Endoplasmic Reticulum and Golgi Complex Vocabulary

50 vocabulary flashcards covering structural components, processes, enzymes, and functional concepts related to the endoplasmic reticulum and Golgi complex as presented in the lecture notes.

Endoplasmic Reticulum (ER)

A continuous system of membranous tubules and sacs enclosing the ER lumen; central to protein and lipid synthesis and part of the endomembrane system.

Rough Endoplasmic Reticulum (RER)

ER sub-compartment studded with ribosomes, forming flat cisternae; site of synthesis and initial glycosylation of secreted, lysosomal, and integral membrane proteins.

Smooth Endoplasmic Reticulum (SER)

ER region lacking ribosomes; composed of curved tubules; specializes in lipid and steroid synthesis, detoxification, and Ca²⁺ sequestration.

ER Lumen

The internal aqueous space of the ER, separated from cytosol, where nascent polypeptides enter for folding, modification, and quality control.

Cisternae

Flattened membrane sacs comprising the RER or Golgi stack; house lumenal reactions and serve as platforms for vesicle budding.

Co-translational Translocation

Process in which a growing polypeptide enters the ER lumen through a translocon while still being synthesized by a ribosome.

Signal Sequence

N-terminal stretch of 6–15 hydrophobic amino acids that targets nascent polypeptides to the ER for co-translational entry.

Signal Recognition Particle (SRP)

Cytosolic ribonucleoprotein that binds the signal sequence and ribosome, pauses translation, and delivers the complex to the ER membrane.

SRP Receptor

ER membrane protein that recognizes SRP-bound ribosome complexes, positioning them over a translocon for peptide translocation.

Translocon

Protein channel in the ER membrane through which nascent polypeptides are threaded into the lumen or inserted into the bilayer.

Signal Peptidase

ER membrane enzyme that cleaves the signal sequence from proteins after their entry into the lumen.

Protein Chaperone (BiP)

ER lumenal Hsp70 family chaperone that binds nascent chains, prevents misfolding, and assists in correct protein folding.

Integral Membrane Protein

Protein with one or more hydrophobic transmembrane domains that anchor it permanently within a lipid bilayer.

Secretory Protein

Protein synthesized into the ER lumen and ultimately released to the extracellular space via the secretory pathway.

Lysosomal Protein

Acid-hydrolase or membrane protein targeted to lysosomes; carries an ER signal sequence and often mannose-6-phosphate tag.

Free Ribosome

Cytosolic ribosome not bound to ER; translates proteins destined for cytosol, nucleus, mitochondria, or chloroplasts.

N-to-C Direction

Polypeptide growth orientation in which amino acids are added to the carboxyl end, yielding proteins written from N terminus to C terminus.

Transmembrane Domain

Hydrophobic α-helical segment that spans the lipid bilayer, serving as both signal for SRP and membrane anchor.

Positive-Inside Rule

Orientation principle stating that positively charged residues flanking a transmembrane domain tend to remain on the cytosolic side.

N-linked Glycosylation

Attachment of an oligosaccharide to the amide nitrogen of asparagine; initiated in RER on dolichol and completed in Golgi.

O-linked Glycosylation

Sequential addition of sugars to the hydroxyl groups of serine or threonine residues; occurs entirely within the Golgi complex.

Dolichol Phosphate

Long-chain lipid carrier embedded in the ER membrane that assembles and flips precursor oligosaccharides during N-linked glycosylation.

Glycosyltransferase

Enzyme that catalyzes transfer of monosaccharide units from activated donors to growing glycans on lipids or proteins.

Calnexin

ER membrane chaperone that binds monoglucosylated glycoproteins, facilitating proper folding before glucose removal.

UGGT

UDP-glucose:glycoprotein glucosyltransferase; ER quality-control enzyme that reglucosylates misfolded glycoproteins for another calnexin cycle.

Proteasome

Cytosolic protease complex that degrades misfolded or damaged proteins retro-translocated from the ER.

Endomembrane System

Interconnected network of ER, Golgi, endosomes, lysosomes, and transport vesicles coordinating membrane and protein traffic.

Golgi Complex

Stack of membrane cisternae organized from cis to trans faces; modifies, sorts, and packages proteins and lipids.

Cis Golgi Network (CGN)

Tubular network at the Golgi entry face; sorts proteins arriving from ER, sending some back via retrograde vesicles.

Trans Golgi Network (TGN)

Tubule- and vesicle-rich Golgi exit compartment where cargo is segregated into vesicles headed for plasma membrane or lysosomes.

Anterograde Transport

Forward movement of cargo from the cis face toward the trans face of the Golgi or from ER to Golgi.

Retrograde Transport

Backward vesicular movement returning resident ER or Golgi proteins from later to earlier compartments.

Cisternal Maturation Model

Golgi transport model proposing that cisternae themselves move from cis to trans, maturing while carrying cargo forward.

Vesicular Transport Model

Alternate model proposing stable Golgi cisternae with cargo moved forward by vesicles that bud and fuse sequentially.

ER-Golgi Intermediate Compartment (ERGIC)

Collection of vesicular tubular carriers between ER and Golgi where cargo is concentrated before Golgi entry.

Vesicular Tubular Carrier (VTC)

Larger transport structure formed by fusion of ER-derived vesicles; shuttles material to the cis Golgi.

Lipid Bilayer

Dual-layered arrangement of phospholipids forming the fundamental structure of cellular membranes.

Glycoprotein

Protein with covalently attached carbohydrate chains; glycosylation aids in folding, stability, and cell recognition.

ER Quality Control

Set of mechanisms—including chaperones, glucosylation cycles, and retro-translocation—that ensure only properly folded proteins exit the ER.

Calcium Ion Sequestration

SER function in muscle cells where Ca²⁺ is stored and released to trigger contraction.

Steroid Hormone Synthesis

SER-mediated enzymatic production of steroid hormones in endocrine tissues.

Detoxification (SER)

SER process in liver cells that hydroxylates and inactivates hydrophobic drugs and toxins.

Glycosylation

Covalent addition and processing of carbohydrate chains on proteins or lipids within the ER and Golgi.

Protein Folding

Process by which a polypeptide achieves its functional three-dimensional structure, assisted by chaperones and glycosylation.

Hydrolytic Enzyme

Digestive enzyme, often destined for lysosomes, that breaks molecular bonds by adding water.

Ribosome

Ribonucleoprotein complex catalyzing peptide bond formation; exists free in cytosol or bound to RER.

Peripheral Membrane Protein

Protein loosely associated with membrane surfaces via non-covalent interactions; synthesized on free ribosomes if cytosolic.

Endocytic Pathway

Route by which extracellular material is internalized into vesicles and delivered to endosomes and lysosomes.

Lysosome

Acidic, enzyme-filled organelle where macromolecules are degraded; receives cargo via the endocytic and autophagic pathways.

Golgi Glycosylation

Series of enzymatic sugar additions/removals within Golgi cisternae that diversify N-linked glycans and build O-linked chains.

Protein Sorting

Selective packaging and directing of proteins to their correct cellular destinations, notably at the CGN and TGN.