Secretory Pathway for Extracellular Enzymes

Steps:

• Transcription of gene into mRNA occurs in the nucleus.
• mRNA travels to ribosomes for translation into polypeptide chain.
• Nascent protein enters rough endoplasmic reticulum for folding and initial glycosylation.
• Vesicles transport protein to Golgi body for final modification and packaging for secretion.

Why A is correct:

• Follows the eukaryotic secretory pathway, where nuclear transcription precedes ribosomal translation, ER processing, and Golgi packaging (per cell biology principles).

Why the others are wrong:

• B: Begins with ribosomes before nucleus, violating transcription-first rule; also repeats Golgi illogically.
• C: Places nucleus after rough ER, reversing transcription order.
• D: Starts with rough ER before nucleus, ignoring gene expression sequence.

Final answer: A