Which organelle is primarily associated with calcium storage, protein synthesis, and lipid metabolism?

• A. Endoplasmic reticulum
• B. Mitochondria
• C. Nucleus
• D. Golgi apparatus

Answer: (A)

Calcium storage, protein synthesis, and lipid metabolism are all functions linked to the endoplasmic reticulum. The rough ER, studded with ribosomes, assembles proteins destined for membranes, secretion, or lysosomes, while the smooth ER lacks ribosomes and handles lipid synthesis and related metabolism. It also serves as a storage site for calcium ions in its lumen, a role especially prominent in muscle cells where the sarcoplasmic reticulum releases calcium during contraction. By contrast, mitochondria mainly generate ATP, the nucleus houses genetic material, and the Golgi apparatus processes and ships proteins. So, the endoplasmic reticulum best fits all three roles.