Genetic information; its properties. The concept of genetic information, its transmission What is hereditary information

Introduction

1. The concept of heredity

3.Mechanism of heredity

Conclusion

Bibliography

Introduction

In the organic world there are amazing similarities between parents and children, between brothers and sisters, and other relatives. This similarity is determined by heredity, that is, the ability of living beings to preserve and transmit over generations the structural, functional and developmental features characteristic of a species or population. Heredity ensures the constancy and diversity of life forms and underlies the transmission of hereditary inclinations responsible for the formation of the characteristics and properties of the organism. Thanks to heredity, some species (for example, the lobe-finned fish Coelacanth, which lived in the Devonian period) remained almost unchanged for hundreds of millions of years, reproducing a huge number of generations during this time.

1. The concept of heredity

Heredity is the inherent property of all organisms to repeat the same signs and developmental features over a series of generations; due to the transfer during the process of reproduction from one generation to another of the material structures of the cell, containing programs for the development of new individuals from them. Thus, heredity ensures the continuity of the morphological, physiological and biochemical organization of living beings, the nature of their individual development, or ontogenesis. As a general biological phenomenon, heredity is the most important condition for the existence of differentiated forms of life, characteristics of organisms, although it is violated by variability - the emergence of differences between organisms. Affecting a wide variety of traits at all stages of the ontogenesis of organisms, heredity manifests itself in the patterns of inheritance of traits, i.e., their transmission from parents to descendants.

Sometimes the term heredity refers to the transmission from one generation to another of infectious principles (the so-called infectious heredity) or skills of learning, education, traditions (the so-called social or signal heredity). Such an expansion of the concept of heredity beyond its biological and evolutionary essence debatable.

Thus, heredity is the most important feature of living organisms, which consists in the ability to transmit their properties and functions from parents to descendants.

2.Identification of the gene. Main function of the gene

A gene is a unit of storage, transmission and implementation of hereditary information. A gene is a specific section of a DNA molecule, the structure of which encodes the structure of a specific polypeptide (protein). This seemingly quite simple position has been known to many since school. It is now clear that many sections of DNA do not code for proteins, but probably perform regulatory functions. In any case, in the structure of the human genome, only about 2% of the DNA represents the sequences on the basis of which the synthesis of messenger RNA occurs (transcription process), which then determines the sequence of amino acids during protein synthesis (translation process). It is currently believed that there are about 30 thousand genes in the human genome.

The main function of a gene is to encode information for the synthesis of a specific protein.

Gene properties

1. discreteness - immiscibility of genes;

2. stability - the ability to maintain structure;

3. lability - the ability to mutate many times;

4. multiple allelism - many genes exist in a population in multiple molecular forms;

5. allelicity - in the genotype of diploid organisms there are only two forms of the gene;

6. specificity - each gene encodes its own product;

7. pleiotropy - multiple effect of a gene;

8. expressiveness - the degree of expression of a gene in a trait;

9. penetrance - the frequency of manifestation of a gene in the phenotype;

10. amplification - increasing the number of copies of a gene.

Gene classification

1. Structural genes are unique components of the genome, representing a single sequence encoding a specific protein or certain types of RNA.

2. Functional genes - regulate the functioning of structural genes.

3.Mechanism of heredity

The cells through which the continuity of generations is carried out - specialized sex cells during sexual reproduction and unspecialized (somatic) cells of the body during asexual reproduction - do not carry the very signs and properties of future organisms, but only the makings of their development. These inclinations are genes. A gene is a section of a DNA molecule (or a section of a chromosome) that determines the possibility of developing a separate elementary trait. A DNA molecule consists of two polynucleotide chains twisted around each other into a spiral. Chains are built from large number monomers of 4 types - nucleotides, the specificity of which is determined by one of 4 nitrogenous bases. The combination of three adjacent nucleotides in a DNA chain makes up the genetic code. DNA is accurately reproduced during cell division, which ensures the transmission of hereditary characteristics and specific forms of metabolism over a series of generations of cells and organisms.

