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Questions and Answers
What are the two separate translocator complexes involved in translocation into chloroplasts?
What are the two separate translocator complexes involved in translocation into chloroplasts?
TOC and TIC
What type of signal sequences are used for importing proteins into chloroplasts and what happens to them after use?
What type of signal sequences are used for importing proteins into chloroplasts and what happens to them after use?
N-terminal signal sequences; they are cleaved after use
What drives the import of proteins into the thylakoid space of chloroplasts?
What drives the import of proteins into the thylakoid space of chloroplasts?
Hydrolysis of ATP and GTP
What is the function of peroxisomes in a cell?
What is the function of peroxisomes in a cell?
What is the structure of peroxisomes?
What is the structure of peroxisomes?
What organelle is considered an ancient metabolic organelle based on its function?
What organelle is considered an ancient metabolic organelle based on its function?
How are proteins directed to their final compartmental location in the cell?
How are proteins directed to their final compartmental location in the cell?
What are the different organelles that proteins synthesized in the cytosol can be trafficked to?
What are the different organelles that proteins synthesized in the cytosol can be trafficked to?
What is the role of the Peroxisomal Targeting Signal (PTS) in protein import into peroxisomes?
What is the role of the Peroxisomal Targeting Signal (PTS) in protein import into peroxisomes?
How does the recycling of Pex5 contribute to protein import into peroxisomes?
How does the recycling of Pex5 contribute to protein import into peroxisomes?
Describe the role of peroxins in the protein import process into peroxisomes.
Describe the role of peroxins in the protein import process into peroxisomes.
Explain the mechanisms involved in peroxisome assembly, both in terms of matrix and membrane protein biogenesis.
Explain the mechanisms involved in peroxisome assembly, both in terms of matrix and membrane protein biogenesis.
What powers the import of mitochondrial proteins?
What powers the import of mitochondrial proteins?
How are mitochondrial proteins imported into the inner mitochondrial membrane?
How are mitochondrial proteins imported into the inner mitochondrial membrane?
What drives the dissociation of proteins from cytosolic Hsp70 in the mitochondria?
What drives the dissociation of proteins from cytosolic Hsp70 in the mitochondria?
How is the movement into the inner mitochondrial membrane facilitated?
How is the movement into the inner mitochondrial membrane facilitated?
Describe the structure of chloroplasts.
Describe the structure of chloroplasts.
What are the compartments present in the structure of chloroplasts?
What are the compartments present in the structure of chloroplasts?
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Study Notes
Importing Proteins into Chloroplasts
- Translocation into chloroplasts occurs post-translationally, similar to mitochondrial transport
- Separate translocator complexes are used in each membrane (TOC and TIC)
- Energy is required for protein import, and N-terminal signal sequences are cleaved after use
- Two signal sequences are required for transport to the thylakoid lumen
- Hydrolysis of ATP and GTP drives import
Peroxisomes
- Peroxisomes are single-membrane organelles that oxidize organic molecules
- They use O2 to remove H2, producing and degrading H2O2
- Breakdown of fatty acids occurs in peroxisomes, producing Acetyl CoA which enters the TCA cycle
- Peroxisomes acquire most proteins by selective import from the cytosol, but some enter via the ER
- Short signal sequences direct the import of proteins into peroxisomes, aided by Peroxisomal Targeting Signal (PTS) receptors and docking receptors
- Import is driven by ATP hydrolysis
Importing Proteins into Peroxisomes
- At least 23 proteins are involved in the import process, including peroxins
- A complex of at least 6 different proteins forms a translocator, which imports proteins in native conformation
- Peroxin 5 (Pex5) carries its cargo into the peroxisome before being recycled
Summary of Protein Import
- Proteins synthesized in the cytosol are directed to their final compartmental location by specific sorting signals
- Proteins can traffic to the nucleus, mitochondria, chloroplast, or peroxisome
- Each organelle has its own unique import mechanisms, including signal sequences, chaperones, and translocator complexes
- Energy is required for protein import, and ATP hydrolysis drives import in most cases
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