The implementation of the genetic code of the DNA molecule is. Genetic code: description, characteristics, research history

Leading scientific journal Nature reported the discovery of a second genetic code - a kind of "code within a code" that was recently cracked by molecular biologists and computer programmers. Moreover, in order to identify it, they did not use evolutionary theory, but information technology.

The new code is called the Splicing Code. It's inside the DNA. This code controls the underlying genetic code in a very complex yet predictable way. The splicing code controls how and when the assembly of genes and regulatory elements occurs. Revealing this code within the code helps to shed light on some of the long-standing mysteries of genetics that surfaced after the Complete Human Genome Sequence Deciphering Project. One such mystery was why there are only 20,000 genes in such a complex organism like a human? (Scientists expected to find a lot more.) Why do genes break into segments (exons) that are separated by non-coding elements (introns) and then, after transcription, are fused together (ie, spliced)? And why do genes turn on in some cells and tissues, and not turn on in others? For two decades, molecular biologists have been trying to figure out the mechanisms of genetic regulation. This article points out a very important point in understanding what's really going on. It doesn't answer all the questions, but it does demonstrate that the inner code exists. This code is a system for transmitting information that can be deciphered so clearly that scientists could predict how the genome might behave in certain situations and with inexplicable accuracy.

Imagine hearing an orchestra in the next room. You open the door, look inside and see three or four musicians in the room playing musical instruments. This is what the human genome looks like, according to Brandon Frey, who helped break the code. He says: “We were only able to find 20,000 genes, but we knew that they form a huge amount of protein products and regulatory elements. How? One of the methods is called alternative splicing "... Different exons (parts of genes) can be assembled in different ways. "For example, three genes for the neurexin protein can create over 3,000 genetic messages that help control the brain's wiring system."Frey says. The article also states that scientists know that 95% of our genes have alternative splicing, and in most cases, in different types of cells and tissues, transcripts (RNA molecules formed as a result of transcription) are expressed differently. There must be something that governs how these thousands of combinations are assembled and expressed. This is the purpose of the Splicing Code.

Readers who want a quick overview of the discovery can read the article at Science Dailyentitled Researchers Cracking 'Splicing Code' Reveal Secret Underlying Biological Complexity... The article says: "Scientists at the University of Toronto have a fundamentally new understanding of how living cells use a limited number of genes to form incredibly complex organs like the brain."... Nature itself begins with Heidi Ledford's article "Code Within Code." This was followed by an article by Tejedor and Valkarcel entitled “Gene Regulation: Breaking the Second Genetic Code. Finally, the pivotal article was "Deciphering the Splicing Code" by a group of researchers from the University of Toronto, led by Benjamin D. Blencoe and Brandon D. Frey.

This article is a victory for information science, which reminds us of the codebreakers from the Second World War. Their methods included algebra, geometry, probability theory, vector calculus, information theory, program code optimization, and other advanced techniques. What they didn't need was evolutionary theorywhich has never been mentioned in scientific articles. Reading this article, you can see how much tension the authors of this overture are under:

“We describe a 'splicing code' scheme that uses combinations of hundreds of RNA properties to predict tissue-induced changes in alternative splicing of thousands of exons. The code establishes new classes of splicing patterns, recognizes different regulatory programs in different tissues, and establishes regulatory sequences controlled by mutations. We have uncovered common regulatory strategies including: the use of unexpectedly large aggregates of properties; identifying low levels of exon inclusion, which are attenuated by the properties of specific tissues; manifestation of properties in introns is deeper than previously thought; and modulating the splice variant levels with the structural characteristics of the transcript. The code helped to establish a class of exons, the inclusion of which mutes expression in adult tissues, activating mRNA degradation, and the exclusion of which promotes expression during embryogenesis. The code facilitates the disclosure and detailed description of genome-wide regulated alternative splicing events. ”

The team that cracked the code included specialists from the Department of Electronic and Computer Engineering, as well as from the Department of Molecular Genetics. (Frey himself works in a division of Microsoft Corporation, Microsoft Research) Like decryptors of the past, Frey and Barash developed "A new method of biological analysis carried out by a computer that detects 'code words' hidden within the genome"... Using the massive amount of data generated by molecular geneticists, a team of researchers “reverse engineered” the splicing code until they could predict how he would act... Once the researchers got it right, they tested this code for mutations and saw how exons were inserted or removed. They found that the code can even induce tissue-specific changes or act differently depending on whether it is an adult mouse or an embryo. One gene, Xpo4, is associated with cancer; The researchers noted: “These data support the conclusion that the expression of the Xpo4 gene must be tightly controlled to avoid possible deleterious consequences, including oncogenesis (cancer), since it is active during embryogenesis, but its amount is reduced in adult tissues. It turns out that they were absolutely surprised at the level of control they saw. Whether intentionally or not, Frey used the language of intelligent design as his clue, not random variability and selection. He noted: "Understanding a complex biological system is like understanding a complex electronic circuit."

Heidi Ledford said that the apparent simplicity of the Watson-Crick genetic code, with its four bases, triplet codons, 20 amino acids, and 64 DNA "symbols" hides a whole world of complexity... Enclosed within this simpler code, the splicing code is much more complex.

But between DNA and proteins is RNA - a separate world of complexity. RNA is a transformer that sometimes carries genetic messages and sometimes manipulates them, using many structures that can influence its function. In an article published in the same issue, a research team led by Benjamin D. Blencoe and Brandon D. Frey at the University of Toronto in Ontario, Canada, reports on attempts to unravel a second genetic code that can predict how messenger RNA segments are transcribed from a specific gene, can be mixed and combined to form a variety of products in different tissues. This process is known as alternative splicing. This time, there is no simple table - instead, algorithms that combine more than 200 different DNA properties with RNA structure determinations.

The work of these researchers indicates the rapid progress that computational methods have made in RNA modeling. In addition to understanding alternative splicing, computer science helps scientists predict RNA structures and identify small regulatory RNA fragments that do not encode proteins. "It's a great time"says Christopher Berg, a computer biologist at the Massachusetts Institute of Technology in Cambridge. "Great success awaits us in the future".

