E. coli can synthesize the amino acid threonine or absorb it from the environment. In the thr operon, the repressor is active when it is bound to threonine. If an E. coli bacterium is in an environment where threonine is absent, will transcription of threonine synthesis genes take place? Why or why not?

Explanation:

1. If an E. coli bacterium is grown, in an environment where threonine is absent, transcription of threonine synthesis genes take place, because threonine will not be bound to the repressor, so the repressor will be inactive.

2. When the repressor is bound to the threonine, it becomes active, and in the absence of threonine , repressor become inactive because there is no threonine to bind with repressor.

3. So, in the absence of threonine , there is synthesis of threonine occurs.

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