It's used as a Climate classification system.
In the absence of tryptophan, the genes trpA-E will not be transcribed.
If there were a mutation in the operator region of the trp operon, there would be a nucleotide change in the sequence of the operator. Mutations in the repressor that prevent its binding to the operator will lead to constitutive expression Mutations that prevent binding of the inducer without affecting the ability to bind to the operator lead to a non‑inducible phenotype.
The tryptophan binds to the trp repressor and causes it to change shape, converting into its active form. The trp repressor with the bound tryptophan attaches to the operator, blocking RNA polymerase from binding to the promoter and preventing transcription of the operon.
To learn more about tryptophan, here
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It seems that you have missed the given option for this question but anyway, here is the answer. The statement that would not be a valid reason for a cell's need to have these control molecules present is that <span>they make it impossible for the cell cycle to occur out of order. Hope this is the answer that you are looking for. </span>
<span>6 CO2 + 12 H2O + light energy --> C6H12O6 + 6 O2 + 6 H2O
Energy from the sun begins the splitting of carbon dioxide and water into a sugar molecule, water and oxygen. Sugar is formed from CO2 using ATP and NADPH</span>
