What Is Protein Synthesis?
Protein synthesis is the process cells use to build proteins from genetic instructions in DNA. It happens in two main stages — transcription, where DNA is copied into mRNA, and translation, where ribosomes read that mRNA to assemble amino acids.
Protein synthesis is the two-step process (transcription then translation) by which a cell reads a gene's DNA sequence and builds the corresponding protein from amino acids.
- 1↓TranscriptionRNA polymerase copies a gene's DNA sequence into a complementary pre-mRNA strand in the nucleus.
- 2↓mRNA processingThe pre-mRNA is capped, polyadenylated and spliced (introns removed) to form mature mRNA.
- 3↓Nuclear exportMature mRNA exits the nucleus through a nuclear pore into the cytoplasm.
- 4↓Translation initiationA ribosome binds the mRNA at the start codon (AUG) and the first tRNA delivers methionine.
- 5↓ElongationtRNAs match codons to anticodons, adding amino acids one by one to the growing chain.
- 6TerminationThe ribosome reaches a stop codon (UAA, UAG or UGA) and releases the finished protein.
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Step-by-step worked examples
An mRNA coding sequence is 300 nucleotides long. How many amino acids does the resulting protein contain?
Amino acids = (L/3) − 1 Amino acids = (300/3) − 1 Amino acids = 100 − 1 = 99 amino acids
The mRNA codon is 5'-AUG-3'. Which amino acid and tRNA anticodon match it?
AUG is the start codon, coding for methionine The matching tRNA anticodon is complementary and antiparallel: 3'-UAC-5'
A gene's mRNA has 603 coding nucleotides (including the stop codon). How many codons are translated into amino acids?
Total codons = 603/3 = 201 codons One codon is the stop codon (not translated) Amino acids incorporated = 201 − 1 = 200
Flashcards
Quick quiz
Q1.What molecule carries the genetic code from the nucleus to the ribosome?
Q2.How many nucleotides make up one codon?
Q3.Which process converts mRNA into a chain of amino acids?
Q4.What stops translation?
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Common mistakes
Thinking DNA is directly translated into protein. — Correct: DNA is first transcribed into mRNA; only mRNA is translated at the ribosome.
Confusing transcription and translation. — Correct: Transcription makes mRNA from DNA (in the nucleus); translation makes protein from mRNA (at ribosomes).
Assuming every 3 nucleotides in mRNA becomes an amino acid. — Correct: The stop codon is a triplet too but doesn't code for an amino acid — it ends the protein.
Forgetting introns are removed before translation. — Correct: Only exons remain in mature mRNA after splicing; introns are cut out.
FAQ
What is protein synthesis?
Protein synthesis is how a cell reads a gene and builds a protein, through transcription (DNA→mRNA) and translation (mRNA→protein).
What is the formula to calculate amino acids from mRNA length?
Amino acids ≈ (mRNA coding length ÷ 3) − 1, since the final codon is a stop codon.
What are examples of protein synthesis in the body?
Producing insulin in pancreatic cells or building keratin in skin cells are everyday examples.
How do you calculate the number of codons in an mRNA?
Divide the mRNA coding sequence length by 3 — each codon is three nucleotides.