Which cellular structure is primarily involved in protein synthesis?

• A. Ribosomes
• B. Mitochondria
• C. Golgi apparatus
• D. Centrioles

Answer: (A)

Protein synthesis occurs at ribosomes, the cellular machines that translate mRNA into a growing chain of amino acids. They read the genetic message carried by messenger RNA and recruit transfer RNAs that bring in the correct amino acids. As each codon is read, amino acids are linked together by peptide bonds to form a polypeptide, which then folds into a functional protein. Ribosomes can float freely in the cytosol or be attached to the rough endoplasmic reticulum, enabling production of cytosolic proteins as well as proteins destined for secretion or for membranes. Other structures have different roles: mitochondria generate ATP, the Golgi apparatus modifies and ships proteins, and centrioles help organize the spindle during cell division. So the structure most directly responsible for building proteins is the ribosome.