Lecture 12: intracellular compartments, protein sorting 2 Flashcards Preview

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Flashcards in Lecture 12: intracellular compartments, protein sorting 2 Deck (20):

What is translocation?

  • protein movement across membranes


How do proteins get into the mitochondria?

  • synthesized on ribosomes
  • signal sequence helps direct across the membrane into the mitochondria


What are mitochondrial locating specific signals that are associated with proteins for translocation?

  • amphiphilic alpha helix, that are at N terminal or in the polypeptide somewhere


How are the mitochondrial sequences recognized?

receptor proteins recognize the configuration and not the sequence


Why are a majority of the mitochondrial signal sequences positively charged?

the cytosol in the inner membrane is negative, therefore a positive charge will be attracted to the inside


What functions can TOM perform?

  1. import nuclear proteins into the mitochondria
  2. insert the proteins in the outer membrane


What functions can TIM perform?

  1. allows passage of proteins through the inner membrane. Forms "continuous" tunnel with TOM


What is the role of TIM23?

  • transport soluble proteins into matrix and inserts membrane proteins in the INNER membrane


What is teh role of TIM 22?

  •  mediates the insertion of specific subclasses of proteins (ATP, ADP)


What are unique regions on the TOM/TIM complex?

  1. receptor for mitochondrial precursor
  2. translocation channel


What is the OXA complex responsible for?

mediating insertion of proteins that were synthesized in the mitochondria, into the inner membrane


How are proteins entered into the mitochondria?

  1. protein is unfolded and bound with Hsp70 (chaperones)
  2. Binds with TOM and chaperones are removed as protein is threaded in
  3. once in the matrix, the signal sequence is cleaved by peptidase


Which complexes require ATP and which rely on membrane potential for protein translocation into the mitochondria?

  • ATP required for TOM
  • Membrane potential for TIM


How do proteins get placed in the outer membrane?

  1. pass through TOM complex, and bind with chaperones in the intermembrane space
  2. SAM complex binds and folds the protein into the outer membrane
  3. porins are good examples


What is the role of Mia 40?

  • provides protein translocation into the intermembrane space
  • uses sulfide bridges which become reduced releasing the protein into the membrane space


What guides the ER signal sequence to the ER membrane?

  • signal recognition particle (SRP)
  • SRP receptor


What is the chemical structure of the SRP

rod-shaped structure with hydrophobic pocket lined by methionines, which can accomodate different sequences and sizes of signal


How does the SRP help move the protein across the ER membrane?

  1. SRP binds with the ribosomal subunit, at the emerging sequence site and elongation factor binding site
  2. stops transcription
  3. SRP binds with SRP receptor and release the ribosome onto the protein translocator
  4. SRP/SRPreceptor unbind from the ribosome/protein translocator units.
  5. SRP is recycled. translocation occurs as gene is translated


What is the structure of the translocator that is present on the ER membrane?

  • Sec61 core complex that is a water filled pore
  • consists of 3 subunits
  • Signal peptide causes conformational changes in the gate allowing the pore to become open


If a protein has multiple transmembrane domains, what must have been present in the sequence to produce this effect?

  • multiple hydrophobic regions that stopped translocation
  • called the stop transfer signal