A gene is a group of adjacent nucleotides that encode one protein that determines one trait. The number of genes is very large: a person has tens of thousands of them. The same gene can influence the development of a number of traits, just as several genes can influence the formation of one trait.

Each species of plants and animals has its own quantitative set of chromosomes. In all organisms of the same species, each gene is located in the same place on a strictly defined chromosome. Each cell of the human body contains 46 chromosomes. Almost all the chromosomes in the set are presented in pairs, each of the 22 pairs includes identical chromosomes of the same size, and the 23rd pair is the sex chromosomes: in women it consists of identical chromosomes XX, and in men - XY. In the halogen set of chromosomes there is only one gene responsible for the development of this trait. The diploid set of chromosomes (in somatic cells) contains two homologous chromosomes and, accordingly, two genes that determine the development of one particular trait.

Genetic information is encoded in the sequence of nitrogenous bases contained in the DNA molecule. Nitrogenous bases can be considered as “letters” of the genetic alphabet. The sequence of bases forms “words”. Genes are a kind of “sentences” written in genetic language. Accordingly, the genetic content of an organism is like a “book” made up of genetic sentences. Unlike the strictly defined arrangement of nitrogenous bases in two complementary parts, there are no restrictions as to the order in which the bases must follow each other along the same chain. Thanks to this, there is a virtually unlimited number of different DNA molecules. The number of possible genetic messages encoded by sufficiently long DNA chains is practically unlimited. Three evolutionarily fixed universal processes are responsible for the reproduction of hereditary properties in generations of plants, animals and humans.

Remember what structure proteins have. What determine the structure, shape and properties of a protein molecule? Why are the proteins of each organism different from each other?

Such signs of living things as self-reproduction, heredity and variability manifest themselves already at the molecular genetic level. They are associated with certain organic substances and with the hereditary (genetic) program of the body.

DNA and genes. By the beginning of the 50s. XX century scientists have suggested that the main function of genes is to determine the structure of proteins, primarily enzyme proteins. Numerous studies have shown that most transformations of substances in living systems occur under the control of enzymes. Therefore, scientists have put forward an assumption that can be formulated as follows: “one gene - one enzyme protein.” Only the discovery of the double helix of the DNA molecule made it possible to find out general principles the process of transferring genetic information in living things.

DNA molecules serve as carriers of hereditary information. They store information about the structure. properties and functions of proteins in each cell and the organism as a whole. A section of a DNA molecule containing information about the structure of one molecule of a protein-enzyme was called a genome (from the Greek genos - genus, origin). It is the hereditary factor of any living body of nature.

Genetic code. Proteins contain 20 amino acids, the sequence of which determines the structure and properties of proteins. Information about the structure of a protein must be recorded as a nucleotide sequence on DNA. The rules for translating the sequence of nucleotides in a nucleic acid into the amino acid sequence of a protein are called the genetic code (from French code - a collection of conventional abbreviations and names).

It was deciphered in the 60s. XX century as a result of a series of experiments and mathematical calculations.

A DNA molecule consists of a set of four nucleotides (A, T, G, C). If each amino acid corresponded to one nucleotide, then only 4 amino acids could be encoded. If we assume that one amino acid is encoded by a combination of two nucleotides, then in this case only 42 = 16 amino acids can be encoded. Scientists have suggested that one amino acid must be encoded by three nucleotides. This number of combinations is more than enough to encode 20 amino acids (Fig. 29). In addition, one amino acid can correspond to not one, but several such combinations.

Rice. 29. The rule for converting the nucleotide sequence in DNA into the amino acid sequence in protein

The genetic code has a number of properties (Fig. 30). The code is intertwined - each amino acid corresponds to a combination of 3 nucleotides. There are 64 such combinations - triplets (codons). Of these, 61 triplets are semantic, i.e., correspond to 20 amino acids, and 3 are meaningless stop codons that do not correspond to amino acids. They fill the gaps between genes.

Rice. 30. Some properties of the genetic code

The code is unambiguous - each triplet (codon) corresponds to only one amino acid. The code is degenerate (redundant) - there are amino acids that are encoded by more than one triplet (codon). Most often, amino acids have 2-3 triplets (codons).

