Final answer:
It is possible for a mutation at nucleotide 4 to yield the same amino acid due to the 'silent mutation' where the genetic code's redundancy allows multiple codons to code for a single amino acid, resulting in no changes to the protein's function.
Step-by-step explanation:
Yes, it is possible to have a mutation in nucleotide 4 that produces the same amino acid due to the redundancy of the genetic code, known as degeneracy. In the genetic code, amino acids are specified by codons, which are sequences of three nucleotides. Because of the degenerate nature of the code, some amino acids are encoded by multiple codons which can differ by a single nucleotide yet still code for the same amino acid. This is known as a silent mutation, as it does not alter the amino acid sequence of the protein. Thus, if nucleotide 4 is part of a codon where its alteration does not change the resulting amino acid, the mutation will be silent and the functionality of the protein remains intact. Examples of such mutations are seen in cases where the third nucleotide of a codon is changed, often having no effect due to the genetic code's redundancy.
Silent mutations do not affect the protein product because different codons can code for the same amino acid. On the other hand, a missense mutation can have severe impacts, like in sickle-cell disease where a single nucleotide change leads to the insertion of a different amino acid, significantly altering the protein's structure and function.