Endoplasmic Reticulum and Golgi Apparatus Flashcards
What is endoplasmic reticulum and describe the different types ?
The endoplasmic reticulum (ER) is an organelle from eukaryotic cells that forms a
continuous interconnected network of tubules and cisternae (sac-like structures)
▸ Rough endoplasmic reticulum synthesizes proteins
▸ Smooth endoplasmic reticulum synthesizes lipids and steroids, metabolizes carbohydrates and steroids, and regulates calcium concentration, and attachment of receptors on cell membrane proteins
▸ Sarcoplasmic reticulum solely regulates calcium levels in muscle cells
What is the function of ER ?
Lipid and protein biosynthesis
Intracellular Ca2+ store used for intracellular signalling
Production site for all trans-membrane proteins
Proteins that are destined for export, Golgi apparatus, and lysosomes are
delivered to the ER lumen
Describe the biosynthetic-secretory pathway, endocytosis and the retrograde retrieval route in membrane traffic
Biosynthetic-Secretory Pathway: ER → Golgi → Plasma membrane or lysosomes (via vesicles).
Endocytosis: Uptake of extracellular molecules via vesicles → early endosomes → lysosomes for degradation.
Retrograde Retrieval Route: Recycles proteins from Golgi to ER (COP-I coated vesicles).
Describe the maintenance of protein integrity in the ER and the COP-II mediated exit
mechanism
Protein Quality Control: Mis-folded proteins retained in the ER and degraded via ERAD (ER-associated degradation).
COP-II Exit: Coated vesicles transport properly folded proteins from ER to Golgi. Sar1, Sec23/24, and Sec13/31 drive vesicle formation.
What is the Role of the Golgi Apparatus in Membrane Transformation and Recycling ?
Modifies, sorts, and packages proteins/lipids for secretion or delivery to other organelles.
Forms vesicles for plasma membrane recycling.
Key in glycosylation, lipid modification, and sorting via cisternal progression.
Describe protein glycosylation in the endoplasmic reticulum and Golgi apparatus
ER Glycosylation: N-linked glycosylation (attachment of oligosaccharides to asparagine).
Golgi Glycosylation: Modifies N-linked glycans, adds O-linked glycans, and processes complex sugars.
Differentiate and describe the features of the constitutive and regulated secretory pathways
Constitutive Pathway: Continuous secretion, vesicles fuse immediately with the plasma membrane.
Regulated Pathway: Vesicles stored and released in response to stimuli (e.g., hormones, neurotransmitters).
Describe the role of the trans Golgi network (TGN):
Acts as a sorting station for proteins.
Constitutive Pathway: Delivers to the plasma membrane.
Regulated Pathway: Stores vesicles for stimulus-triggered release.
Directs proteins to lysosomes or secretion.
Describe the sorting activity of the TGN in relation to the 3 major destinations of proteins handled by the system:
Plasma Membrane: Delivery via constitutive or regulated pathways.
Lysosomes: Mannose-6-phosphate tags direct vesicles to lysosomes.
Secretory Vesicles: Storage and release of proteins upon stimulation.
Explain specialised functions of secretory vesicles
Store and release hormones, neurotransmitters, or enzymes.
Fuse with the plasma membrane for exocytosis.
Contain machinery for rapid response (e.g., synaptic vesicles in neurons).
