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 reveal it, they did not use evolutionary theory, but information technology.

The new code is called the Splicing Code. It is within the DNA. This code controls the underlying genetic code in a very complex yet predictable way. The splicing code controls how and when genes and regulatory elements are assembled. Revealing this code within a code helps shed light on some of the long-standing mysteries of genetics that have surfaced since the Complete Human Genome Sequencing Project. One such mystery was why there are only 20,000 genes in an organism as complex as the human being? (Scientists expected to find a lot more.) Why are genes broken into segments (exons) that are separated by non-coding elements (introns) and then joined together (i.e., spliced) after transcription? And why are genes turned on in some cells and tissues and not in others? For two decades, molecular biologists have tried to elucidate the mechanisms of genetic regulation. This article points to a very important point understanding what is really going on. It doesn't answer every question, but it does demonstrate that the internal code exists. This code is a communication system that can be deciphered so clearly that scientists could predict how a genome might behave in certain situations and with inexplicable accuracy.

Imagine that you hear an orchestra in the next room. You open the door, look inside and see three or four musicians playing musical instruments in the room. This is what Brandon Frey, who helped break the code, says the human genome looks like. He says: “We were only able to detect 20,000 genes, but we knew that they form a huge number 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. Right there in the article, it says that scientists know that 95% of our genes have alternative splicing, and in most cases in different types transcripts (RNA molecules resulting from transcription) are expressed differently in cells and tissues. There must be something that controls how these thousands of combinations are assembled and expressed. This is the task of the Splicing Code.

Readers who want a quick overview of the discovery can read the article at Science Daily entitled "Researchers who cracked the 'Splicing Code' unravel the mystery behind biological complexity". The article says: “Scientists at the University of Toronto have gained a fundamental new understanding of how living cells use a limited number of genes to form incredibly complex organs like the brain.”. Nature magazine itself begins with Heidi Ledford's "Code Within Code." This was followed by a paper by Tejedor and Valcarcel titled “Gene Regulation: Breaking the Second Genetic Code. Finally, a paper by a group of researchers from the University of Toronto led by Benjamin D. Blencoe and Brandon D. Frey, "Deciphering the Splicing Code," was decisive.

This article is an information science victory that reminds us of codebreakers from World War II. 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 theory, which 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-mediated 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 mutation-controlled regulatory sequences. We have uncovered widely used regulatory strategies, including: using unexpectedly large property pools; detection low levels exon inclusions that are attenuated by the properties of specific tissues; the manifestation of properties in introns is deeper than previously thought; and modulation of the levels of the splice variant by the structural characteristics of the transcript. The code helped establish a class of exons whose inclusion mutes expression in adult tissues, activating mRNA degradation, and whose exclusion promotes expression during embryogenesis. The code facilitates the disclosure and detailed description of genome-wide regulated events of alternative splicing.”

The team that cracked the code included specialists from the Department of Electronics and Computer Engineering, as well as from the Department of Molecular Genetics. (Frey himself works for Microsoft Research, a division of Microsoft Corporation) Like the decoders of the past, Frey and Barash developed « new method computer-assisted biological analysis that discovers the 'code words' hidden within the genome". With the help of a huge amount of data created by molecular geneticists, a group of researchers carried out "reverse engineering" of the splicing code until they could predict how he would act. Once the researchers got the hang of it, they tested the code for mutations and saw how exons were inserted or removed. They found that the code could even cause tissue-specific changes or act differently depending on whether it was an adult mouse or an embryo. One gene, Xpo4, is associated with cancer; The researchers noted: “These data support the conclusion that Xpo4 gene expression must be tightly controlled to avoid potential detrimental effects, including oncogenesis (cancer), since it is active during embryogenesis but is reduced in adult tissues. It turns out that they were absolutely surprised by the level of control they saw. Intentionally or not, Frey did not use random variation and selection as a clue, but the language of intelligent design. He noted: "Understanding complex biological system like understanding a complex electronic circuit.”

