Protein Synthesis Simulator — DNA to mRNA to Protein
Simulate the central dogma step by step. Enter a DNA coding strand and see it unwound, transcribed to mRNA, read codon-by-codon with tRNA anticodons, and translated into a polypeptide chain. No signup, runs entirely in your browser.
⏱ 7 min read · Complete guide below
How to Use the Protein Synthesis Simulator
- 1Enter a DNA coding strand — the simulator uses the coding strand to match exam convention.
- 2Watch transcription: the strand is copied to mRNA with U replacing T.
- 3Follow translation codon by codon, with each tRNA anticodon and its amino acid.
- 4Read off the finished polypeptide from start codon to stop.
Worked Example: The Sickle-Cell Point Mutation
The sixth codon of the healthy beta-globin gene is GAG on the mRNA, which codes for glutamic acid (Glu). Enter the corresponding coding strand and the simulator transcribes and translates it normally. Now change a single base so that codon becomes GUG — a one-letter A→U substitution. That codon now codes for valine (Val). One base, one amino acid swap: Glu → Val at position 6.
That is the entire molecular cause of sickle-cell anaemia. The valine is hydrophobic where the glutamic acid was charged, so haemoglobin molecules stick together and deform red blood cells into a sickle shape. Run it through the simulator to see how a substitution changes exactly one codon — then contrast with deleting a base, which shifts the reading frame and garbles every codon downstream. Seeing both side by side is the clearest way to understand why frameshifts are usually far more damaging than point substitutions.
The Two Stages: Transcription and Translation
Protein synthesis happens in two distinct stages, and the simulator shows each in turn. In transcription, which takes place in the cell nucleus, the DNA is read and copied into a messenger RNA (mRNA) molecule — a portable copy of the gene that can leave the nucleus. The key chemical change is that the base thymine (T) is replaced by uracil (U). In translation, which happens at the ribosome, the mRNA is read three bases at a time. Each three-base codon is matched by a transfer RNA (tRNA) carrying the complementary anticodon and the specific amino acid that codon calls for. The ribosome links these amino acids into a growing chain — the polypeptide that will fold into the finished protein.
Reading the Genetic Code
The mapping from codons to amino acids is the genetic code, and it has some elegant features the simulator makes visible. There are 64 possible codons but only about 20 amino acids, so the code is degenerate — most amino acids are specified by several different codons, which often differ only in the third base. This redundancy is a built-in error buffer: many single-base changes in that third position are silent, producing the same amino acid and no change to the protein. Every protein begins at the start codon AUG (which also codes for methionine), and translation stops at one of three stop codons (UAA, UAG, UGA) that code for no amino acid but signal the ribosome to release the chain.
How Mutations Change the Protein
Because proteins are built codon by codon, the simulator is an ideal way to see how DNA mutations translate into biological effects. A point substitution — swapping one base — changes at most a single codon, and thanks to the code's redundancy it may change nothing at all (a silent mutation) or a single amino acid (a missense mutation, as in the sickle-cell example above). An insertion or deletionof a base causes a frameshift, shifting every downstream codon and usually producing a completely different, non-functional protein. Trying these edits and watching the resulting polypeptide change makes an abstract genetics concept concrete: it shows exactly why some mutations are harmless while others are catastrophic.
Protein Synthesis Revision Tips
Template vs coding strand
The template strand is read by RNA polymerase during transcription. The coding strand has the same sequence as the mRNA (with T instead of U). This simulator uses the coding strand as input to match exam convention.
Codon degeneracy
The genetic code is degenerate — most amino acids are encoded by more than one codon (e.g. Leucine has 6 codons). This redundancy means many point mutations in the third codon position are silent and do not change the amino acid.
Frameshift mutations
Inserting or deleting a nucleotide shifts the reading frame, changing every codon downstream. This typically produces a non-functional protein. Substitutions only change one codon; frameshifts affect all subsequent codons.
Post-translational modification
After translation the polypeptide is often folded, cleaved, glycosylated, or combined with other subunits to form the final functional protein. The simulator shows the primary sequence — folding into secondary/tertiary structure is a separate step.
Frequently Asked Questions
What is transcription?
Transcription is the process of copying a DNA sequence into messenger RNA (mRNA) in the cell nucleus. The DNA template strand is read 3'→5' and the mRNA is synthesised 5'→3'. Thymine (T) in DNA is replaced by Uracil (U) in mRNA.
What is translation?
Translation occurs in the ribosome. The mRNA sequence is read in triplets called codons. Each codon is recognised by a tRNA molecule carrying the complementary anticodon and the corresponding amino acid. The chain of amino acids is the polypeptide.
What is a start codon?
AUG is the start codon that initiates translation. It also codes for the amino acid Methionine (Met). Every protein begins with AUG, though the initiating Met is often cleaved afterward by post-translational processing.
What are stop codons?
UAA, UAG, and UGA are stop codons. They do not code for an amino acid — instead they signal the ribosome to release the polypeptide chain. Translation ends when the ribosome reaches one of these three codons.
What is the central dogma?
The central dogma of molecular biology states that genetic information flows from DNA → RNA → Protein. DNA is transcribed into mRNA; mRNA is translated into protein. Reverse transcriptase (in retroviruses like HIV) can reverse the first step.
Is my DNA sequence stored?
No. All processing runs locally in your browser. No data is sent to any server.
What is the difference between the template strand and the coding strand?
DNA has two strands. The template (or antisense) strand is the one RNA polymerase actually reads during transcription. The coding (or sense) strand has the same sequence as the resulting mRNA, except that DNA uses thymine (T) where RNA uses uracil (U). This simulator takes the coding strand as input to match common exam convention, then shows the mRNA that would be produced from the corresponding template.
Why does the genetic code have more codons than amino acids?
There are 64 possible three-base codons but only about 20 amino acids, so the code is "degenerate" — most amino acids are specified by more than one codon, which usually differ only in the third base. This redundancy is protective: many single-base changes in the third position are silent, producing the same amino acid and leaving the protein unchanged. The simulator's codon table shows this many-to-one mapping directly.
What is the role of tRNA and anticodons?
Transfer RNA (tRNA) is the adapter that turns the genetic message into protein. Each tRNA carries a specific amino acid and displays a three-base anticodon that is complementary to an mRNA codon. During translation, the tRNA whose anticodon matches the current codon delivers its amino acid to the ribosome, which links it onto the growing chain. The simulator shows the anticodon for each codon so you can see this pairing step by step.
How does a single DNA mutation cause a disease like sickle-cell anaemia?
A point substitution changes one base, which can change one codon and therefore one amino acid. In sickle-cell anaemia, a single A-to-T change in the beta-globin gene turns the sixth codon from one coding for glutamic acid into one coding for valine. That single amino acid swap alters how haemoglobin molecules interact, deforming red blood cells into a sickle shape. The simulator lets you make exactly this one-base change and watch the resulting protein change.
What happens to the protein after translation?
The polypeptide chain the simulator produces is the primary structure — just the sequence of amino acids. In the cell it then folds into a specific three-dimensional shape and often undergoes post-translational modifications such as cleaving off the initial methionine, adding sugar groups, or joining with other chains to form the final functional protein. Folding and modification are separate steps beyond the primary sequence shown here, but they are essential to a protein's function.