in this video I'll discuss how the trip operon functions in E coli so this is what the trip operon looks like you can see that it contains five structural genes trip e trip D trip C trip B and trip a these genes each encode enzymes that are necessary for tryptophan synthesis which is the process of making tryptophan in the cell tryptophan is an amino acid that is necessary in the bacterial cell for any protein synthesis because proteins are constantly being made in the cell tryptophan needs to be present at all times for E coli to survive these five structural genes share a promoter and an operator and then further Upstream of the operon you will find the regulatory Gene trip r this regulatory Gene encodes an inactive repressor when this repressor is in its inactive form it cannot bind to the operator and therefore cannot limit transcription of the structural genes in the trip operon in this situation RNA polymerase can freely bind to the promoter and transcribe the structural genes leading to the production of enzymes that help make tryptophan in this state the operon is said to be de-repressed meaning the structural genes are expressed when there's an excess of tryptophan in the environment or in the cell it would be a waste of energy and resources for the cell to continue making tryptophan so the transcription of the structural genes should be limited how does this happen it turns out that tryptophan is a co-repressor of the trip operon it's called a co-repressor because it works with the repressor to prevent transcription of the structural genes it will bind to the inactive repressor changing its shape and making it active in this state the DNA binding region of the trip repressor is able to bind to the operator allowing it to prevent RNA polymerase from transcribing these genes in this way a high concentration of tryptophan in the environment will limit transcription of these structural genes saving the cell lots of energy in this state the operon is said to be repressed so you can see that the trip operon is a repressible operon because its genes are naturally expressed and you must have an excess of tryptophan present in the environment for the genes to be repressed so that's the trip operon when tryptophan is lacking in the cell the repressor is inactive and the genes are able to be transcribed and translated resulting in tryptophan production when tryptophan is abundant in the cell it activates the repressor which then limits transcription of the trip structural genes preventing the production of additional tryptophan if you'd like to review your general opera on understanding check out my video on operon Basics if you want to learn about another operon check out my videos on the lock operon