Computer science, computer biology, algorithms and codes - these concepts were not part of the Darwinian vocabulary when he was developing his theory. Mendel had a very simplified model of how traits are distributed during inheritance. In addition, the idea that traits are encoded was not introduced until 1953. We see that the original genetic code is regulated by an even more complex code included in it. These are revolutionary ideas... In addition, there are all the signs that this level of control is not the last... Ledford reminds us that, for example, RNA and proteins have a three-dimensional structure. The functions of molecules can change as their shape changes. There must be something that controls folding so that the three-dimensional structure does what the function requires. In addition, access to genes appears to be controlled other code, histone code... This code is encoded by molecular markers or “tails” on histone proteins that serve as centers for DNA twisting and supercoiling. In describing our time, Ledford speaks of "A constant renaissance in RNA informatics".

Tejedor and Valkarsel agree that there is complexity behind simplicity. "In theory, everything looks very simple: DNA makes RNA, which then makes protein.", - they begin their article. "But in reality, everything is much more complicated."... In the 1950s, we learned that all living organisms, from bacteria to humans, have a basic genetic code. But soon we realized that complex organisms (eukaryotes) have some unnatural and difficult to understand property: their genomes have peculiar regions, introns that must be removed so that exons can join together. Why? The fog clears today: "The main advantage of this mechanism is that it allows different cells to choose alternative ways of splicing the messenger RNA (pre-mRNA) precursor, and thus one gene generates different messages." - they explain, - "And then different mRNAs can encode different proteins with different functions"... You get more information from less code, provided that there is this other code inside the code that knows how to do it.

What makes cracking the splicing code so difficult is that the factors that control exon assembly are set by many other factors: sequences close to exon boundaries, intron sequences, and regulatory factors that either help or inhibit the splicing mechanism. In addition, "The effects of a particular sequence or factor may vary depending on its location relative to the intron-exon boundaries or other regulatory motives", - Tejedor and Valkarsel explain. "Therefore, the most difficult task in predicting tissue-specific splicing is calculating the algebra of the myriad of motifs and the relationship between the regulatory factors that recognize them.".

To solve this problem, the team of researchers entered into a computer a huge amount of data about the RNA sequences and the conditions in which they were formed. "Then the computer was given the task to determine the combination of properties that would best explain the experimentally established tissue-specific exon selection."... In other words, the researchers reverse engineered the code. Like World War II decoders, once scientists know the algorithm, they can make predictions: "He correctly and accurately identified alternative exons and predicted their differential regulation between pairs of tissue types." And just like any good scientific theory, the discovery provided new insights: "This allowed us to re-explain previously established regulatory motives and pointed to previously unknown properties of known regulators, as well as unexpected functional connections between them.", - noted the researchers. "For example, the code implies that exon insertion leading to processed proteins is a common mechanism for controlling gene expression during the transition from embryonic tissue to adult tissue.".

Tejedor and Valkarsel consider publishing their article an important first step: "The work ... is best seen as the discovery of the first fragment of the much larger Rosetta Stone needed to decipher alternative messages from our genome." According to these scientists, future research will undoubtedly improve their knowledge of this new code. At the end of their article, they mention evolution in passing, and they do it in a very unusual way. They say, “This does not mean that evolution created these codes. This means that progress will require an understanding of how codes interact. Another surprise was that the degree of conservation observed today raises the question of the possible existence of "species-specific codes".

The code probably works in every single cell and, therefore, should probably be responsible for more than 200 types of mammalian animal cells. It also has to deal with a huge variety of alternative splicing schemes, not to mention simple decisions to include or skip a single exon. The limited evolutionary retention of regulation of alternative splicing (which is estimated to be about 20% between humans and mice) raises the question of the existence of species-specific codes. Moreover, the link between DNA processing and gene transcription influences alternative splicing, and recent data indicate DNA packaging by histone proteins and covalent histone modifications (called epigenetic code) in the regulation of splicing. Therefore, future methods will have to establish the exact interaction between the histone code and the splicing code. The same applies to the still little understood influence of complex RNA structures on alternative splicing.

Codes, codes and again codes. The fact that scientists say virtually nothing about Darwinism in these articles indicates that evolutionary theorists - adherents of old ideas and traditions - have a lot to ponder after reading these articles. Those who are enthusiastic about the biology of codes will be on the front lines. They have a great opportunity to take advantage of a fascinating web application that decryptors have created to stimulate further research. It can be found on the University of Toronto website titled "Alternative Splicing Prediction Website". Visitors will look in vain for references to evolution here, despite the old axiom that nothing in biology makes sense without it. A new version of this expression from 2010 might sound like this: "Nothing in biology makes sense if not viewed in the light of computer science." .

References and notes

We're glad we were able to tell you about this story on the day it was published. This is possibly one of the most significant scientific articles of the year. (Of course, every big discovery made by other groups of scientists, like the discovery of Watson and Crick, is significant.) The only thing we can say to this: "Wow!" This discovery is a remarkable confirmation of the Design by Design and a huge challenge to the Darwinian empire. It is interesting how evolutionists will try to correct their simplistic history of random mutation and natural selection, which was invented back in the 19th century, in light of this new data.

Do you understand what Tejedor and Valkarsel are talking about? Views can have their own code that is unique to these species. "Therefore, future methods will have to establish the exact interaction between the histone [epigenetic] code and the splicing code," they note. Translated, this means: “Darwinists have nothing to do with it. They just can't handle it. " If the simple Watson-Crick genetic code was a problem for Darwinists, what do they say now about the splicing code that creates thousands of transcripts from the same genes? How do they deal with the epigenetic code that drives gene expression? And who knows, maybe in this incredible "interaction", about which we are just beginning to learn, other codes are involved, reminiscent of the Rosetta stone, just beginning to appear from the sand?

Now that we think about codes and computer science, we start thinking about different paradigms of new research. What if the genome acts in part as a storage area network? What if it has cryptography or compression algorithms? We should remember about modern information systems and information storage technologies. We may even find elements of steganography. There are undoubtedly additional resistance mechanisms, such as duplication and patching, that may help explain the existence of pseudogenes. Copying the entire genome can be stress responses. Some of these phenomena may prove to be useful indicators of historical events that have nothing to do with a universal common ancestor, but help explore comparative genomics within informatics and resilience design, and help understand the cause of disease.

