The control of gene expression is critical to all living organisms. the amino acid tryptophan is important for making many proteins. when there is plenty of tryptophan in a cell, a protein binds to the gene that codes for an enzyme that will make tryptophan. when there is no tryptophan present this protein falls off the dna allowing the gene to be expressed so more tryptophan can be made. a protein that binds to a site on dna next to a gene and blocks the transcription of that gene, thus preventing the synthesis of a protein that the gene prescribes is known as a:

Repressor

Explanation:

Repressors are transcription factors produced by regulatory genes during a process called repression.

During this process, a regulatory gene produces a repressor (a protein) that binds to an operator. Then, the promoter (site of the DNA where RNA polymerase binds to perform transcription) is blocked, thereby preventing transcription. In other words, the expression of structural genes does not occur.

true is the final answer!

when you breathe in, or inhale, your diaphragm contracts (tightens) and moves downward. this increases the space in your chest cavity, into which your lungs expand. the intercostal muscles between your ribs also enlarge the chest cavity. they contract to pull your rib cage both upward and outward when you inhale.