Ribosomiin

Ribosomiin, commonly known as the ribosome, is the universal molecular machine of protein synthesis in cells. It translates information encoded in messenger RNA into polypeptide chains, assembling amino acids in the order specified by the genetic code. The ribosome is a ribonucleoprotein complex composed of ribosomal RNA (rRNA) and ribosomal proteins, divided into a small subunit that reads the mRNA and a large subunit that catalyzes peptide bond formation.

In bacteria the subunits are 30S and 50S, forming a 70S ribosome; in eukaryotes the equivalents are 40S and 60S, forming an 80S ribosome. Organellar ribosomes in mitochondria and chloroplasts resemble bacterial ribosomes (often 70S).

Biogenesis occurs in the nucleolus in most eukaryotes, where rRNA genes are transcribed and assembly begins before export to the cytosol. In bacteria, ribosome assembly occurs in the cytoplasm. During translation, initiation factors help recruit ribosomes to mRNA, the complex scans for a start codon, then elongation adds amino acids via tRNA delivery and peptidyl transferase activity within the rRNA. Translocation moves the ribosome along the mRNA, and termination occurs at stop codons with release factors. The process requires GTP and multiple factors.

Ribosomes are targets for antibiotics that disrupt bacterial subunits without affecting eukaryotic ribosomes. Defects in ribosome biogenesis or ribosomal proteins can cause ribosomopathies, such as Diamond-Blackfan anemia and Shwachman-Diamond syndrome, and can impact cell growth and development.