Changing one mRNA codon can change a protein because each codon normally specifies a particular amino acid, so altering the codon can alter the amino acid sequence and therefore the proteinā€™s shape and function.

What a codon does

  • An mRNA codon is a sequence of three bases (like AUG, GCU, UGA). Each codon corresponds to one amino acid or a stop signal in the genetic code.
  • During translation, tRNA molecules match their anticodons to mRNA codons and bring in specific amino acids, building the protein chain in order.

How one codon change affects the protein

Changing one codon means changing which amino acid is placed at that position, or whether translation stops there. This is called a point mutation when only one base is altered.

Main possibilities

  1. Missense mutation (different amino acid)
    • One base change makes a different codon that codes for a different amino acid.
 * This can:
   * Slightly change the protein (small effect) if the new amino acid is similar.
   * Strongly disrupt folding, the active site of an enzyme, or binding sites if the new amino acid is very different (e.g., charged vs nonpolar).
  1. Nonsense mutation (early stop)
    • One base change can turn a normal codon into a stop codon (e.g., UAU ā†’ UAA).
 * Translation stops too early, producing a shortened protein that is often nonfunctional or quickly degraded.
  1. Silent mutation (same amino acid)
    • Thanks to redundancy in the genetic code, some codon changes still code for the same amino acid (e.g., GAA ā†’ GAG both code for glutamate).
 * Even then, changing the codon can subtly affect:
   * Translation speed and co-translational folding.
   * mRNA stability and how much protein is made.

Why even one amino acid can matter

  • The amino acid sequence is the primary structure of a protein and determines how it folds into its 3D shape (secondary and tertiary structures).
  • A single change can:
    • Break or create ionic, hydrogen, or disulfide bonds.
    • Distort the active site of enzymes or binding interfaces.
    • Change how the protein interacts with membranes or other molecules.

When one codon change has huge vs small effects

  • Huge effect (often diseaseā€‘causing):
    • Missense in a critical region (e.g., enzyme active site, receptor binding pocket).
* Nonsense mutation near the start of the coding sequence (very short, nonfunctional protein).
  • Small or no obvious effect :
    • Silent mutation or conservative missense (new amino acid with similar properties) in a less critical region.

In short: changing one mRNA codon can change which amino acid is added (or introduce a stop), and because protein function depends tightly on sequence and folding, even a single change can dramatically alter or destroy functionā€”though in some cases, the effect is minimal or silent.

TL;DR: One codon = one ā€œwordā€ in the protein recipe; change the word, and you may change a letter, truncate the sentence, or occasionally leave the meaning the sameā€”but the impact ranges from none to completely nonfunctional protein.

Information gathered from public forums or data available on the internet and portrayed here.