Glycoprotein Biosynthesis and Secretory Pathway

Steps:

• Transcription of mRNA for the protein occurs in the nucleus (organelle 1).
• Translation and initial glycosylation of the protein happen on ribosomes attached to the rough endoplasmic reticulum (organelle 2).
• Further glycosylation and modification occur in the Golgi apparatus (organelle 4).
• The glycoprotein is packaged into secretory vesicles in the Golgi for exocytosis.

Why B is correct:

• Glycoproteins are synthesized via the secretory pathway, defined as nucleus (mRNA production), rough ER (protein assembly and core glycosylation), and Golgi (maturation, sorting, and secretion packaging).

Why the others are wrong:

• A omits rough ER (essential for translation) and includes smooth ER (mainly lipid synthesis).
• C excludes nucleus and Golgi; lysosomes degrade, not secrete, glycoproteins.
• D excludes nucleus and rough ER; mitochondria provide energy but not direct synthesis/secretion.

Final answer: B