Module 1 Organelles (Lesson 3) Flashcards
What is the largest continuous membrane structure in a cell?
Endoplasmic Reticulum (ER)
What are the two types of ER?
Rough ER and Smooth ER
What structure is responsible for giving rough ER its “rough” appearance?
Ribosomes attached to its surface
What is the main function of the ER in protein synthesis?
It is the site where secretory and membrane proteins are synthesized, folded, and modified.
What type of ER is associated with lipid metabolism and detoxification?
Smooth ER
What protein family is responsible for shaping the curved ER membrane?
Reticulons
What small GTPase is responsible for ER membrane fusion?
Atlastin
What process ensures that only properly folded proteins leave the ER?
ER quality control mechanism
What post-translational modification is important for protein folding in the ER?
Glycosylation
What hereditary disease is associated with mutations in reticulons and atlastin?
Hereditary Spastic Paraplegia (HSP)
Why is the ER considered a continuous structure despite having distinct rough and smooth regions?
The ER is a single interconnected network, sharing a common luminal space, including connections to the nuclear membrane.
How do ER tubules maintain their shape despite phospholipid bilayers preferring a flat structure?
Reticulons insert into the membrane in a wedge-like fashion, inducing curvature.
What role do microtubules play in ER movement?
ER membranes extend, retract, and move along microtubules through motor protein interactions.
Why must ER targeting occur during protein synthesis for secretory proteins?
Because cotranslational translocation is required for proteins to enter the ER lumen as they are being synthesized.
How do glycosylation and disulfide bond formation contribute to protein quality control in the ER?
These modifications help ensure proper protein folding and stability, preventing misfolded proteins from leaving the ER.
Why do Type II and Type III membrane proteins have different orientations despite similar translocation mechanisms?
The positioning of positively charged residues around the signal-anchor sequence determines their orientation in the membrane.
What happens to misfolded proteins in the ER?
They are targeted for degradation through the ER-associated degradation (ERAD) pathway.
How does ER dysfunction contribute to neurodegenerative diseases like HSP?
Defects in ER membrane shaping and organization disrupt axon maintenance, leading to neuronal degeneration.
How would you determine if a newly discovered protein is ER-targeted?
Look for an ER signal sequence at the N-terminus, perform co-translational translocation assays, or use fluorescence microscopy with ER markers.
If a protein fails to fold properly in the ER, what experimental techniques could be used to study its fate?
Western blot for ubiquitinated proteins, proteasome inhibition assays, or fluorescent protein misfolding sensors.
How could you artificially target a cytoplasmic protein to the ER?
Add an ER signal peptide sequence to its N-terminus.
If a researcher mutates the signal recognition particle (SRP), what impact would this have on secretory protein synthesis?
Translation would be impaired, and proteins would fail to enter the ER, leading to mislocalization in the cytoplasm.
What would happen to ER membrane structure if Atlastin function were inhibited?
The three-way branching of ER tubules would be disrupted, leading to fragmented and unconnected ER networks.
If a drug inhibits glycosylation in the ER, how would this affect protein function?
Proteins may misfold or lose their proper function, leading to ER stress and degradation.
How would you differentiate Type I, II, and III membrane proteins experimentally?
Use protease protection assays, immunofluorescence, or analyze sequence features like signal-anchor sequences and stop-transfer signals.
If a patient has a mutation in reticulons, what cellular defects might you expect?
Abnormal ER morphology, reduced ER tubule formation, and potential neurological impairments.
