Expression of genes is what? Definition of concept

What is gene expression? What is its role? How does the mechanism of gene expression work? What are the prospects for it? How does the regulation of gene expression in eukaryotes and prokaryotes occur? Here is a short list of issues that will be considered in the framework of this article.

general information

Gene expression is the name of the process of transferring genetic information from DNA through RNA to proteins and polypeptides. Let's make a little digression for understanding. What are genes? These are linear DNA polymers that are connected in a long chain. With the help of the chromatin protein they form chromosomes. If we talk about a man, then we have forty-six of them. They contain about 50 000-10 000 genes and 3.1 billion pairs of nucleotides. How are they guided here? The length of the sites with which work is performed is indicated in thousands and millions of nucleotides. One chromosome contains about 2000-5000 genes. In a somewhat different expression - about 130 million pairs of nucleotides. But this is only a very rough estimate, which is more or less true for significant sequences. If you work in short sections, then the ratio will be violated. This can also be affected by the sex of the body, over the material of which the work is being done.

About genes

They have the most varied length. For example, globin is 1500 nucleotides. A dystrophin - already as much as 2 million! Their regulatory cis-elements can be removed from the gene for a considerable distance. So, in the globin they are at a distance of 50 and 30 thousand nucleotides in the 5 'and 3' direction, respectively. The existence of such an organization makes it very difficult for us to determine the boundaries between them. Also, genes contain a significant number of highly repetitive sequences, the functional duties of which are not yet clear to us.

To understand their structure, one can imagine that 46 chromosomes are separate volumes in which information is located. They are grouped into 23 pairs. One of the two elements is inherited from the parent. "Text", which is in the "volumes", was repeatedly "re-read" by thousands of generations, which introduced many mistakes and changes (called mutations) into it. And they are all inherited by posterity. Now there is enough theoretical information to begin to understand what is the expression of genes. This is the main topic of this article.

Operon Theory

It is based on genetic studies of the induction of β-galactosidase, which was involved in the hydrolytic degradation of lactose. It was formulated by Jacques Monod and Francois Jacob. This theory explains the mechanism of control over the synthesis of proteins in prokaryotes. Transcription is also important. The theory says that genes of proteins, which are functionally closely related in metabolic processes, are often grouped together. They create structural units called operons. Their importance lies in the fact that all the genes that enter it are expressed in concert. In other words, they can all be transcribed, or none of them can be "read". In such cases, the operon is considered active or passive. The level of gene expression can change only if there is a set of individual elements.

Induction of protein synthesis

Let's imagine that we have a cell that uses carbon glucose as its source of growth. If it is changed for lactose disaccharide, then in a few minutes it will be possible to fix that it has adapted to the conditions that have been changed. There is such an explanation: the cell can work both sources of growth, but one of them is more suitable. Therefore, there is a "sight" for a more easily processed chemical compound. But if it disappears and lactose appears to replace it, then the responsible RNA polymerase is activated and begins to exert its influence on the production of the necessary protein. This is more theory, and now let's talk about how genes actually are expressed. This is very exciting.

Organization of chromatin

The material from this paragraph is a model of a differentiated cell of a multicellular organism. In the nuclei, chromatin is laid out in such a way that only a small part of the genome is available for transcription (about 1%). But, despite this, due to the variety of cells and the complexity of the processes going in them, we can influence them. At the moment, for an individual, such an influence on the organization of chromatin is available:

1. Change the number of structural genes.
2. Effectively transcribe different parts of the code.
3. Rebuild genes in chromosomes.
4. Make modifications and synthesize polypeptide chains.

But effective expression of the target gene is achieved as a result of strict compliance with the technology. It does not matter what the work is, even if the experiment is going on a small virus. The main thing is to follow the plan of intervention.

