What is the primary function of ribosomes in a cell?

Ribosomes play a pivotal role in the process of protein synthesis, which is essential for cellular function and growth. They are complex molecular machines found in both prokaryotic and eukaryotic cells that facilitate the translation of messenger RNA (mRNA) into polypeptide chains, which eventually fold into functional proteins.

During translation, ribosomes read the sequences of codons in mRNA, aligning the appropriate transfer RNA (tRNA) molecules, which carry specific amino acids. As the ribosomes move along the mRNA strand, they catalyze the formation of peptide bonds between adjacent amino acids, gradually building a protein based on the genetic instructions coded in the mRNA. This function is critical as proteins are involved in virtually every cellular process, including acting as enzymes, structural components, and regulators of biological pathways.

In contrast, the other options reflect different cellular processes. Energy production primarily occurs in mitochondria (in eukaryotes), while DNA replication involves specific enzymes like DNA polymerases. Cell division encompasses various stages, including mitosis and cytokinesis, which are likewise orchestrated by a multitude of proteins and cellular machinery, but not ribosomes directly. Thus, the primary and distinguishing function of ribosomes is indeed protein synthesis.