Term
| What is the nuclear envelope? |
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Definition
| boundary between cytosol & nucleus |
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Term
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Definition
| area in a prokaryotic cell where DNA is confined |
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Term
| What are the two main functions of the nucleus? |
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Definition
Compartmentalization of the cellular genome & its activities e.g. replication, transcription
Coordination of cellular activities
eg. control protein synthesis, metabolism, reproduction |
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Term
| What are the main components of the nuclear envelope? |
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Definition
nuclear membrane
nuclear lamina
nuclear pores |
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Term
| What are the main components of the nuclear content? |
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Definition
chromatin
nucleoplasm
nuclear matrix
nucleolus |
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Term
| Describe the structure of the nuclear envelope & its continuity with the ER |
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Definition
-2 phospholipid bilayers
-outer membrane contains ribosomes, is continuous with RER
-inner & outer membranes join at nuclear pores
-lumen of the nuclear envelope is continuous with the ER lumen |
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Term
True or False
The protein composition of the inner membrane of the nuclear envelope is distinctly different from that of the outer membrane? |
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Definition
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Term
| How are the inner and outer membranes of the nuclear envelope connected? |
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Definition
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Term
| What are the functions of the nuclear envelope? |
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Definition
-separates nuclear content from the cytoplasm
e.g. genome from cytosol, transcription from translation
selective barrier
binds nuclear lamina (provides structural framework for nucleus) |
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Term
| Describe the structure of the nuclear lamina |
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Definition
| A thin meshwork of long filament-like proteins on the inner surface of the nuclear envelope |
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Term
| What proteins form the meshwork that lines the inside of the nuclear envelope? |
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Definition
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Term
| What is the purpose of the nuclear lamina? |
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Definition
-support structure for nuclear envelope
-scaffold for attachment of nuclear matrix & chromatin |
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Term
| What is the nuclear pore complex? |
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Definition
| a protein structure which fill the nuclear pore & regulates passage of molecules between nucleus & cytosol |
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Term
| What are the 3 types of proteins that can associate with membranes? |
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Definition
Peripheral
Integral
Lipid-anchored |
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Term
| What proteins are found within the nuclear pore complex? |
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Definition
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Term
True or False
The NPC structure shows a lot of variation in different eukaryotes |
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Definition
False
The structure of the NPC is highly conserved |
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Term
| What are the structural components of the NPC? |
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Definition
-octagonal symmetry organized around an aqueous central channel
-central scaffold anchors NPC to NE
-inner surface lined with nucleoporins
-cytoplasmic & nuclear rings
-cytoplasmic filaments
-nuclear basket |
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Term
| What is the unusual amino acid composition & structure of nucleoporins (NUPs)? |
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Definition
contain a large number of FG Domains
secondary structure is extended & flexible, forms a hydrophobic mesh which prevents diffusion of large molecules |
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Term
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Definition
| repeated sequences of phenylalanine & glycine found in NUPs |
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Term
| What is the 'cut off' size limit for the diffusion of molecules through the NPC? |
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Definition
| molecules larger than 40kDa cannot diffuse |
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Term
| What is the function of cytoplasmic filaments? |
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Definition
| they are involved in nuclear receptor-cargo protein recognition & import |
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Term
| How do nucleotides & histones pass through the NPC? |
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Definition
| by diffusion (they are less than 40kDa) |
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Term
| How does RNA pass through the NPC? |
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Definition
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Term
| Which is more efficient, passive diffusion or regulated movement of molecules across the NPC? |
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Definition
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Term
| What 3 things are required for cytosol-to-nuclear transport? |
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Definition
| energy, protein receptors & unique targeting signals |
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Term
| What is a nuclear localization signal? |
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Definition
| specific sequence of AAs which act as a necessary 'label' for targeting to and recognition by nuclear receptor proteins |
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Term
| What are the two types of NLSs? |
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Definition
Classic: single stretch of positive (basic) AA residues
Bipartite: two short segments of basic AAs separated by a 7-10 AA space sequence |
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Term
Explain this statement:
An NLS is both necessary and sufficient for cytosol-to-nucleus targeting |
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Definition
Necessary: mutation/absence of an NLS will mean the protein will not be targeted to the nucleus
Sufficient: adding this sequence to a non-nuclear protein will result in the protein being targeted to the nucleus |
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Term
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Definition
| mobile protein which carry macromolecules across the nuclear envelope |
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Term
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Definition
molecular switches involved in moving cargo in & out of nucleus
e.g. Ran proteins |
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Term
| What are we looking at here?[image] |
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Definition
A) cytoplasmic view of NPC
B) nuclear view of NPC |
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Term
| Describe the intrinsic GTPase activity of G proteins |
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Definition
| GTP binding & hydrolysis causes conformational changes to the proteins, switching them between active & inactive states |
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Term
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Definition
| a protein consisting of two subunits, involved in protein import into the nucleus |
