Pex5 Import: Quiz and Flashcards on Peroxisome Protein Import

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Questions and Answers

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?

N-terminal signal sequences; they are cleaved after use

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?

Oxidizes organic molecules, produces and degrades H2O2, and breaks down fatty acids Signup and view all the answers

What is the structure of peroxisomes?

Single membrane organelle Signup and view all the answers

What organelle is considered an ancient metabolic organelle based on its function?

Peroxisome Signup and view all the answers

How are proteins directed to their final compartmental location in the cell?

Proteins are directed to their final compartmental location by specific sorting signals. Signup and view all the answers

What are the different organelles that proteins synthesized in the cytosol can be trafficked to?

Proteins synthesized in the cytosol may traffic to the nucleus, mitochondria, chloroplast, or peroxisome. Signup and view all the answers

What is the role of the Peroxisomal Targeting Signal (PTS) in protein import into peroxisomes?

The short signal sequences direct the import of proteins into peroxisomes. Signup and view all the answers

How does the recycling of Pex5 contribute to protein import into peroxisomes?

Pex5 carries its cargo all the way into the peroxisome before being recycled. Signup and view all the answers

Describe the role of peroxins in the protein import process into peroxisomes.

At least 23 proteins, known as peroxins, are involved in the import process into peroxisomes. Signup and view all the answers

Explain the mechanisms involved in peroxisome assembly, both in terms of matrix and membrane protein biogenesis.

The mechanisms of peroxisome assembly, involving matrix and membrane protein biogenesis, are not well understood, but over 23 proteins, including peroxins, are involved in the process. Signup and view all the answers

What powers the import of mitochondrial proteins?

ATP hydrolysis, membrane potential, and redox potential Signup and view all the answers

How are mitochondrial proteins imported into the inner mitochondrial membrane?

Via several routes with the help of multi-subunit protein complexes acting as translocators. Signup and view all the answers

What drives the dissociation of proteins from cytosolic Hsp70 in the mitochondria?

ATP hydrolysis Signup and view all the answers

How is the movement into the inner mitochondrial membrane facilitated?

Combination of translocator protein complexes, signal sequences, and sometimes chaperones. Signup and view all the answers

Describe the structure of chloroplasts.

Specialized plastids with 6 compartments: inner and outer envelope membrane, intervening membrane space, stroma, thylakoid membrane, and lumen. Signup and view all the answers

What are the compartments present in the structure of chloroplasts?

Inner and outer envelope membrane, intervening membrane space, stroma, thylakoid membrane, lumen. Signup and view all the answers

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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Description

Learn about the process of importing proteins into peroxisomes, which are surrounded by a single membrane. Understand how most proteins are acquired through selective import from the cytosol, while some proteins enter via the ER using short signal sequences and PTS receptors. Explore the mechanisms driven by ATP hydrolysis. Content from Ma, Changle & Agrawal, Gaurav & Subramani, Suresh (2011).

Molecular Biology of the Cell: Importing Proteins into Peroxisomes