biology 181: intracellular transport

membrane bound ribosomes are translated on the

rough ER

free ribosomes are translated in the

cytosol

sorting signal

specific amino acid sequences that direct proteins from the site of translation to a final destination

nuclear pores

passage of proteins into nucleus; allows for movement of small molecules by diffusion, but requires selective active transport of large molecules in and out of nuclear membrane

nuclear localization signal (NLS)

bound by a nuclear import receptor protein in the cytosol and is carried through nuclear pore where it is then released; requires energy from GTP

translocator

transports across organelle membranes, translated and folded in cytosol by chaperone protein.

mitochondrial import signal

binds to mitochondrial import receptor embedded in outer mitochondrial membrane

chaperone protein

assists in refolding, removes signal sequences

translation begins…

in the cytosol

signal recognition particle (SRP)

binds to emerging ER sequence signal during cytosolic translation and stalls reaction, then binds to SRP receptor, then is released and translation continues

endomembrane system

a group of membranes and organelles in eukaryotic cells that work together to modify, package, and transport lipids and proteins

exocytosis

secretory pathway

endocytosis

endocytic pathway

constitutive secretions

always on (ex. NA+ channels)

regulated secretion

sometimes on (ex. neurotransmitters)

receptor-mediated endocytosis

selective uptake

endosomes

sort endocytosed material

lysosomes

digest endocytosed materials