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Term
| What are the steps of nuclear import? (brief summary!) |
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Definition
1. Alpha unit of importin recognizes NLS of a cargo protein and binds to form a complex
2. Importin-protein receptor complex moves through cytosol towards the nucleus, where beta importin binds to a cytoplasmic filament at the NPC
3. Protein-importin receptor complex translocates through NPC
4. Complex associates with nuclear basket on inner surface of NPC, binds to Ran-GTP via beta importin, is released from NPC and disassembles
5. Ran-GTP bound to beta importin moves back to cytosol |
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Term
| Desribe the current model for the translocation of the cargo protein-importin receptor complex through the channel of the NPC |
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Definition
-complex interacts with FG domains of the NUPs inside the channel
-FG network is dissolved allowing the cargo-receptor complex to pass through |
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Term
True or False
NLS is cleaved from the cargo protein when the cargo protein-receptor complex is released from the NPC and disassembles in the nucleoplasm |
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Definition
False
The NLS remains attached! |
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Term
| Describe the movement of Ran-GTP-beta importin from the nucleus into the cytosol |
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Definition
-higher [RAN-GTP] in nucleus than cytosol causes this complex to travel down the concentration gradient
Ran-Gap-1 protein hydrolyzes GTP, now have Ran-GDP
beta importin is released
Ran-GDP moves back into nucleus due to concentration gradient and converted back into Ran-GTP by RCC1 |
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Term
| What protein mediates the hydrolysis of GTP on Ran-GTP in the cytosol? |
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Definition
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Term
| What protein mediates the conversion of of Ran-GDP to Ran-GTP in the nucleus? |
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Definition
GEF (Guanine nucleotide Exchange Factor)
e.g. RCC1 |
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Term
| How is the necessary energy for transport of proteins into the nucleus supplied? |
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Definition
| hydrolysis of Ran-GTP to Ran-GDP in nucleus by Gap-1 |
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Term
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Definition
| a guanine nucleotide exchange factor (GEF) which exchanges GDP for a GTP on Ran protein in the nucleus |
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Term
| True or False The generation of Ran-GTP from Ran-GDP in the nucleus is a phosphorylation event |
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Definition
| FALSE!!!! It is an exchange event |
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Term
| Where is the a higher concentration of Ran-GTP, in the nucleus or cytoplasm? |
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Definition
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Term
| What prevents the concentration of Ran-GTP from reaching an equilibrium between the cytosol and nucleus? |
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Definition
| Ran-GTP can only move when bound to beta importin |
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Term
| Describe how alpha importin & other cargo proteins are exported out of the nuceus (brief summary!) |
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Definition
1. alpha importin or cargo proteins bind to exportin to form a complex
2. Complex binds to Ran-GTP and follows concentration gradient out of the nucleus
3. Ran-GTP is hydrolyzed by Gap-1, Ran-GDP is released from exportin, alpha importin or cargo proteins are released
4. Ran-GDP moves back into nucleus due to concentration gradient, exportin moves back in via a specific carrier |
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Term
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Definition
Nuclear Export Signal
specific sequence of AA's recognized by exportin, which targets an NES protein from the nucleus to the cytosol |
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Term
| What is the most common NES? |
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Definition
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Term
| What is 'piggyback' nuclear import? |
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Definition
| Indirect nuclear import. Proteins without an NLS can bind to a protein that does have one, and the usual steps for import are followed. |
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Term
True or False
Nuclear subdomains are not membrane bound |
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Definition
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Term
| What is the nuclear matrix analogous to? |
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Definition
| the cytoskeletal network in the cytosol |
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Term
| What is the role of the nuclear matrix? |
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Definition
-maintains 3D structure of the nucleus
-acts as a scaffold for organizing subdomains & anchoring proteins |
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Term
| Where are the most actively transcribed genes found? |
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Definition
| in the periphery of a chromosomal subdomain |
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Term
| Regions between chromosomal domains which prevent unwanted interactions between DNA & proteins are called..... |
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Definition
| interchromosomal channels |
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Term
| What are transcription factories? |
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Definition
| region of transcription factors, where active genes from various chromosomal subdomains extend into interchromosomal channels |
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Term
| What are nuclear speckles? |
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Definition
| subdomains where mRNA splicing factors are found |
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Term
| Where does pre-mRNA processing occur? (be specific, just just 'the nucleus') |
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Definition
| In nuclear speckles, usually found in interchromosomal channels next to transcription factories |
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Term
True or False
Nuclear speckles are very constant in terms of size & degree of dispersion |
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Definition
False
They can move, grow and shrink very quickly in response to the needs of the cell/transcription levels |
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Term
True or False
If metabolic activity/protein synthesis in the cell is increased, the size & number of nucleoli will also increase |
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Definition
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Term
True or False
The nucleolus is membrane-bound |
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Definition
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Term
| Describe the appearance of the nucleolus |
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Definition
| irregular, dense, granular |
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Term
| What is the function of the nucleolus? |
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Definition
-transcription & processing of ribosomal DNA
-initial stages of ribosomal subunit assembly |
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Term
| Where does the final assembly of ribosomes take place? |
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Definition
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Term
| What does a ribosome consist of? |
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Definition
| rRNA & ribosomal proteins |
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