Cell Transport and Endocytosis Flashcards

Flashcards covering molecular transport mechanisms including passive diffusion, active pumps, ion channels, phagocytosis, and clathrin/caveolin-dependent endocytosis.

Permeative transports

Mechanisms responsible for the supply of metabolites, elimination of waste, and maintenance of concentration differences between the cytosol and lumen.

Simple diffusion

A form of passive transport without energy or permease that follows the concentration gradient; speed is determined by hydrophobicity, small molecular size, and lack of charge.

Permeases (Passive Transporters)

Specific, saturable, uniport structures with a multi-pass arrangement of $12$ transmembrane domains that facilitate transport faster than simple diffusion without ATP.

Prot GLUT

A specific glucose permease that undergoes a conformational change between states A and B when all binding sites are occupied.

Gap junctions

Large, non-selective simple pores that communicate between the cytoplasm of two cells; structured by $2$ connexons facing each other, each composed of $6$ connexines.

Porines

Bacterial and mitochondrial transmembrane proteins arranged in $\beta$-sheets that serve a role in cellular nutrition.

Ion channels

Highly selective and specific protein channels typically regulated by signals like ligands (e.g., acetylcholine), mechanical forces, or membrane potential.

CFTR protein

A chloride channel whose dysfunction leads to the pathology known as mucoviscidose (cystic fibrosis).

Aquaporine

An hourglass-shaped, highly selective channel containing $2$ asparagines that facilitates the passage of water molecules one at a time, often regulated by Vasopressine.

Active transport

Transport involving a permease that moves substances against their concentration gradient using energy ($E$), characterized by being saturable.

Symport

A type of coupled transport where two different participants move in the same direction, such as the glucose/$Na^+$ transporter.

Antiport

A type of coupled transport where substances move in opposite directions across the membrane.

Na+/K+ pump

An ATPase that utilizes ATP hydrolysis to export $3$ sodium ($Na^+$) ions and import $2$ potassium ($K^+$) ions through cycles of phosphorylation and dephosphorylation.

Ca 2+ pump

A pump essential for eukaryotic cell signaling that prevents calcium accumulation in the cytosol by expelling it or internalizing it into the mitochondria or RE.

RE sarcoplasmique

The specialized endoplasmic reticulum in striated muscle cells where calcium ($Ca^{2+}$) is stored.

Proton pump (H+)

A pump that decreases pH by moving hydrogen ions into compartments like endosomes, lysosomes, or the inner mitochondrial membrane (ATP synthase).

Cytotic transports

Active processes involving membrane deformation (vacuolization) and the cytoskeleton, performed by all cells except red blood cells (hématie) and cells in mitosis.

Phagocytosis

The "zipper" mechanism used by macrophages and PNN to ingest large solid particles ($> 250\text{ nm}$) into vacuoles called phagosomes.

Opsonization

The process of coating a cell with antibodies ($Ac$) to make it digestible, where the $Fc$ region is recognized by a macrophage.

Listeria monocytogenes

A pathogenic bacterium that causes listériose by diverting phagocytosis and disorganizing the lysosome membrane.

Apoptotic bodies

Cellular fragments that trigger phagocytosis via a lectin domain after phosphatidylsérine is moved to the extracellular leaflet, losing phospholipid asymmetry.

Clathrine

A cytosolic protein with a "crab basket" (triskèle) structure composed of $3$ heavy chains and $3$ light chains, essential for specific endocytosis.

Dynamine

A GTPase protein that acts like a lasso to cleave the membrane and release clathrin-coated vesicles.

HSP 70

A protein responsible for the dismantling of the clathrin coat and adapters to produce a "naked" vesicle.

LDL-cholesterol

Cholesterol packaged with apoprotéine B100 to be transported in the blood and internalized by cells via clathrin-dependent receptors.

Transferrin

A soluble liver protein that transports iron; it releases iron in the acidic endosome and returns to the plasma membrane as Apo transferrine.

Caveolin

A membrane protein with a hairpin structure that stabilizes caveolae in lipid rafts (areas rich in sphingomyéline and cholesterol).

Caveosome

A neutral pH compartment where caveolin-dependent vesicles fuse, protecting internalised ligands from acidity.

Transcytose

A mechanism, primarily caveolin-mediated, that moves vesicles from one cell pole to another (basal to apical), common in endothelial cells for blood-tissue exchange.

Virus SV40

A virus that infects cells by binding to Gangliosides GM1, internalizing via caveosomes, and traveling through the RE to reach the nucleus for DNA replication.