Evolutionists find themselves in great difficulty. The researchers tried to modify the code, and only got cancer and mutations. How are they going to traverse the fitness field if it is all mined by catastrophes waiting in the wings as soon as someone begins to interfere with these inextricably linked codes? We know there is some built-in resilience and portability, but the whole picture is an incredibly complex, sophisticated, streamlined information system, not a messy jumble of pieces to play with endlessly. The whole idea of \u200b\u200bcode is a concept of intelligent design.

A. E. Wilder-Smith attached particular importance to this. The code assumes an agreement between the two parts. Agreement is advance consent. It involves planning and purpose. The SOS symbol, as Wilder-Smith would say, we use by convention as a distress signal. SOS doesn't look like a disaster. It doesn't smell like a disaster. It doesn't feel like a disaster. People would not understand that these letters stand for disaster if they did not understand the essence of the agreement itself. Likewise, the alanine codon, HCC, does not look, smell, or feel like alanine. The codon would not have anything to do with alanine if there was no pre-established agreement between the two coding systems (protein code and DNA code) that "HCC should mean alanine." To convey this agreement, a family of transducers, aminoacyl-tRNA synthetases, are used, which translate one code into another.

This should have reinforced the theory of design in the 1950s, and many creationists preached it effectively. But evolutionists are like articulate traders. They composed their tales of the Tinker Bell fairy who parses code and creates new species through mutation and selection, and convinced many people that miracles can still happen today. Well, well, today the 21st century is outside the window and we know the epigenetic code and the splicing code - two codes that are much more complex and dynamic than a simple DNA code. We know about codes within codes, about codes above codes and below codes - we know a whole hierarchy of codes. This time, evolutionists can't just stick their finger in a pistol and bluff us with their beautiful speeches, when there are cannons on both sides - a whole arsenal aimed at their main structural elements. It's all a game. A whole era of informatics has grown up around them, they have long gone out of fashion and are like the Greeks who are trying to climb with spears on modern tanks and helicopters.

Sad to admit, evolutionists do not understand this, or even if they do, they are not going to give up. Incidentally, this week, just as the Splicing Code article was published, the most hateful and hateful rhetoric in recent times against creationism and intelligent design has been raining from the pages of Prodarwyn's magazines and newspapers. There are many more such examples to be heard. And as long as they hold microphones in their hands and control institutions, many people will fall for them, thinking that science continues to give them good reason. We tell you all this so that you read this material, study it, understand it and stock up on the information you need in order to defeat this fanatical, misleading nonsense with truth. Now, let's go!

Chemical composition and structural organization of the DNA molecule.

Nucleic acid molecules are very long chains of many hundreds or even millions of nucleotides. Any nucleic acid contains only four types of nucleotides. The functions of nucleic acid molecules depend on their structure, their constituent nucleotides, their number in the chain and the sequence of the compound in the molecule.

Each nucleotide consists of three components: a nitrogenous base, a carbohydrate, and phosphoric acid. IN composition each nucleotide DNA includes one of four types of nitrogenous bases (adenine - A, thymine - T, guanine - G, or cytosine - C), as well as deoxyribose water carbon and a phosphoric acid residue.

Thus, DNA nucleotides differ only in the type of nitrogenous base.
A DNA molecule consists of a huge set of nucleotides linked in a chain in a specific sequence. Each kind of DNA molecule has its own number and sequence of nucleotides.

DNA molecules are very long. For example, writing the sequence of nucleotides in DNA molecules from one human cell (46 chromosomes) in letters would require a book of about 820,000 pages. The alternation of the four types of nucleotides can form an infinite number of variants of DNA molecules. These structural features of DNA molecules allow them to store a huge amount of information about all the characteristics of organisms.

In 1953, the American biologist J. Watson and the English physicist F. Crick created a model of the structure of the DNA molecule. Scientists have found that each DNA molecule consists of two chains, linked together and spirally twisted. It looks like a double helix. In each strand, the four types of nucleotides alternate in sequence.

Nucleotide dNA composition differs in different types of bacteria, fungi, plants, animals. But it does not change with age, depends little on changes in the environment. The nucleotides are paired, that is, the number of adenine nucleotides in any DNA molecule is equal to the number of thymidine nucleotides (AT), and the number of cytosine nucleotides is equal to the number of guanine nucleotides (C-G). This is due to the fact that the connection of two chains to each other in a DNA molecule obeys a certain rule, namely: the adenine of one chain is always linked by two hydrogen bonds only with the thymine of the other chain, and guanine - by three hydrogen bonds with cytosine, that is, the nucleotide chains of one molecule DNA is complementary, complementary to each other.

Nucleic acid molecules - DNA and RNA are made up of nucleotides. The composition of DNA nucleotides includes a nitrogenous base (A, T, G, C), a deoxyribose carbohydrate, and the remainder of a phosphoric acid molecule. The DNA molecule is a double helix consisting of two strands connected by hydrogen bonds according to the principle of complementarity. The function of DNA is to store hereditary information.

DNA properties and functions.

DNA is a carrier of genetic information recorded as a sequence of nucleotides using the genetic code. DNA molecules are associated with two fundamental properties of living organisms - heredity and variability. In a process called DNA replication, two copies of the original strand are formed, inherited by the daughter cells during division, thus the resulting cells are genetically identical to the original.

Genetic information is realized during gene expression in the processes of transcription (synthesis of RNA molecules on a DNA matrix) and translation (synthesis of proteins on an RNA matrix).

The sequence of nucleotides "encodes" information about different types of RNA: informational, or messenger (mRNA), ribosomal (rRNA) and transport (tRNA). All of these types of RNA are synthesized from DNA during the process of transcription. Their role in protein biosynthesis (translation process) is different. Messenger RNA contains information about the sequence of amino acids in a protein, ribosomal RNAs serve as the basis for ribosomes (complex nucleoprotein complexes, the main function of which is the assembly of protein from individual amino acids based on mRNA), transport RNAs deliver amino acids to the site of protein assembly - to the active center of the ribosome, " creeping "by mRNA.

