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tanarillToday is the forty-sixth day of the Omer, which is six weeks and four days into the Omer.
Operons are a thing which I have spoken of before, and even promised to explain, but have not actually explained. I shall do so now. First, you must understand what a promoter is; go ahead and review that, I will wait.
Okay, so. Pretend you are a bacteria. Like just about everything, everywhere, your favorite thing to eat is glucose sugar. If you are a lab bacteria, this is what you are fed practically all of the time. But if you are in the wild, glucose isn't available all the time. Sometimes, you have to be able to digest other things, like lactose. This is not a problem, exactly - you have the gene to make a lactose-digesting protein - but it is a big protein, and expensive to make. So really you don't want to be making this protein all of the time, only at times when there is no glucose but is lactose.
To do this, you make an operon. An operon is a protein which binds very tightly and very specifically to a certain DNA sequence, but only if there is no chemical in the cell. The lacZ protein, for example, binds DNA only if there is no lactose; if there is lactose, it falls off the DNA.
Buttanarill, you might ask, how does this help? It helps because you put the specific DNA sequence very close to a gene promoter - so close that the large operon protein physically blocks binding. The gene cannot be transcribed until the operon falls off, and the operon will not fall off unless there is a certain "key" chemical. In the lactose system, the promoter that is blocked is for lactose-digesting genes. If there is no lactose, those proteins are not made. If there is lactose, the lacZ operon will fall off, gene->protein, and the cell can now digest the food. Once the lactose in the cell is all digested, the operons go find their DNA and block promoters again. It is an elegant little system that bacteria evolved to help them conserve protein-making efforts for when they are really needed.
Of course, we humans take advantage of this system by putting operon-binding DNA onto our plasmids. Then we grow the bacteria in culture. The operons bind and prevent protein expression. When we are ready, we add a bit of lactose* to the solution. All of the lactose-activated genes turn on - including the one that isn't a gene that really helps deal with lactose at all, but we told the cells to treat as if it were. In this way, we can turn the proteins on or off, just by adding bits of chemical.
Are we awesome or what? :D
*Not actually lactose. We use a chemical that is similar enough to make the lacZ operon fall off, but impossible for the cells to digest. This is so you don't have to keep adding lactose for the gene to stay "on;" otherwise, it would digest the lactose and turn the gene "off" again.
Operons are a thing which I have spoken of before, and even promised to explain, but have not actually explained. I shall do so now. First, you must understand what a promoter is; go ahead and review that, I will wait.
Okay, so. Pretend you are a bacteria. Like just about everything, everywhere, your favorite thing to eat is glucose sugar. If you are a lab bacteria, this is what you are fed practically all of the time. But if you are in the wild, glucose isn't available all the time. Sometimes, you have to be able to digest other things, like lactose. This is not a problem, exactly - you have the gene to make a lactose-digesting protein - but it is a big protein, and expensive to make. So really you don't want to be making this protein all of the time, only at times when there is no glucose but is lactose.
To do this, you make an operon. An operon is a protein which binds very tightly and very specifically to a certain DNA sequence, but only if there is no chemical in the cell. The lacZ protein, for example, binds DNA only if there is no lactose; if there is lactose, it falls off the DNA.
But
tanarill, you might ask, how does this help? It helps because you put the specific DNA sequence very close to a gene promoter - so close that the large operon protein physically blocks binding. The gene cannot be transcribed until the operon falls off, and the operon will not fall off unless there is a certain "key" chemical. In the lactose system, the promoter that is blocked is for lactose-digesting genes. If there is no lactose, those proteins are not made. If there is lactose, the lacZ operon will fall off, gene->protein, and the cell can now digest the food. Once the lactose in the cell is all digested, the operons go find their DNA and block promoters again. It is an elegant little system that bacteria evolved to help them conserve protein-making efforts for when they are really needed.Of course, we humans take advantage of this system by putting operon-binding DNA onto our plasmids. Then we grow the bacteria in culture. The operons bind and prevent protein expression. When we are ready, we add a bit of lactose* to the solution. All of the lactose-activated genes turn on - including the one that isn't a gene that really helps deal with lactose at all, but we told the cells to treat as if it were. In this way, we can turn the proteins on or off, just by adding bits of chemical.
Are we awesome or what? :D
*Not actually lactose. We use a chemical that is similar enough to make the lacZ operon fall off, but impossible for the cells to digest. This is so you don't have to keep adding lactose for the gene to stay "on;" otherwise, it would digest the lactose and turn the gene "off" again.
no subject
Date: 2012-05-23 09:02 pm (UTC)