Mitochondrial Protein Transport
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Questions and Answers

What is the primary function of the TOM complex?

  • To synthesize mitochondrial proteins in the cytosol
  • To recognize signal sequences of mitochondrial proteins (correct)
  • To degrade misfolded mitochondrial proteins
  • To transport proteins from the intermembrane space to the mitochondrial matrix

    • Which of the following machinery is responsible for the import of nucleus-encoded mitochondrial proteins?

  • TIM 5 translocator of the inner mitochondrial membrane
  • MIM 5 mitochondrial import machinery (correct)
  • SAM 5 sorting and assembly machinery
  • TOM 5 translocator of the outer membrane

    • Where are the mitochondrial proteins initially transported to after being recognized by the TOM complex?

  • Mitochondrial matrix
  • Intermembrane space (correct)
  • Outer mitochondrial membrane
  • Cytosol

    • What determines the different itineraries of mitochondrial proteins after being transported into the intermembrane space?

    <p>The sequence features encoded in the protein</p> Signup and view all the answers

    Which of the following is NOT a component of the mitochondrial import machinery?

    <p>OXA 5 cytochrome oxidase activity</p> Signup and view all the answers

    What is the role of protein translocators in the mitochondrial membranes?

    <p>To transport proteins across the mitochondrial membranes</p> Signup and view all the answers

    What is the primary function of signal sequences in mitochondrial precursor proteins?

    <p>To direct proteins to their appropriate mitochondrial sub-compartment</p> Signup and view all the answers

    What is the role of signal peptidase in the import of mitochondrial proteins?

    <p>To rapidly remove N-terminal signal sequences from precursor proteins</p> Signup and view all the answers

    Where are protein translocator complexes located in mitochondria?

    <p>In both the inner and outer mitochondrial membranes</p> Signup and view all the answers

    How many different precursor proteins do protein translocators direct to their appropriate sub-compartment in mitochondria?

    <p>Approximately 1500</p> Signup and view all the answers

    What controls which translocator(s) a precursor protein engages and the order in which the signals are used?

    <p>The organization of signals in the precursor protein</p> Signup and view all the answers

    What is the primary function of protein translocators in mitochondrial membranes?

    <p>To mediate protein movement across or into mitochondrial membranes</p> Signup and view all the answers

    What is the primary function of peroxisomes in eukaryotic cells?

    <p>Oxygen utilization and oxidation reactions</p> Signup and view all the answers

    What is the byproduct of oxidation reactions in peroxisomes?

    <p>Hydrogen peroxide</p> Signup and view all the answers

    How are fatty acid molecules broken down in peroxisomes?

    <p>Through β-oxidation</p> Signup and view all the answers

    What is the destination of acetyl CoA produced in peroxisomes?

    <p>Cytosol</p> Signup and view all the answers

    How are integral membrane proteins of the peroxisomal membrane delivered?

    <p>First inserted into the ER</p> Signup and view all the answers

    What is the function of the sequence Ser-Lys-Leu in peroxisomal proteins?

    <p>Import signal</p> Signup and view all the answers

    What is required for peroxisomal protein import?

    <p>ATP hydrolysis</p> Signup and view all the answers

    Which peroxin recognizes C-terminal peroxisomal sorting signals?

    <p>Pex5</p> Signup and view all the answers

    What is the function of Pex7 in peroxisomal protein transport?

    <p>Recognition of N-terminal peroxisomal signal sequences</p> Signup and view all the answers

    What is a unique feature of the peroxisomal protein translocator?

    <p>It can transport fully folded and oligomeric proteins</p> Signup and view all the answers

    What is the primary function of mitochondria?

    <p>ATP synthesis</p> Signup and view all the answers

    Where are most mitochondrial proteins encoded?

    <p>Cell nucleus</p> Signup and view all the answers

    What is the space between the inner and outer mitochondrial membranes called?

    <p>Intermembrane space</p> Signup and view all the answers

    How are new mitochondria produced?

    <p>By the growth of preexisting organelles, followed by fission</p> Signup and view all the answers

    What is the function of the cristae in mitochondria?

