DNA. Mechanisms of information storage and processing. Part I
Many people use the term DNA. But the articles that normally describe how it works are almost non-understandable (not for biologists). I have already described in general terms the device of the cell and the very foundations of its energy processes . Now go to the DNA.
DNA stores information. Everyone knows this. But here's how she does it?
Let's start with where it is stored in the cage. Approximately 98% is stored in the kernel. The rest is in the mitochondria and chloroplasts (in these children photosynthesis takes place). DNA is a huge polymer consisting of monomer units. It looks something like this.
What do we see here? First, DNA is a double-stranded molecule. Why is it so important - a little later. Next we see the blue pentagons. These are ribose molecules (such sugar, slightly less glucose). Small circles are the remains of phosphoric acid. Well, there is actually a nitrogen base. There are 5 of them in total, but in the DNA they are mostly found. They are Adenin, Guanin, Timin and Cytosine. That is, there is a ribose with which the nitrogenous base is connected. Together, they form the so-called nucleosides, which bind to each other with the help of phosphoric acid residues. Thus we obtain a long chain consisting of monomers. Now look at the enlarged left chain. You see C and G are connected by three dashed lines, and T and A are two. What does it mean? Yes, DNA consists of two chains, but what keeps them together? There is such a thing as a hydrogen bond. It looks something like this. Oxygen (O) and nitrogen (N) atoms form a partial negative charge, and on hydrogen (H) - a positive one. This leads to the formation of weak bonds.
cool video .
Packing of DNA in eukaryotes
Everything is much more interesting. Our DNA is well packed and hidden inside the nucleus. And it is much more efficiently packed than bacteria. During mitosis (cell division), the size of the 22nd chromosome is 2 μm. If it is untangled and pulled out, it will be already 1.5 cm. That corresponds to a packing ratio of 1?000 times. This is about the maximum degree of packing our DNA. During division, you need to maximally pack the DNA, which would effectively divide it between the daughter cells. In everyday life, the degree of compactification is approximately 500 times. With too packaged DNA, it is difficult to read information.
There are several levels of packaging of eukaryotic DNA
The first is the nucleosome level. 8 proteins-histones form a particle on which DNA is wound. Then another protein fixes it. It looks something like this.
It turns out a kind of beads. The density of packaging due to this increases by 7-10 times. Next, nucleosomes are packed into fibrils. Slightly similar to the saleniod. Here the total degree of packaging can reach 60 times.
The next stage of DNA compactification is associated with the formation of loop-like structures, which are called chromomeres. Fibril is divided into sections of 10 - 80 thousand pairs of nitrogenous bases. In the places of breakdown are the globules of non-histone proteins. DNA-binding proteins recognize the globules of non-histone proteins and bring them closer together. The mouth of the loop forms. The average length of the loop includes approximately 5?000 bases. This structure is called interphase chromoneemia. And it is in it that our DNA is most of the time. The level of packaging here reaches 500-1500 times.
If necessary, the cell can further compact the genetic material. There is a formation of larger loops from the chromomeric fibril. These loops in turn form new loops (loops in loops and this is not knitting). Which ultimately form the chromosome.
In general, the packaging process can be described approximately like this.
As a result, from strands of DNA, we get, in division, super-twisted structures that can be seen under a microscope. We call them chromosomes.
Actually the substance of chromosomes is called chromatin. And the degree of its packaging differs depending on the site of the chromosome. There is euchromatin and heterochromatin. Euchromatin is a rather intertwined region of chromatin, in it the DNA is at the chromomeric level (packing 500 - 1000 times). There is an active reading of information. For example, if the cell is now actively synthesizing protein A, the DNA region that encodes it will be in the state of euchromatin, so that enzymes that "read" DNA can reach it. Heterochromatin also contains that part of the DNA that the cell does not really need now. That is, the DNA is packed as tightly as possible, so as not to get under your feet. Depending on the needs of the cells, some regions of the chromatin can be partially weaved, while others can be weaved. In this way, regulation is also carried out (very rough approximation), because it is impossible to get to the twisted region, and therefore it is not read.
Actually, that's all for now. We discussed how the storage medium is stored. Let's take a short pause and after a couple of days we'll talk about the very coding of information.
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Izi, complicate the boldly
Izi, you can leave it. More articles!
A lot of incomprehensible, more explain, more examples!
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Now I work in the field of sports physiology. I can write something interesting from there (about the prediction of talents, the device of muscles, etc.)
Cool, write to your choice
not interesting, I do not go to the quality :)
Interesting all! Enough to ask, write already
If you write about the applied aspects, it will be great!
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