Does a change within an amino acid always cause a change in the protein activity?

Protein synthesis occurs in two steps : Transcription and Translation. Transcription is the process of creating an mRNA copy of a DNA template; the mRNA is then translated into protein. The Messenger RNA (mRNA) contains the genetic information is copied from DNA during transcription . During translation, ribosomes synthesize the proteins using the mRNA copy produced during transcription.
Proteins are complex molecules that each has a very unique shape, structure and function. The shape of the proteins is held up by a chain of subunits called amino acids that are connected by peptide bonds. Protein structures are formed by four levels of folding. The primary structure is the linear sequence of amino acids. The secondary structure describes the folding of alpha helixes and beta pleated sheets. The tertiary structure represents the overall shape of the protein and the quaternary structure only occurs in a protein consisting of more than one amino acid chain. When the shape, the structure or the function of proteins is incorrect, it is likely because of some type of change in the sequence of the amino acids or whether a certain amino acid required is present.
Mutations are alterations in the nucleotides that change the amino acid sequence within the genotype of an organism; mutations can occur from either insertion or deletions of nucleotides in a protein . The protein created from the base pairings of a mutated nucleotide may result in the making of an incorrect protein . Mutations, in important genes, may cause the cell to die if the gene synthesizes a defective protein. Muttions can occur in a few nucleotide pairs as well as long segments of DNA. A nucleotide pair substitution is an example of a small-scale mutation ; it is the replacement of one nucleotide and its pair with another pair of nucleotides. A change in an amino acid sequence may not always result in any changes on the encoded protein.
Codons are nucleotide triplets; during translation, the sequence of codons along the mRNA is translated into a sequence of amino acids. Some codons have a dual function; for example, AUG codes for the amino acid methionine but it is also the codon initiates the translation. For example, codons GUU, GUC, GUA and GUG all code for amino acid called Valine. In many cases, codons that correspond to the same amino acid differ only in the third nucleotide base of the triplet. Silent mutations are mutations in a codon that codes for the same amino acid needed for that protein synthesis. Another type of mutation is missense mutation in which the alteration of one of the nucleotides codes for a different amino acid, which makes the synthesized protein non-functional. Nonsense mutations result in a untimely termination of a protein synthesis resulted by the change in a nucleotide that coded for a “stop” signal. For example, codons UAU and UAC both code for an amino acid called Tyrosine, but codons UAA and UAC are codons that function as “stop” signals where ribosomes will end translation. If these codons are accidentally created, then the combinations of these acids may not create the right type of protein or a functional protein. Although mutations cause a permanent alteration of nitrogenous bases in an amino acid, the occurrence of silent mutation will not result in the change of protein activity. Unless the mutations have caused the cell to die, mutations are not always harmful. The cells themselves have developed mechanisms that help repair many of the mutations that occur during protein synthesis.