Chapter 16, Problem 13P

The previous problem raises some interesting issues:

a.

In most experiments using the lac operon, researchers use the synthetic inducer IPTG to turn on operon expression, instead of lactose or allolactose. What do you think is the advantage of using IPTG?

b.

Scientists were originally puzzled by what they termed the lactose paradox. To turn on expression of the lac operon, an inducer (whether IPTG or lactose/allolactose) needs to be able to get into the cell. Import of this inducer requires the presence of the Lac permease enzyme in the cell membrane (Fig. 16.2). But if the lac operon is being repressed prior to addition of the inducer, no Lac permease should be present, so no inducer could be imported, and induction could never occur. Yet induction obviously does occur; how might this be possible?