Intracellular COmpartments and Protein Transport II

exocytosis

vesicle fuses with the plasma membrane, releasing its content to the cell’s surroundings. 

endocytosis

extracellular materials are captured by vesicles that bud inward from the plasma membrane and are carried into the cell.

Transport vesicles

carry membrane components and soluble proteins between compartments of the endomembrane system and the plasma membrane. 

Protein coat

Vesicle Budding Is Driven by the Assembly of a what?

Clathrin

molecules that form basketlike cages and help shape membranes into vesicles

Receptor-mediated endocytosis

specialized cell surface receptors bind to molecules and pulls it into the cell

Clathrin-coated

vesicles that transport specific cargo molecules to their destinations.

Dynamin proteins

proteins that assemble around the neck of budding vesicles and hydrolyze GTP to help pinch off the vesicle with the aid of other recruited proteins. After the vesicle buds off, the coat proteins are removed, allowing the naked vesicle to fuse with its target membrane.

GTP

Dynamin proteins hydrolyze ____ to help pinch off the vesicle.

Rab proteins

help guide transport vesicles to the correct target membrane.

• tethering proteins

V-SNARE

proteins on the vesicle bind to complementary t-SNAREs on the target membrane to ensure precise docking.

• v → vesicle

• t → tethers

complementary

V-SNARE proteins bind to _________ t-SNAREs.

hydrophilic

The glycocalyx is ________.

asparagine

Many proteins are glycosylated on _______ residues in the ER.

oligosaccharide

When an appropriate asparagine in a growing polypeptide enters the ER lumen, a branched _________ is added.

dolichol

Each oligosaccharide chain is transferred as a complete unit from what lipid?

oligosaccharyl transferase

Dolichol is catalyzed by what?

constitutive secretory

Many soluble proteins are continually secreted from the cell by the ______ ______ pathway.

lipids; proteins

The constitutive secretory pathway supplies the plasma membrane with newly synthesized ______ and ______.

eukaryotic

The constitutive pathway operates in all _______ cells.

exocytosis

Specialized secretory cells have a regulated ______ pathway.

extracellular

Selected proteins are stored in secretory vesicles until an ________ signal triggers their release.

free cholesterol

What is the final product released from LDL degradation in the lysosomes?

endosomes

In Receptor-mediated endocytosis:

What do the uncoated vesicles fuse with?

dissociate

In Receptor-mediated endocytosis:

After vesicles fuse with lysosomes, the acidic environment causes LDL to ________ from its receptors.

Receptor mediated endocytosis

•LDL binds to LDL receptors on the cell surface and is internalized in clathrin-coated vesicles.

•The vesicles lose their coat and fuse with endosomes, where the acidic environment causes LDL to dissociate from its receptors.

•LDL is delivered to lysosomes, where it is degraded to release free cholesterol, while LDL receptors are recycled back to the plasma membrane via transport vesicles.

viruses

In receptor mediated endocytosis, _____ may hijack the same process we use to bring in essential cargo inside so that they can enter eukaryotic cells.

• e.g., COVID

Pinocytosis

“cell-drinking” because it’s bringing into the   cell fluids with materials suspended in it 

endosomal compartment

acts as the main sorting station in the inward endocytic pathway

outward

The Golgi functions in the ______ secretory pathway.

acidic

The ______ environment of the endosome helps sort receptors by causing many of them to release their bound cargo.

F

T or F?

All receptors entering endosomes return to the same membrane surface

return; lysosomes; transcytosis

3 possible fates of receptors after entering an endosome are:

• ______ to same membrane domain

• to the ______ for degradation

• directed to a different plasma membrane domain for _______.

phagocytes

Cells capable of phagocytosis are called

Chemotaxis; Adhesion; Ingestion; Maturation; Killing; Elimination

Phagocytosis can be divided into six stages called what?

Autophagy

The process by which cells degrade obsolete (not-useful) organelle of themselves

autophagosome

Autophagy involves the enclosure of the organelle by a double membrane, which creates what?

starved; remodeling

Autophagy could happen because the cells is ______ of nutrients or when cellular _______ is needed.

acid-dependent

Early endosomes, phagosomes, and autophagosomes can fuse with lysosomes or late endosomes, both containing _______-______ hydrolytic enzymes.

hydrolytic; acidic

A lysosome contains many _______ enzymes that are active only under ______ conditions.

lumen

The ______ of the lysosome is kept acidic by an ATP-driven H⁺ pump in the membrane.