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

But between DNA and proteins lies RNA, a separate world of complexity. RNA is a transformer that sometimes carries genetic messages, and sometimes controls them, while using many structures that can influence its function. In an article published in the same issue, a team of researchers led by Benjamin D. Blencoe and Brandon D. Frey at the University of Toronto in Ontario, Canada, report attempts to unravel a second genetic code that can predict how messenger RNA segments are transcribed from a particular genes can mix and match 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 properties of DNA with definitions of the structure of RNA.

The work of these researchers points to the rapid progress that computational methods have made in modeling RNA. In addition to understanding alternative splicing, computer science is helping scientists predict RNA structures and identify small regulatory fragments of RNA that do not code for proteins. "It's a wonderful time", says Christopher Berg, a computer biologist at the Massachusetts Institute of Technology in Cambridge. “In the future, we will have a huge success”.

Computer science, computer biology, algorithms, and codes were not part of Darwin's vocabulary when he developed his theory. Mendel had a very simplified model of how traits are distributed during inheritance. In addition, the idea that features are encoded was only introduced in 1953. We see that the original genetic code is regulated by an even more complex code included in it. These are revolutionary ideas.. Moreover, there are all indications that this level of control is not the last. Ledford reminds us that, for example, RNA and proteins have a three-dimensional structure. The function of molecules can change when 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 another code, histone code. This code is encoded by molecular markers or "tails" on histone proteins that serve as centers for DNA coiling and supercoiling. Describing our time, Ledford speaks of "permanent renaissance in RNC informatics".

Tejedor and Valcarcel agree that complexity lies behind simplicity. “In theory, everything looks very simple: DNA forms RNA, which then creates a protein”, - they begin their article. “But the reality is much more complicated.”. In the 1950s, we learned that all living organisms, from bacteria to humans, have a basic genetic code. But we soon realized that complex organisms (eukaryotes) have some unnatural and difficult to understand property: their genomes have peculiar sections, introns, that must be removed so that exons can join together. Why? The fog is clearing today "The main advantage of this mechanism is that it allows different cells to choose alternative ways of splicing the precursor messenger RNA (pre-mRNA) and thus one gene forms different messages," they explain, "and then different mRNAs can code for different proteins with different functions". From less code, you get more information, as long as 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 near exon boundaries, intron sequences, and regulatory factors that either aid or inhibit the splicing mechanism. Besides, "the effects of a certain sequence or factor may vary depending on its location relative to the boundaries of the intron-exon or other regulatory motifs", - Tejedor and Valcarcel explain. "Therefore challenging task in predicting tissue-specific splicing is to compute the algebra of a myriad of motifs and the relationships between the regulatory factors that recognize them".

To solve this problem, a team of researchers entered into the computer a huge amount of data about the RNA sequences and the conditions under which they were formed. "The computer was then given the task of identifying 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 codebreakers, once scientists know the algorithm, they can make predictions: "It 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 motivations and pointed to previously unknown properties of known regulators, as well as unexpected functional connections between them", the researchers noted. “For example, the code implies that the inclusion of exons leading to processed proteins is a general mechanism for controlling the process of gene expression during the transition from embryonic tissue to adult tissue.”.

Tejedor and Valcarcel consider the publication of their paper an important first step: "The work... is better seen as the discovery of the first fragment of the much larger Rosetta Stone needed to decipher the alternative messages of 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, “That doesn't mean that evolution created these codes. This means that progress will require an understanding of how the codes interact. Another surprise was that the degree of conservation observed to date raises the question of the possible existence of "species-specific codes".