Genetic code, its properties.

Genetic code - inherent in all living organisms, a method of encoding the amino acid sequence of proteins using a sequence of nucleotides. PROPERTIES:

1. Tripletness - the significant unit of the code is a combination of three nucleotides (triplet, or codon).
2. Continuity - there are no punctuation marks between the triplets, that is, information is read continuously.
3. Non-overlap - the same nucleotide cannot be simultaneously a part of two or more triplets (it is not observed for some overlapping genes of viruses, mitochondria and bacteria that encode several proteins that are read with a frame shift).
4. Unambiguity (specificity) - a certain codon corresponds to only one amino acid (however, the UGA codon in Euplotes crassus encodes two amino acids - cysteine \u200b\u200band selenocysteine)
5. Degeneracy (redundancy) - several codons can correspond to the same amino acid.
6. Versatility - the genetic code works in the same way in organisms of different levels of complexity - from viruses to humans (genetic engineering methods are based on this; there are a number of exceptions, shown in the table of the section "Variations of the standard genetic code" below).
7. Immunity - mutations of nucleotide substitutions that do not lead to a change in the class of the encoded amino acid are called conservative; mutations of nucleotide substitutions leading to a change in the class of the encoded amino acid are called radical.

5. Autoreproduction of DNA. Replicon and its functioning .

The process of self-reproduction of nucleic acid molecules, accompanied by the inheritance (from cell to cell) of exact copies of genetic information; R... carried out with the participation of a set of specific enzymes (helicase<helicase\u003e, which controls the unwinding of the molecule DNA, DNA-polymerase<DNA polymerase\u003e I and III, DNA-ligase<DNA ligase\u003e), passes along the semi-conservative type with the formation of a replicative fork<replication fork\u003e; on one of the chains<leading strand\u003e synthesis of the complementary strand is continuous, and on the other<lagging strand\u003e occurs due to the formation of fragments of Dkazaki<Okazaki fragments>; R... - high-precision process, the error rate in which does not exceed 10 -9; in eukaryotes R... can occur simultaneously at several points of the same molecule DNA; speed R... in eukaryotes about 100, and in bacteria - about 1000 nucleotides per second.

6. Levels of organization of the eukaryotic genome .

In eukaryotic organisms, the mechanism of transcription regulation is much more complex. As a result of cloning and sequencing of eukaryotic genes, specific sequences were found that are involved in transcription and translation.
A eukaryotic cell is characterized by:
1. The presence of introns and exons in the DNA molecule.
2. Maturation of i-RNA - excision of introns and stitching of exons.
3. The presence of regulatory elements that regulate transcription, such as: a) promoters - 3 types, each of which has a specific polymerase. Pol I replicates ribosomal genes, Pol II - structural protein genes, Pol III - genes encoding small RNAs. The Pol I and Pol II promoter are in front of the site of transcription initiation, the Pol III promoter is within the structural gene; b) modulators - DNA sequences that enhance the level of transcription; c) amplifiers - sequences that enhance the level of transcription and act regardless of their position relative to the coding part of the gene and the state of the initial point of RNA synthesis; d) terminators - specific sequences that stop both translation and transcription.
These sequences differ in their primary structure and location relative to the initiation codon from prokaryotic ones, and bacterial RNA polymerase does not "recognize" them. Thus, for the expression of eukaryotic genes in prokaryotic cells, the genes must be under the control of prokaryotic regulatory elements. This circumstance must be taken into account when constructing vectors for expression.

7. Chemical and structural composition of chromosomes .

Chemical chromosome composition - DNA - 40%, Histone proteins - 40%. Non-histone - 20% a little RNA. Lipids, polysaccharides, metal ions.

The chemical composition of a chromosome is a complex of nucleic acids with proteins, carbohydrates, lipids and metals. In the chromosome, the activity of genes is regulated and restored in the event of chemical or radiation damage.

STRUCTURAL????

Chromosomes - nucleoprotein structural elements of the cell nucleus, containing DNA, which contains the hereditary information of the organism, are capable of self-reproduction, have a structural and functional individuality and retain it in a number of generations.

in the mitotic cycle, the following features of the structural organization of chromosomes are observed:

Distinguish between mitotic and interphase forms of the structural organization of chromosomes, mutually transforming into each other in the mitotic Cycle - these are functional and physiological transformations

8. Levels of packing of hereditary material in eukaryotes .

Structural and functional levels of organization of the hereditary material of eukaryotes

Heredity and variability provide:

1) individual (discrete) inheritance and change of individual traits;

2) reproduction in individuals of each generation of the entire complex of morphological and functional characteristics of organisms of a particular biological species;

3) redistribution in species with sexual reproduction in the process of reproduction of hereditary inclinations, as a result of which the offspring has a combination of characters that is different from their combination in the parents. The patterns of inheritance and variability of characters and their aggregates follow from the principles of the structural and functional organization of genetic material.

There are three levels of organization of the hereditary material of eukaryotic organisms: gene, chromosomal, and genomic (genotype level).

The gene is the elementary structure of the gene level. The transfer of genes from parents to offspring is necessary for the development of certain characteristics in him. Although several forms of biological variation are known, only a violation of the gene structure changes the meaning of hereditary information, in accordance with which specific traits and properties are formed. Due to the presence of the gene level, individual, separate (discrete) and independent inheritance and changes in individual traits are possible.

The genes of eukaryotic cells are distributed in groups along the chromosomes. These are the structures of the cell nucleus, which are characterized by individuality and the ability to self-reproduce with the preservation of individual structural features in a number of generations. The presence of chromosomes determines the isolation of the chromosomal level of organization of the hereditary material. The placement of genes in chromosomes affects the relative inheritance of traits, makes it possible to influence the function of a gene from its closest genetic environment - neighboring genes. The chromosomal organization of hereditary material serves as a necessary condition for the redistribution of the hereditary inclinations of the parents in the offspring during sexual reproduction.

