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Questions and Answers
Which of the following organelles is NOT involved in the endomembrane system?
Which of the following organelles is NOT involved in the endomembrane system?
All nuclear-encoded proteins are synthesized in the nucleus.
All nuclear-encoded proteins are synthesized in the nucleus.
False
What role do signal sequences play in protein sorting?
What role do signal sequences play in protein sorting?
They direct proteins to their correct location within the cell.
Proteins that lack a signal sequence are typically __________.
Proteins that lack a signal sequence are typically __________.
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Match the signal sequence to its corresponding characteristic:
Match the signal sequence to its corresponding characteristic:
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What sequence signals the import of soluble proteins into peroxisomes?
What sequence signals the import of soluble proteins into peroxisomes?
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The SKL signal sequence on soluble proteins is cleaved off within the peroxisome.
The SKL signal sequence on soluble proteins is cleaved off within the peroxisome.
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Where is catalase likely located in cells that do not contain peroxisomes?
Where is catalase likely located in cells that do not contain peroxisomes?
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In normal cells, catalase shows up as small dots of fluorescence due to its localization in __________.
In normal cells, catalase shows up as small dots of fluorescence due to its localization in __________.
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Match the following cellular components with their respective functions:
Match the following cellular components with their respective functions:
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What is the role of the TOM complex in mitochondria?
What is the role of the TOM complex in mitochondria?
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TIM23 and TOM complexes can work together to create a translocation channel across both mitochondrial membranes.
TIM23 and TOM complexes can work together to create a translocation channel across both mitochondrial membranes.
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What is the function of catalase in peroxisomes?
What is the function of catalase in peroxisomes?
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Mitochondrial proteins are imported through the TOM and TIM complexes, which require _____ for active transport.
Mitochondrial proteins are imported through the TOM and TIM complexes, which require _____ for active transport.
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Match the following mitochondria-related complexes with their functions:
Match the following mitochondria-related complexes with their functions:
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What would happen if you changed the charged amino acids in a mitochondrial signal sequence to acidic amino acids?
What would happen if you changed the charged amino acids in a mitochondrial signal sequence to acidic amino acids?
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Peroxisomes are involved in the production of cholesterol and long-chain fatty acids.
Peroxisomes are involved in the production of cholesterol and long-chain fatty acids.
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What type of reactions do peroxisomes carry out using O2?
What type of reactions do peroxisomes carry out using O2?
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Study Notes
Protein Sorting I: Nucleus, Mitochondria, and Peroxisomes
- Eukaryotic cells contain many membrane-bound compartments
- These compartments include the nucleus, mitochondria, chloroplasts (plants), endoplasmic reticulum (ER), Golgi apparatus, endosomes, lysosomes, and peroxisomes
- Organelles occupy about half the volume of a eukaryotic cell
- Different organelles contain different proteins and specialized functions
- The cytosol is the fluid component that occupies the majority in the cell. Other membrane-bound organelles are excluded.
Protein Transport Mechanisms
- Organelles import proteins using one of three mechanisms
- Transport through nuclear pores
- Transport across membranes
- Transport by vesicles
Protein Sorting in Eukaryotic Cells
- Proteins are synthesized in the cytosol
- Signal sequences direct proteins to the right location or organelle—like a postal code
- Proteins lacking signal sequences remain in the cytosol (or are degraded) or enter the nucleus.
- Different compartments have specific signal sequences
- The import process can be either co-translational or post-translational
- Nuclear localization signals (NLS) direct cargo into the nucleus
- Nuclear import receptors bind the cargo NLS and nuclear pores. Ran GTP/GDP regulates the cycle. Ran GTP binding causes the release of cargo.
- Nuclear export utilizes similar mechanisms as nuclear import, but in reverse, using nuclear export signals (NES)
Protein Import into Mitochondria
- Mitochondrial precursor proteins are unfolded during import
- A signal peptide at the N Terminus directs the protein to the mitochondria.
- Import occurs via different complexes (TOM & TIM) in the outer and inner membranes
- Energy (ATP) is required to import proteins
Protein Import into Peroxisomes
- Soluble proteins are imported in a folded state through a specific receptor that recognizes C-terminal signals (SKL)
- The receptor shuttles cargo into peroxisomes
- The import signals are not cleaved from the protein during the process.
- Return of the receptor to the cytosol necessitates ATP hydrolysis
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Description
This quiz covers the organization and transport mechanisms of proteins within eukaryotic cells, including the nucleus, mitochondria, and peroxisomes. You'll learn about the various membrane-bound compartments and how proteins reach their designated organelles through different transport methods. Test your knowledge on protein sorting and cellular compartmentalization!