The code probably works in every single cell, and therefore must be responsible for more than 200 types of mammalian cells. It also has to cope with a huge variety of alternative splicing schemes, not to mention simple solutions on the inclusion or skipping of a single exon. The limited evolutionary retention of regulation of alternative splicing (estimated to be about 20% between humans and mice) raises the question of the existence of species-specific codes. Moreover, the relationship between DNA processing and gene transcription influences alternative splicing, and recent evidence points to DNA packaging by histone proteins and histone covalent modifications (the so-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 more codes. The fact that scientists say almost nothing about Darwinism in these papers indicates that evolutionary theorists, adherents of old ideas and traditions, have a lot to think about after they read these papers. But those who are enthusiastic about the biology of codes will be at the forefront. They have a great opportunity to take advantage of the exciting web application that the codebreakers have created to encourage further exploration. It can be found on the University of Toronto website called "Alternative Splicing Prediction Website". Visitors will look in vain for mention of evolution here, despite the old axiom that nothing in biology makes sense without it. The new 2010 version of this expression might sound like this: "Nothing in biology makes sense unless viewed in the light of computer science" .

Links and notes

We're glad we were able to tell you about this story on the day it was published. Perhaps this is 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 is: “Wow!” This discovery is a remarkable confirmation of Designed Creation and a huge challenge to the Darwinian empire. It is interesting how evolutionists will try to correct their simplified history of random mutations and natural selection, which was invented back in the 19th century, in the light of these new data.

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

Now that we're thinking about codes and computer science, we're starting to think about different paradigms for new research. What if the genome partially acts as a storage network? What if cryptography takes place in it or compression algorithms occur? We should remember about modern information systems and information storage technologies. Maybe we will even find elements of steganography. Undoubtedly, there are additional resistance mechanisms, such as duplications and corrections, that may help explain the existence of pseudogenes. Whole genome copying may be a response to stress. 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 resistance design, and help understand the cause of a disease.

Evolutionists find themselves in a major quandary. The researchers tried to modify the code, but got only cancer and mutations. How are they going to navigate the field of fitness when it's all mined with catastrophes waiting in the wings as soon as someone starts tampering with these inextricably linked codes? We know there is some built-in resilience and portability, but the whole picture is an incredibly complex, designed, optimized information system, not a jumble of pieces that can be played around endlessly. The whole idea of ​​code is the concept of intelligent design.

A.E. Wilder-Smith emphasized this. The code assumes an agreement between the two parts. An agreement is an agreement in advance. It implies planning and purpose. The SOS symbol, as Wilder-Smith would say, we use by convention as a distress signal. SOS does not 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. Similarly, an alanine codon, HCC, does not look, smell, or feel like alanine. A codon would have nothing to do with alanine unless there was a pre-established agreement between the two coding systems (protein code and DNA code) that "GCC should stand for alanine." To convey this agreement, a family of transducers, aminoacyl-tRNA synthetases, are used, which translate one code into another.

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

Sad to admit, evolutionists don't understand this, or even if they do, they're not going to give up. Incidentally, this week, just as the article on the Splicing Code was published, the most vicious and hateful anti-creation and intelligent design rhetoric in recent memory has been pouring from the pages of pro-Darwinian magazines and newspapers. We are yet to hear of many more such examples. And as long as they hold the microphones in their hands and control the institutions, many people will fall for them, thinking that science continues to give them a good reason. We are telling you all this so that you will read this material, study it, understand it, and stock up on the information you need in order to combat this fanatical, misleading nonsense with the truth. Now, go ahead!

Chemical composition and structural organization of the DNA molecule.

Nucleic acid molecules are very long chains consisting of many hundreds and 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 is made up of three components: a nitrogenous base, a carbohydrate, and phosphoric acid. AT compound each nucleotide DNA one of the four types of nitrogenous bases (adenine - A, thymine - T, guanine - G or cytosine - C) is included, as well as a deoxyribose carbon and a phosphoric acid residue.

Thus, DNA nucleotides differ only in the type of nitrogenous base.
The DNA molecule consists of a huge number of nucleotides connected in a chain in a certain sequence. Each type of DNA molecule has its own number and sequence of nucleotides.

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

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

Nucleotide DNA composition differs in different types of bacteria, fungi, plants, animals. But it does not change with age, it depends little on changes. environment. Nucleotides are paired, that is, the number of adenine nucleotides in any DNA molecule is equal to the number of thymidine nucleotides (A-T), 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: adenine of one chain is always connected by two hydrogen bonds only with Thymine of the other chain, and guanine by three hydrogen bonds with cytosine, that is, the nucleotide chains of one molecule DNA is complementary, complement 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 a residue 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.

