Phosphorylates Ran-GTP to let go of cargo |
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Structure of nuclear lamina |
Very simple, made of 3 proteins (lamins A,B and C) and between inner nuclear envelope and marginal heterochromatin |
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Interaction of lamins |
Lamin B attaches to integral protein in inner nuclear envelope called LBR
Lamins A and C attach to lamin B and marginal heterochromatin |
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Function of nuclear lamina |
Maintains nucleus as a sphere in interphase
In mitosis, hyperphosphorylation causes lamins A and C to become soluble and detach from lamin B; this disrupts the nuclear envelope |
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Diseases that have to do with the nuclear lamina |
LMNB gene encodes lamin B
LMNA encodes lamins A and C; mutation of this causes muscular dystrophy, premature aging and cardiomyopathy
Does the nuclear lamina regulate aging? MAYBE! |
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Nucleolus |
Only function is to make ribosomes
We have 400 ribosome genes among the 10 chromosomes that make up the nucleolus, which is only seen during interphase
These make the ribosome subunits and send them to the cytoplasm where they come together |
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Internal nuclear matrix |
98% of total nuclear matrix, with thousands of non histone proteins
Confers the non random order of chromatin |
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Evidence for non random order in internal nuclear matrix |
1. Matrix proteins tissue specific 2. Chromosomes occupy specific locations 3. DNA replication/transcription occur in nuclear matrix |
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Non random order in INM: matrix proteins tissue specific |
Different in normal cells vs cancer cells, so diagnostic tool for bladder and cervical cancers |
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Non random order in INM: chromosomes occupy specific locations |
- Rabl 1885 found centromeres always at one side, telomeres on other
- 1982, burnt holes in nucleus, repairs with radioactive DNA, repair sites in same place every generation
- Barr body ALWAYS along nuclear lamina
- FISH chromosomes painting shows that chromosomes move within assigned territories |
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Non random order in INM: DNA replication/transcription occurs in nuclear matrix |
- if you remove DNA, still see where sites of mRNA are in matrix
- active genes are associated with nuclear matrix
- replicons, sites of DNA replication, are in nuclear matrix (still remain when matrix remains) |
