Questions and Answers
What is the role of Importin-RanGTP complex in nuclear transport?
Transport cargo from the nucleus to the cytoplasm
Which molecule is only present in the nucleus and has a high affinity for Importin?
RanGTP
What happens to Ran-GTP once the Importin-RanGTP complex reaches the cytoplasm?
It transforms into Ran-GDP
Which type of proteins contain a NLS and are actively transported inside the nucleus?
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What is the role of Exportin1 (Xpo1) in nuclear export?
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How does mRNA get transported from the nucleus to the cytoplasm?
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What is the function of Nuclear Localization Sequence (NLS) in proteins?
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Which proteins are involved in transporting proteins to the nucleus through the nuclear pore complex?
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What is the primary role of Importin proteins in nuclear transport?
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Where is Ran-GTP primarily found in the cell during nuclear transport?
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Which statement best describes the function of Importin a and Importin b in protein transport?
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What is the energy requirement associated with the process of protein transport into the nucleus?
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Which statement accurately describes the process of protein translocation into peroxisomes?
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What is the role of import receptors in mitochondrial protein sorting?
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What distinguishes the process of protein sorting in mitochondria from that in the ER?
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What is the main function of Importin in nuclear transport?
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How does Ran-GTP contribute to nuclear transport?
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Which statement correctly describes the regulation of nuclear localization for some proteins?
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The Importin-RanGTP complex is able to freely pass to the cytoplasm where Ran-GTP will be transformed into RanGDP.
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Proteins with a NES are actively transported inside the nucleus.
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Ran-GTP is primarily found in the cytoplasm during nuclear transport.
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The Cargo-Importin complex releases Ran protein in the cytoplasm.
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NLS-containing proteins are shuttled from the cytoplasm into the nucleus.
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RanGDP is formed in the nucleus during nuclear transport.
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The Nuclear Pore Complex is smaller than ribosomes in a cell.
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Nuclear Localization Sequences (NLS) are typically long and complex in structure.
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Importin a and Importin b are responsible for recognizing NLS in proteins and directing them to the cytoplasm.
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Proteins targeted to the nucleus must be unfolded before translocation.
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RanGDP is predominantly found in the nucleus during nuclear transport.
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Importin has a higher affinity for Ran-GTP than for Ran-GDP.
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Importin has a higher affinity for Ran-GDP compared to Ran-GTP.
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CargoImportin complex formation happens in the cytoplasm before being transported into the nucleus.
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Nuclear transport exclusively involves proteins that are cotranslationally translocated into the nucleus.
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The presence of Nuclear Localization Sequence (NLS) in proteins ensures their active transport into the cytoplasm.
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Ran-GDP is predominantly found in the nucleus during nuclear transport processes.
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The regulation of nuclear localization is a key factor in ensuring proper functioning of nuclear proteins.
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Study Notes
Protein Sorting Signals
- Mitochondria sorting: specific sequence in mitochondrial proteins is recognized by import receptor, leading to posttranslational translocation
- Mitochondria sorting is more complicated than in ER, requiring translocation to both mitochondrial membranes
- Peroxisome proteins: recognized by PEX5 receptor, transported to receptor on peroxisome surface, and then translocated inside peroxisome
- No cotranslational translocation in peroxisome: proteins are already translated before translocation
- Proteins are translocated unfolded and fold properly inside peroxisome
Nuclear Transport
- One of the most important trafficking mechanisms in cells
- Proteins involved in DNA metabolism (e.g., Histones, transcription factors, polymerases, helicases, primases) are made in cytoplasm and transported into nucleus
- Some proteins constantly shuttle in and out of nucleus, while others remain in nucleus
- Regulation of nuclear localization plays an important regulatory role for nuclear proteins
Nuclear Pore Complex
- One of the largest complexes in cells (16x bigger than ribosomes)
- Made of multiple copies of over 30 different proteins
- Octagonal shape, embedded between inner and outer nuclear membranes
- In nucleoplasm, NPC forms a basket-like structure where proteins create filamentous structures
Nuclear Localization Sequence (NLS)
- Proteins targeted to nucleus possess a Nuclear Localization Sequence (NLS)
- NLS recognized by Importin a and Importin b, directing proteins to nuclear pore for translocation
- Only protein sorting mechanism where proteins are already folded before translocation
- Energy is required for this process
- NLS tend to have a basic short sequence with few variants
Nuclear Export
- NLS-containing proteins are actively transported inside nucleus
- Proteins that shuttle in and out of nucleus have a Nucleus Export Sequence (NES) in addition to NLS
- NES recognized by Exportin1 (Xpo1), which binds RanGTP
- In cytoplasm, RanGTP is transformed into RanGDP, causing the complex to dissociate
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