Which organelle is the site of protein synthesis?

• A. Ribosomes
• B. Mitochondria
• C. Nucleus
• D. Cytoplasm

Answer: (A)

Ribosomes are the machines that carry out protein synthesis. They translate the genetic code carried by mRNA into a chain of amino acids, assembling proteins step by step. These ribosomes can float freely in the cytoplasm to make proteins for use inside the cell, or be attached to the rough endoplasmic reticulum to produce proteins that are secreted or embedded in membranes. While mitochondria and the nucleus play important roles in energy production and genetic information, respectively, the actual synthesis of proteins—the construction of amino acid chains—takes place on ribosomes. The cytoplasm is the surrounding space where translation occurs, but the dedicated site doing the assembling is the ribosome.