The DNA genetic code is made up of. What is the genetic code: general information

In any cell and organism, all features of the anatomical, morphological and functional nature are determined by the structure of the proteins that are included in them. The hereditary property of an organism is the ability to synthesize certain proteins. Amino acids are located in a polypeptide chain, on which biological characteristics depend.
Each cell has its own sequence of nucleotides in the DNA polynucleotide chain. This is the genetic code of DNA. Through it, information about the synthesis of certain proteins is recorded. About what the genetic code is, about its properties and genetic information is described in this article.

A bit of history

The idea that perhaps a genetic code exists was formulated by J. Gamow and A. Down in the middle of the twentieth century. They described that the nucleotide sequence responsible for the synthesis of a particular amino acid contains at least three links. Later they proved the exact number of three nucleotides (this is a unit of the genetic code), which was called a triplet or codon. There are sixty-four nucleotides in total, because the acid molecule, where or RNA occurs, consists of residues of four different nucleotides.

What is the genetic code

The method of coding the amino acid protein sequence due to the nucleotide sequence is characteristic of all living cells and organisms. That's what the genetic code is.
There are four nucleotides in DNA:

• adenine - A;
• guanine - G;
• cytosine - C;
• thymine - T.

They are indicated by capital letters in Latin or (in Russian-language literature) Russian.
RNA also has four nucleotides, but one of them is different from DNA:

• adenine - A;
• guanine - G;
• cytosine - C;
• uracil - U.

All nucleotides line up in chains, and in DNA a double helix is ​​obtained, and in RNA it is single.
Proteins are built on where they, located in a certain sequence, determine its biological properties.

Properties of the genetic code

Tripletity. The unit of the genetic code consists of three letters, it is triplet. This means that the twenty existing amino acids are coded for by three specific nucleotides called codons or trilpets. There are sixty-four combinations that can be created from four nucleotides. This amount is more than enough to encode twenty amino acids.
Degeneracy. Each amino acid corresponds to more than one codon, with the exception of methionine and tryptophan.
Unambiguity. One codon codes for one amino acid. For example, in the gene of a healthy person with information about the beta target of hemoglobin, the triplet of GAG and GAA encodes A in everyone who has sickle cell anemia, one nucleotide is changed.
Collinearity. The amino acid sequence always corresponds to the nucleotide sequence that the gene contains.
The genetic code is continuous and compact, which means that it does not have "punctuation marks". That is, starting at a certain codon, there is a continuous reading. For example, AUGGUGTSUUAAAUGUG will be read as: AUG, GUG, CUU, AAU, GUG. But not AUG, UGG, and so on, or in any other way.
Versatility. It is the same for absolutely all terrestrial organisms, from humans to fish, fungi and bacteria.

Table

Not all available amino acids are present in the presented table. Hydroxyproline, hydroxylysine, phosphoserine, iodo derivatives of tyrosine, cystine, and some others are absent, since they are derivatives of other amino acids encoded by mRNA and formed after protein modification as a result of translation.
From the properties of the genetic code, it is known that one codon is able to code for one amino acid. The exception is the genetic code that performs additional functions and codes for valine and methionine. RNA, being at the beginning with a codon, attaches a t-RNA that carries formyl methion. Upon completion of the synthesis, it splits off itself and takes the formyl residue with it, transforming into a methionine residue. Thus, the above codons are the initiators of the synthesis of a chain of polypeptides. If they are not at the beginning, then they are no different from others.

genetic information

This concept means a program of properties that is transmitted from ancestors. It is embedded in heredity as a genetic code.
Implemented during protein synthesis genetic code:

• information and RNA;
• ribosomal rRNA.

Information is transmitted by direct communication (DNA-RNA-protein) and reverse (environment-protein-DNA).
Organisms can receive, store, transfer it and use it most effectively.
Being inherited, information determines the development of an organism. But due to interaction with the environment, the reaction of the latter is distorted, due to which evolution and development take place. Thus, new information is laid in the body.

