Protein is one of the most important components of our body. They perform an enormous number of functions. They are probably the main molecules in our body, and they are the basis of life.
What proteins are made of
Protein is a constructor with 20 types of blocks – amino acids. Each amino acid has its own unique set of properties.
You can compare each amino acid to a simple tool like a hammer, a nail, a vise. A hammer, for example, can be used to straighten out some battered iron or to break a nut. A nail can be used to scratch information on glass about the size and thickness of that glass. In a vise, you can press two pieces of wood smeared with glue so that you don’t have to press them by hand and wait for the glue to dry.
That is, a hammer, nails, and vise are all useful tools in their own right. But if you do not use them separately, but combine them, then the range of possibilities expands significantly. By combining a hammer and a nail, you can fasten wood even tighter than with glue. And if you also tightly clamp these woods, it will be much more convenient to hammer nails into them.
Similarly, by combining different amino acids, it is possible to obtain complex biological mechanisms. The most complex proteins are enzymes (or as they are called in the English-language literature, enzymes).
How enzymes work
All enzymes consist of two parts – the auxiliary part and the active center. The auxiliary part is the framework of the enzyme. It gives the enzyme its shape and protects it from molecules floating around it. Without the framework, these molecules would mess with the enzyme, destroying it. It’s like the case of a microscope. Technically, in order to see bacteria, all you have to do is hold a few lenses at a certain distance from each other. But this is uncomfortable, the lenses will fall off and your hands will shake, throwing off the focus. That’s why these lenses are placed in a sturdy plastic case with a handy handle, a screw to adjust the lens, a stand on which you can put the bacteria colony glass, and a handy foot. You could do without all these additions, but they make life much easier.
The auxiliary part also forms a “pocket” into which molecules of the necessary substances can penetrate, and in which the second part of the enzyme, the active center, is located.
It in turn consists of two parts, the contact site and the catalytic center. The contact site is the signaling system, which checks whether the right substance has really got to them. It’s like we’re checking to see if we’re going to hit a nail with a hammer now instead of our hand. And if the substance is right, the amino acids of the contact site lock it into position. In the catalytic center, what this enzyme was created to do happens directly. That is, the transformation of some substances into other substances.
How enzymes work
To make it clearer how enzymes work, let’s look at the active center of the enzyme aconitase.
This enzyme converts citrate (i.e. citric acid) into isocitrate (i.e. citric acid, which has a slightly altered structure).
The enzyme first strips the OH and H groups from the citrate. The result is the intermediate cis-aconitrate (which is why the enzyme is called aconitase). The enzyme then attaches the OH and H groups back together, just reverses them. Where citrate had an OH group, it now has an H group, and vice versa.
Two amino acids, histidine and serine, play a major role in this process. Histidine is an ideal tool for stripping the OH group from the citrate, while serine is good at stripping the H group.
After histidine and serine have taken away the OH and H groups from the citrate, other amino acids-tools turn the citrate molecule (or rather, a new substance, cis-aconitrate, because after losing these groups it ceased to be citrate). They turn the citrate molecule in such a way that in front of the histidine there is not the original part of the molecule, but the one where it is necessary to give the OH group. In the same way, the serine is opposite the correct site. Serine and histidine give the OH and H groups back to the citrate. That is, the citrate has the OH and H groups reversed. Because of this, the isocitrate molecule has a slight change in properties. It leaves this enzyme and then goes to another enzyme that turns isocitrate into α-ketoglutarate, using different tools. And so on, depending on which substance the body needs at the moment.
And the enzyme aconitase, after turning citrate into isocitrate, takes over the next citrate molecule. And so it converts about 100 molecules per second.
There are thousands of different enzymes in the body for all sorts of things. They help to make from a small set of substances the ones that are needed and the body doesn’t have them.
The “blueprints” of these enzymes are in DNA. It is in the DNA that the information is stored in coded form, exactly which amino acids should make up the mechanism, and in what order they should follow. Special proteins read these blueprints from the DNA and transfer them to the machinery factory, an organelle called the ribosome. There, these enzymes are assembled from amino acids and then sent to the next organelle, the Endoplasmic Network. In it, some enzymes are upgraded, if it is laid down in the DNA instructions – different molecules are added to the enzyme. For example, molecules of sugars, molecules of vitamins, metal atoms. Such “additives” are called coenzymes. And they give the enzyme additional properties.
Each protein usually has one strictly specialized function. But there are so-called “moonlight squirrels” (moonlight, similar to people working two jobs). They can perform quite different functions. For example, the whites of the lens of the eye are crystalline. In the lens they are responsible for refracting light, but in other tissues the same protein performs completely different functions – for example, is involved in the transformation of alcohols into aldehydes.
What other squirrels are there
Amino acids can be used not only to build mechanisms that transform certain chemical molecules into other molecules. It is possible, for example, to bind a rigid string of amino acids from chains of amino acids. Such a protein is called collagen. Ligaments and tendons, for example, are made of it.
Cell receptors are also made of proteins. Receptors are located in the thickness of the cell membrane. When a hormone or a neurotransmitter or a drug molecule is attached to such a receptor, it sends a signal to the cell and this triggers some mechanism. For example, the production of the substance that the body needs at that moment begins to increase.
Proteins also play an important role in immunity. These proteins are called Antibodies or Immunoglobulins. And it is thanks to them that harmful bacteria and viruses entering the body are recognized and destroyed.
Proteins also make up the cellular skeleton of each cell, or the cytoskeleton. And these are not all the functions of proteins in our bodies.
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