Despite the distribution over different chromosomes, the entire set of genes functionally behaves as a whole, forming a single system representing the genomic (genotypic) level of organization of the hereditary material. At this level, there is a wide interaction and mutual influence of hereditary inclinations, localized both in one and in different chromosomes. The result is the mutual correspondence of the genetic information of different hereditary inclinations and, therefore, the balanced development of characters in time, place and intensity in the process of ontogenesis. The functional activity of genes, the mode of replication and mutational changes in the hereditary material also depend on the characteristics of the genotype of the organism or the cell as a whole. This is evidenced, for example, by the relativity of the property of dominance.

Eu - and heterochromatin.

Some chromosomes appear condensed and intensely colored during cell division. These differences were called heteropycnosis. To designate regions of chromosomes demonstrating positive heteropycnosis at all stages of the mitotic cycle, the term “ heterochromatin". Distinguish between euchromatin - the main part of mitotic chromosomes, which undergoes the usual cycle of compaction decompaction during mitosis, and heterochromatin - sections of chromosomes that are constantly in a compact state.

In most eukaryotic species, chromosomes contain both eu- and heterochromatic regions, the latter constituting a significant part of the genome. Heterochromatin is located in pericentromeric, sometimes in telomeric regions. Heterochromatin regions were found in the euchromatin arms of chromosomes. They look like inclusions (intercalations) of heterochromatin into euchromatin. Such heterochromatin called intercalary. Compaction of chromatin. Euchromatin and heterochromatin differ in compaction cycles. Euhr. goes through a full cycle of compaction-decompaction from interphase to interphase, hetero. maintains a state of relative compactness. Differential coloration.Different areas of heterochromatin are stained with different dyes, some areas with one, others with several. By using various dyes and using chromosomal rearrangements that break apart heterochromatic regions, in Drosophila, it was possible to characterize many small regions where the affinity for colors is different from the neighboring regions.

10. Morphological features of the metaphase chromosome .

The metaphase chromosome consists of two longitudinal strands of deoxyribonucleoprotein - chromatids, connected to each other in the region of the primary constriction - centromere. The centromere is a specially organized chromosome region, common to both sister chromatids. The centromere divides the chromosome body into two arms. Depending on the location of the primary constriction, the following types of chromosomes are distinguished: equal arms (metacentric), when the centromere is located in the middle, and the arms are approximately equal in length; unequal (submetacentric), when the centromere is displaced from the middle of the chromosome, and the arms are of unequal length; rod-shaped (acrocentric), when the centromere is displaced to one end of the chromosome and one arm is very short. There are also point (telocentric) chromosomes, they have one shoulder missing, but they are not in the karyotype (chromosome set) of a person. In some chromosomes, there may be secondary constrictions separating a region called a satellite from the chromosome body.

In the metabolism of the body main role belongs to proteins and nucleic acids.
Protein substances form the basis of all vital cell structures, have an unusually high reactivity, and are endowed with catalytic functions.
Nucleic acids are part of the most important organ of the cell - the nucleus, as well as the cytoplasm, ribosomes, mitochondria, etc. Nucleic acids play an important, paramount role in heredity, variability of the organism, in protein synthesis.

Plan synthesis protein is stored in the cell nucleus, and synthesis occurs directly outside the nucleus, therefore it is necessary delivery service coded plan from the nucleus to the site of synthesis. This delivery service is performed by RNA molecules.

The process starts at core cells: part of the DNA “ladder” unwinds and opens. Thanks to this, the RNA letters form bonds with the open DNA letters of one of the DNA strands. The enzyme transfers the letters of the RNA to join them into a strand. This is how DNA letters are "rewritten" into RNA letters. The newly formed RNA strand is detached and the DNA “ladder” winds up again. The process of reading information from DNA and synthesizing it from its RNA matrix is \u200b\u200bcalled transcription , and the synthesized RNA is called informational or i-RNA .

After further modifications, this kind of encoded i-RNA is ready. i-RNA exits the core and goes to the site of protein synthesis, where the letters i-RNA are decoded. Each set of three letters i-RNA forms a "letter" representing one particular amino acid.

Another type of RNA looks for this amino acid, captures it with an enzyme and delivers it to the site of protein synthesis. This RNA is called transport RNA, or t-RNA. As the i-RNA message is read and translated, the amino acid chain grows. This chain twists and folds into a unique shape to create one kind of protein. Even the process of protein folding is remarkable: to calculate everything using a computer options it would take 1027 (!) years to pack a medium-sized protein consisting of 100 amino acids. And it takes no more than one second to form a chain of 20 amino acids in the body, and this process takes place continuously in all cells of the body.

Genes, genetic code and its properties.

About 7 billion people live on Earth. Except for 25-30 million pairs of identical twins, genetically all people are different : each is unique, has inimitable hereditary characteristics, character traits, abilities, temperament.

Such differences are explained differences in genotypes- sets of genes of the organism; each one is unique. The genetic traits of a particular organism are embodied in proteins - therefore, the structure of one person's protein differs, albeit quite slightly, from the protein of another person.

It does not meanthat people do not have exactly the same proteins. Proteins that perform the same functions may be the same or only slightly differ by one or two amino acids from each other. But does not exist on Earth, people (with the exception of identical twins), who would have all the proteins are the same .

Information about the primary structure of the protein encoded as a sequence of nucleotides in a region of a DNA molecule, gene - a unit of hereditary information of an organism. Each DNA molecule contains many genes. The totality of all genes of an organism makes it genotype ... Thus,

A gene is a unit of hereditary information of an organism, which corresponds to a separate section of DNA

Hereditary information is encoded using genetic code , which is universal for all organisms and differs only in the alternation of nucleotides that form genes and coding for proteins of specific organisms.

Genetic code consists of triplets (triplets) of DNA nucleotides, combined in a different sequence (AAT, HCA, ACG, THC, etc.), each of which encodes a specific amino acid (which will be inserted into the polypeptide chain).

Actually code considered the sequence of nucleotides in an i-RNA molecule since it removes information from DNA (process transcriptions ) and translates it into a sequence of amino acids in the molecules of synthesized proteins (process broadcasts ).
The composition of i-RNA includes nucleotides A-C-G-U, the triplets of which are called codons : the triplet on DNA CGT on i-RNA will become the HCA triplet, and the AAG DNA triplet will become the UUC triplet. Exactly i-RNA codons the genetic code is reflected in the record.

