Final answer:
Ribosomes are responsible for polypeptide synthesis in both prokaryotes and eukaryotes. They are found in the cytoplasm of both cell types and bind mRNA and tRNAs to translate proteins.
Step-by-step explanation:
The organelles that are responsible for polypeptide synthesis in both prokaryotes (70S ribosomes) and eukaryotes (80s ribosomes) are ribosomes. Ribosomes exist in the cytoplasm of prokaryotic cells and in the cytoplasm as well as on the rough endoplasmic reticulum of eukaryotic cells. They play a crucial role in translating the mRNA into a polypeptide chain, where the small subunit binds to the mRNA template and the large subunit binds to transfer RNAs (tRNAs) that add amino acids to the growing polypeptide chain.
Ribosomes are essential for the protein synthesis in all living cells. Even organelles like mitochondria and chloroplasts have their own ribosomes, which are similar in size to prokaryotic ribosomes. Each ribosome is composed of a large and a small subunit, which come together during translation—the process of synthesizing a polypeptide.