70SRibosoms

70S ribosomes are the primary site of protein synthesis in prokaryotic cells and also found in mitochondria and chloroplasts of eukaryotic cells. They are composed of two subunits, a large 50S subunit and a small 30S subunit. The S designation refers to Svedberg units, a measure of sedimentation rate during centrifugation, which is not directly additive. The 30S subunit contains 16S ribosomal RNA (rRNA) and approximately 21 proteins. The 50S subunit consists of 23S rRNA, 5S rRNA, and about 34 proteins. Together, these subunits form a functional ribosome with a molecular weight of approximately 2.5 MDa. During translation, the mRNA molecule binds to the 30S subunit, and the growing polypeptide chain is formed within the catalytic site of the 50S subunit. The precise arrangement of rRNA and proteins within the 70S ribosome is crucial for its function in decoding genetic information and catalyzing peptide bond formation. Differences between 70S ribosomes and the 80S ribosomes found in the eukaryotic cytoplasm are significant, making 70S ribosomes a common target for antibiotics that aim to inhibit bacterial protein synthesis without harming the host.