We change the number of genes

How can this be realized? Imagine that we are interested in the influence on the expression of genes. As a prototype, we took the eukaryote material. It has a high plasticity, so we can make the following changes:

1. Increase the number of genes. Used in cases where it is necessary that the body increases the synthesis of a certain product. In such an amplified state, there are many useful elements of the human genome (for example, rRNA, tRNA, histones, etc.). Such sites can have a tandem arrangement within the chromosome and even go beyond them in an amount from 100 thousand to 1 million pairs of nucleotides. Let's look at practical application. The metallothionein gene is of interest to us. Its protein product can bind heavy metals like zinc, cadmium, mercury and copper and, accordingly, protect the body from poisoning them. Its activation can be useful to people who work in unsafe conditions. If a person has an increased concentration of previously mentioned heavy metals, then the activation of the gene occurs gradually automatically.
2. Reduce the number of genes. This is a relatively infrequent method of regulation. But here you can give examples. One of the most famous is the red blood cells. When they mature, the nucleus collapses and the carrier loses its genome. Similar in the course of maturation pass both lymphocytes, and also plasma cells of various clones that synthesize secreted forms of immunoglobulins.

Gene rearrangement

Important is the ability to move and combine material, in which it will be capable of transcription and replication. This process was called genetic recombination. By what mechanisms is it possible? Let's consider the answer to this question with the example of antibodies. They are created by B-lymphocytes that belong to some particular clone. And in case of getting into the body of an antigen, on which there is an antibody with a complementary active center, their attachment will take place with the subsequent proliferation of the cell. Why does the human body have the ability to create such a variety of proteins? This possibility is provided by recombination and somatic mutations. But this may be a consequence of artificial changes in the structure of DNA.

Change in RNA

Expression of genes is a process in which a significant role is played by ribonucleic acid. If we consider mRNA, it should be noted that after transcription, the primary structure may change. The sequence of nucleotides in the genes is the same. But in the different tissues of mRNA, substitutions, insertions, or simply couples may appear. As an example from nature, apoprotein B, produced in cells of the small intestine and liver, can be cited. What is the difference in editing? The version created by the intestine has 2152 amino acids. Whereas the liver variant boasts 4563 residues! And despite this difference, we have apoprotein B.

The stability of the mRNA

We have almost reached the point where we could deal with proteins and polypeptides. But let's look at this before, how stability of mRNA can be fixed. For this, initially, it must leave the nucleus and exit the cytoplasm. This is due to the existing pores. A large number of mRNAs will be cleaved by nuclease. Those who avoid this fate, organize complexes with proteins. The lifetime of eukaryotic mRNA fluctuates over a wide range (up to several days). If mRNA is stabilized, then at a fixed rate it will be possible to observe that the amount of the newly formed protein product increases. The level of gene expression will not change, but, more importantly, the body will act more efficiently. With the help of molecular biology methods, the end product can be encoded, which will have a significant lifespan. So, for example, it is possible to create β-globin, which functions for about ten hours (for him it is very much).

Process speed

That's considered in general the system of gene expression. Now it remains only to supplement the existing knowledge with information on how quickly processes occur, and also how long the proteins live. Let's just say we'll control the expression of genes. It should be noted that the effect on speed is not considered the main way to regulate the diversity and quantity of the protein product. Although its change to achieve this goal is still used. An example is the synthesis of a protein product in reticulocytes. Hemopoietic cells at the level of differentiation are devoid of nucleus (and hence DNA). Levels of regulation of gene expression are generally based on the ability of some compound to actively influence the processes that are being performed.

Duration of existence

When the protein is synthesized, the time during which it will live depends on the proteases. Here you can not accurately name the time, because the range in this case is from a few hours to a couple of years. The rate of protein breakdown varies widely, depending on which cell it is in. Enzymes that can catalyze processes tend to be quickly "used". Because of this, they are also created by the body in large quantities. Also, the physiological state of the organism can influence the life of the protein. Also, if a defective product was created, it will be quickly eliminated by a protective system. Thus, we can confidently say that the only thing we can judge is the standard lifetime obtained in the laboratory.

Conclusion

This direction is very promising. For example, the expression of foreign genes can help cure hereditary diseases, and also eliminate negative mutations. Despite the availability of extensive knowledge on this topic, we can confidently say that humanity is just at the very beginning of the road. Genetic engineering has only recently learned to isolate the necessary nucleotide sites. 20 years ago, one of the biggest events of this science occurred - Dolly the sheep was created. Now we are conducting research with human embryos. We can say with confidence that we are already on the threshold of the future, where there are no diseases and physiological suffering. But before we get there, it will be necessary to work very well for prosperity.