Properties and functions of DNA.

DNA is a carrier of genetic information, written in the form of a sequence of nucleotides using the genetic code. DNA molecules are associated with two fundamental properties of living organisms - heredity and variability. During a process called DNA replication, two copies of the original chain are formed, which are inherited by daughter cells when they divide, so that 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 template) and translation (synthesis of proteins on an RNA template).

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

Genetic code, its properties.

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

1. Tripletity- a 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, the information is read continuously.
3. non-overlapping- the same nucleotide cannot be part of two or more triplets at the same time (not observed for some overlapping genes of viruses, mitochondria and bacteria that encode several frameshift proteins).
4. Unambiguity (specificity)- a certain codon corresponds to only one amino acid (however, the UGA codon in Euplotes crassus codes for two amino acids - cysteine ​​and selenocysteine)
5. Degeneracy (redundancy) Several codons can correspond to the same amino acid.
6. Versatility- the genetic code works the same way in organisms different levels complexity - from viruses to humans (genetic engineering methods are based on this; there are a number of exceptions, shown in the table in the section "Variations of the standard genetic code" below).
7. Noise immunity- mutations of nucleotide substitutions that do not lead to a change in the class of the encoded amino acid are called conservative; nucleotide substitution mutations that lead to a change in the class of the encoded amino acid are called radical.

5. DNA autoreproduction. Replicon and its functioning .

The process of self-reproduction of nucleic acid molecules, accompanied by the transmission by 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>, which controls the unwinding of the molecule DNA, DNA-polymerase<DNA polymerase> I and III, DNA-ligase<DNA ligase>), passes through a semi-conservative type with the formation of a replication fork<replication fork>; on one of the chains<leading strand> the synthesis of the complementary chain is continuous, and on the other<lagging strand> occurs due to the formation of Dkazaki fragments<Okazaki fragments>; R. - high-precision process, the error rate in which does not exceed 10 -9 ; in eukaryotes R. can occur at several points on the same molecule at once DNA; speed R. eukaryotes have about 100, and bacteria have about 1000 nucleotides per second.

6. Levels of organization of the eukaryotic genome .

In eukaryotic organisms, the transcriptional regulation mechanism is much more complex. As a result of cloning and sequencing of eukaryotic genes, specific sequences involved in transcription and translation have been found.
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 sits a specific polymerase. Pol I replicates ribosomal genes, Pol II replicates protein structural genes, Pol III replicates genes encoding small RNAs. The Pol I and Pol II promoters are upstream of the transcription initiation site, the Pol III promoter is within the framework of the structural gene; b) modulators - DNA sequences that enhance the level of transcription; c) enhancers - 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 starting point of RNA synthesis; d) terminators - specific sequences that stop both translation and transcription.
These sequences differ from prokaryotic sequences in their primary structure and location relative to the initiation codon, 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. The regulation of gene activity and their restoration in case of chemical or radiation damage occurs in the chromosome.

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 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:

There are mitotic and interphase forms of the structural organization of chromosomes, mutually passing into each other in the mitotic cycle - these are functional and physiological transformations

8. Packing levels 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 changes in individual characteristics;

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. Patterns of inheritance and variability of traits and their combinations 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 elementary structure of the gene level is the gene. The transfer of genes from parents to offspring is necessary for the development of certain traits in him. Although several forms of biological variability are known, only a disruption in the structure of genes 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 reproduce themselves with the preservation of individual structural features in a number of generations. The presence of chromosomes determines the allocation of the chromosomal level of organization of 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 immediate genetic environment - neighboring genes. The chromosomal organization of hereditary material serves necessary condition redistribution of the hereditary inclinations of 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 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, consequently, the development of traits balanced 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. Such differences were called heteropyknosis. The term " heterochromatin". There are euchromatin - the main part of the mitotic chromosomes, which undergoes the usual cycle of compaction decompactization during mitosis, and heterochromatin- regions of chromosomes that are constantly in a compact state.

