Question

The human gene for a protein hormone has been isolated. Scientists want to introduce this gene into a bacterial host, modifying the bacteria so that it can be used to produce this hormone. After successfully introducing the gene on a plasmid, the bacteria produced the protein hormone, but the protein was defective, longer than normal, with intervening stretches of amino acids not found in the native protein. What is the most likely explanation?

A. The bacteria can’t transcribe the human gene.

B. The gene that was introduced contained introns.

C. Bacterial cells cannot translate mRNAs transcribed from human genes.

D. Bacterial ribosomes make errors when transcribing human mRNAs.

Answer 1

B) The gene that was introduced contained introns

Bacteria can express (transcribe and translate) human genes or any genes inside the cell. But they lack the splicing system. So if the inserted gene contains introns, bacteria will translate introns as well along with exons, so resulting protein will be non-functional as it contains extra amino acids.

So if you want to translate exact functional human protein in bacterial cell, you need to introduce cDNA of that gene. cDNA is made by making complementary DNA of the particular mature-mRNA of that protein. Because mature-mRNA do not contain introns, synthesized cDNA will not contain introns as well.