DNAThe cell's genetic code, kept in the nucleus. The stretch of it that codes for one protein is a gene.
TranscriptionThe first stage, in the nucleus. A gene in the DNA is copied into mRNA.
mRNAMessenger RNA, the copy of the gene. It carries the code out of the nucleus to a ribosome.
NucleusThe part of the cell that holds the DNA. Transcription happens here.
TranslationThe second stage, at a ribosome in the cytoplasm. The mRNA's code is read and amino acids are joined in that order.
RibosomeReads the mRNA one codon (three bases) at a time. It joins the amino acids. It has a large and a small subunit.
ProteinThe finished molecule: the polypeptide chain folded into its working shape.
In the nucleus: 6 2
RNA polymeraseThe enzyme that opens the DNA and reads the gene. It builds a matching strand of mRNA.
Nuclear poreA gap in the envelope round the nucleus. The finished mRNA leaves the nucleus through one.
In the cytoplasm: 7 4
CytoplasmThe inside of the cell outside the nucleus. Translation happens here.
tRNATransfer RNA brings one amino acid. Its anticodon pairs with the matching codon on the mRNA.
Amino acidOne building block of a protein. Carried on the end of a tRNA.
Polypeptide chainThe chain of amino acids the ribosome builds, one at a time.
How this list was compiled: Read 2026-09-27. (1) Wikipedia, Protein biosynthesis, https://en.wikipedia.org/wiki/Protein_biosynthesis : two stages; in transcription, in the nucleus, RNA polymerases convert a gene into mRNA; the mature mRNA leaves the nucleus through nuclear pores to the cytoplasm; in translation, ribosomes read the mRNA and join amino acids brought by tRNA, whose anticodon pairs with each codon; the polypeptide chain then folds. (2) OpenStax Biology 2e, 15.1 to 15.5, https://openstax.org/books/biology-2e/pages/15-introduction (used to check, nothing copied): the same stages and parts, the ribosome's large and small subunits, a codon of three bases. Licence: own work
The drawing: Drawn for this site by script, 2026-09-27. Own work, nothing traced. Licence: own work
How it works
A protein synthesis diagram labeled in one cell: transcription in the nucleus at the top, translation in the cytoplasm below. Start with the 7 main parts, then the rest of each stage.
Read the full guide
Transcription, in the nucleus
RNA polymerase opens a stretch of DNA and copies one gene into a strand of mRNA. The mRNA leaves the nucleus through a nuclear pore.
Translation, in the cytoplasm
A ribosome reads the mRNA three bases at a time. Each tRNA brings the amino acid that matches, and the ribosome joins them into a polypeptide chain, which folds into a protein.
Follow the mRNA with a finger from the DNA to the ribosome: it is the one strand that joins both stages.
Questions and answers
What are the two stages of protein synthesis?
Transcription, in the nucleus, where a gene is copied into mRNA, and translation, in the cytoplasm, where a ribosome reads the mRNA and joins amino acids into a protein.
What does tRNA do in protein synthesis?
Transfer RNA carries one amino acid to the ribosome. Its anticodon pairs with the matching codon on the mRNA, so the amino acids join in the right order.
Where does protein synthesis take place?
It starts in the nucleus, where the DNA is copied into mRNA, and finishes at the ribosomes in the cytoplasm, where the protein is built.