cell biology mark robinson

• What is the process of delivering newly synthesized proteins to their correct cellular locations called?

  Protein targeting
• Why is protein targeting crucial for cellular function?


  To ensure proteins are in the right location to perform their specific functions
• What are the two basic mechanisms of protein targeting?


  • Signal-based targeting
  • Vesicle-based targeting
• What is the typical number of proteins in a mammalian cell?

  Up to 10,000 proteins
• What happens to proteins synthesized by free ribosomes in the cytosol?

  Many remain in the cytosol
• What is the outcome of signal-based targeting for water-soluble proteins?

  Translocation into the interior of the organelle
• Which organelles are proteins sorted into via signal-based targeting?


  ER, mitochondria, chloroplasts, peroxisomes, nucleus
• What is vesicle-based targeting also known as?

  The secretory pathway
• What governs the specificity of protein targeting?


  • Interaction of signal sequences on proteins
  • Organelle-specific receptors
• What are signal sequences?

  20 amino acid segments encoding targeting information
• Where do signal sequences usually occur in proteins?

  At the N-terminus
• What happens when a protein interacts with an organelle receptor?

  It is transferred to a translocation channel
• What is required for the protein to pass into or through the organelle membrane?

  Energy from ATP or GTP hydrolysis
• What usually happens to the signal sequence after protein targeting?


  It is cleaved off by a signal peptidase
• What is the best-known example of protein targeting?

  Targeting to the ER