Why can an exogenous protein, protein that is added by experimentalists that has the same amino acid sequence as endogenous protein, be resistant to RNA interference while the endogenous protein is susceptible to RNA interference?

(A) The genetic code is degenerate, meaning that there is more than one codon for a single amino acid.

(B) The exogenous protein consists of introns rendering the exogenous protein resistant.

(C) The endogenous protein contains introns which is why its susceptible to RNA interference.

(D) The genetic code is degenerate, meaning that there is only one codon for a single amino acid.

(A) The genetic code is degenerate, meaning that there is more than one codon for a single amino acid.

Explanation:

RNA interference occurs when small single-stranded RNA molecules inhibit the expression of the mRNA having a sequence complementary to them. The sequence of mRNA is read in the form of triplets during the process of translation. The base triplets make the genetic code and specify amino acids to be added to the protein. One genetic code specifies a particular amino acid but some amino acids have more than one genetic code, that is, the genetic code is degenerate.

Therefore, an exogenous protein with the same amino acid sequence as that of the endogenous protein may be resistant to the RNA interference as its mRNA has alternative genetic codes for the same amino acid. For example, if mRNA with "GCU" code is susceptible to RNA interference, the mRNA with GCA may be resistant to it. Though both specify the amino acid alanine.