ch 8 pt4

• phagocytosis: process where the phagosome fuses with a lysosome to become a phagolysosome whose contents are destroyed
• Phagocytosis is used to uptake large particles and is a receptor mediated process in mammals
• Proteins that imported into the peroxisomes and mitochondria undergo post translational translocation after being completely synthesized on free ribosomes in the cytosol

  
• Proteins must be unfolded to enter the mitchondria
• Both the outer mitochondrial membrane and the inner mitochondrial membrane includes a protein import complex
• Internal signal sequences for the inner mitochondrial membrane are not removed, but signal sequences for the matrix at the N-terminus are removed
• TOM complex: transporter of the outer mitochondrial membrane including a receptor and channel
• TIM complexes: transporter of inner membrane
• TIM22: transporter for the inner mitochondrial membrane
• TIM 23: transporter for matrix proteins of the mitochondria
• Nuclear lamina: structure composed of intermediate filaments that provides mechanical support to the nuclear envelope
• The nuclear envelope consists of 2 membranes, and the outer membrane is continuous with the ER
• Everything enters and exits the nucleus via the nuclear pores

  • folded nuclear proteins synthesized in the cytoplasm enter
  • mRNAs, tRNAs, ribosomal subunits synthesized in the nucleus for use in the cytosol
• Nucleoporins: Referring to the group of ~30 proteins that make up the nuclear pore complex
• Small ions, metabolites, and globular proteins can diffuse through the NPC
• Larger proteins are transported by mobile transport units into the nucleus
• importin a/b has an NLS receptor that binds to the NLS of the cytoplasmic cargo protein, later docking to the cytoplasmic filament on the NPC and moves trough the NPC
• In the nucleoplasm, importin b interacts with ran-gtp

  • cargo is released
  • importin b and ran-gtp relocate to the cytoplasm
  • ran-gtp is hydrolyzed to ran-gdp
  • importin-b is released
  • importin b can bind to importin a
• Exportin is a protein that delivers importin a to the cytosol
• Ran-gdp and ran-gtp is a member of a class of proteins called small-GTPases that have the ability to hydrolyze the gtp in their nucleotide binding site
• GTPase activating proteins (GAPS) help initiate the hydrolysis of ran-gtps to ran-gdps
• Guanine nucleotide exchange factors (GEF) exchange the GDP in ran-gdp to GTP