Answer:
The replacement of a base at a codon, as occurs when the GGA codon is changed to CGA, causes a change in the amino acid glycine to arginine.
Explanation:
Nitrogen base changes in a codon usually result from base changes in the DNA before transcription into mRNA,called point gene mutations.
In the case presented, the substitution of the guanine base by cytosine in the GGA codon--resulting in a CGA codon--generates a change in the coding amino acid resulting in arginine instead of glycine.
The change of an amino acid in a peptide or protein can mean an alteration in the structure or function of these molecules.
Because an amino acid can be encoded by several codons, changes of a nitrogen base at a codon sometimes do not involve changes in the amino acid sequence of a protein.
