What structure is responsible for protein synthesis in the cell?

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

Answer: (B)

The ribosome is the key structure responsible for protein synthesis in the cell. Ribosomes are molecular machines that facilitate the translation of messenger RNA (mRNA) into polypeptide chains, which then fold into functional proteins. They can be found floating freely in the cytoplasm or attached to the endoplasmic reticulum, forming rough ER. During protein synthesis, ribosomes read the sequence of mRNA and use transfer RNA (tRNA) to add the appropriate amino acids in the correct order, ultimately leading to the formation of proteins critical for various cellular functions.

Other structures mentioned, such as the nucleus, are important for storing and transcribing DNA, which is the template for mRNA synthesis but do not participate directly in the protein synthesis process. The endoplasmic reticulum plays a role in the post-translational modification and folding of proteins but is not the site of synthesis itself. The Golgi apparatus is involved in modifying, sorting, and packaging proteins for secretion or use within the cell, but again, it does not synthesize proteins. Thus, while each of these organelles plays a crucial role in the overall process of protein synthesis and processing, the ribosome is the primary site where proteins are synthesized.