In most eukaryotic species, the chromosomes contain both eu- and heterochromatic regions, the latter being a significant part of the genome. Heterochromatin located in the centromeric, sometimes in the telomeric regions. Heterochromatic regions were found in the euchromatic arms of chromosomes. They look like intercalations (intercalations) of heterochromatin into euchromatin. Such heterochromatin called intercalary. Compaction of chromatin. Euchromatin and heterochromatin differ in compactization cycles. Euhr. goes through a full cycle of compactization-decompactization from interphase to interphase, hetero. maintains a state of relative compactness. Differential staining. Different sections of heterochromatin are stained with different dyes, some areas - with some one, others - with several. Using various dyes and using chromosome rearrangements that break heterochromatic regions, many small regions in Drosophila have been characterized where the affinity for color is different from neighboring regions.

10. Morphological features of the metaphase chromosome .

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

In the body's metabolism leading 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, primary role in heredity, body variability, and protein synthesis.

Plan synthesis protein is stored in the cell nucleus, and direct synthesis occurs outside the nucleus, so it is necessary delivery service encoded 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. Due 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 connect them into a thread. So the letters of DNA are "rewritten" into the letters of RNA. The newly formed RNA chain is separated, and the DNA "ladder" twists again. The process of reading information from DNA and synthesizing its RNA template is called transcription , and the synthesized RNA is called informational or i-RNA .

After further modifications, this kind of encoded mRNA is ready. i-RNA comes out of the nucleus and goes to the site of protein synthesis, where the letters i-RNA are deciphered. Each set of three letters of i-RNA forms a "letter" that stands for one specific amino acid.

Another type of RNA looks for this amino acid, captures it with the help of an enzyme, and delivers it to the site of protein synthesis. This RNA is called transfer RNA, or tRNA. As the mRNA message is read and translated, the chain of amino acids grows. This chain twists and folds into a unique shape, creating one kind of protein. Even the process of protein folding is remarkable: to use a computer to calculate all options it would take 1027 (!) years to fold a medium-sized protein consisting of 100 amino acids. And for the formation of a chain of 20 amino acids in the body, it takes no more than one second, and this process occurs 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, then genetically all people are different : each is unique, has unique hereditary characteristics, character traits, abilities, temperament.

Such differences are explained differences in genotypes- sets of genes of an organism; each one is unique. The genetic traits of a particular organism are embodied in proteins - consequently, the structure of the protein of one person differs, although quite a bit, from the protein of another person.

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

Information about the primary structure of a protein encoded as a sequence of nucleotides in a section of a DNA molecule, gene - a unit of hereditary information of an organism. Each DNA molecule contains many genes. The totality of all the genes of an organism makes up its genotype . In this way,

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 code for proteins of specific organisms.

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

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

In this way, 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 nucleotide letters that differ in nitrogenous bases: A, T, G, C.

The main properties of the genetic code:

1. Genetic code triplet. A triplet (codon) is a sequence of three nucleotides that codes for 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, in this case 16 amino acids remain uncoded). Two nucleotides for coding amino acids are also not enough, since in this case only 16 amino acids can be encoded. This means that the smallest number of nucleotides encoding one amino acid must be at least three. In this case, the number of possible nucleotide triplets is 43 = 64.

2. Redundancy (degeneracy) The 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 there are 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 mRNA molecule, the triplets UAA, UAG, UGA are terminating codons, i.e. stop-signals that stop the synthesis of the polypeptide chain. The triplet corresponding to methionine (AUG), standing at the beginning of the DNA chain, does not encode an amino acid, but performs the function of initiating (exciting) reading.

3. Unambiguity code - along with redundancy, the code has the property uniqueness : each codon matches only one specific amino acid.

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

5. Genetic code non-overlapping and compact , i.e. 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 goes continuously triplet by triplet until stop-signals ( termination codons).

