How Mutations Affect Proteins

From DNA letters to protein shape

Proteins are built from amino acids, and amino acid order is determined by genetic information.

So when a mutation changes DNA, it can sometimes change the protein made from that DNA. The important word is sometimes. Not every mutation changes a protein.

Start with the code

During translation, ribosomes read messenger RNA in three-base units called codons.

Each codon corresponds to an amino acid or a stop signal. If a mutation changes a codon, it may change what the ribosome adds to the growing protein chain.

Silent mutations

A silent mutation changes the DNA sequence without changing the amino acid sequence.

This can happen because the genetic code is redundant. Several codons may code for the same amino acid.

Silent mutations are often neutral at the protein sequence level, though some can still matter by affecting RNA processing, stability, or regulation.

Missense mutations

A missense mutation changes one amino acid to another.

The effect depends on where the amino acid is and how different the replacement is. A change on the surface of a protein may have little effect, while a change in an active site or binding region can strongly alter function.

This is why a single DNA letter change can sometimes cause disease.

Nonsense mutations

A nonsense mutation changes a codon into a stop signal.

Translation may stop too early, producing a shortened protein. A shortened protein may be unstable, nonfunctional, or missing important regions.

Frameshift mutations

Insertions or deletions can shift the reading frame if the number of added or removed bases is not a multiple of three.

After a frameshift, the ribosome groups the downstream bases differently. This can change many amino acids and often creates an early stop signal.

Frameshifts are often more disruptive than a single amino acid substitution.

Protein folding and function

A protein's amino acid sequence helps determine how it folds.

Shape matters because proteins work by binding, catalyzing, signaling, supporting, or moving other molecules. If a mutation changes the shape enough, it can change the job the protein can do.

The key idea

Mutations matter because sequence, shape, and function are connected.

The same DNA change can be harmless in one context and serious in another, depending on the gene, the protein region, and the cell's biology.