15.3 Endocytosis Flashcards
allows cell to take up macromolecules, fluids, and large particles such as bacteria
endocytosis
general principle of endocytosis
taken up material is surrounded by an area of PM, which buds off inside the cell to form a vesicle containing the ingested material
2 main activities in endocytosis
- phagocytosis
- macropinocytosis
ingestion of large particles → cell eating
phagocytosis
give an overview of phagocytosis
- binding of particle to receptors on the cell surface triggers the extension of pseudopodia
- pseudopodia surround the particle and fuse to form a large vesicle called a phagosome
- phagosomes fuse with lysosomes to form phagolysosomes, in which material is digested by lysosomal acid hydrolases
in phagocytosis, pseudopodia surround the particle and fuse to form a large vesicle called a ()
phagosome
in phagocytosis, phagosomes fuse with lysosomes to form (), in which material is digested by lysosomal acid hydrolases
phagolysosomes
function/application of phagocytosis
- many amoebas use phagocytosis to capture food particles (e.g. bacteria)
- in multicellular animals, phagocytosis is used as a defense mechanism against invading microorganisms and to eliminate aged or damaged cells
in mammals, macrophages, neutrophils, and dendritic cells (WBCs) are ()
professional phagocytes
in mammals, () are professional phagocytes
macrophages, neutrophils, and dendritic cells (WBCs)
() in particular eliminate aged or dead cells from tissues throughout the body
macrophages
uptake of extracellular fluids in large vesicles
macropinocytosis
give an overview of macropinocytosis
- lamellipodia (sheet-like projections of PM) curve into open cups
- membrane then fuses to form large intracellular vesicles
() provides a mechanism for the selective uptake of specific macromolecules
clathrin-mediated endocytosis
overview of clathrin-mediated endocytosis
- macromolecules bind to cell surface receptors in specialized regions called clathrin-coated pits
- internalization signals on the receptors bind to cytosolic adaptor proteins, which in turn bind clathrin on the cytosolic side of the membrane
- clathrin then assembles into a basket-like structure that distorts the membrane and forms invaginated pits
- pits bud from the membrane with the help of dynamin driven by GTP hydrolysis to form small clathrin-coated vesicles
- clathrin-coated vesicles then fuse with early endosomes
in clathrin-mediated endocytosis, macromolecules bind to cell surface receptors in specialized regions called ()
clathrin-coated pits
in clathrin-mediated endocytosis, pits bud from the membrane with the help of (1) driven by (2) to form (3)
- dynamin
- GTP hydrolysis
- small clathrin-coated vesicles
() provided a key model of understanding clathrin-mediated endocytosis at the molecular level
uptake of cholesterol by mammalian cells
cholesterol is transported through the bloodstream in the form of lipoprotein particles, most commonly ()
low-density lipoprotein, LDL
clathrin-mediated endocytosis was first studied in patients with ()
familial cholesterolemia (FH)
cells of familial cholesterolemia (FH) patients were unable to internalize (1) from extracellular fluids due to (2)
- LDL
- inability to bind to LDL
why were familial cholesterolemia (FH) cells unable to bind to LDL?
- mutations prevented LDL receptor from concentrating in the coated pits within the cytoplasmic tail of the receptor
- mutations are commonly the replacement of tyrosine with cystein in the internalization signals of the LDL receptor
cells also possess several pathways of (), which does not appear to involve selection of specific plasma membrane receptors or the formation of coated vesicles
clathrin-independent endocytosis
following their internalization, clathrin-coated vesicles rapidly shed their coats and fuse with ()
early endosomes
important feature of early endosomes is that they () as the results of a membrane H+ pump
maintain acidic internal pH (about 6.0 to 6.2)
why is it important for early endosome to maintain acidic internal pH?
acidic pH leads to dissociation of many ligands from their receptors → ligands can be transported to different intracellular destinations
() is a major fate of membrane proteins taken up by clathrin-mediated endocytosis
recycling in the plasma membrane
