Name a bacterial, yeast, and mammalian expression system and a characteristic advantage for each.

• A. Bacterial (E. coli) for fast, inexpensive production; Yeast (Saccharomyces) for eukaryotic processing; Mammalian cells for authentic post-translational modifications.
• B. Bacterial for slow, costly production; Yeast for lack of processing; Mammalian cells for no post-translational modifications.
• C. Bacterial for glycosylation; Yeast for bacterial expression; Mammalian for simple purification.
• D. Bacterial for automation; Yeast for cost; Mammalian for membrane integration.

Answer: (B)

The key idea is matching the expression system to what the protein needs in terms production speed, cost, and processing capability. Bacteria like E. coli are prized for fast growth and low cost, which makes large-scale production practical. But they lack machinery for complex post-translational modifications, so proteins requiring those edits often can’t be produced authentically in bacteria. Yeast systems, such as Saccharomyces, strike a middle ground: they’re easier and cheaper than mammalian cells and provide a eukaryotic folding environment with some processing, giving more native-like proteins than bacteria. Mammalian cells offer authentic post-translational modifications that closely resemble those in humans, which is crucial for many therapeutic proteins, but they come with higher cost and slower production. The described combination—bacterial for fast, inexpensive production; yeast for eukaryotic processing; mammalian cells for authentic post-translational modifications—is the best alignment of advantages with needs. The other statements misstate these tradeoffs, such as claiming bacteria are slow or costly, enzymes lack processing in yeast, or mammalian cells have no post-translational modifications.