The code is universal - all organisms have the same genetic code, i.e. the same amino acids in different organisms are encoded by the same triplets (codons).

The code is continuous - within the gene there are no gaps between triplets (codons).

The code is non-overlapping - the final nucleotide of one triplet (codon) cannot serve as the beginning of another.

In a certain section of the DNA molecule, the amino acid sequence of a single protein molecule is encrypted using a genetic code. Since protein synthesis occurs in the cytoplasm, and DNA molecules are located in the nucleus, a structure is needed that would copy the nucleotide sequence on DNA and transfer it to the site of protein synthesis. Information RNA serves as such an intermediary.

In addition to the information carrier, substances are needed that would ensure the delivery of the corresponding amino acids to the site of synthesis and determine their places in the polypeptide chain. Such substances are transfer RNAs. They not only ensure the delivery of amino acids to the site of synthesis, but also their coding. Protein synthesis occurs on ribosomes, the assembly of which requires another type of nucleic acid - ribosomal RNA. Consequently, for the implementation of hereditary information in living things at the molecular genetic level, DNA molecules and all types of RNA are required.

Exercises based on the material covered

1. Why were the hereditary properties of the organism initially associated with proteins?
2. How is the protein structure encoded in a DNA molecule?
3. What is a gene?
4. What is the genetic code? Describe each of its properties.
5. What is the function of stop codons?

French geneticists have discovered an unusual mechanism for the transmission of hereditary information in mice that is not associated with genomic DNA. Sometimes mice may exhibit characteristics characteristic of their parents, even if the mice do not have the genes that determine these characteristics. Apparently, innate qualities are determined not only by DNA molecules inherited from parents - generally recognized carriers of hereditary information - but also by other molecules, primarily RNA, which are not only the “results of reading” the information recorded in DNA, but also actively influence the process itself “reading”, forcing the cell to “read” in genes what is not there.

Gene Kit encodes a multifunctional protein that affects, among other things, the formation of the dark pigment melanin. At one time, geneticists who studied the operation of this gene in mice artificially created a non-working version of the gene by inserting a large “extra” piece of DNA into it. In mice heterozygous for this mutation (that is, having one normal copy of the gene and one altered one), Kit+/-) the paws and the tip of the tail remain uncolored (white). Homozygotes (owners of two damaged copies of the gene, Kit -/-) die soon after birth.

French geneticists from the University of Nice, crossing heterozygotes with each other Kit +/-, faced a violation of the laws of classical genetics. According to these laws, a quarter of the offspring should have died immediately (genotype Kit -/-), half - have white paws and tail (genotype Kit +/-), and a quarter have normal coloring (genotype Kit +/+). Instead, of the 57 surviving mice obtained from eight crosses, only three were normally colored, and the remaining 54 had white paws and tails.

Genetic analysis showed that out of 54 white-tailed mice, 24 have the genotype Kit +/+, that is, they simply do not have the “white-tail gene.” These mice must have had normal coloring! It turned out that the mice inherited a certain congenital trait from their parents, without inheriting the genes responsible for the formation of this trait.

The results needed verification. Scientists began to cross heterozygotes Kit +/- with normally colored wild-type mice Kit +/+. In this case, half of the offspring receive the genotype Kit +/+, half - Kit +/-. That is, a 1:1 distribution of white-tailed and common mice was expected. Instead, again almost all the pups turned out to be white-tailed, although many of them had the genotype Kit +/+.

If you cross these abnormal mice (white-tailed, but without the “white-tailed gene”) with each other, then their offspring also turn out to be white-tailed. True, in subsequent generations, the manifestations of this trait weaken and eventually disappear - the phenotype (that is, the structure of the body, physical characteristics) finally comes into agreement with the genotype.

Thus, it turned out that if at least one of the mouse’s parents (it doesn’t matter whether the father or mother) is white-tailed, then the mouse is likely to be white-tailed, regardless of whether it itself has the “white-tailed gene.”

