Biotechnology : Principles and Processes

DNA is bigger in molecular size than enzymes. We know this because DNA is made up of very long chains of nucleotides, whereas enzymes are proteins made of amino acids and are comparatively smaller molecules. In biotechnology, DNA fragments are handled, cut, and separated, but enzymes such as restriction endonucleases and ligases act on them, showing that DNA is the larger substrate.

Yes, eukaryotic cells have restriction endonucleases. The chapter explains that restriction endonucleases were first isolated from bacteria, where they restrict the growth of bacteriophages. Their main role is described in prokaryotes as a defense mechanism. Since the chapter discusses these enzymes as tools of recombinant DNA technology and specifically mentions their isolation from bacterial strains, the answer is that they are associated with bacteria/prokaryotes, not eukaryotic cells. So eukaryotic cells are not said to have them in this chapter.

Besides better aeration and mixing, stirred-tank bioreactors have several advantages over shake flasks:
- They provide optimum growth conditions such as temperature, pH, substrate, salts, vitamins, and oxygen.
- They have systems for foam control, temperature control, pH control, and sampling ports.
- They allow large-scale culture and hence produce larger biomass and higher yields of the desired product.
- The culture can be maintained in the log/exponential phase by continuous addition of fresh medium and removal of used medium.
- They are suitable for processing large volumes of culture, unlike shake flasks.

So, stirred tank bioreactors are more efficient and controllable for industrial production.