6. Genetic code universal , i.e., the nuclear genes of all organisms encode information about proteins in the same way, regardless of the level of organization and the 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 exactly reproduces all the details of the form 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. In these reactions, an exact, strictly specific sequence of monomeric units in the synthesized polymers is provided.

This is where 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 carried out quickly and accurately. The role of the matrix macromolecules of nucleic acids 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 arranged and fixed on the matrix in a strictly defined, predetermined order.

Then comes "crosslinking" of monomer units into a polymer chain, and the finished polymer is dropped from the matrix.

Thereafter matrix ready to the assembly of a new polymer molecule. It is clear that just as only one coin, one letter can be cast on a given mold, so only one polymer can be "assembled" on a given matrix molecule.

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 lat. 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 a DNA molecule that 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 replisome . The material for synthesis is free nucleotides present in the cytoplasm of cells. The biological meaning of replication lies in the exact transfer of hereditary information from the parent molecule to the daughter ones, which normally occurs during the division of somatic cells.

The DNA molecule consists of two complementary strands. These chains are held together by weak hydrogen bonds that can be broken by enzymes. The 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 mRNA 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 follow a matrix principle, comparable to the work of a printing press in a printing house. Information from DNA is copied over and over again. If errors occur during copying, they will be repeated in all subsequent copies.

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

2. Transcription (from Latin transcriptio - rewriting) - the process of RNA synthesis using DNA as a template, occurring 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 direction 3 " → 5". Transcription consists of steps initiation, elongation and termination . The unit of transcription is the operon, a fragment of the DNA molecule consisting of promoter, transcribed moiety, 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 mRNA molecule enters the cytoplasm on the ribosomes, where the synthesis of polypeptide chains takes place.

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

4. reverse transcription is the process of forming double-stranded DNA based on information from single-stranded RNA. This process is called reverse transcription, since the transfer of genetic information occurs in the “reverse” direction relative to transcription. The idea of ​​reverse transcription was initially very unpopular, as it went against the central dogma of molecular biology, which assumed that DNA is 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 integrates into 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 reversease is to create complementary DNA (cDNA) from the viral genome. The associated enzyme ribonuclease cleaves RNA, and reversetase synthesizes cDNA from the DNA double helix. cDNA is integrated into the host cell genome by integrase. The result is synthesis of viral proteins by the host cell that form new viruses. In the case of HIV, apoptosis (cell death) of T-lymphocytes is also programmed. In other cases, the cell may remain a distributor of viruses.

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

In this way, protein biosynthesis- this is one of the types of plastic exchange, during which the hereditary information encoded in the DNA genes is realized in a certain sequence of amino acids in protein molecules.

Protein molecules are essentially polypeptide chains made up of individual amino acids. But amino acids are not active enough to connect with each other on their own. Therefore, before they combine with each other and form a protein molecule, amino acids must activate . This activation occurs 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- RNA, which finds "its" amino acid and endures it into the ribosome.

Therefore, the ribosome receives various activated amino acids linked to their t- RNA. The ribosome is like conveyor to assemble a protein chain from various amino acids entering it.

Simultaneously with t-RNA, on which its own amino acid "sits", " 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 intermediary - matrix or messenger RNA (mRNA or i-RNA), which synthesized into the nucleus It is not influenced by DNA, so its composition reflects the composition of DNA. The RNA molecule is, as it were, a cast from the form of DNA. The synthesized mRNA enters the ribosome and, as it were, transfers it to this structure plan- in what order should the activated amino acids entering the ribosome be combined with each other in order to synthesize a certain protein. Otherwise, genetic information encoded in DNA is transferred to mRNA and then to protein.

The mRNA molecule enters the ribosome and flashes her. The segment that is in this moment in the ribosome codon (triplet), interacts in a completely specific way with a structure suitable for it triplet (anticodon) in the transfer RNA that brought the amino acid into the ribosome.

