Biology
Protein synthesis (transcription & translation) — quick study summary
Protein synthesis is how cells decode DNA into functional proteins. It runs in two phases: transcription (DNA → mRNA in the nucleus) and translation (mRNA → polypeptide at the ribosome). RNA polymerase reads DNA and builds an mRNA copy; the mRNA leaves the nucleus, ribosomes read it in three-base codons, and tRNA brings the matching amino acids. The result is a polypeptide chain that folds into a functional protein.
Key points
- Transcription: RNA polymerase copies a gene from DNA into mRNA
- mRNA is processed (5' cap, poly-A tail, splicing) before leaving the nucleus
- Translation: ribosome reads mRNA codons; tRNA delivers matching amino acids
- Start codon AUG (methionine); stop codons UAA / UAG / UGA
- The genetic code is redundant — 64 codons code for 20 amino acids
Practice quiz
Click each question to reveal the answer.
1. Where does transcription occur in a eukaryotic cell?
- Cytoplasm
- Nucleus
- Mitochondrion
- Ribosome
Answer: Nucleus
Eukaryotic DNA is housed in the nucleus, so transcription happens there. Translation then occurs at ribosomes in the cytoplasm.
2. How many bases form a single codon?
Answer: Three
Each codon is a triplet of mRNA bases that codes for one amino acid (or a start/stop signal).
3. What molecule carries amino acids to the ribosome during translation?
Answer: tRNA (transfer RNA)
Each tRNA has an anticodon that base-pairs with an mRNA codon and carries the corresponding amino acid.
Last reviewed: May 2026