Thus, genetic code - a unified system for recording hereditary information in nucleic acid molecules in the form of a sequence of nucleotides ... The genetic code is based on the use of an alphabet consisting of only four letters-nucleotides, differing in nitrogenous bases: A, T, G, C.

The main properties of the genetic code:

1. Genetic code triplet ... Triplet (codon) - a sequence of three nucleotides that encodes one amino acid. Since proteins contain 20 amino acids, it is obvious that each of them cannot be encoded by one nucleotide ( since there are only four types of nucleotides in DNA, then in this case 16 amino acids remain uncoded). Two nucleotides are also missing to encode amino acids, since only 16 amino acids can be encoded in this case. This means that the smallest number of nucleotides encoding one amino acid must be at least three. In this case, the number of possible triplets of nucleotides is 43 \u003d 64.

2. Redundancy (degeneracy) code is a consequence of its triplet nature and means that one amino acid can be encoded by several triplets (since there are 20 amino acids and 64 triplets), with the exception of methionine and tryptophan, which are encoded by only one triplet. In addition, some triplets perform specific functions: in the i-RNA molecule, the triplets UAA, UAH, UGA are termination codons, i.e. stop-signals stopping the synthesis of the polypeptide chain. The triplet corresponding to methionine (AUG), located at the beginning of the DNA chain, does not encode an amino acid, but performs the function of initiation (excitation) of reading.

3. Unambiguity code - simultaneously with redundancy, the code has the property unambiguity : each codon only matches alone a specific amino acid.

4. Collinearity code, i.e. sequence of nucleotides in a gene exactly corresponds to the sequence of amino acids in a protein.

5. Genetic code non-overlapping and compact , that is, it does not contain "punctuation marks". This means that the reading process does not allow for the possibility of overlapping columns (triplets), and, starting at a certain codon, the reading proceeds continuously triplet by triplet up to stop-signals ( termination codons).

6. Genetic code versatile that is, the nuclear genes of all organisms in the same way encode information about proteins, regardless of the level of organization and systematic position of these organisms.

Exist genetic code tables for decryption codons i-RNA and building chains of protein molecules.

Matrix synthesis reactions.

In living systems, there are reactions unknown in inanimate nature - matrix synthesis reactions.

The term "matrix" in technology, they denote the form used for casting coins, medals, typographic type: the hardened metal reproduces exactly all the details of the form that was used for casting. Matrix synthesis resembles a casting on a matrix: new molecules are synthesized in strict accordance with the plan laid down in the structure of already existing molecules.

The matrix principle lies at the core the most important synthetic reactions of the cell, such as the synthesis of nucleic acids and proteins. These reactions provide an accurate, strictly specific sequence of monomer units in the synthesized polymers.

Here the directional pulling monomers to a specific location cells - into molecules that serve as a matrix where the reaction takes place. If such reactions occurred as a result of a random collision of molecules, they would proceed infinitely slowly. The synthesis of complex molecules based on the matrix principle is fast and accurate. The role of the matrix nucleic acid macromolecules play in matrix reactions DNA or RNA .

Monomeric molecules, from which the polymer is synthesized - nucleotides or amino acids - in accordance with the principle of complementarity are located and fixed on the matrix in a strictly defined, prescribed order.

Then happens "crosslinking" of monomer units into a polymer chainand the finished polymer is discarded from the matrix.

After that the matrix is \u200b\u200bready to the assembly of a new polymer molecule. It is clear that just as on a given form only one coin, one letter can be cast, so on a given matrix molecule only one polymer can be "assembled".

Matrix type of reactions - a specific feature of the chemistry of living systems. They are the basis of the fundamental property of all living things - its ability to reproduce its own kind.

Matrix synthesis reactions

1. DNA replication - replication (from Latin replicatio - renewal) - the process of synthesis of a daughter molecule of deoxyribonucleic acid on the matrix of the parent DNA molecule. During the subsequent division of the mother cell, each daughter cell receives one copy of the DNA molecule, which is identical to the DNA of the original mother cell. This process ensures the accurate transmission of genetic information from generation to generation. DNA replication is carried out by a complex enzyme complex consisting of 15-20 different proteins, called replicasoma ... The material for the synthesis is free nucleotides present in the cytoplasm of cells. The biological meaning of replication lies in the accurate transfer of hereditary information from the parent molecule to the daughter ones, which normally occurs during the division of somatic cells.

A DNA molecule consists of two complementary strands. These chains are held together by weak hydrogen bonds that can be broken by enzymes. A DNA molecule is capable of self-doubling (replication), and a new half of it is synthesized on each old half of the molecule.
In addition, an i-RNA molecule can be synthesized on a DNA molecule, which then transfers the information received from DNA to the site of protein synthesis.

Information transfer and protein synthesis are based on a matrix principle, comparable to the operation of a printing press in a printing house. Information from DNA is copied many times. If errors occur during copying, they will be repeated in all subsequent copies.

True, some errors when copying information by a DNA molecule can be corrected - the process of eliminating errors is called reparation... The first of the reactions in the process of transferring information is the replication of the DNA molecule and the synthesis of new DNA strands.

2. Transcription (from Lat. transcriptio - rewriting) - the process of RNA synthesis using DNA as a matrix, which occurs in all living cells. In other words, it is the transfer of genetic information from DNA to RNA.

Transcription is catalyzed by the enzyme DNA-dependent RNA polymerase. RNA polymerase moves along the DNA molecule in the 3 "→ 5" direction. Transcription consists of stages initiation, elongation and termination ... The unit of transcription is an operon, a fragment of a DNA molecule consisting of promoter, transcribed portion and terminator ... i-RNA consists of one strand and is synthesized on DNA in accordance with the rule of complementarity with the participation of an enzyme that activates the beginning and end of the synthesis of the i-RNA molecule.

The finished i-RNA molecule enters the cytoplasm onto the ribosomes, where the synthesis of polypeptide chains occurs.

