Target Practice
This process imports proteins into the endoplasmic reticulum concurrently with polypeptide elongation by the ribosome.
co-translational translocation
Precursor proteins destined for the mitochondrial matrix must pass through this outer membrane translocase complex first.
the TOM complex (Translocase of the Outer Membrane)
This fundamental cellular transport mechanism involves cargo packaging into membrane-bound carriers.
vesicular transport
These heterotrimeric GTPases cycle between active GTP-bound and inactive GDP-bound states to regulate vesicle budding, uncoating, and tethering.
Rab GTPases
This organelle (known for looking like a stack of pancakes) acts as the chief processing center that receives newly synthesized proteins from the ER.
Golgi apparatus
These specific, often cleavable amino acid stretches located at the N-terminus dictate whether a protein is routed to the ER, nucleus, or mitochondria.
signal sequences (or targeting sequences)
These ATP-dependent folding assistants prevent premature folding and pull polypeptides across membranes.
molecular chaperones
This coat protein complex primarily mediates anterograde transport from the endoplasmic reticulum to the Golgi apparatus.
COPII
These complementary membrane-bound protein families (v- and t-) coil tightly together into four-helix bundles to drive membrane fusion.
SNARE proteins
This degradative pathway engulfs damaged organelles and protein aggregates into double-membrane vesicles for delivery to lysosomes.
autophagy
This core eukaryotic protein-conducting channel spans the endoplasmic reticulum membrane, featuring a central pore ring and a lateral gate.
Sec61 complex
In bacteria, this general secretion system uses a proton motive force and ATP hydrolysis to export unfolded proteins across the cytoplasmic membrane via the SecYEG complex.
general secretory (Sec) pathway
This specialized coated vesicle mediates endocytosis from the plasma membrane and transport from the trans-Golgi network to endosomes.
clathrin-coated vesicle
This specific type of endocytosis utilizes cell-surface receptors to concentrate and internalize extracellular macromolecules via clathrin-coated pits.
receptor-mediated endocytosis
Professional antigen-presenting cells utilize this specialized membrane traffic pathway to load peptide fragments onto MHC class II molecules for presentation to T-cells.
MHC class II antigen presentation pathway
This translocation pathway requires the polypeptide to be fully synthesized in the cytosol and kept unfolded before crossing a membrane.
post-translational translocation
This endoplasmic reticulum-associated membrane complex associates with Sec61 in yeast to drive post-translational protein translocation.
the Sec62/Sec63 complex
This coat protein complex mediates retrograde transport from the Golgi apparatus back to the endoplasmic reticulum.
COPI
This crucial cellular organelle contains acid hydrolases operating at an optimal low pH to degrade macromolecules and recycle cellular components.
a lysosome
This complex systemic disease can arise when mutations disrupt LDL receptor recycling via receptor-mediated endocytosis, leading to severely elevated blood cholesterol levels.
Familial Hypercholesterolemia
This ribonucleoprotein particle binds to the N-terminal signal sequence of a nascent polypeptide and temporarily halts translation.
Signal Recognition Particle (SRP)
This alternative bacterial secretion system exports folded proteins containing twin-arginine motifs across the cytoplasmic membrane.
Tat (Twin-arginine translocation) pathway
This non-vesicular transport mechanism involves direct transfer of lipids between contacting organelles through specialized bridge proteins without passing through the aqueous cytoplasm.
non-vesicular lipid transfer at membrane contact sites
This process involves the inward budding of endosomal membranes to form multivesicular bodies (MVBs), sequestering membrane proteins destined for lysosomal degradation.
the ESCRT pathway
Defects in protein translocation and vesicular trafficking can lead to massive accumulation of misfolded proteins, triggering this cellular stress response that can result in apoptosis if unresolved.
Unfolded Protein Response (UPR)