40 Questions
What percentage of the cytoplasmic volume does mitochondria occupy in a eukaryotic cell?
Up to 20%
What is the typical length of mitochondria?
1–2μm
Which organelle is often associated with the microtubular cytoskeleton?
Mitochondria
What is the main function of mitochondria?
Providing the cell with ATP generated by oxidative phosphorylation
What is the lipid content of the cristae membranes in mitochondria?
25%
What is the main integral protein in the outer membrane of mitochondria?
Porin
What is the approximate number of genes in the human mitochondrial genome?
37
What is the main function of the TIM23 complex in mitochondria?
Protein translocation across the inner membrane
What is the origin of mitochondria according to the text?
Engulfment of a bacterium by eukaryotic cells
What is the primary mode of inheritance for mitochondrial DNA?
Maternal inheritance
What is the approximate protein content of the cristae membranes in mitochondria?
75%
What is the role of the TOM complex in mitochondria?
Protein import from the cytosol
What is the function of the porin protein in the outer membrane of mitochondria?
Forming channels for molecules less than 5000Da to pass freely
What is the role of mitochondrial hsp70 in the TIM23 complex?
Import ATPase using ATP hydrolysis to pull proteins through the pore
What is the structure of the mitochondrial genome?
Circular, double-stranded DNA
What is the primary source of most mitochondrial proteins?
Encoded by nuclear genes and imported from the cytosol
What maintains mitochondrial precursor proteins in an unfolded state before translocation?
Cytosolic chaperone proteins like Hsp70
What is required for the release of cytosolic Hsp70 from the protein for translocation across the membrane?
ATP hydrolysis
Which component is involved in translocating precursor proteins into the matrix once inside?
mtHsp70 chaperone and ATP hydrolysis
What is the consequence of defects in mitochondrial import machinery components?
Mitochondrial diseases
What is the role of the TOM complex in mitochondrial protein import?
Recognizing N-terminal signal sequence
What is the function of the TIM23 complex in mitochondrial protein import?
Translocating proteins through both mitochondrial membranes
Which proteins are involved in translocating precursor proteins into the matrix once inside?
mtHsp70 chaperone and ATP hydrolysis
How are some inner membrane proteins imported into the mitochondria?
Presequence import pathway
What is the role of the TOM complex in the insertion of a subset of outer membrane proteins?
Sufficient for insertion
Where are β-barrel proteins imported before being transferred to the SAM complex?
Intermembrane space
What can defects in mitochondrial import machinery components lead to?
Mitochondrial diseases
Which syndrome can result from a defect in a small Tim protein?
Mohr-Tranebjaerg syndrome
Which complex recognizes the N-terminal signal sequence of mitochondrial precursor proteins?
TOM complex
What maintains precursor proteins in an unfolded state in the cytosol?
Hsp70
What is required for the release of cytosolic Hsp70 from the protein for translocation across the membrane?
ATP hydrolysis
Which complex forms a channel across the inner mitochondrial membrane?
TIM23 complex
What is involved in translocating precursor proteins into the matrix?
mtHsp70 chaperone and ATP hydrolysis
Which protein cleaves the presequence once inside the matrix?
Matrix processing peptidase
What can cause mitochondrial diseases, such as Mohr-Tranebjaerg syndrome?
Defects in mitochondrial import machinery components
Which complex is sufficient for insertion of a subset of outer membrane proteins?
TOM complex
Where are β-barrel proteins imported before being transferred to the SAM complex?
Intermembrane space
What is involved in translocating precursor proteins across the inner membrane?
PAM complex
Which chaperone is involved in maintaining precursor proteins in an unfolded state?
Hsp70
What recognizes some inner membrane proteins for insertion via carrier translocase or Oxa1?
Tom70
Study Notes
Mitochondrial Protein Import Mechanism Overview
- Mitochondrial precursor proteins have an N-terminal signal sequence recognized by TOM complex receptors
- Proteins are translocated through TIM23 complex, spanning both mitochondrial membranes, then cleaved by a signal peptidase
- Precursor proteins are maintained in an unfolded state by cytosolic chaperone proteins like Hsp70
- Presequence binds to outer membrane receptors, then transfers to the TOM complex for translocation
- ATP hydrolysis is required for the release of cytosolic Hsp70 from the protein for translocation across the membrane
- TIM23 complex forms a channel across the inner membrane, requiring the ATP-driven PAM for translocation
- mtHsp70 chaperone and ATP hydrolysis in the matrix are involved in translocating precursor proteins into the matrix
- Once inside the matrix, the presequence is cleaved by the matrix processing peptidase
- Some inner membrane proteins use the presequence import pathway, while others are recognized by Tom70 and inserted via carrier translocase or Oxa1
- The TOM complex is sufficient for insertion of a subset of outer membrane proteins, while β-barrel proteins are imported into the intermembrane space and then transferred to the SAM complex
- Defects in mitochondrial import machinery components can cause mitochondrial diseases, such as Mohr-Tranebjaerg syndrome due to a defect in a small Tim protein
- Mitochondrial diseases can result from defects in the mitochondrial import machinery components, such as Mohr-Tranebjaerg syndrome due to a defect in a small Tim protein
Test your knowledge of mitochondria's structure and function with this quiz. Explore the origin of mitochondria, their membranes, genetic characteristics, and the mechanism of protein import. Learn about the key components involved in mitochondrial import and how defects in these components can lead to mitochondrial diseases.
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