Lac Operon Model

Control of gene
Kinetics of induction of "Lac Operon"

This was one of the first important experiments undertaken in the founding of the field we now call "Molecular Biology" - the biochemical basis of gene expression and control. Four scientists with the Nobel Prize for this work: Jacob, Monod, Brenner and Cuzin. His work was initially deemed worthy of publication, so he set up his new paper - Journal of Molecular Biology and his article in Lac Operon filled about 80 pages in the first edition!




..... Most of the DNA, the genetic material of the bacterium E. Chromosome usually found as intricate and endless "circular" Measuring about 1.5 millimeters circumference and is packed in a box, which is only 0.01 mm long and 0.003 mm in diameter. .. A small amount of DNA optional "extra-chromosome is in the form of plasmids, which are much smaller, but they are also round.

..... If someone has to stretch the chromosome as a circle without wires, one could imagine some 7000 genes scattered on their length. .. (There are around 1000-when packaged in individual genes, almost all cells of complicated! .. Know the name of this exception?) Here is a picture diagram of chromosome of E. cars, and it will constitute only a few of their genes spread.

..... The list of "history" of random genes, we have chosen for R-genes, and Latin America, both because they represent extremes, and we know much about them. R-genes encode for the realization of R-RNA necessary function, which is always "on" in the cell growth. .. But free trade agreement is a gene that is only "in" when the cell has a lactose sugar in your environment, otherwise the gene is switched "off." .. Thus, the widespread regulatory scheme for the transmission of genetic code from DNA to proteins.

..... Let us first take a look at seven nearly identical R-genes as a group. .. These seven short sections of DNA are responsible for the production of almost 85% of the RNA produced in bacterial cells. .. In fact, this amount of ribosomal RNA (rRNA) makes up to 30% of the water stuff in the box! .. These seven genes are really hot, as some molecular biologists like to say.(rRNA + rProteins - ribosomes> which are working groups in which all proteins are synthesized different.)

..... In the part of a gene called the "organizer", P, can be seen as bowing to RNA polymerase (aka: .. reverse transcriptase) to begin the process of reading and gene conversion (copy) of the Code of DNA sequence in a sequence of RNA in the form of what is called messenger RNA (mRNA). .. While the normal gene would be only a starting point transcriptase, a seven-R gene has three. .. No self-respecting transcriptase can ignore this cheese! .. Therefore, it is a rare moment that there is a line of transcriptases expected to begin deciphering gene NFA. .. This hyperactivity is, of course, it is necessary to provide all RNA molecules that are needed. .. Oh, one more point: .. R-gene is rarely otherwise - this does not lead to the adoption of M-RNA. .. However, codes [especially] for the structural components of RNA that are integrated into the ribosome - Tables, Work, where proteins are made of codes obtained from M-RNA products of other genes (translation). .. Although the rest of the gene is decoded into amino acid transfer (tRNA RNA) to get specific amino acids and help the ribosome / mRNA complex line to be connected properly in the formation of protein.

..... And do not overlook the fact that the group of molecular biologists, who call themselves "ominous" Terminator "because they have an interest in what the end of the gene code, we see that R-genes ends with some kind of" stop "signal to . .. Probably transcriptase reaches the "stop" and de-criticized and fall of the DNA should not continue reading later in the next gen. .. It is then available to come back and start again.

..... Now back to fairly normal gene - one that is necessary for the cells to be fed with energy bags of sugar, called lactose (milk sugar).

The "Lac" gene can be turned on (induced) leading to the production of two instruments of an enzyme - a component of the membrane called lactose permease molecules get go and puts them in a cage where the other tool, an enzyme called beta-galactosidase, lactose cut into two to obtain glucose and galactose. .. Another gene in another part of the codes of the chromosomes of the enzyme galactose / glucose epimerase that converts galactose into glucose, glucose to become fodder for glycolysis.

..... Now let's see how this is achieved through genetic system. .. We must become aware of the case not only the permease and the SS-galactosidase, but also for the inclusion / exclusion of induction and repression. Diagram below the gene, we can see some familiar friends: P see some loci (called "cistrons"), which led to the products and stop. .. But there are a couple of newcomers - independent DNA sequence called the "R" (locus repressor) and another series called "O" (operator of the path). .. If Lac-gene had no R and O, then it will be something of a chilling act R-Gen: .. will be "in" all the time - a little slow, since there is only "S". .. But it would be a waste of time and energy for the cell if not go to lactose are about to chew - and that most of the time, lactose is rare in the Earth's environment.

..... So what does the P and O all this? .. Well, R is the normal size of the sequence of DNA that are transcribed into mRNA, which in turn becomes a protein. .. This particular protein, called the "tyrant". .. Repressor has a tendency to link DNA sequence with a very specific - only and only found in the "O". .. So Caesar wraps around and overlapping or adjacent sequences, one of which is the main area P. .. If P has no exposure to attract the reverse transcriptase gene is not reading arises: .. in fact, make the gene "off".

..... But now, the gene is on roll: it is useless, "off" all the time! .. How you ever something? .. It turns out that small amounts of lactose in themselves are capable of inactivating the repressor protein, which can not compel O. .. debilitating such small amounts can leak into the cell from the surrounding environment. .. Once a gene is de-repressed and permease is inserted into the outer surface of the cell, which increases the flow of 10000 for lactose. .. And it is attacked lactose by beta-galactosidase, and so on. .. After the repression / derepression of the operator or a key sequence of everything downstream from it, operon invented the word to refer to all the neighboring sequence of O to stop.

..... Jacob and Monod shared the Nobel Prize for describing the Lac operon. .. If we use for our purposes, a popular video game conceptual figure as representative of proteins that are normally hard to connect things - one Oh, if it is a rapist or a substrate in the case of an enzyme - we can see that there are two ways of lactose that can eliminate it. .. The easiest way is to turn the lactose repressor binding site (as shown for lactose stuck in the teeth of a creature). .. In Tirana, with a mouth full of lactose, could no longer bind and deactivate Oh, and the gene, which remain ". .. This is called steric inhibition. .. Another way that lactose may inactivating the lactose repressor binds proteins is somewhere else in the second repressor, which prevents the repressor (in this case represented by lactose acts as a dummy to keep the tyrant find O) ... The official name for this is "Allosteric inhibition.

..... How about checking our understanding of what is happening here? .. One of the best ways for scientists to check on these matters be handled by your system - in this case we will think of some mutants. .. Note the obvious results of an experiment in mutants that are damaged one Z-sequence: .. in no case can use this mutant lactose, because there was no chance of ever making SS-galactosidase. .. In the laboratory, let's look at different types of mutants. .. So, in the right mood to see if you can understand what is happening in each of the following mutations: .. R is damaged or corrupted, P is damaged and broken.