Class 14 - Endocytosis (GOOD) Flashcards
Endocytosis
Route to endosomes from cell surface, by which plasma membrane components, fluid, solutes, macromolecules, and particulate substances are taken up.
Allows regulation of plasma membrane composition according to changing extracellular conditions.
Endocytic vesicle
Small pinched-off portion of plasma membrane containing materials to be ingested.
Endosome maturation
Process from early to late endosome where changes in protein composition of the endosome membrane occur and intralumenal vesicles are formed.
The endosome moves from the cell periphery to close to the nucleus. Ceases to recycle material to plasma membrane, instead fusing with one another and with lysosomes, degrading their contents.
Early endosome
Endocytic vesicles fuse together to form these; where internalized cargo is sorted.
Have tubular (surface) and vacuolar domains (volume).
Late endosome
Contains matured membrane and intralumenal vesicles. Located near nucleus and fuses with endosomes and lysosomes. H+ pump acidifies, lowering pH.
Endolysosome
Occur when lysosomes, endosomes, or other endolysosomes fuse together.
Recycling endosome
Return cargo molecules from early endosomes back to the plasma membrane.
Multivesicular body
Maturing endosomes forming intralumenal vesicles. Carry membrane proteins to be degraded, which selectively partition into the invaginating membrane, keeping them away from cytosol and allowing access to digestive enzymes
Intralumenal vesicles
Invaginated portions of multivesuicular bodies (maturing endosomes).
Ensure membrane proteins are degraded.
Sorting into them requires ubiquitin tag - first in the plasma membrane and again at endosome.
ESCRT protein complexes
At cytosolic side of endosome membrane; recognize ubiquitin tags. Bind and mediate sorting process into intralumenal vesicles.
Require both PI3P and ubiquitylated cargo to bind to endosome membrane
Receptor-mediated endocytosis
Macromolecules bind to transmembrane receptor proteins in coated pits and enter the cell as receptor-macromolecule complexes in clathrin-coated vesicles.
A selective ligand concentration method.
Many animal cells this method to take in cholesterol required for making new membrane.
LDL
Low density lipoproteins. The form most cholesterol is transported into the blood in.
Experience receptor-mediated endocytosis.
LDL receptor
When cholesterol (LDL) is needed, cell increases these receptors where they diffuse at the plasma membrane until endocytosis signal binds to AP2, which recruits clathrin.
Defects in genes encoding these results in high blood cholesterol —> heart attacks, coronary artery disease.
Receptor downregulation
When EGG receptors accumulate in clathrin-coated pits after binding their ligand, and are not recycled but degraded in lysosomes, along with ingested EGF.
Therefore, EGF binding activates signaling leading to decrease in EGF receptor concentration on cell surface, reducing cell’s sensitivity to EGF.
Highly regulated. Receptors have ubiquitin tags.
Transcytosis
Vesicular transport of macromolecules from one extracellular space to another, allowing selective moving of materials.
Goes from early endosome, to recycling endosome, to plasma membrane.
Example: newborn receiving antibodies from mother’s milk.
