What is true about tryptophan and the tryptophan operon?
a.Tryptophan is a sugar
b.The genes for tryptophan biosynthesis are organized in an operon with no promoter
c.The multiple proteins coded for in the operon are involved in the breakdown of tryptophan
d.The repressor, TrpR, binds to the operator, when tryptophan is absent
e.The repressor, TrpR, when bound to tryptophan, blocks expression of the trp operon