Final answer:
The ribosome is the cellular component responsible for protein synthesis in eukaryotic cells. They are composed of large and small subunits and translate mRNA into proteins. The RNA components of ribosomes are synthesized in the nucleolus.
Step-by-step explanation:
The cellular component primarily responsible for protein synthesis in eukaryotic cells is the Ribosome (Answer A). Ribosomes are enzyme complexes essential for protein synthesis and are found in practically every cell. They are composed of large and small subunits that work together to translate messenger RNA (mRNA) into proteins by linking amino acids in the sequence specified by the mRNA. Ribosomes can either float freely in the cytoplasm or be attached to the cytoplasmic side of the endoplasmic reticulum.
The RNA components of ribosomes are synthesized in the nucleolus (Answer D), which is located within the nucleus of eukaryotic cells. This process is the initial step in ribosome assembly. Following their synthesis in the nucleolus, ribosomes proceed to the cytoplasm where they fulfill their critical role in generating proteins.