Advanced Cell Chapter 13

COPI-coated vesicles

unique in that the components make up the inner and outer coat layers are recruited as a preassembled complex (coatomer); function as a retrieval pathway that carry back ER resident proteins that have escaped as well as proteins such as cargo receptors and SNAREs that participated in ER budding and vesicle fusion reactions; assembly beings only seconds after COPII coats have been shed, and remains a mystery how this switch in coat assembly is controlled

Golgi Apparatus

Major site of carbohydrate synthesis; makes lot of polysaccharides; sorting and dispatching center for products of the ER - attaches many of the oligosaccharides it makes to proteins and lipids sent from the ER

Lysosome

membrane-enclosed compartment filled with soluble hydrolytic enzymes that control intracellular digestion of macromolecules; are all acid hydrolases; activated by proteolytic cleavage and require an acid environment; cytosol contents are doubly protected against attack by cells own digestive system

Lysosome Functions

breakdown of intra- and extracellular debris, destruction of phagocytized microorganisms, production of nutrients

Macropinocytosis

type of endocytosis, functions in the nonspecific uptake of fluids, membrane, and particles attached to the plasma membrane; among the first types of endocytosis to be described because it is visible b light microscopy, where cells can be seen taking up the surrounding fluid into large vesicles called macropinosomes

Autophagy

used to digest cytosol, worn-out organelles, and microbes that invade the cytosol; a way to dispose of obsolete parts

Endocytosis

material to be ingested is progressively enclosed by a small portion of plasma membrane, which first invaginates and then pinches off to form an endocytic vesicle

ER Exit Sites

regions on ER where COPII vesicles bud off; regions have no bound ribosomes (smooth ER)

COPII-Coated Vesicles

carry proteins that have entered the ER and are destined for the Golgi or beyond

Homotypic Fusion

a membrane from one compartment fuses with the membrane of the same compartment; fusion with one another; rab proteins help regulate extent of fusion

Heterotypic Fusion

membrane from one compartment fuses with the membrane of a different compartment

Oligosaccharide-Linked Proteins and Lipids

serves as a tag to direct specific proteins into vesicles that then transport them to lysosomes; or packaged into vesicles via other targeting mechanisms in order to go to other destinations

Multistage Processing Unit

proteins are modified in successive stages as they move from cisterna across the stack

Purpose of Glycosylation

direct role in making folding intermediates more soluble preventing their aggregation; sequential modifications establish a glyco-code that marks the progression of protein folding and mediates the binding of the protein to chaperones; make glycoproteins more resistant to digestion by proteolytic enzymes; oligosaccharides on cell-surface proteins can provide a cellular protective coat; protect against pathogens; function in developmental processes and in cell-cell recognition and cell-surface signaling

Lysosomal Membrane Proteins

highly glycosylated to protect them from proteases

Late Endosomes

contain material received from the PM by endocytosis and newly synthesized lysosomal hydrolases

Endolysosomes

when late endosomes and lysosomes fuse

Mannose 6-Phosphate Receptor

a receptor that facilitates the sorting of lysosomal enzymes by binding to mannose 6-phosphate residues, directing them to lysosomes; M6P receptor proteins in TGN bind lysosomal proteins in lumen and adaptor proteins on exterior to build clathrin-coated vesicles

Signal Patch

recognition signal made up of cluster of neighboring amino acids on each proteins surface

Phagocytosis

special form of endocytosis in which a cell uses large endocytic vesicles to ingest large particles; is a triggered process requiring binding and activation of receptors

Recycling

most receptors are recycled and returned to the same plasma membrane domain from which they came

Transcytosis

some proceed to a different domain of the plasma membrane

Degradation

some progress to lysosomes - may be influenced by amount of aggregate material left in endosome

Constitutive Secretory Pathways

operates in all cells; secrete soluble proteins and get lipids and proteins to the plasma membraneSpe

Regulated Secretory Pathway

selected proteins in the TGN are stored in secretory vesicles until an extracellular signal stimulates their secretion