In which part of the cell does protein synthesis occur?

Protein synthesis primarily occurs in the ribosome, making this the correct answer. Ribosomes are the cellular structures responsible for translating 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 what is known as the rough endoplasmic reticulum.

The process begins when mRNA, which is synthesized in the nucleus, is transported to the ribosome, where the genetic code is read and amino acids are linked together in the sequence dictated by the mRNA. This involves transfer RNA (tRNA) molecules that bring specific amino acids to the ribosome, ensuring the correct incorporation based on the mRNA sequence.

The nucleus is responsible for transcription, the process by which DNA is turned into mRNA, but does not directly synthesize proteins. Mitochondria provide energy for the cell and have their own ribosomes to produce some proteins, primarily related to their function, but they are not the primary site of protein synthesis in the cell. The Golgi apparatus is involved in modifying, sorting, and packaging proteins for secretion or delivery to various cellular locations, but it does not synthesize proteins.