Scientists have engineered bacteria to produce human proteins, such as human growth

Bacteria do not possess the tendency to withdraw sequences of introns from a gene, thus, if the gene for the human growth hormone were transcribed, it would translate into a non-functional protein.  

When the expression of a gene takes place in eukaryotes, the budding mRNA comprising introns are removed consequently at the time of post-translational processing to produce mature mRNA. Also, the human growth hormone is produced by the pituitary gland in the form of a pre-hormone comprising a leader peptide of about 20 amino acids in length, which need to get removed post-translationally to produce a mature functional protein.  

Bacteria do not possess the biochemical machinery either to effectively withdraw the leader peptide after translation or to splice out the introns. Thus, when an unchanged human growth hormone is cloned, the bacteria cannot produce the functional human growth hormone.  

Name of part A is Nucleus