The calculation of the laws of molecular biology and the discovery of the genetic code illustrated the need to combine genetics with Darwin's theory, on the basis of which a synthetic theory of evolution emerged - non-classical biology.
Heredity, variability and Darwin's natural selection are complemented by genetically determined selection. Evolution is realized at the genetic level through random mutations and inheritance of the most valuable traits that are most adapted to the environment.

Deciphering the human code

In the nineties, the Human Genome Project was launched, as a result of which, in the 2000s, fragments of the genome containing 99.99% of human genes were discovered. Fragments that are not involved in protein synthesis and are not encoded remained unknown. Their role is still unknown.

Chromosome 1, last discovered in 2006, is the longest in the genome. More than three hundred and fifty diseases, including cancer, appear as a result of disorders and mutations in it.

The role of such research can hardly be overestimated. When they discovered what the genetic code is, it became known what patterns development occurs, how the morphological structure, the psyche, predisposition to certain diseases, metabolism and vices of individuals are formed.

Gene- a structural and functional unit of heredity that controls the development of a particular trait or property. Parents pass on a set of genes to their offspring during reproduction. A great contribution to the study of the gene was made by Russian scientists: Simashkevich E.A., Gavrilova Yu.A., Bogomazova O.V. (2011)

Currently, in molecular biology, it has been established that genes are sections of DNA that carry any integral information - about the structure of one protein molecule or one RNA molecule. These and other functional molecules determine the development, growth and functioning of the organism.

At the same time, each gene is characterized by a number of specific regulatory DNA sequences, such as promoters, which are directly involved in regulating the expression of the gene. Regulatory sequences can be located either in close proximity to the open reading frame encoding the protein, or the beginning of the RNA sequence, as is the case with promoters (the so-called cis cis-regulatory elements), and at a distance of many millions of base pairs (nucleotides), as in the case of enhancers, insulators and suppressors (sometimes classified as trans-regulatory elements trans-regulatory elements). Thus, the concept of a gene is not limited to the coding region of DNA, but is a broader concept that includes regulatory sequences.

Originally the term gene appeared as a theoretical unit for the transmission of discrete hereditary information. The history of biology remembers disputes about which molecules can be carriers of hereditary information. Most researchers believed that only proteins can be such carriers, since their structure (20 amino acids) allows you to create more options than the structure of DNA, which is composed of only four types of nucleotides. Later, it was experimentally proved that it is DNA that includes hereditary information, which was expressed as the central dogma of molecular biology.

Genes can undergo mutations - random or purposeful changes in the sequence of nucleotides in the DNA chain. Mutations can lead to a change in the sequence, and therefore a change in the biological characteristics of a protein or RNA, which, in turn, can result in a general or local altered or abnormal functioning of the organism. Such mutations in some cases are pathogenic, since their result is a disease, or lethal at the embryonic level. However, not all changes in the nucleotide sequence lead to a change in the protein structure (due to the effect of the degeneracy of the genetic code) or to a significant change in the sequence and are not pathogenic. In particular, the human genome is characterized by single nucleotide polymorphisms and copy number variations. copy number variations), such as deletions and duplications, which make up about 1% of the entire human nucleotide sequence. Single nucleotide polymorphisms, in particular, define different alleles of the same gene.

The monomers that make up each of the DNA chains are complex organic compounds that include nitrogenous bases: adenine (A) or thymine (T) or cytosine (C) or guanine (G), a five-atom sugar-pentose-deoxyribose, named after which and received the name of DNA itself, as well as the residue of phosphoric acid. These compounds are called nucleotides.

Gene properties

1. discreteness - immiscibility of genes;
2. stability - the ability to maintain a structure;
3. lability - the ability to repeatedly mutate;
4. multiple allelism - many genes exist in a population in a variety of molecular forms;
5. allelism - in the genotype of diploid organisms, only two forms of the gene;
6. specificity - each gene encodes its own trait;
7. pleiotropy - multiple effect of a gene;
8. expressivity - the degree of expression of a gene in a trait;
9. penetrance - the frequency of manifestation of a gene in the phenotype;
10. amplification - an increase in the number of copies of a gene.