3. Broadcast (from lat. translatio - transfer, movement) - the process of protein synthesis from amino acids on the matrix of informational (matrix) RNA (mRNA, mRNA), carried out by the ribosome. In other words, this is the process of translating information contained in the nucleotide sequence of an m-RNA into a sequence of amino acids in a polypeptide.

4. Reverse transcription is the process of double-stranded DNA formation based on information from single-stranded RNA. This process is called reverse transcription, since the transfer of genetic information in this case occurs in the "reverse", relative to transcription, direction. The idea of \u200b\u200breverse transcription was initially very unpopular, as it contradicted the central dogma of molecular biology, which assumed that DNA was transcribed into RNA and then translated into proteins.

However, in 1970, Temin and Baltimore independently discovered an enzyme called reverse transcriptase (revertase) , and the possibility of reverse transcription was finally confirmed. In 1975, Temin and Baltimore were awarded the Nobel Prize in Physiology or Medicine. Some viruses (such as the human immunodeficiency virus that causes HIV infection) have the ability to transcribe RNA into DNA. HIV has an RNA genome that is embedded in DNA. As a result, the DNA of the virus can be combined with the genome of the host cell. The main enzyme responsible for the synthesis of DNA from RNA is called revertase ... One of the functions of revertase is to create complementary DNA (cDNA) from the viral genome. The associated enzyme ribonuclease cleaves RNA, while reverse transcriptase synthesizes cDNA from the DNA double helix. cDNA is integrated into the genome of the host cell using integrase. The result is synthesis of viral proteins by the host cellthat form new viruses. In the case of HIV, apoptosis (cell death) of T-lymphocytes is also programmed. In other cases, the cell can remain a distributor of viruses.

The sequence of matrix reactions in protein biosynthesis can be represented as a diagram.

Thus, protein biosynthesis - This is one of the types of plastic metabolism, during which hereditary information encoded in DNA genes is realized in a specific sequence of amino acids in protein molecules.

Protein molecules are essentially polypeptide chainscomposed of individual amino acids. But amino acids are not active enough to bind together on their own. Therefore, before connecting with each other and forming a protein molecule, amino acids must activate ... This activation takes place under the action of special enzymes.

As a result of activation, the amino acid becomes more labile and, under the action of the same enzyme, binds to t- RNA... Each amino acid corresponds to a strictly specific t- RNAwhich finds "its" amino acid and carries over her into the ribosome.

Consequently, the ribosome receives various activated amino acids combined with their t- RNA... The ribosome is, as it were, conveyor to assemble a protein chain from various amino acids entering it.

Simultaneously with the t-RNA, on which its own amino acid "sits", the ribosome receives " signal"From the DNA that is contained in the nucleus. In accordance with this signal, one or another protein is synthesized in the ribosome.

The directing influence of DNA on protein synthesis is not carried out directly, but with the help of a special mediator - matrix or messenger RNA (m-RNA or i-RNA), which synthesized into the nucleuse under the influence of DNA, therefore its composition reflects the composition of DNA. The RNA molecule is like a mold of the form of DNA. The synthesized i-RNA enters the ribosome and, as it were, transfers to this structure plan - in what order the activated amino acids entering the ribosome should be connected to each other in order to synthesize a certain protein. Otherwise, genetic information encoded in DNA is transferred to m-RNA and then to protein.

The i-RNA molecule enters the ribosome and stitches her. That segment of it, which is at the moment in the ribosome, determined codon (triplet), interacts in a completely specific way with a suitable structure triplet (anticodon) in the transport RNA, which brought the amino acid into the ribosome.

The transport RNA with its amino acid is matched to a specific i-RNA codon and connects with him; to the next, adjacent site i-RNA joins another t-RNA with a different amino acid and so on until the entire chain of i-RNA is read, until all amino acids are strung in the appropriate order, forming a protein molecule. And t-RNA, which delivered the amino acid to a specific region of the polypeptide chain, freed from its amino acid and leaves the ribosome.

Then again in the cytoplasm, the desired amino acid can attach to it, and it will again transfer it to the ribosome. In the process of protein synthesis, not one, but several ribosomes - polyribosomes - are simultaneously involved.

The main stages of the transfer of genetic information:

1. Synthesis on DNA as on a template i-RNA (transcription)
2. Synthesis in ribosomes of the polypeptide chain according to the program contained in m-RNA (translation) .

The stages are universal for all living things, but the temporal and spatial relationships of these processes differ in pro- and eukaryotes.

Have prokaryote transcription and translation can be carried out simultaneously, since the DNA is in the cytoplasm. Have eukaryotes transcription and translation are strictly separated in space and time: the synthesis of various RNAs occurs in the nucleus, after which the RNA molecules must leave the nucleus, passing through the nuclear membrane. Then, in the cytoplasm, RNAs are transported to the site of protein synthesis.

GENETIC CODE, a system for recording hereditary information in the form of a sequence of bases of nucleotides in DNA molecules (in some viruses - RNA), which determines the primary structure (location of amino acid residues) in protein molecules (polypeptides). The problem of the genetic code was formulated after proving the genetic role of DNA (American microbiologists O. Avery, K. McLeod, M. McCarthy, 1944) and deciphering its structure (J. Watson, F. Crick, 1953), after establishing that genes determine the structure and function of enzymes (the principle of "one gene - one enzyme" by J. Beadle and E. Tatem, 1941) and that there is a dependence of the spatial structure and activity of a protein on its primary structure (F. Senger, 1955). The question of how combinations of 4 bases of nucleic acids determine the alternation of 20 common amino acid residues in polypeptides was first posed by G. Gamow in 1954.

On the basis of an experiment in which the interaction of insertions and deletions of a pair of nucleotides was investigated, in one of the genes of the bacteriophage T4, F. Crick and other scientists in 1961 determined the general properties of the genetic code: tripletness, i.e., each amino acid residue in the polypeptide chain corresponds to a set of three bases (triplet, or codon) in the DNA of a gene; reading of codons within a gene goes from a fixed point, in one direction and “without commas”, that is, codons are not separated by any signs from each other; degeneracy, or redundancy - the same amino acid residue can be encoded by several codons (synonym codons). The authors assumed that the codons do not overlap (each base belongs to only one codon). The direct study of the coding ability of triplets was continued using a cell-free protein synthesis system under the control of synthetic messenger RNA (mRNA). By 1965, the genetic code was completely deciphered in the works of S. Ochoa, M. Nirenberg and H. G. Korana. Uncovering the secret of the genetic code was one of the outstanding achievements of biology in the 20th century.

