Questions and Answers
What is the primary function of peroxisomes in cells?
In which organelle does the synthesis of bile acids occur?
How are proteins without a sorting signal processed in the cell?
Which of the following correctly describes transmembrane transport?
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What is a primary function of the smooth endoplasmic reticulum (SER) in liver cells?
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What is the role of GEF in the Rab family of proteins?
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Which component of the endomembrane system is responsible for processing and packaging proteins?
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Which statement correctly describes the function of GAP in Rab protein regulation?
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What is the primary function of the Arf family of proteins?
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What are the components of the large subunit of ribosomes?
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How does the Rho family contribute to cellular functions?
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What process primarily occurs in the inner mitochondrial lumen to produce ATP?
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Which protein assists in the folding of mitochondrial proteins in the matrix?
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What is the consequence of Ran binding to GEF in the nucleus?
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Which of the following statements about mIONA is true?
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What initiates the release of the N-terminal segment from the SRP during protein translocation?
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Which characteristic distinguishes an integral membrane protein with a 'lateral gate'?
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What role do chaperones play in protein processing?
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How do misfolded proteins manage to be tagged for re-engagement in the ER?
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What happens to misfolded proteins that fail to achieve proper folding after re-engagement cycles in the ER?
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What role does glucose-6-phosphatase play in hepatocytes?
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What happens to the signal sequence during protein synthesis and translocation?
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Which pathway describes the synthesis of secretory proteins?
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What happens to proteins synthesized on free ribosomes without sorting signals?
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Which of the following best describes the role of the translocator during protein synthesis in the ER?
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Study Notes
GDI, GEF, GAP
- GDI (GDP Dissociation Inhibitor): Prevents GDP release, remains inactive, and hinders membrane movement.
- GEF (Guanine Exchange Factor): Facilitates the exchange of GDP for GTP, activating proteins to move to the membrane.
- GAP (GTPase-Activating Protein): Promotes GTP hydrolysis to GDP, rendering proteins inactive.
Rab Family
- Regulates vesicle trafficking, influencing movement, tethering, docking, and fusion of vesicles.
- Rab is inactive with GDP and resides in the cytoplasm.
- Activation through GEF converts GDP to GTP, allowing membrane association and interaction with effectors.
- Active Rab-GTP orchestrates vesicle movement and fusion, while GAP inactivates it through GTP hydrolysis.
Arf Family
- Activates coat proteins for cargo sorting and vesicle formation.
- Arf with GTP binds to membranes; Arf with GDP states inactive.
- Sar1 governs assembly of COPII-coated vesicles from the ER to Golgi; COPI facilitates reverse transport from Golgi to ER.
Rho Family
- Involved in cellular processes including endocytosis, adhesion, motility, proliferation, and apoptosis.
Ras Family
- Promotes cell proliferation through activation; GTP translocates Raf, initiating the MAP kinase cascade.
Ran Family
- Ran-GAP in the cytoplasm hydrolyzes GTP to GDP for nuclear import/export.
- Ran-GEF in the nucleus converts GDP to GTP for nuclear transport through nuclear pore complexes.
Endomembrane System
- Includes the nucleus, ER, Golgi, lysosomes, vesicles, and endosomes; excludes mitochondria and peroxisomes.
- Cell fractionation separates cellular components based on size, larger components settle first.
Ribosomes
- Composed of large (3 rRNA and ~50 proteins) and small subunits (1 rRNA and ~30 proteins).
- Assemble during protein synthesis and dissociate afterward.
Mitochondria
- Contains circular DNA and synthesizes some of its proteins; most proteins sourced from the cell.
- Features cristae with an inner membrane and matrix (lumen).
- Generates ATP primarily through oxidative phosphorylation.
- Cytochrome c is linked to apoptosis processes and is involved in the breakdown of interdigitations between fingers during development.
mIONA Process
- Mitochondrial proteins are unfolded by Hop 70, bind to TOM, stripped of interacting proteins, and pass through TIM.
- N-terminus (presequence) gets cleaved, and Hsp60 assists in proper folding within the matrix.
Endosomes and Vesicles
- Endosomes are specialized vesicles involved in endocytosis.
- Smooth ER: Responsible for lipid synthesis and detoxification, contrasting with peroxisomes, which break down lipids and detoxify hydrogen peroxide.
Peroxisome Functions
- β-Oxidation for fatty acid breakdown.
- Synthesis of bile acids and cholesterol, removal of hydrogen peroxide.
- Production of myelin sheaths.
Protein Movement
- Proteins are synthesized in ribosomes, ER, and mitochondria.
- Without sorting signals, proteins remain in the cytosol; with signals, they are directed to specific locations.
Protein Transport Mechanisms
- Gated transport: Exchanges molecules between the cytosol and nucleus.
- Transmembrane transport: Movement across membranes to organelles like mitochondria and peroxisomes.
- Vesicular transport: Transports proteins to and from the ER, Golgi, lysosomes, and the cell surface.
Endoplasmic Reticulum (ER)
- Rough ER: Studded with ribosomes, facilitates the transport of proteins to Golgi, lysosomes, plasma membrane, and secretion.
- Smooth ER: Specializes in lipid synthesis, glycogen metabolism, and calcium storage in muscle cells.
Glycogen Metabolism
- Glycogen is stored in the liver and muscle for energy use; breakdown is influenced by insulin (for storage) and glucagon (for release).
Secretory Protein Synthesis
- Involves mRNA being read by ribosomes, formation of signal sequences, and SRP-mediated transport to the ER.
- Proteins are synthesized into the lumen where the N-terminus signal is cleaved.
Integral Membrane Protein Synthesis
- Integral proteins partially embed in membranes and utilize lateral gates for insertion, differing from secretory proteins which are fully translocated into the lumen.
Protein Processing
- Proteins undergo modifications: signal sequences are cleaved, while chaperones and enzymes assist in proper folding and bond formation.
Handling Misfolded Proteins
- Misfolded proteins are identified via glucosidases and retained or recycled by calnexin/calreticulin; failed proteins are directed to cytosolic degradation via proteasomes.
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Description
This quiz covers the mechanisms involved in vesicle trafficking within cell biology, specifically focusing on the roles of GDI, GEF, and GAP. Additionally, the activation and function of the Rab family in vesicle movement and membrane interactions are explored.
