Human genes may be too large for bacterial plasmids. Or, bacterial cells may not be complex enough to process RNA transcriptions into mRNA. Or, if translation and transcription occurs using cDNA, there are no enzymes in bacteria that can catalyze the post-translational processing required by proteins used by humans.
Work Step by Step
Eukaryotic cells are more complex than bacterial cells, and their genes are longer too. Bacterial cells cannot process RNA transcripts into mRNA. Even after RNA processing done by using cDNA, bacterial cells do not have enzymes that can catalyze the post-translational processes that are crucial to human protein function.