Why does the deletion of a single nucleotide in a gene often results in a very defective protein ?

The deletion of a single nucleotide in a gene often results in a very defective protein because it changes the reading frame of the DNA which leads to the production of a protein with amino acid sequence that is different from the original protein.

Explanation: When a single nucleotide is deleted in a gene, it results in a frameshift mutation. A frameshift mutation is a type of mutation caused by either insertion or deletion of a nucleotide in a DNA sequence which changes the reading frame of a DNA sequence. During protein synthesis, DNA is first copied into an mRNA and the mRNA is used to make a protein. mRNA sequence is read in triplet of nucleotides known as codons which code for specific amino acids. When a single nucleotide is deleted from a DNA sequence, the mRNA that will be produced will have an altered reading frame which leads to the addition of wrong amino acid and the entire amino acid sequence after the point of mutation will be incorrect. This results in a completely different protein from the original thus causing a defect in protein function.

it marks things for degradation via the proteasome. it alters there celluar location.