Final answer:
A ribosome consists of two subunits: in prokaryotes, a 70S ribosome is composed of a 50S large subunit and a 30S small subunit; in eukaryotes, an 80S ribosome comprises a 60S large subunit and a 40S small subunit.
Step-by-step explanation:
A ribosome is a complex cellular structure responsible for protein synthesis, and it comprises multiple subunits. In prokaryotes and eukaryotes, ribosomes consist of two distinct subunits: the large subunit and the small subunit.
In eukaryotic cells, such as those found in animals, plants, fungi, and protists, ribosomes are composed of a large (60S) and a small (40S) subunit, combining to form a complete ribosome of 80S (S stands for Svedberg units, a measure of sedimentation rate).
The large subunit, named 60S, contains the peptidyl transferase activity that catalyzes the formation of peptide bonds during protein synthesis. It also helps in decoding the mRNA (messenger RNA) sequence.
The small subunit, named 40S, is responsible for binding to the mRNA and the initiator tRNA (transfer RNA), playing a crucial role in the initiation phase of protein synthesis.
In prokaryotic cells like bacteria, ribosomes consist of a 50S large subunit and a 30S small subunit, forming a complete ribosome of 70S.
Each subunit is composed of ribosomal RNA (rRNA) molecules and various ribosomal proteins. These subunits come together during the translation process to facilitate the assembly of amino acids into polypeptide chains, thereby synthesizing proteins according to the information carried by the mRNA.
In summary, a ribosome consists of two subunits, a large and a small subunit, which work together in a coordinated manner during protein synthesis in both prokaryotic and eukaryotic cells.