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Protein Sorting and Transport in Cells

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Termini in questo insieme (20)

  • What is the role of signal sequences in protein sorting?
    Signal sequences are specific amino acid sequences (15-60 long) that act as a "zip code" directing proteins to their correct cellular destination.
  • Where does protein synthesis begin in the cell?
    Protein synthesis begins on free ribosomes located in the cytoplasm.
  • What determines if a ribosome remains free or attaches to the ER?
    Whether a ribosome stays free or attaches to the ER depends on the protein being synthesized and its signal sequence.
  • Describe co-translational transport of proteins.
    Proteins are transported into the ER while still being synthesized by ribosomes attached to the ER membrane.
  • Describe post-translational transport of proteins.
    Proteins are fully synthesized on free ribosomes and transported to their destination after synthesis is complete.
  • How are proteins imported into the nucleus?
    Proteins with a nuclear localization signal are recognized by nuclear import receptors and transported through nuclear pores in a post-translational, energy-dependent process.
  • How are proteins transported into mitochondria and chloroplasts?
    Proteins are kept unfolded by chaperones, bind to receptors on the outer membrane, and are threaded through channels into the organelle post-translationally.
  • What role do chaperones play in mitochondrial protein import?
    Chaperones keep proteins unfolded in the cytosol and assist in their translocation and folding inside mitochondria.
  • What is the function of the signal recognition particle (SRP)?
    SRP recognizes the ER signal sequence on a nascent protein and directs the ribosome to the ER membrane for co-translational import.
  • What happens to proteins in the rough ER during synthesis?
    Proteins enter the ER lumen where they may undergo modifications like glycosylation before being transported to the Golgi apparatus.
  • What is glycosylation?
    Glycosylation is the enzymatic addition of oligosaccharides to proteins in the rough ER, forming glycoproteins.
  • How are proteins sorted in the Golgi apparatus?
    Proteins are sorted into vesicles based on tags and receptors that direct them to their final destinations like lysosomes, plasma membrane, or secretion.
  • What are transport vesicles?
    Transport vesicles carry soluble proteins and membrane components between cellular compartments during vesicular transport.
  • What is the difference between constitutive and regulated secretion?
    Constitutive secretion continuously delivers proteins to the plasma membrane, while regulated secretion stores proteins in vesicles for release upon specific signals.
  • How are integral membrane proteins inserted into the ER membrane?
    Integral membrane proteins have internal stop-transfer sequences that halt translocation, allowing lateral release into the ER membrane.
  • What is the nuclear pore complex?
    A large protein complex that controls the passage of molecules like proteins and RNA between the nucleus and cytoplasm.
  • What is the role of nuclear import receptors?
    They recognize nuclear localization signals on proteins and mediate their transport through nuclear pores into the nucleus.
  • How is energy used in protein import into mitochondria?
    ATP is required for chaperone function and translocation of proteins through mitochondrial membranes.
  • What is the secretory pathway?
    A cellular process where proteins are synthesized in the ER, modified in the Golgi, and transported in vesicles to the plasma membrane or other destinations.
  • What is the function of the translocon in the ER membrane?
    The translocon is a channel through which nascent proteins enter the ER lumen during co-translational import.