what are the different stages of gene regulation?explain thr lac-operon modek of transciptional regulation.
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The lac operon of E. coli contains genes involved in lactose metabolism. It's expressed only when lactose is present and glucose is absent.
Two regulators turn the operon "on" and "off" in response to lactose and glucose levels: the lacrepressor and catabolite activator protein (CAP).
The lac repressor acts as a lactose sensor. It normally blocks transcription of the operon, but stops acting as a repressor when lactose is present. The lacrepressor senses lactose indirectly, through its isomer allolactose.
Catabolite activator protein(CAP) acts as a glucose sensor. It activates transcription of the operon, but only when glucose levels are low. CAP senses glucose indirectly, through the "hunger signal" molecule cAMP.
Introduction
Lactose: it's what's for dinner! While that may not sound delicious to us (lactose is the main sugar in milk, and you probably don't want to eat it plain), lactose can be an excellent meal for E. coli bacteria. However, they'll only gobble up lactose when other, better sugars – like glucose – are unavailable.
With that for context, what exactly is the lac operon? The lac operon is anoperon, or group of genes with a single promoter (transcribed as a single mRNA). The genes in the operon encode proteins that allow the bacteria to use lactose as an energy source.
What makes the lacoperon turn on?
E. coli bacteria can break down lactose, but it's not their favorite fuel. If glucose is around, they would much rather use that. Glucose requires fewer steps and less energy to break down than lactose. However, if lactose is the only sugar available, the E. coli will go right ahead and use it as an energy source.
To use lactose, the bacteria must express the lac operon genes, which encode key enzymes for lactose uptake and metabolism. To be as efficient as possible, E. coli should express the lac operon only when two conditions are met:
Lactose is available, and
Glucose is not available
How are levels of lactose and glucose detected, and how how do changes in levels affect lac operon transcription? Two regulatory proteins are involved:
One, the lac repressor, acts as a lactose sensor.
The other, catabolite activator protein (CAP), acts as a glucose sensor.
These proteins bind to the DNA of the lac operon and regulate its transcription based on lactose and glucose levels. Let's take a look at how this works.
Structure of the lacoperon
The lac operon contains three genes: lacZ, lacY, and lacA. These genes are transcribed as a single mRNA, under control of one promoter.
Genes in the lac operon specify proteins that help the cell utilize lactose. lacZ encodes an enzyme that splits lactose into monosaccharides (single-unit sugars) that can be fed into glycolysis. Similarly, lacY encodes a membrane-embedded transporter that helps bring lactose into the cell.
In addition to the three genes, the lacoperon also contains a number of regulatory DNA sequences. These are regions of DNA to which particular regulatory proteins can bind, controlling transcription of the operon.
The promoter is the binding site for RNA polymerase, the enzyme that performs transcription.
The operator is a negative regulatory site bound by the lacrepressor protein. The operator overlaps with the promoter, and when the lac repressor is bound, RNA polymerase cannot bind to the promoter and start transcription.
The CAP binding site is a positive regulatory site that is bound by catabolite activator protein (CAP). When CAP is bound to this site, it promotes transcription by helping RNA polymerase bind to the promoter
Two regulators turn the operon "on" and "off" in response to lactose and glucose levels: the lacrepressor and catabolite activator protein (CAP).
The lac repressor acts as a lactose sensor. It normally blocks transcription of the operon, but stops acting as a repressor when lactose is present. The lacrepressor senses lactose indirectly, through its isomer allolactose.
Catabolite activator protein(CAP) acts as a glucose sensor. It activates transcription of the operon, but only when glucose levels are low. CAP senses glucose indirectly, through the "hunger signal" molecule cAMP.
Introduction
Lactose: it's what's for dinner! While that may not sound delicious to us (lactose is the main sugar in milk, and you probably don't want to eat it plain), lactose can be an excellent meal for E. coli bacteria. However, they'll only gobble up lactose when other, better sugars – like glucose – are unavailable.
With that for context, what exactly is the lac operon? The lac operon is anoperon, or group of genes with a single promoter (transcribed as a single mRNA). The genes in the operon encode proteins that allow the bacteria to use lactose as an energy source.
What makes the lacoperon turn on?
E. coli bacteria can break down lactose, but it's not their favorite fuel. If glucose is around, they would much rather use that. Glucose requires fewer steps and less energy to break down than lactose. However, if lactose is the only sugar available, the E. coli will go right ahead and use it as an energy source.
To use lactose, the bacteria must express the lac operon genes, which encode key enzymes for lactose uptake and metabolism. To be as efficient as possible, E. coli should express the lac operon only when two conditions are met:
Lactose is available, and
Glucose is not available
How are levels of lactose and glucose detected, and how how do changes in levels affect lac operon transcription? Two regulatory proteins are involved:
One, the lac repressor, acts as a lactose sensor.
The other, catabolite activator protein (CAP), acts as a glucose sensor.
These proteins bind to the DNA of the lac operon and regulate its transcription based on lactose and glucose levels. Let's take a look at how this works.
Structure of the lacoperon
The lac operon contains three genes: lacZ, lacY, and lacA. These genes are transcribed as a single mRNA, under control of one promoter.
Genes in the lac operon specify proteins that help the cell utilize lactose. lacZ encodes an enzyme that splits lactose into monosaccharides (single-unit sugars) that can be fed into glycolysis. Similarly, lacY encodes a membrane-embedded transporter that helps bring lactose into the cell.
In addition to the three genes, the lacoperon also contains a number of regulatory DNA sequences. These are regions of DNA to which particular regulatory proteins can bind, controlling transcription of the operon.
The promoter is the binding site for RNA polymerase, the enzyme that performs transcription.
The operator is a negative regulatory site bound by the lacrepressor protein. The operator overlaps with the promoter, and when the lac repressor is bound, RNA polymerase cannot bind to the promoter and start transcription.
The CAP binding site is a positive regulatory site that is bound by catabolite activator protein (CAP). When CAP is bound to this site, it promotes transcription by helping RNA polymerase bind to the promoter
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