What is gene expression? What is her role? How does gene expression work? What prospects does he open before us? How is gene expression regulated in eukaryotes and prokaryotes? Here is a short list of issues that will be addressed in this article.
general information
Gene expression is the name for the process of transferring
genetic information from DNA through RNA to proteins and polypeptides. Let us make a digression for understanding. What are genes? These are linear polymers of DNA that are connected in a long chain. Using
chromatin protein, they form chromosomes. If we talk about man, then we have forty-six of them. They contain approximately 50,000-10,000 genes and 3.1 billion pairs of nucleotides. How are they oriented here? The length of the sections with which work is being carried out is indicated in thousands and millions of nucleotides. One chromosome contains about 2000-5000 genes. In a slightly 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, the ratio will be violated. It can also be affected by the sex of the body, the material of which is being worked on.
About genes
They have the most diverse length. For example, globin is 1,500 nucleotides. And dystrophin - as much as 2 million! Their regulatory cis elements can be removed from the gene at a considerable distance. So, at globin, they are at a distance of 50 and 30 thousand nucleotides in the 5'- and 3'-direction, respectively. The presence of such an organization greatly complicates our determination of the boundaries between them. Genes also contain a significant number of highly repetitive sequences, the functional responsibilities of which are not yet clear to us.
To understand their structure, we can imagine that 46 chromosomes are separate volumes in which information is located. They are grouped in 23 pairs. One of the two elements is inherited from the parent. The “text” that is in the “volumes” has been repeatedly “re-read” by thousands of generations, which has brought many errors and changes (called mutations) into it. And all of them are inherited by posterity. Now there is enough theoretical information to begin to understand what gene expression is. 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 cleavage of lactose. It was formulated by Jacques Monot and Francois Jacob. This theory explains the mechanism of control over protein synthesis in prokaryotes. An important role is also given to transcription. The theory says that protein genes that are functionally closely related in metabolic processes are often grouped together. They create structural units called operons. Their importance is 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.
Protein Synthesis Induction
Let's imagine that we have a cell that uses carbon glucose as its source of growth. If it is exchanged 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: a cell can work with 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 of a theory, but now let's talk about how genes are actually expressed. This is very exciting.
Chromatin organization
The material in this paragraph is a model of a differentiated cell of a multicellular organism. In the nuclei, chromatin is arranged in such a way that only a small part of the genome is accessible for transcription (about 1%). But, despite this, due to the variety of cells and the complexity of the processes going on in them, we can influence them. At the moment, such an effect on chromatin organization is accessible to humans:
- Change the number of structural genes.
- Effectively transcribe different sections of code.
- Rearrange genes on chromosomes.
- Modify and synthesize polypeptide chains.
But effective expression of the target gene is achieved as a result of strict adherence to technology. It doesn’t matter what the work is done on, even if the experiment is on a small virus. The main thing is to adhere to a prepared intervention plan.
Change the number of genes
How can this be implemented? Imagine that we are interested in the effect on gene expression. As a prototype, we took the material of eukaryote. It has high ductility, so we can make such changes:
- Increase the number of genes. Used in cases where it is necessary for the body to increase the synthesis of a particular product. In this amplified state are many useful elements of the human genome (for example, rRNA, tRNA, histones, and so on). Such sites can have a tandem arrangement within the chromosome and even go beyond their scope in an amount of from 100 thousand to 1 million nucleotide pairs. Let's look at a practical application. Of interest to us is the metallothionein gene. Its protein product can bind heavy metals like zinc, cadmium, mercury and copper and, accordingly, protect the body from poisoning by them. Its activation can be useful to people who work in unsafe conditions. If a person has an increased concentration of the previously mentioned heavy metals, then the activation of the gene occurs gradually automatically.
- Reduce the number of genes. This is a rather rarely used method of regulation. But here you can give examples. One of the most famous is red blood cells. When they mature, the core is destroyed and the carrier loses its genome. Similar in the process of maturation pass and lymphocytes, as well as plasma cells of various clones that synthesize secreted forms of immunoglobulins.
Gene remodeling
Important is the ability to move and combine material in which it will be capable of transcription and replication. This process is called genetic recombination. With what mechanisms is it possible? Let's look at the answer to this question using antibodies as an example. They are created by B-lymphocytes that belong to a specific clone. And if an antigen, on which there is an antibody with a complementary active center, enters the body, they will adhere, followed by cell proliferation. Why does the human body have the opportunity to create such a variety of proteins? This possibility is provided by recombination and
somatic mutations. But this may also be a consequence of artificial changes in the structure of DNA.
RNA change
Gene expression is a process in which ribonucleic acid plays a significant role . 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 different tissues of mRNA, substitutions may appear, insertions, or pairs will simply fall out. Apoprotein B, which is created in the cells of the small intestine and liver, can be given as an example from the side of nature. What is the difference in editing? The intestinal version has 2152 amino acids. Whereas the liver variant boasts 4563 residues! And despite this difference, we have exactly apoprotein B.
Change in mRNA stability
We have almost come to the point where we can deal with proteins and polypeptides. But let's look at this before, how the stability of mRNA can be fixed. To do this, initially it must leave the nucleus and exit the cytoplasm. This is done thanks to the available pores. A large amount of mRNA will be cleaved by nucleases. Those who avoid this fate will organize complexes with proteins. The lifetime of eukaryotic mRNA varies in a wide range (up to several days). If the mRNA is stabilized, then at a fixed speed 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 with greater efficiency. Using
molecular biology methods, you can encode the final product, which will have a significant lifespan. So, for example, it is possible to create a β-globin that functions for about ten hours (for him this is a lot).
Process speed
So the whole system of gene expression has been considered. Now it remains only to supplement the existing knowledge with information about how quickly the processes occur, as well as how long the proteins live. Let's just say that we 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 protein product. Although its change to achieve this goal was still used. An example is the synthesis of a protein product in reticulocytes. Hematopoietic cells at the level of differentiation lack a nucleus (and, therefore, DNA). Levels of regulation of gene expression are generally constructed depending on the ability of a compound to actively influence ongoing processes.
Duration of existence
When a protein is synthesized, the time during which it will live depends on proteases. It’s not possible to give exact dates here, since the range in this case is from several hours to a couple of years. The rate of protein breakdown varies widely depending on the cell in which it is located. Enzymes that can catalyze processes are usually quickly consumed. Because of this, they are also created by the body in large quantities. Also, the physiological state of the body can affect the life of the protein. Also, if a defective product was created, then it will be quickly eliminated by the protective system. Thus, we can confidently say that the only thing we can judge about is the standard life time obtained in the laboratory.
Conclusion
This direction is very promising. For example, the expression of foreign genes can help cure hereditary diseases, as well as eliminate negative mutations. Despite the extensive knowledge on this topic, we can confidently say that humanity is still only at the very beginning of the path. Genetic engineering has recently learned how to isolate the necessary nucleotide sites. 20 years ago, one of the biggest events of this science happened - Dolly the sheep was created. Now research is underway with human embryos. It is safe to say that we are already on the verge of a future where there are no diseases and physiological suffering. But before we get there, it will be necessary to work very well for the benefit of prosperity.