Which part of a cell makes protein?

• A. Lysosomes
• B. Endoplasmic reticulum
• C. Golgi apparatus
• D. Ribosomes

Answer: (D)

Proteins are built by ribosomes. These molecular machines translate the genetic message in mRNA into a chain of amino acids, forming a polypeptide that folds into a functional protein. Ribosomes can float freely in the cytoplasm or be attached to the rough endoplasmic reticulum, where they synthesize proteins destined for secretion or membrane insertion.

Lysosomes break down waste and old organelles. The endoplasmic reticulum is a site for protein folding and processing and, in the rough part, for synthesizing many proteins, but the actual assembly of amino acids into a protein happens at the ribosome. The Golgi apparatus then modifies, sorts, and ships proteins that were made elsewhere in the cell.