In escherichia coli e coli the tryptophan operon encodes...

In Escherichia coli (E. coli), the tryptophan operon encodes structural genes, including trpC, trpB, and trpA, that encode the tryptophan synthetase protein complex. A repressor protein encoded by the trpA gene regulates the trp operon. In the presence of high levels of tryptophan, tryptophan molecules bind the repressor protein and allow the repressor to recognize and bind to the operator, called trpO, and repress the expression of the structural tryptophan synthetase genes. In the absence of tryptophan, the repressor is unable to bind the operator and gene expression can occur. Assume any minus symbol represents a null mutant. What is the type of expression of each functional structural gene for the three bacterial strains? trpR+ trpO+ trpA- trpB+ trpC+ for trpA for trpB for trpC trpR+ trpO- trpA+ trpB+ trpC+ for trpA for trpB for trpC trpR- trpO+ trpA- trpB+ trpC+ / trpR+ trpO+ trpA+ trpB+ trpC- for trpA for trpB for trpC repressible constitutive no expression

Transcript

00:01 Is regarding what we call a equiline trippoprop.

00:07 So you have trip e and trip c gene.

00:10 We know that in wild type strain, what happened is when you, the trip e and c gene are fully induced in no triptophen.

00:25 And then you can see when triptophen is not there, then trip e and c will turn on, let's just say plus.

00:42 But when the triptophen is present, there's no need to produce more.

00:47 So the trip e and c will be repressed, and it's going to be minus.

00:54 So this is what happened in wild type, and you have a bunch of mutine and a question asked you to find out the expression.

00:59 So let's start with the first one.

01:03 So the first one is r plus p minus o plus operator plus attenuate is there, and both e and c r plus.

01:22 So this means that the promoter is not there.

01:25 So from there you can see that since there's no promoter, this is, promoter is essential or is required for transcription to happen.

01:39 So regardless of repressor operator or triptophen, there's no expression.

01:44 No promoter, no expression.

01:52 So regardless of others, this one will be negative.

01:59 So where triptophen is present, no expression.

02:03 When triptophen is absence, no expression.

02:06 Both are negative.

02:09 Second, you have r -negative, positive promoter, positive operator, uptenuate plus both gene are present functional.

02:25 So in this case, the r minus means that the repressor can bind operator.

02:43 The operator is a cis -regulatory region.

02:47 So this means that since the repressor can't bind to the operator, this caused the expression to be, the transcription to be always on.

03:07 And it's always on.

03:08 So this means that if you have triptophen, it's supposed to suppress the gene expression.

03:19 But since the repressor can bind to an operator, no suppression or no repression, it still is going to be plus.

03:28 And when you have no triptophan, obviously, it's plus expressed anyway.

03:33 So it's always on.

03:37 Third one is rn p plus o plus a t t plus trip e trip c plus.

03:57 So rn means that the repressor can't buy triptophen.

04:11 So this means that this will act like triptophen never present, which means that the triptophen is never there.

04:26 That means no inducer.

04:33 So basically, when tripsin is present, it still equals tripsin, trip negative, which means that it will cost it to be plus when actually there's no triptophen and then there's again plus.

04:48 So in both cases, it will cause the two gene to be expressed because even though the triptophen is in the system due to the mutation, the system cannot sense the excess triptophen and it act like a negative triptophen.

05:07 So no inducer is present.

05:10 It always act like negative triptophen, so both are plus.

05:19 4.

05:22 R minus p plus o plus attenuate negative, both gene are plus.

05:34 So since a again, negative, our negative, again, we know that our negative means that the repressive cannot bind to the operator.

05:45 So this means that there's no repression...

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