Vesicle Formation, Golgi Maturation, and Endocytosis

Flashcards covering vesicle formation, Golgi maturation models, and endocytosis types and processes including endosomal maturation and lysosome function.

COP two coated vesicles

Vesicles that leave the ER, looking for specific receptors binding cargo and also grabbing soluble proteins.

KDEL sequence

A specific sequence (KL) found on ER resident proteins that ensures they remain in the ER or are returned to it.

KDEL receptor proteins

Receptors located in the ER membrane that recognize and bind to ER resident proteins with the KDEL sequence, returning them to the ER in COP one vesicles.

Vesicular tubular clusters

Irregularly shaped structures formed when COP two vesicles coming from the ER join together before fusing with the cis Golgi network.

Cisternal maturation model

A model for Golgi maturation where the cisternae themselves (cis, medial, trans) physically mature, with cargo remaining inside, while enzymes are transported backwards in vesicles.

Vesicular transport model

A model for Golgi maturation where cis, medial, and trans cisternae are stable, enzymes remain in their compartments, and cargo is transported forward between cisternae via vesicles.

Endocytosis

The process by which cells take in substances from outside by engulfing them in a vesicle that forms from the plasma membrane.

Phagocytosis

A type of endocytosis for bringing large particles (e.g., bacteria) into a cell; it is non-coated and can be specific or nonspecific ('cellular eating').

Pinocytosis

A type of endocytosis for bringing small vesicles, primarily fluids, into a cell; it is always coated and nonspecific ('cellular drinking').

Receptor-mediated endocytosis

A highly specific type of endocytosis that uses receptors to selectively bind and internalize specific cargoes; it is always coated.

Transcytosis

A process, often mediated by caveolae, that involves moving membrane components or cargo from one side of the cell's plasma membrane to the other, across the cell.

AP2 (Adaptin Protein 2)

A specific type of adaptin protein found exclusively at the plasma membrane, involved in cargo selection and recruiting clathrin for endocytosis.

Dynamin

A protein that acts like 'molecular scissors,' wrapping around the neck of a budding vesicle to pinch it off during vesicle formation.

HSC 70 (Heat Shock Cognate protein 70)

A constitutively expressed chaperone protein (an HSP family member) that uses ATP to remove the coat from clathrin-coated vesicles after endocytosis.

Early endosome

The initial sorting station for endocytosed vesicles; it is weakly acidic (pH 6-6.8) and identified by the presence of RAB five protein.

Late endosome

A maturated form of the early endosome; it is more acidic (pH below 5) and characterized by the presence of RAB seven protein.

Lysosome

The final destination for the breakdown and digestion of cellular waste and foreign materials; it is very acidic (pH around 4.5) and identified by the protein LAMP one.

RAB five

A protein that serves as a specific marker for early endosomes.

RAB seven

A protein that serves as a specific marker for late endosomes.

RAB eleven

A protein that serves as a specific marker for recycling endosomes.

Recycling endosomes

Early endosomes from which receptors are separated from their ligands and returned to the plasma membrane for reuse.

Compartment conversion

The process of maturation by which an early endosome transforms into a late endosome.

RAB cascade

A sequential event involving the activation and inactivation of different RAB proteins (RAB five, RAB seven, RAB c), driving the maturation of endosomes from early to late and ultimately to lysosomes.

Multivesicular bodies

Endosomes containing numerous smaller internal (intraluminal) vesicles, formed to sequester and stop signaling from receptors internalized with ligands.

Hydrogen ion ATPases

Pumps recruited to endosomes and lysosomes that use ATP to actively pump hydrogen ions inside, thereby increasing their acidity and facilitating cargo breakdown.

Endolysosome

An intermediate structure formed by the fusion of a late endosome with a lysosome.

Mannose six phosphate (M6P)

A specific sugar modification added to enzymes in the Golgi, acting as a tag to direct these proteins to the endosomal-lysosomal network for function.

Lysosomal storage diseases

Genetic disorders resulting from dysfunctional lysosomes and endosomes, leading to the accumulation of undigested substances and severe cellular damage.

Exocytosis

The process of secreting substances out of the cell by fusing vesicles with the plasma membrane, essentially the reverse of endocytosis.

Constitutive exocytosis

A type of exocytosis that occurs continuously, secreting substances out of the cell all the time.

Regulated exocytosis

A type of exocytosis that occurs only when triggered by a specific signal, such as the secretion of insulin in response to glucose.