Endoplasmic Reticulum and Membrane Proteins

Flashcards covering key vocabulary related to the Endoplasmic Reticulum and Membrane Proteins.

Endoplasmic Reticulum (ER)

A network of membranes found within eukaryotic cells, involved in protein and lipid synthesis.

Lipid Bilayer

The site of action of some toxins like the cholera toxin.

Ganglioside GM1

A cell-surface receptor for the cholera toxin on intestinal epithelial cells.

Cholera Toxin

Enters cells, causing an increase in intracellular cyclic AMP, leading to massive secretion of water and electrolytes into the intestine.

Adenylate Cyclase (AC)

Activated by the cholera toxin A subunit after it's translocated across the ER membrane, increasing cAMP levels.

Pore-Forming Toxins (β-PFTs)

Produced by pathogens, damage the cell membrane, leading to leakage and lysis of target cells.

Endoplasmic Reticulum Lumen

The single internal space enclosed by the ER, topologically equivalent to the exterior of the cell.

Sorting Signals

Specific amino acid sequences recognized by sorting receptors to direct proteins to their destination.

Sorting Receptors

Function catalytically, returning to their origin after each round of targeting.

Golgi Apparatus

Receives lipids and proteins from the ER, modifies them (commonly glycosylation), and dispatches them to various destinations in transport vesicles.

KDEL

A translocation signal within the cell.

Rough Endoplasmic Reticulum (RER)

Part of the ER with ribosomes attached, giving it a rough appearance; synthesizes proteins destined for the cell surface, ER, lysosomes, Golgi, or secretion.

Smooth Endoplasmic Reticulum (SER)

Part of the ER with a more tubular appearance and no ribosomes; synthesizes lipids, including cholesterol and phospholipids, and is involved in detoxification.

Microsomes

Small vesicles formed when the ER fragments during cell disruption.

Rough Microsomes

Microsomes derived from the rough ER, lined with ribosomes on their outer surface.

Smooth Microsomes

Microsomes drived from the smooth ER, lacking ribosomes.

Unfolded Protein Response (UPR)

Feedback mechanism from the rough ER to the nucleus in response to problems in protein synthesis and folding.

Cytochrome P450

A large family of enzymes in the smooth ER that catalyze reactions to transform water-insoluble drugs or metabolites into water-soluble molecules.

Sarcoplasmic Reticulum

Specialized smooth ER in muscle cells that sequesters and stores Ca2+.

Transmembrane Proteins

Proteins that extend through the lipid bilayer, having hydrophobic regions that pass through the membrane and hydrophilic regions exposed to water.

GPI Anchor

A way membrane proteins are anchored to the lipid bilayer via a covalently bound lipid.

Apical Surface

The surface of epithelial cells confined with certain plasma membrane enzymes and transport proteins.

Basal and Lateral Surfaces

Other surfaces of epithelial cells confined with certain plasma membrane enzymes and transport proteins.

Signal Peptide

Directs the protein into the ER where they fold.

Post-translational Modifications (PTM)

Modifications to proteins after translation, such as glycosylation, disulfide bond formation, and GPI anchor addition.

Na+, K+, HCO3

Key ions involved in the massive secretion caused by cholera toxin, leading to diarrhea.

β-barrel structure

Formed by β-PFTs after oligomerization, creating a channel in the lipid bilayer.

Transitional ER

The part of the ER that transports lipids and proteins to the Golgi apparatus.

ER Lumen

Continuous with the nuclear membrane, forming the secretory pathway.

Glycosylation

A common modification of lipids and proteins in the Golgi apparatus.

Calsequestrin

Ca2+-binding protein in the smooth ER for Ca2+ storage

Calmodulin

Ca2+-binding protein in the smooth ER for Ca2+ storage

Myofibril contraction

Triggered by the release and reuptake of Ca2+ by the sarcoplasmic reticulum.

ATP production

Membranes of mitochondria or chloroplasts are involved in this process. ~75% or mass is protein (enzymes are proteins).

Cell-surface receptors

Usually transmembrane proteins that bind ligands in the extracellular space and transduce intracellular signals on the opposite side of the plasma membrane.

Palmitic acid

A saturated 16-carbon fatty acid, to a cysteine (Cys) side chain of the protein.

Enterocytes

Epithelial cells lining the gut.

7 TMDs

Second most common protein transmembrane domain. GPCRs.

Bilirubin

Bilirubin is transported within the hepatocyte to the smooth endoplasmic reticulum, where its carboxyl groups are conjugated with glucuronic acid.

Lipid Biomass

The ER therefore has a major influence on cellular lipid biomass and balances the production of different lipid categories, classes, and species.