Classification

1. Structural genes are unique components of the genome, representing a single sequence encoding a specific protein or some types of RNA. (See also the article housekeeping genes).
2. Functional genes - regulate the work of structural genes.

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

Four nucleotides are used in DNA - adenine (A), guanine (G), cytosine (C), thymine (T), which in Russian-language literature are denoted by the letters A, G, C and T. These letters make up the alphabet of the genetic code. In RNA, the same nucleotides are used, with the exception of thymine, which is replaced by a similar nucleotide - uracil, which is denoted by the letter U (U in Russian-language literature). In DNA and RNA molecules, nucleotides line up in chains and, thus, sequences of genetic letters are obtained.

Genetic code

There are 20 different amino acids used in nature to build proteins. Each protein is a chain or several chains of amino acids in a strictly defined sequence. This sequence determines the structure of the protein, and therefore all its biological properties. The set of amino acids is also universal for almost all living organisms.

The implementation of genetic information in living cells (that is, the synthesis of a protein encoded by a gene) is carried out using two matrix processes: transcription (that is, the synthesis of mRNA on a DNA template) and translation of the genetic code into an amino acid sequence (synthesis of a polypeptide chain on mRNA). Three consecutive nucleotides are enough to encode 20 amino acids, as well as the stop signal, which means the end of the protein sequence. A set of three nucleotides is called a triplet. Accepted abbreviations corresponding to amino acids and codons are shown in the figure.

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 simultaneously be part of two or more triplets (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 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 in the "Variations of the standard genetic code" section 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.

Protein biosynthesis and its steps

Protein biosynthesis- a complex multi-stage process of synthesis of a polypeptide chain from amino acid residues, occurring on the ribosomes of cells of living organisms with the participation of mRNA and tRNA molecules.

Protein biosynthesis can be divided into stages of transcription, processing and translation. During transcription, the genetic information encoded in DNA molecules is read and this information is written into mRNA molecules. During a series of successive stages of processing, some fragments that are unnecessary in subsequent stages are removed from mRNA, and nucleotide sequences are edited. After the code is transported from the nucleus to the ribosomes, the actual synthesis of protein molecules occurs by attaching individual amino acid residues to the growing polypeptide chain.

Between transcription and translation, the mRNA molecule undergoes a series of successive changes that ensure the maturation of a functioning template for the synthesis of the polypeptide chain. A cap is attached to the 5' end, and a poly-A tail is attached to the 3' end, which increases the lifespan of the mRNA. With the advent of processing in a eukaryotic cell, it became possible to combine gene exons to obtain a greater variety of proteins encoded by a single DNA nucleotide sequence - alternative splicing.

Translation consists in the synthesis of a polypeptide chain in accordance with the information encoded in messenger RNA. The amino acid sequence is arranged using transport RNA (tRNA), which form complexes with amino acids - aminoacyl-tRNA. Each amino acid has its own tRNA, which has a corresponding anticodon that “matches” the mRNA codon. During translation, the ribosome moves along the mRNA, as the polypeptide chain builds up. Energy for protein synthesis is provided by ATP.

The finished protein molecule is then cleaved from the ribosome and transported to the right place in the cell. Some proteins require additional post-translational modification to reach their active state.

Genetic functions of DNA lie in the fact that it provides the storage, transmission and implementation of hereditary information, which is information about the primary structure of proteins (i.e., their amino acid composition). The relationship of DNA with protein synthesis was predicted by biochemists J. Beadle and E. Tatum back in 1944 while studying the mechanism of mutations in the mold fungus Neurospora. Information is recorded as a specific sequence of nitrogenous bases in a DNA molecule using the genetic code. The deciphering of the genetic code is considered one of the great discoveries of natural science in the 20th century. and are equated in importance with the discovery of nuclear energy in physics. Success in this area is associated with the name of the American scientist M. Nirenberg, in whose laboratory the first codon, YYY, was deciphered. However, the whole process of decoding took more than 10 years, many famous scientists from different countries participated in it, and not only biologists, but also physicists, mathematicians, cybernetics. A decisive contribution to the development of the mechanism for recording genetic information was made by G. Gamow, who was the first to suggest that a codon consists of three nucleotides. Through the joint efforts of scientists, a complete characterization of the genetic code was given.

