Question

Which organelle in a eukaryotic cell is primarily responsible for synthesizing proteins destined for secretion?

• A. Mitochondrion
• B. Rough endoplasmic reticulum
• C. Golgi apparatus
• D. Lysosome

Hint:

Associate the rough endoplasmic reticulum with protein synthesis for secretion or membranes due to its ribosome-studded structure. The Golgi apparatus handles subsequent modification and packaging.

Answer 1

The Correct Option is B

In eukaryotic cells, the rough endoplasmic reticulum (RER) is primarily responsible for synthesizing proteins destined for secretion, membrane integration, or lysosomal targeting. The RER is studded with ribosomes, which translate mRNA into polypeptide chains. These proteins enter the RER lumen, where they are folded and modified (e.g., glycosylated) before being transported to the Golgi apparatus for further processing and sorting.
The roles of the other organelles are:
- Mitochondrion: Generates ATP through cellular respiration but does not synthesize secretory proteins.
- Golgi apparatus: Modifies, packages, and sorts proteins received from the RER for secretion or other destinations, but it is not the primary site of protein synthesis.
- Lysosome: Contains hydrolytic enzymes for intracellular digestion, not involved in protein synthesis.
Thus, the organelle primarily responsible for synthesizing proteins destined for secretion is the rough endoplasmic reticulum.