lec 14-Endocytosis and Intracellular Vesicle Trafficking

Comprehensive vocabulary flashcards covering endocytosis types, mechanisms, specific proteins, and the endocytic pathway based on the Cell Biology and Neuroscience lecture.

Endocytosis

The process of uptake of outside material (fluids and macromolecules) by invagination of the plasma membrane followed by pinching off and intracellular vesicle formation.

Vesicle carriers for macromolecules

Endosomes measuring $50-100\,nm$ which allow macromolecules like proteins ($2-10\,nm$) to enter the cell.

Phagocytosis

A type of cellular uptake mechanism specialized for the ingestion and removal of bacteria sized approximately $1-10\,\mu{m}$.

Phagolysosome

A structure formed by the fusion of a phagosome with lysosomes where the degradation of content occurs.

Professional phagocytic cells

Cells, such as neutrophils, that possess receptors able to bind antibodies that tag bacteria to initiate ingestion.

Pathogenic bacteria inducing phagocytosis

Specific bacteria like Yersinia (Plague), Listeria (Listeriosis), and Shigella (Shigellosis) that force their own entry into non-phagocytic mammalian cells.

Macropinocytosis

The uptake of fluid for feeding and removal of growth factor receptors from the plasma membrane, resulting in large vesicles ($50-1000\,nm$).

Ruffles

Actin-driven protrusions of the plasma membrane, stimulated by growth factors, that are taken up as large vesicles during macropinocytosis.

Clathrin-mediated endocytosis (CME)

A receptor-mediated process requiring clathrin and adapter molecules to take up specific macromolecules not abundant in the extracellular fluid.

Constitutive receptor-mediated endocytosis

Examples include iron uptake via the transferrin receptor and cholesterol uptake via the LDL-receptor.

Clathrin structure

Consists of heavy and light chains that form a three-legged structure.

Adaptin

A molecule recruited during CME that in turn recruits clathrin to the plasma membrane.

Dynamin

A large ($100\,kDa$) protein that can oligomerize into spirals and is required for the fission of vesicles from the membrane.

HSC70 and Auxillin

Proteins involved in the uncoating of clathrin-mediated endocytic vesicles.

Caveolae

Small $50\,nm$ invaginations enriched in cholesterol and caveolin that function as a plasma membrane reservoir to balance membrane tension.

Rab proteins

Primary determinants of compartmental specificity that recruit motor proteins for transport and effector proteins like SNAREs for targeting and docking.

Rab5

A Rab protein associated with specificity for the early endosome ($pH\,6.5$).

Rab7

A Rab protein associated with specificity for the late endosome ($pH\,5$).

Rab4 and Rab11

Rab proteins specifically associated with the recycling endosome.

Rab9

A Rab protein associated with the TGN (Trans-Golgi Network).

SNARE (SNAP receptor) proteins

Transmembrane proteins specific for compartments; v-SNAREs and t-SNAREs on opposing membranes form a trans-SNARE complex for fusion.

SNARE recycling mechanism

The ATPase NSF (N-ethyl maleimide sensitive factor) dissociates the cis-SNARE complex after fusion to recycle the SNARE proteins.