Ribosome

Definition

A ribonucleoprotein complex found in all living cells that serves as the site of protein synthesis (translation). Composed of large and small subunits containing ribosomal RNA (rRNA) and proteins, it reads messenger RNA (mRNA) codons and catalyzes assembly of amino acids into polypeptide chains. In eukaryotic cells, ribosomes occur free in the cytoplasm or bound to the endoplasmic reticulum; in prokaryotes, they are smaller and lack membrane association. Ribosome structure and function are conserved across arthropods, though inhibitors targeting prokaryote-like mitochondrial ribosomes serve as important insecticides and acaricides.

Etymology

From ribonucleic acid + -some (body), coined in the 1950s to describe RNA-rich cytoplasmic particles.

Example

During the larval–pupal molt in holometabolous insects, ribosome abundance and translational activity surge in the fat body to support massive synthesis of storage proteins and cuticle-forming enzymes.

Synonyms

• ribonucleoprotein particle
• translational apparatus

Related Terms

• translation
• messenger RNA
• transfer RNA
• Endoplasmic reticulum
• polyribosome
• protein synthesis
• mitochondrial ribosome
• Insect growth regulator

Usage Notes

Distinguish 80S cytoplasmic ribosomes (eukaryotes, including insects and arachnids) from 70S prokaryotic ribosomes; this size difference underlies selective toxicity of many antibiotics and insect growth regulators. 'Translational apparatus' is broader, encompassing ribosomes plus associated factors. Free ribosomes synthesize cytosolic proteins; membrane-bound ribosomes produce secreted and membrane proteins such as those in silk glands or venom ducts.