Examkin

Question

Difficulty: MediumCell Biology, Genetics, and Evolution

In eukaryotic cells, proteins destined for secretion follow a strictly coordinated endomembrane pathway from their initial synthesis to extracellular release. Arrange the following stages of the secretory pathway in the correct chronological order from start to finish.

  1. 1Translation and co-translational translocation of the nascent polypeptide into the lumen of the rough endoplasmic reticulum
  2. 2Packaging of correctly folded proteins into transport vesicles and transfer from the endoplasmic reticulum to the cis-Golgi face
  3. 3Biochemical modification, glycosylation processing, and molecular sorting across the Golgi cisternae toward the trans-Golgi network
  4. 4Condensation and budding of mature secretory transport vesicles from the trans-Golgi network toward the cell periphery
  5. 5Fusion of secretory vesicles with the plasma membrane to release cargo proteins into the extracellular space via exocytosis

Answer

The correct chronological order begins with translation and translocation into the rough endoplasmic reticulum, followed by vesicular transfer to the cis-Golgi, modification across the Golgi cisternae, packaging into secretory vesicles at the trans-Golgi network, and ends with exocytosis at the plasma membrane.
In eukaryotic cells, the secretory pathway operates in a strict unidirectional sequence: nascent proteins are translocated into the rough endoplasmic reticulum lumen, exported in transport vesicles to the cis-Golgi network, processed through the Golgi cisternae to the trans-Golgi network, pinched off into secretory vesicles, and released externally via plasma membrane exocytosis.

Step-by-Step Solution

1
Identify the primary site of entry into the endomembrane system
The polypeptide chain is synthesized by ribosomes and translocated into the lumen of the rough endoplasmic reticulum.
Secretory proteins contain an N-terminal signal sequence directing them to the rough endoplasmic reticulum before any downstream transport can occur.
2
Trace vesicular transfer to the first receiving compartment of the Golgi complex
Transport vesicles bud from the endoplasmic reticulum and fuse with the cis-Golgi network.
The endoplasmic reticulum serves as the initial quality-control station before cargo moves anterograde to the cis-face of the Golgi.
3
Track maturation and biochemical modification through the Golgi stack
Proteins undergo sequential post-translational modifications as they traverse from cis- to trans-Golgi cisternae.
Enzymes in successive Golgi cisternae modify oligosaccharide chains and tag molecules for proper sorting.
4
Identify post-Golgi vesicle formation
Secretory vesicles bud off from the trans-Golgi network.
The trans-Golgi network acts as the major dispatch center packaging proteins into dedicated post-Golgi transport vesicles.
5
Identify the terminal export event at the cell boundary
Secretory vesicles fuse with the plasma membrane during exocytosis to discharge their cargo.
Exocytosis delivers the mature protein into the extracellular fluid while incorporating vesicle lipids into the plasma membrane.

Key Concept

Eukaryotic Endomembrane Secretory Pathway
Estimated Time:1m 15s
Rate this question

Topics

Cell Biology, Genetics, and Evolution

More questions from this topic