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Endomembrane System — Protein Secretion Pathway

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About This MicroSim

This interactive diagram traces the journey of a secretory protein through the endomembrane system — from its synthesis on ribosomes at the rough ER, through the Golgi apparatus for processing and sorting, to its release outside the cell via exocytosis. All 13 labeled structures can be explored interactively.

How to Use

  • Explore mode: Hover over any numbered marker or label in the side panel to see a description of that structure, its function in the secretory pathway, and AP exam tips.
  • Quiz mode: Click the Quiz button to test your knowledge. Marker labels are hidden — click the correct marker when prompted to identify each structure.
  • Edit mode: Open main.html?edit=true to calibrate marker positions by dragging them onto the image.

Structures in This Diagram

  1. Nucleus — Houses DNA; mRNA for secretory proteins is transcribed here
  2. Nuclear pores — Regulate mRNA export and protein import
  3. Rough endoplasmic reticulum — Site of co-translational translocation and initial glycosylation
  4. Smooth endoplasmic reticulum — Lipid synthesis and detoxification (not directly in secretory pathway)
  5. COPII transport vesicle — Carries proteins from ER to cis Golgi
  6. Golgi apparatus (cis face) — Receiving side; quality control
  7. Golgi apparatus (medial cisternae) — Further glycosylation and modification
  8. Golgi apparatus (trans face) — Sorting and packaging into destination-specific vesicles
  9. Secretory vesicle — Carries proteins to the plasma membrane for export
  10. Lysosome — Digestive vesicle receiving enzymes tagged with mannose-6-phosphate
  11. Plasma membrane — Final destination for exocytosis
  12. Exocytosis site — Vesicle fusion releases contents extracellularly
  13. Free ribosomes — Synthesize cytoplasmic proteins (not part of secretory pathway)

The Secretory Pathway in Order

\[\text{Nucleus} \rightarrow \text{Rough ER} \rightarrow \text{COPII vesicle} \rightarrow \text{cis Golgi} \rightarrow \text{medial Golgi} \rightarrow \text{trans Golgi} \rightarrow \text{Secretory vesicle} \rightarrow \text{Exocytosis}\]

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