    <p>To increase the surface area of the inner mitochondrial membrane</p> Signup and view all the answers

    What is the significance of the different sub-compartments in mitochondria?

    <p>They contain a distinct set of proteins</p> Signup and view all the answers

    What is the primary function of the OXA complex?

    <p>Insertion of proteins into the inner mitochondrial membrane</p> Signup and view all the answers

    What is the role of chaperones of the hsp70 family in protein import by mitochondria?

    <p>To interact with mitochondrial precursor proteins and prevent their native structure formation</p> Signup and view all the answers

    Where are mitochondrially encoded membrane proteins assembled with nuclear-encoded membrane proteins?

    <p>In the mitochondrial inner membrane</p> Signup and view all the answers

    What is the mechanism of protein import by mitochondria?

    <p>Post-translational import of proteins into the mitochondrial outer membrane</p> Signup and view all the answers

    What is the function of the MIM complex?

    <p>Mitochondrial import machinery</p> Signup and view all the answers

    What is the characteristic of mitochondrial precursor proteins after synthesis?

    <p>They interact with chaperones of the hsp70 family</p> Signup and view all the answers

    What is the role of the TIM complex?

    <p>Translocation of proteins across the inner mitochondrial membrane</p> Signup and view all the answers

    What is the fate of mitochondrially encoded membrane proteins and nuclear-encoded membrane proteins?

    <p>They are assembled into functional protein complexes</p> Signup and view all the answers

    Study Notes

    The Transport of Proteins into Mitochondria

    • Mitochondria are double membrane-enclosed organelles that specialize in ATP synthesis using energy derived from electron transport and oxidative phosphorylation.
    • Although mitochondria have their own DNA, ribosomes, and other components required for protein synthesis, almost all of their proteins are encoded in the cell nucleus and imported from the cytosol.
    • Each imported protein must reach the particular organelle sub-compartment in which it functions.

    Mitochondrial Sub-compartments

    • The inner mitochondrial membrane encloses the matrix space and forms extensive invaginations called cristae.
    • The outer mitochondrial membrane is in contact with the cytosol.
    • The intermembrane space is the space between the inner and outer membranes, subdivided into the crista space and intermembrane space, with protein complexes at the junctions where the cristae invaginate.
    • Each sub-compartment contains a distinct set of proteins.

    Protein Import into Mitochondria

    • Signal sequences direct all mitochondrial precursor proteins to their appropriate mitochondrial sub-compartment.
    • One or more signal sequences are necessary and sufficient for the import and correct localization of proteins.
    • Protein translocators in the mitochondrial membranes recognize particular types of signals and direct ~1500 different precursor proteins from the cytosol to the appropriate sub-compartment of mitochondria.
    • The TOM complex is required for the import of nearly all nucleus-encoded mitochondrial proteins.
    • The TOM complex recognizes signal sequences and transports them from the cytosol into the intermembrane space.

    Peroxisomes

    • Peroxisomes are major sites of oxygen utilization and are found in virtually all eukaryotic cells.
    • Peroxisomes contain oxidative enzymes, such as catalase and urate oxidase, at high concentrations.
    • Peroxisomes use molecular oxygen and hydrogen peroxide to perform oxidation reactions.
    • Peroxisomes break down fatty acid molecules through β oxidation, converting fatty acids to acetyl CoA.

    Protein Import into Peroxisomes

    • Integral membrane proteins of the peroxisomal membrane are first inserted into the ER and then packaged into specialized peroxisomal precursor vesicles.
    • Peroxisomal proteins can be imported directly from the cytosol into preexisting peroxisomes.
    • A specific sequence of three amino acids (Ser-Lys-Leu) at the C-terminus of many peroxisomal proteins functions as an import signal.
    • Peroxisomal protein import is driven by ATP hydrolysis and utilizes a collection of proteins called peroxins.
    • The protein translocator in the peroxisomal membrane is composed of at least six different peroxins.

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    Description

    Learn about the process of transporting proteins into mitochondria, including the role of the cell nucleus and cytosol in protein synthesis and import.

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