Final answer:
Ribosomes, composed of a small and a large subunit, are crucial for protein synthesis. The small subunit binds the mRNA template, while the large subunit binds tRNAs and catalyzes the peptide bonds between amino acids. Eukaryotic ribosomes are 80S with separate subunit sizes, while prokaryotic and organellar ribosomes are 70S.
Step-by-step explanation:
Ribosomes are essential for the process of protein synthesis, and they are made up of two subunits, each with a different role. The small subunit is where the mRNA template binds. This subunit essentially acts as a workbench where the genetic code from the mRNA is translated into an amino acid sequence. The large subunit, on the other hand, is responsible for the peptidyl transferase activity; it helps to bind tRNAs and catalyzes the formation of peptide bonds between amino acids to form a polypeptide chain. Together, these subunits work in harmony to assemble amino acids into proteins following the genetic instructions encoded in mRNA. During the phase of translation known as initiation, these subunits come together to form a functional ribosome.
Ribosomes exist in different parts of the cell depending on whether the organism is a prokaryote or a eukaryote. In prokaryotic organisms like E. coli, ribosomes are described in Svedberg units as 70S, with the small subunit being 30S and the large subunit being 50S. In contrast, eukaryotic organisms have 80S ribosomes in the cytoplasm with small 40S and large 60S subunits. Interestingly, mitochondria and chloroplasts within eukaryotic cells contain 70S ribosomes, similar to those found in prokaryotes.