Summary
Highlights
Ribosomes are found in animal, plant, and prokaryotic cells. They are small particles made of proteins. Their main job is translation, which means reading genetic information to create various proteins.
Ribosomes are small, oval particles, about 20-30 nanometers in size. They are composed of several proteins and ribosomal RNA (rRNA), which is formed in the cell nucleus. When two or more ribosomes link together, they form a polysome or polyribosome, speeding up mRNA translation. mRNA acts as a messenger, carrying copied DNA information to other cell organelles.
Ribosomes can exist in two states within a cell: freely in the cytoplasm or attached to the membrane of the endoplasmic reticulum, forming the rough ER.
All ribosomes consist of two subunits of different sizes, each with distinct functions. Their size is measured using the Svedberg unit ('S'), which indicates how quickly a particle settles in a centrifuge, depending on its mass and shape.
Prokaryotes (organisms without a cell nucleus) have 70S ribosomes. The large subunit is 50S (made of two rRNA molecules and 31 proteins), and the small subunit is 30S (made of one rRNA molecule and 21 proteins). Eukaryotes (organisms with a cell nucleus) have 80S ribosomes. The large subunit is 60S (three rRNA molecules and 49 proteins), and the small subunit is 40S (one rRNA molecule and 33 proteins). Ribosomes can also be found in certain cell organelles like mitochondria and chloroplasts.
The most important function of ribosomes is the translation of mRNA into various proteins. The small subunit reads the mRNA to ensure no errors occur in protein composition. It then relays the correct sequence information to the large subunit, which processes the individual protein building blocks by connecting amino acids to form the desired proteins.