Recombinant human insulin is a protein produced using recombinant DNA technology. Bacteria can serve as host cells to express the recombinant protein. For the human insulin gene to be expressed successfully in bacteria, one method used to obtain the gene is to remove mRNA from $\beta$-cells in the pancreas. The insulin coding gene is not expressed in the bacterial host if it has been obtained by excising it from genomic DNA. Suggest and explain how the structural difference between cDNA and genomic DNA results in only cDNA being expressed successfully.
State the role of DNA ligase in the formation of recombinant plasmids.
Explain why a promoter, as well as the gene, may have to be transferred into the plasmid.
Explain how a marker gene that codes for a fluorescent product could be used.
The unicellular fungus Saccharomyces cerevisiae is a species of yeast that has been used to produce human insulin. S. cerevisiae cells are able to take up recombinant plasmids. Suggest advantages of using yeast instead of bacteria for human insulin production.