Question

The cell subunits engaged in protein synthesis and maturation of polypeptide chains are
(A) Ribosome
(B) Rough endoplasmic reticulum
(C) Lysosome
(D) Golgi apparatus
Choose the correct answer from the options given below:

• A. (A), (B) and (D) only.
• B. (A), (B) and (C) only.
• C. (A), (C) and (D).
• D. (B), (C) and (D) only.

Hint:

The secretory pathway flows in a logical sequential order:
Ribosome (Synthesis) \(\rightarrow\) RER (Folding/Initial Glycosylation) \(\rightarrow\) Golgi (Further Modification/Sorting).
Lysosomes act at the end of the line for degradation, not production.

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
The synthesis, folding, modification, and targeting of proteins destined for membranes or secretion involve a coordinated pathway of cellular organelles.
This pathway is known as the secretory pathway.

Step 2: Detailed Explanation:
Let us analyze the role of each organelle in this pathway:
- Ribosomes (A): These are the primary sites of translation, where mRNA is decoded to synthesize polypeptide chains.
- Rough Endoplasmic Reticulum (RER) (B): Ribosomes translating secretory or membrane proteins dock onto the RER.
The newly synthesized polypeptide is translocated into the RER lumen, where it undergoes folding and early post-translational modifications (such as N-linked glycosylation and disulfide bond formation), representing the initial maturation of the polypeptide.
- Golgi Apparatus (D): Folded proteins are transported via vesicles from the RER to the Golgi.
The Golgi is responsible for further modification (such as O-linked glycosylation and trimming of sugars), sorting, and packaging of these mature proteins for their final destinations.
- Lysosomes (C) contain hydrolytic enzymes and are responsible for the degradation of biomolecules, not protein synthesis or maturation.
Thus, (A), (B), and (D) are the organelles engaged in the synthesis and maturation pathway.

Step 3: Final Answer:
The cell subunits engaged in protein synthesis and maturation are (A), (B), and (D) only.