BIOL 2030 Lecture Notes - Lecture 42: Trp Operon, Corepressor, Operon

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10 Nov 2018

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The crp-camp complex then binds to a site near the promoter, enhancing the effectiveness of rna polymerase binding and hence transcription: the (tryptophan) trp operon is an example of a repressible system. The presence of tryptophan, the end product of a metabolic pathway, represses synthesis of the enzymes involved in that pathway. Tryptophan acts as a corepressor by binding to an inactive repressor protein and making it active. When the activated repressor binds to the operator, transcription is turned off. Receptors located in plasma membrane include ion channels, protein kinases, and g protein-linked receptors. Receptor changes (from inactive to active form) shape- cascade . Most animal cells can communicate with one another directly through small pores in their plasma membranes called gap junctions (spanned by connexin channels that permit electrical or chemicals signals molecules and ions can pass these pores through).

Related Questions

In the following points, I have summarized Lac operon in Ecoli. I need to check if this is on the right track? and where does 'cleavage of disaccharides' fit into this picture?

Lactose is a disaccharide and the bacteria need specific genes to manage catabolism

1) The lacl promotor gene synthesis the repressor protein which binds to the operator gene stopping the RNA polymerase from coding the lac operon genes

2)But when lactose is present, it needs the specific genes to catabolise lactose

3) So, When allolactose (a derivative of lactose)is present, it binds to the repressor protein, the repressor releases from the operator gene

4) This allows the RNA polymerase can attach to the DNA control region

5) And drive down the operon for transcription and induction of the enzyme lacZ(beta-galactosidase) lacY and lacA which breaks lactose down into glucose and galactose

6) When the lactose is all gone, the repressor returns to the operator in a feedback loop system

Fill in the blank:

promotor, induction, presence, will not, will, operon, repressor, repression, overabundance, operator, control region,

1. If the repressor is bound to the operator, then RNA polymerase______ transcribe the structural genes.

2. The ________ controls whether RNA polymerase can advance along the DNA strand or not.

3. The _______ operates differently depending on whether the operon is inducible or repressible.

4. An _________ controls the expression of functionally related genes and consists of a control region and structural genes.

5. ______ decreases expression of the structural genes. This typically occurs in response to an _____ of a substrate.

6. The _____ contains a promoter and an operator.

7. If the repressor is not bound to the operator, then RNA polymerase _____ transcribe the structural genes.

8. ______ increases expression of the structural genes. This typically occurs in response to the _______ of a substrate.

9. The ______ is the region of DNA where RNA polymerase initially binds.

The following test deals with the regulation of the trp operon of Escherichia coli. Two mutants of this operon are described: in mutant A, the operator region of the operon carries a point mutation so that it is unable to carry out its function; mutant B expresses a trp repressor protein unable to bind tryptophan. Review the principle of the regulation of this operon and then solve the following questions related to the behavior of the mutant cells using the options below.

A: Mutant A B: Mutant B C: Both of them D: Neither of them

a) _____ In the presence of tryptophan these cells behave like wild-type cells. b) _____ In the absence of tryptophan these cells behave like wild-type cells. c) _____ These cells are able to synthesize tryptophan.
d) _____ These cells are able to break down tryptophan.

e) _____ Tryptophan is able to act as an inducer in these cells.
f) _____ Tryptophan is able to act as a corepressor in these cells.
g) _____ The structural genes of the trp operon can be transcribed in these cells.
h) _____ In the presence of tryptophan RNA polymerase binds to the promoter of the trp operon in these cells.
i) _____ In the absence of tryptophan RNA polymerase binds to the promoter of the trp operon in these cells.
j) _____ These cells die if tryptophan is omitted from their medium.
k) _____ These mutants can be ââcuredââ by expressing wild-type trp repressor in them.
l) _____ These mutants can be ââcuredââ by transforming them with a wild-type trp operator.

BIOL 2030 Lecture Notes - Lecture 42: Trp Operon, Corepressor, Operon

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