Ribosomien

Ribosomien are molecular machines that translate genetic information into proteins. They are essential to all living cells, operating in the cytoplasm and on the endoplasmic reticulum in eukaryotes, and freely in the cytoplasm of prokaryotes. They decode messenger RNA and assemble amino acids into polypeptides.

Ribosomien consist of two subunits made of ribosomal RNA (rRNA) and proteins. In eukaryotes the small subunit is 40S and the large 60S (80S total); in prokaryotes they are 30S and 50S (70S total). The small subunit reads mRNA; the large subunit forms peptide bonds.

During translation, initiation factors assemble the ribosomien at a start codon; tRNAs deliver amino acids; elongation factors drive sequential addition of residues. Stop codons trigger release factors to terminate synthesis. The peptidyl transferase site is formed largely by rRNA, making the ribosomien a ribozyme. In eukaryotes, ribosomien may be free or bound to rough endoplasmic reticulum.

Biogenesis begins in the nucleolus, where rRNA genes are transcribed and assembled with proteins. Mitochondrial and chloroplast ribosomen resemble bacterial 70S ribosomes, reflecting their origin. Differences between bacterial and eukaryotic ribosomen enable selective antibiotic targeting.

Many antibiotics inhibit bacterial ribosomien, including tetracyclines, aminoglycosides, macrolides, chloramphenicol, and oxazolidinones. These agents disrupt protein synthesis at different steps. Because mitochondrial ribosomen resemble bacterial ones, some antibiotics cause host toxicity. Resistance arises via mutations, enzymatic modification, or reduced drug uptake.