Term
Describe the nuclear envelope
1. Function
2. Structure
3. Permeability |
|
Definition
1. separates the nucleus from cytoplasm
-act as barrier
2. two membranes with underlying nuclear lamina
-perinuclear space in between
-same as lumen of ER
3. only permeable to small non polar molecules
-nuclear pores are only channels for passage |
|
|
Term
Describe the nuclear envelope
1. Outer membrane
2. Inner membrane |
|
Definition
1. connected directly to ER
-contains ribosomes and is functionally similar to ER
-enriched in membrane proteins to bind to cytoskeleton
2. contains proteins specific to nucleus
-bind to nuclear lamina |
|
|
Term
Describe the nuclear lamina
1. Definition
2. Structure
3. Inner membrane binding |
|
Definition
1. fibrous mesh of proteins called lamins that provides structural support
-lamins dissolve in mitosis
-mutation in lamins lead to progeria
2. 3 lamin genes (A,B,C) code for 7 proteins
-2 lamins interact to form dimer where alpha helical regions combine to form coil
3. bind to inner membrane proteins such as Emerin and Lamin B receptor
-lamins bind to lamin associated proteins that bind to chromatin
-also extend into nucleus |
|
|
Term
Describe the nuclear pore complex
1. Function
2. Structure |
|
Definition
1. only channels that polar molecules, ions, and RNA can pass through
-RNA has to leave and TFs have to enter
-smaller molecules pass freely through
-macros pass through central pore by active process
2. large structure made of 30 different proteins (nucleoporins)
-8 fold symmetry (spoke rings) with large central channel
-protein filaments extend from the rings forming basket-like structure on nuclear side to bring proteins in
-other filaments outside nucleus
*these filaments have AA that code for nuclear transport |
|
|
Term
| Describe nuclear localization signals |
|
Definition
-stretch of AA that code for nuclear transport
-some stretches are continuous and some are bipartite
ex. SV40 T ag is 7 AA
ex. Nucleopasmin is separated by 10 AA but fold together |
|
|
Term
| Describe importins and Ran |
|
Definition
-receptors that recognize nuclear localization signals
-importins are regulated by Ran that binds to GTP |
|
|
Term
Describe the process of nuclear transport and Ran
a. Setting
b. Process |
|
Definition
a. outside: GAP that cleaves ATP->ADP so there is a higher concentration of ADP outside
inside: GEF takes GDP->GTP so there is more ATP inside
b. 1. importins bind to nuc loc sigs
2. importin binds to cytoplasmic filaments on nuc pore
3. importin binds to proteins throughout pore (Phe-Gly repeats)
4. importin/cargo complex is disrupted by Ran/GTP
-cargo is released into nucleus
5. importin and Ran/GTP go out because of concen gradient
6. GAP hydrolyzes GTP->GDP and importin in released
7. Ran/GDP goes back into nucleus by NTF2 and Ran/GTP is regenerated by GEF |
|
|
Term
| Describe protein export from nucleus |
|
Definition
Exportins instead of importins
-bind to similar AA sequence as nuc log sig (nuc exp sig)
-belong to family called karyopherins
1. Ran/GTP promotes binding to exportins
2. Ran/GDP dissociates complex
*opposite of importins |
|
|
Term
| Describe nuclear import regulation by phosphorylation |
|
Definition
Yeast TF Pho4
1. phosphorylated at Ser next to nuc loc sig and causes interference
2. can't be imported and can't be TF
3. those genes are then turned off
*can be reversed |
|
|
Term
| Describe RNA transport out of nucleus |
|
Definition
-most RNAs are export to cytoplasm
-active, energy dependent process
-RNAs are transported across as RNP complexes
-snRNAs function inside nucleus |
|
|
Term
| Describe internal organization of nucleus: chromatin |
|
Definition
-genetic material is organized to localize function
-lamins attach to chromatin
-heterochromatin is tightly packed but euchromatin is de condensed and distributed throughout nucleus
-euchromatin is placed together so TFs can access
Constitutive Heterochromatin: not transcribed at all (centromeres)
Facultative: not transcribed in particular cells
-localized into specific territories that is consistent
-Actively transcribed genes are located at periphery |
|
|
Term
| Describe internal organization of nucleus: DNA replication and mRNA splicing |
|
Definition
DNA: replication takes place at clustered site
-replication factories are distinct functional bodies with multiple replication forks
mRNA: splicing machinery is concentrated in discrete nuclear bodies called nuclear speckles
-staining snRNPs
PMLs: collection of TFs and chromatin modifying proteins |
|
|
Term
| Describe the nucleolus: composition |
|
Definition
-site of rRNA transcription and processing and some assembly of ribosomes
-no membrane
-associate with rRNAs: 5.8, 18, 28S and transcribe with RNA poly 1
-all cells have multiple rRNA gene copies |
|
|
Term
| Describe the nucleolus: structure |
|
Definition
3 regions
1. fibrillar center 2. dense fibrillar component 3. granular
-after transcription of 45S pre-rRNA they form one large cluster |
|
|
Term
| Describe the nucleolus: rRNA processing |
|
Definition
-series of cleavages like mRNA
-addition of methyl groups and conversion of uridine
-snoRNAs function in processing (spliceosomes) |
|
|
Term
| Describe the nucleolus: ribosome assembly |
|
Definition
-ribosomal proteins are transcribed outside nucleus and transported back in
-5s are transcribed outside nucleolus
-release both subunits into cytoplasm |
|
|
