You extract DNA from some of your cells and cut out the complete human growth hormone gene directly from this DNA. You put this gene into a plasmid and transform E. coli with the plasmid. To your dismay, you find that E. coli does not make any human growth hormone. What is the most likely explanation for the failure of this experiment?

A) Bacteria cannot carry out RNA splicing to remove introns and so produced a much larger protein.

B) Bacteria lack a nucleus for proper transcription of eukaryotic genes.

C) Human DNA cannot be cloned in a bacterium.

D) Human DNA can be maintained in cloned form only for brief periods in bacteria.

A) Bacteria cannot carry out RNA splicing to remove introns and so produced a much larger protein.

Explanation:

Human is a eukaryote and has both introns and exons in its genes. Transcription of human genes forms a primary transcript that undergoes post-transcriptional modification.

One of the important even during the post-transcriptional modification is the removal of introns and joining the exons together to make a mature mRNA which in turn serves as the template for protein synthesis.

E. coli is a prokaryote and does not have the enzymatic machinery required for the splicing of introns.

Cloning of a complete human gene into the E. coli cells would not form the respective human protein since the bacterial cells would not be able to splice the introns from the primary transcript.