Translation Diagram Labeled – 14 Parts at the Ribosome

All 14 parts on the diagram

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Start here: 8 main parts 8

mRNA (messenger RNA) Carries the gene's code from the DNA; the ribosome reads it three bases at a time, from 5' to 3'.
Codon Three mRNA bases that code for one amino acid; this one sits in the A site.
Small ribosomal subunit The smaller part of the ribosome; it binds the mRNA.
Large ribosomal subunit The larger part of the ribosome; it holds the three tRNA sites and joins the amino acids.
tRNA (transfer RNA) Brings one amino acid and matches it to a codon with its anticodon.
Anticodon Three tRNA bases that pair with the matching codon on the mRNA.
Amino acid One building block of a protein, carried in by its tRNA.
Polypeptide chain The growing chain of amino acids that will fold into a protein.

mRNA and tRNA: 6 2

Start codon (AUG) AUG, the codon where translation starts; it codes for methionine.
Stop codon UAA, UAG or UGA: no tRNA matches it, so a release factor ends translation there.

Ribosome and its sites: 5 3

E site (exit site) Where the empty tRNA leaves the ribosome.
P site (peptidyl site) Holds the tRNA carrying the growing chain.
A site (aminoacyl site) Where each new tRNA with its amino acid comes in.

Amino acids and the chain: 3 1

Peptide bond The bond joining one amino acid to the next.

How this list was compiled: Read 2026-09-26. OpenStax Biology 2e, 15.5 Ribosomes and Protein Synthesis, https://openstax.org/books/biology-2e/pages/15-5-ribosomes-and-protein-synthesis : small and large ribosomal subunits; mRNA read 5' to 3'; the AUG start codon; charged tRNAs enter the A site and the anticodon base-pairs with the codon; after peptide bond formation the A-site tRNA moves to the P site and the empty P-site tRNA to the E site and out; release factor at a stop codon. Wikipedia, Translation (biology), https://en.wikipedia.org/wiki/Translation_(biology) : A, P and E sites, small and large subunits, codon and anticodon, start and stop codons, peptide bonds, polypeptide. Licence: own work

The drawing: Drawn for this site by script, 2026-09-26. Own work, nothing traced. Licence: own work

How it works

This translation diagram labeled part by part shows a ribosome part way along an mRNA, reading it from 5' to 3', left to right. The simple set asks the 8 main parts; the full set adds the three sites and the codons that start and stop it.

Read the full guide

Reading the code

The mRNA runs between the small and large ribosomal subunits. Each codon, three bases, is matched by the anticodon of a tRNA carrying one amino acid. Reading began at the start codon, AUG, and will end at a stop codon.

A, P and E

A new tRNA enters the A site. A peptide bond joins its amino acid to the chain held by the tRNA in the P site. The ribosome then moves one codon along: the chain's tRNA shifts to the P site and the empty one leaves from the E site.

Read the sites in the order a tRNA passes through them: A, then P, then E.

Questions and answers

What is the difference between a codon and an anticodon?

A codon is three bases on the mRNA. An anticodon is the matching three bases on a tRNA. They pair up, so each tRNA brings the amino acid its codon calls for.

What happens at the stop codon?

No tRNA matches a stop codon. A release factor enters the A site instead, the finished polypeptide is let go, and the ribosome comes apart from the mRNA.

Where does translation happen?

At ribosomes in the cytoplasm, free or on the rough endoplasmic reticulum. The mRNA is made in the nucleus by transcription and then carried out to them.