How can DNA mutations alter the structure of a protein?

Regions of an organism's genome that code for proteins are known as genes. The sequence of deoxyribonucleic acids (bases) in a gene directly translates to the sequence of amino acids in the protein it encodes. The cell uses the 'genetic code' to decipher triplets of bases in the DNA (known as codons) which code for one amino acid in the protein. DNA mutations arise spontaneously and mutation rate can be increased as a result of exposure to mutagenic agents. Point mutations are a change only one base (and therefore only one codon). Substitution mutations within a codon lead to a change in the amino acid at that position in the protein, for example, the triplet sequence GGT codes for glycine while AGT codes for serine. Due to the degenerate nature of the genetic code, point mutations can be silent and result in no amino acid change. For example, GGT and GGG both code for glycine. If a point mutation results in the generation of a stop codon then the resulting protein will be truncated. Some mutations will alter all triplet codons downstream from the mutation site. Addition/substitution mutations arise when a base is added/removed into the gene's sequence and lead to a frameshift of all downstream codons, altering the amino acids they code for and severely disrupting the protein.