Transfer RNA with its amino acid approaches a certain codon of mRNA and connects with him; to the next, neighboring site of i-RNA joins another tRNA with a different amino acid and so on until the entire i-RNA chain is read, until all the amino acids are strung in the appropriate order, forming a protein molecule. And t-RNA, which delivered the amino acid to a specific site of the polypeptide chain, freed from its amino acid and exits the ribosome.

Then again in the cytoplasm, the desired amino acid can join 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 an mRNA template (transcription)
2. Synthesis of the polypeptide chain in ribosomes according to the program contained in i-RNA (translation) .

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

At prokaryotes transcription and translation can occur simultaneously because DNA is located in the cytoplasm. At eukaryote 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. The RNA is then transported in the cytoplasm to the site of protein synthesis.

GENETIC CODE, a system for recording hereditary information in the form of a sequence of nucleotide bases in DNA molecules (in some viruses - RNA), which determines the primary structure (arrangement 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 functions of enzymes (the principle of "one gene - one enzyme" by J. Beadle and E. Tatema, 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 raised by G. Gamow in 1954.

Based on an experiment in which the interactions of insertions and deletions of a pair of nucleotides were studied, in one of the genes of the bacteriophage T4, F. Crick and other scientists in 1961 determined general properties genetic code: triplet, i.e., each amino acid residue in the polypeptide chain corresponds to a set of three bases (triplet, or codon) in the DNA of the 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 encode several codons (synonymous codons). The authors suggested that codons do not overlap (each base belongs to only one codon). 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. Unraveling the mystery of the genetic code was one of the outstanding achievements of biology in the 20th century.

The implementation of the genetic code in the cell occurs in the course of two matrix processes - transcription and translation. The mediator between a gene and a 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 the ribosomes, the nucleotide sequence of the mRNA is read by transfer RNA (tRNA). The latter have an acceptor end, to which an amino acid residue is attached, and an adapter end, or triplet anticodon, which recognizes the corresponding mRNA codon. The interaction of codon and anti-codon occurs on the basis of complementary base pairing: Adenine (A) - Uracil (U), Guanine (G) - Cytosine (C); in this case, the mRNA base sequence is translated into the amino acid sequence of the synthesized protein. Different organisms use different codons for the same amino acid. different frequency. Reading of the mRNA encoding the polypeptide chain starts (initiates) from the AUG codon corresponding to the amino acid methionine. Less commonly in prokaryotes, the initiating 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 triple by triplet of tRNA until any of the three terminator codons, often called stop codons, is found on the mRNA: UAA, UAG , UGA (table). The reading of these triplets leads to the completion of the synthesis of the polypeptide chain.

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

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 significant; for example, in the mitochondria of some eukaryotes and in mycoplasmas, UGA codes for tryptophan. In addition, in some mRNAs of bacteria and eukaryotes, UGA encodes an unusual amino acid, selenocysteine, and UAG, in one of the archaebacteria, encodes 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 has 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 only two of the three bases in the triplet determine the amino acid.

Lit .: Crick F. N. a. 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. V. 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, strange as it may sound, everything is united by one, universal, common genetic code. It was formed over a long time period, and the process ended about 3.5 billion years ago. Therefore, in the structure of the code, traces of its evolution can be traced, from the moment of its inception to today.

When talking about the sequence of elements in the genetic code, it means that it is far from being 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 will read on the pages of books or newspapers will turn into ridiculous gibberish.

Basic 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 distinctive features.

So, the main properties of the genetic code are:

• triplet;
• degeneracy or redundancy;
• uniqueness;
• continuity;
• the versatility already mentioned above.

Let's take a closer look at each property.

1. Tripletity

This is when three nucleotide compounds 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.

Codons (they are code words!) are distinguished by their connection sequence 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 3 nucleotides each. This is equivalent 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 is observed when several codons are required to encrypt one amino acid, usually within 2-6. And only tryptophan can be encoded with a single triplet.

3. Uniqueness

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

4. Continuity

When writing this property of the genetic code, it should be remembered that codons, like chain links, are located not at a distance, but in direct proximity, one after another in the 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 that has barely hatched out of the ground, similar amino acids are encoded in identical triplets.

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