This chapter contains a lengthy discussion of the trp operon involved in regulating the synthesis of tryptophan. in the case of e. coli, the bacterium may need to synthesize tryptophan, or its host, a human, may supply all the tryptophan it needs. think back to chapter 17. why do both bacteria and humans need tryptophan? (etext concept 18.1)
the whole human body is a lever system, that's how muscle work. your joins are the fulcrum, your muscle contracts and hence is the effort. on the other side, whatever you're holding and the weight of your hand is the load. there are all 3 classes of lever system in your body.