It became obvious that the carrier of hereditary information in this case is not genes or DNA. What then? Naturally, suspicion fell primarily on RNA—the second class of “information” biopolymers of a living cell. As is known, RNA acts as an intermediary between genes (sections of DNA) and proteins (which determine most phenotypic traits). Hereditary information, recorded as a sequence of nucleotides in a DNA molecule, is first “transcribed” - rewritten into a sequence of RNA nucleotides. The resulting RNA molecules (“transcripts”) undergo complex processing. Extra pieces (introns) are cut out of them, special signal regions are sewn onto them, etc. The result is “mature messenger RNA,” which is used as an instruction (template) for protein synthesis.

Scientists have suggested that the white-tailed mouse with the genotype Kit +/+ may be caused by the fact that parental RNA read from a mutant copy of the gene entered the fertilized egg from which it developed Kit. Although the mouse itself has both copies of the gene Kit- normal, the presence of “mutant” RNA may somehow affect their work, especially the process of transcription (reading) and subsequent modifications of RNA.

This assumption was completely confirmed. Researchers found that heterozygotes Kit +/- from a mutant copy of the gene Kit“mutant” RNA is read, which subsequently breaks down into fragments of different sizes. If these fragments are isolated and introduced into a control fertilized egg (obtained from wild gray-tailed parents), a white-tailed mouse with the genotype will develop from the egg Kit +/+. Apparently, these RNA fragments not only regulate the reading (transcription) of the gene Kit, which leads to a decrease in protein concentration Kit in cells, but also somehow self-replicate, otherwise they could not be transmitted over a number of generations. How can they reproduce themselves? After all, they were initially “read” from a damaged copy of the gene, which the parents had, but which the offspring do not have!

The mechanism of self-replication of these RNAs is still unknown. Apparently, they modify the transcription process of a “healthy” gene Kit or subsequent processing of the RNA read from it, so that as a result, the RNA read from the “healthy” gene turns out to be “mutant”. This is somewhat reminiscent of the mechanism of spread of so-called prion diseases (“mad cow disease”): the appearance of a “misfolded” protein stimulates the incorrect folding of other protein molecules, and as a result, a kind of chain reaction of the formation of “mutant” proteins occurs, although the gene encoding this protein this does not change.

Scientists also discovered that in the sperm of white-tailed mice Kit +/- the RNA content is sharply increased compared to normal sperm. This indicates active transcription of a number of genes, including the gene Kit. Normally, in spermatozoa, most genes are “silent” and almost no RNA is produced.

It must be said that this is not the first time that living organisms have discovered the transmission of hereditary information not through DNA nucleotide sequences, but by other means. There is even a special term for such phenomena - epigenetic (“supragenetic”) inheritance. The role of RNA in epigenetic inheritance in higher animals has been proven for the first time. Something similar was recently discovered in higher plants (Lolle et al., 2005. Genome-wide non-mendelian inheritance of extra-genomic information in Arabidopsis // Nature. V. 434. P. 505—509).

The sensational result obtained by French geneticists, along with some other discoveries recent years, shows that classical ideas about the nature of “hereditary information” and the mechanisms of its “reading” are too simplified. In reality, everything is much more complicated. We have to admit that the analogies between living organisms and artificial information systems(for example, computers), which came into fashion at the end of the 20th century, are largely invalid. Unlike a computer, in living systems the so-called “information”, its media, as well as “devices” for reading and implementing it are fused together and practically inseparable. For example, RNA turns out to be not only the “result of reading” the genetic code and a means of transmitting information from DNA to the protein synthesis system, but also an active participant and regulator of the “reading” process itself, capable of changing the meaning of the read “messages”. It is no coincidence that some leading theorists are currently questioning the very applicability of the concept of “information” to DNA and RNA nucleotide sequences.

(see Information, Genetics) - a program of the properties of an organism, embedded in inherited structures (DNA, partly in RNA) and received from ancestors in the form of a genetic code. Inherited information determines the morphological structure, growth, development, metabolism, mental makeup, predisposition to certain diseases and genetic defects of the body.

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