The implementation of the genetic code in a cell occurs in the course of two matrix processes - transcription and translation. The mediator between the gene and the protein is mRNA, which is formed during transcription on one of the DNA strands. In this case, the DNA base sequence, which carries information about the primary structure of the protein, is "rewritten" in the form of an mRNA base sequence. Then, during translation on ribosomes, the mRNA nucleotide sequence is read by transport RNAs (tRNAs). The latter have an acceptor end, to which an amino acid residue is attached, and an adapter end, or anticodon-triplet, which recognizes the corresponding mRNA codon. The interaction of the codon and anti-codon occurs on the basis of complementary base pairing: Adenine (A) - Uracil (U), Guanine (G) - Cytosine (C); the sequence of mRNA bases is converted into the amino acid sequence of the synthesized protein. Different organisms use different synonymous codons with different frequencies for the same amino acid. The reading of the mRNA encoding the polypeptide chain begins (is initiated) from the AUG codon corresponding to the amino acid methionine. Less commonly, in prokaryotes, the initiation codons are GUG (valine), UUG (leucine), AUU (isoleucine), in eukaryotes - UUG (leucine), AUA (isoleucine), ACG (threonine), CUG (leucine). This sets the so-called frame, or phase, of reading during translation, that is, then the entire nucleotide sequence of mRNA is read triplet by triplet of tRNA until any of the three terminator codons, often called stop codons, are encountered on the mRNA: UAA, UAG , UGA (table). The reading of these triplets leads to the completion of the synthesis of the polypeptide chain.

AUG codons and stop codons are respectively at the beginning and end of the mRNA regions encoding polypeptides.

The genetic code is quasi-universal. This means that there are small variations in the meaning of some codons in different objects, and this concerns, first of all, terminator codons, which can be meaningful; for example, in the mitochondria of some eukaryotes and in mycoplasmas, UGA encodes tryptophan. In addition, in some mRNAs of bacteria and eukaryotes, UGA encodes an unusual amino acid - selenocysteine, and UAG in one of the archaea - pyrrolysine.

There is a point of view according to which the genetic code arose by chance (the “frozen case” hypothesis). It is more likely that he evolved. This assumption is supported by the existence of a simpler and, apparently, more ancient version of the code, which is read in mitochondria according to the “two out of three” rule, when an amino acid is determined only by two out of three bases in a triplet.

Lit .: Crick F. N. and. about. General nature of the genetic code for proteins // Nature. 1961. Vol. 192; The genetic code. N. Y. 1966; Ichas M. Biological code. M., 1971; Inge-Vechtomov S.G. How the genetic code is read: rules and exceptions // Modern Natural Science. M., 2000. T. 8; Ratner V.A.Genetic code as a system // Soros educational journal. 2000. T. 6.No. 3.

S.G. Inge-Vechtomov.

Under the genetic code, it is customary to understand such a system of signs denoting the sequential arrangement of nucleotide compounds in DNA and RNA, which corresponds to another sign system that displays the sequence of amino acid compounds in a protein molecule.

It is important!

When scientists managed to study the properties of the genetic code, universality was recognized as one of the main ones. Yes, as strange as it sounds, everything is united by one, universal, common genetic code. It was formed over a long time interval, and the process ended about 3.5 billion years ago. Consequently, in the structure of the code, traces of its evolution can be traced, from the moment of inception to the present day.

When we talk about the sequence of the arrangement of elements in the genetic code, we mean that it is far from chaotic, but has a strictly defined order. And this also largely determines the properties of the genetic code. This is equivalent to the arrangement of letters and syllables in words. It is worth breaking the usual order, and most of what we read on the pages of books or newspapers will turn into ridiculous gibberish.

The main properties of the genetic code

Usually the code carries some information encrypted in a special way. In order to decipher the code, you need to know the distinctive features.

So, the main properties of the genetic code are:

• tripletness;
• degeneracy or redundancy;
• unambiguity;
• continuity;
• already mentioned above universality.

Let's dwell on each property in more detail.

1. Triplet

This is when three compounds of nucleotides form a sequential chain within a molecule (i.e. DNA or RNA). As a result, a triplet compound is created or encodes one of the amino acids, its location in the peptide chain.

Distinguish codons (they are also code words!) By their sequence of connection and by the type of those nitrogenous compounds (nucleotides) that are part of them.

In genetics, it is customary to distinguish 64 codon types. They can form combinations of four types of nucleotides, 3 in each. This is tantamount to raising the number 4 to the third power. Thus, the formation of 64 nucleotide combinations is possible.

2. Redundancy of the genetic code

This property can be traced when several codons are required to encrypt one amino acid, usually in the range of 2-6. And only tryptophan can be encoded with a single triplet.

3. Unambiguity

It is included in the properties of the genetic code as an indicator of healthy genetic inheritance. For example, the GAA triplet, which is in sixth place in the chain, can tell doctors about the good condition of the blood, about normal hemoglobin. It is he who carries information about hemoglobin, and it is also encoded by it. And if a person is sick with anemia, one of the nucleotides is replaced by another letter of the code - Y, which is a signal of the disease.

4. Continuity

When recording this property of the genetic code, it should be remembered that codons, as chain links, are not located at a distance, but in direct proximity, one after another in a nucleic acid chain, and this chain is not interrupted - it has no beginning or end.

5. Versatility

It should never be forgotten that everything on Earth is united by a common genetic code. And therefore, in a primate and a person, in an insect and a bird, a hundred-year-old baobab and a blade of grass barely hatching from the ground, similar amino acids are encoded by the same triplets.

It is in the genes that the basic information about the properties of an organism is laid, a kind of program that the organism inherits from those who lived earlier and which exists as a genetic code.