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WK7 Cell Bio

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winniesmith's version from 2017-01-04 21:22

Section 1

Question Answer
Role of the nuclear envelope separates the nuclear contents from the cytoplasm
What does the nuclear envelope controlthe traffic of proteins and RNAs through nuclear pore complexes, and plays a critical role in regulating gene expression.
What does the nuclear envelope consist oftwo nuclear membranes, an underlying nuclear lamina, nuclear pore complexes. Outer membrane is continuous with the endoplasmic reticulum (ER). Inner membrane has proteins that bind the nuclear lamina.
What are the membranes permeable too(phospholipid bilyar) only to small nonpolar molecules. Nuclear pore complexes are the only channels for small polar molecules, ions, proteins, and RNA.
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Section 2

Question Answer
What is the nuclear lamina a fibrous mesh that provides structural support.
What does nuclear lamina consist of fibrous proteins called lamins, and other proteins.
What do mutations in lamin genes cause several different inherited tissue-specific diseases (such as hutchinson-gilford progeria- fast ageing)
How many genes for lamin do mammals have 3 lamin genes (A, B, and C) which code for 7 proteins.
Two lamins interact to form a whata dimer: the α-helical regions wind around each other to form a coiled coil. Two lamin dimers=lamina
Where/What are lamins binded/connected too•bind to inner membrane proteins such as emerin and lamin B receptor (LBR). •are connected to the cytoskeleton by LINC complexes. •bind to chromatin. •extend in a loose meshwork throughout the interior of the nucleus
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Section 3

Question Answer
What are nuclear pore complexes composed ofabout 30 different pore proteins (nucleoporins)
Why are nuclear pores needed As RNAs synthesized in the nucleus must be exported to the cytoplasm for protein synthesis and proteins needed for nuclear functions must be imported from synthesis sites in the cytoplasm.
How do molecules pass through pore complexes By two mechanisms: Passive diffusion—small molecules pass freely in either direction. •Proteins and RNAs are selectively transported; requires energy.
Basic structure of pore complexesElectron microscopy shows they have 8 subunits organized around a large central channel.
Detailed structure of pore complexesEight spokes are connected to rings at the nuclear and cytoplasmic surfaces. The spoke-ring assembly surrounds a central channel. Protein filaments extend from the rings, forming a basketlike structure on the nuclear side. Model
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Section 4

Question Answer
Proteins that must enter the nucleus have AA sequences called what?nuclear localization signals.
What are nuclear localization signals (NLS)recognised by nuclear transport receptors.
How were nuclear localisation signals (NLS) first identified 1984, using a viral replication protein SV40 T antigen (T antigen mutant) same sequence attached to other proteins= transported into nucleus.
What is the T antigen nuclear localization signal a single stretch of amino acids.
What are bipartite signals two amino acids sequences are separated by another amino acid sequence.
What are NLS recognized byreceptors called importins
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Section 5

Question Answer
What is the movement of proteins regulated byRan, a GTP-binding protein.
How is Ran/GTP hydrolysedin the cytoplasm,catalyzed by Ran GAP.In the nucleus, Ran GEF stimulates conversion of Ran/GDP to Ran/GTP. This leads to higher concentration of Ran/GTP in the nucleus, and determines directionality of transport.
What does Ran control nuclear transport receptors.
How does Ran work? step 1A specific importin binds to the NLS of a cargo protein.
step 2This complex binds to cytoplasmic filaments of the pore complex
step 3Sequential binding to nuclear pore proteins moves the complex further into the pore complex.
step 4At the nuclear side the cargo/importin complex is disrupted by binding of Ran/GTP.
step 5This causes a conformation change in the importin, which releases the cargo protein into the nucleus. The
step 6 The importin-Ran/GTP complex is then exported back to the cytoplasm where the GTP is hydrolyzed to GDP.
step 7 The importin is released and can participate in another round of transport. Ran/GDP is transported back to the nucleus by its own import receptor (NTF2). The
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Section 6

Question Answer
What are nuclear export signals (NES)an AA sequence which targets proteins for export.
How do NES work?are recognized by receptors in the nucleus (exportins), which direct protein transport to the cytoplasm. The
What family do many importins/exportins a member ofkaryopherins
What role does RAN play in nuclear export Ran/GTP promotes binding of exportins and cargo proteins (but dissociates complexes between importins and cargos).
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Section 7

Question Answer
Protein transport is a point at which nuclear protein activity can be controlled; e.g., regulation of import and export of transcription factors.
Example of protein transport mechanism transcription factors associate with cytoplasmic proteins that mask their NLS, and so they remain in the cytoplasm. The
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