ribosome
Meaning of ribosome: The molecular machine that reads a genetic message three letters at a time and builds the protein it specifies.
Definition of ribosome
A ribosome is the structure inside a cell that manufactures proteins. Built from ribosomal RNA and dozens of proteins, it comes in two subunits that clamp around a strand of messenger RNA. The ribosome moves along that strand, reads it in groups of three letters, and joins the matching amino acids into a chain in the order the message specifies.
How does it build a protein?
Messenger RNA carries a copy of the instructions from a gene. The ribosome grips it and reads three bases at a time, each triplet naming one amino acid. Transfer RNA molecules act as couriers: each carries one amino acid and a matching three-letter tag. When a courier fits the triplet in the reading slot, its cargo is joined to the growing chain and the ribosome shifts along by three bases. The order of triplets determines the amino acid sequence, and that sequence determines how the finished protein folds and what it does.
What is it made of?
| Part | Role |
|---|---|
| Large subunit | Joins amino acids together and holds the growing chain |
| Small subunit | Grips the message and checks each courier fits |
| Ribosomal RNA | Forms the structure and performs the joining reaction |
| Ribosomal proteins | Stabilize the shape and assist the process |
The joining reaction is carried out by RNA rather than by a protein enzyme, which is unusual and is taken as evidence that RNA machinery came first in the history of life.
Why do antibiotics target it?
Bacterial ribosomes differ from human ones in size and detail, and several important antibiotic families exploit that gap. Macrolides, tetracyclines and aminoglycosides all attach to a bacterial ribosome and jam protein production, while leaving the human version largely alone. The margin is not absolute, which contributes to some of their side effects. Human cells also contain a second, separate set of ribosomes inside mitochondria, and these resemble the bacterial type, a resemblance that supports the view that mitochondria descend from ancient bacteria and explains certain drug toxicities.
Used in a sentence
The antibiotic acts by binding the bacterial ribosome and halting protein synthesis.
Good to know
Several antibiotic families work by binding the bacterial ribosome, and human mitochondrial ribosomes resemble the bacterial type closely enough to account for some of their side effects.
Word origin
Where “ribosome” comes from
Combines ribose, the sugar in RNA, with the Greek soma, meaning body.