The letters in the inner circle are the bases in the 1st position in the codon, the letters in the second circle are
the bases in 2nd position and the letters outside the second circle are the bases in 3rd position.
In the last circle - abbreviated names of amino acids. NP - non-polar,
P - polar amino acid residues.

The main properties of the genetic code are: tripletity, degeneracy and non-overlapping. Tripletity means that the sequence of three bases determines the inclusion of a specific amino acid in the protein molecule (for example, AUG - methionine). The degeneracy of the code is that the same amino acid can be encoded by two or more codons. Non-overlapping means that the same base cannot be present in two adjacent codons.

The code is found to be universal, i.e. The principle of recording genetic information is the same in all organisms.

Triplets that code for the same amino acid are called synonymous codons. They usually have the same bases in the 1st and 2nd positions and differ only in the third base. For example, the inclusion of the amino acid alanine in a protein molecule is encoded by synonymous codons in the RNA molecule - GCA, GCC, GCG, GCY. The genetic code contains three non-coding triplets (nonsense codons - UAG, UGA, UAA), which play the role of stop signals in the process of reading information.

It has been established that the universality of the genetic code is not absolute. While maintaining the principle of coding common to all organisms and the characteristics of the code, in some cases a change in the semantic load of individual code words is observed. This phenomenon was called the ambiguity of the genetic code, and the code itself was called quasi-universal.

Read also other articles topics 6 "Molecular bases of heredity":

Go to reading other topics of the book "Genetics and selection. Theory. Tasks. Answers".

Lecture 5 Genetic code

Concept definition

The genetic code is a system for recording information about the sequence of amino acids in proteins using the sequence of nucleotides in DNA.

Since DNA is not directly involved in protein synthesis, the code is written in the language of RNA. RNA contains uracil instead of thymine.

Properties of the genetic code

1. Tripletity

Each amino acid is encoded by a sequence of 3 nucleotides.

Definition: A triplet or codon is a sequence of three nucleotides that codes for one amino acid.

The code cannot be monopleth, since 4 (the number of different nucleotides in DNA) is less than 20. The code cannot be doublet, because 16 (the number of combinations and permutations of 4 nucleotides by 2) is less than 20. The code can be triplet, because 64 (the number of combinations and permutations from 4 to 3) is greater than 20.

2. Degeneracy.

All amino acids, with the exception of methionine and tryptophan, are encoded by more than one triplet:

2 AKs for 1 triplet = 2.

9 AKs x 2 triplets = 18.

1 AK 3 triplets = 3.

5 AKs x 4 triplets = 20.

3 AKs x 6 triplets = 18.

A total of 61 triplet codes for 20 amino acids.

3. The presence of intergenic punctuation marks.

Definition:

Gene is a segment of DNA that codes for one polypeptide chain or one molecule tPHK, rRNA orsPHK.

GenestPHK, rPHK, sPHKproteins do not code.

At the end of each gene encoding a polypeptide, there is at least one of 3 triplets encoding RNA stop codons, or stop signals. In mRNA they look like this: UAA, UAG, UGA . They terminate (end) the broadcast.

Conventionally, the codon also applies to punctuation marks AUG - the first after the leader sequence. (See lecture 8) It performs the function of a capital letter. In this position, it codes for formylmethionine (in prokaryotes).

4. Uniqueness.

Each triplet encodes only one amino acid or is a translation terminator.

The exception is the codon AUG . In prokaryotes, in the first position (capital letter) it codes for formylmethionine, and in any other position it codes for methionine.

5. Compactness, or the absence of intragenic punctuation marks.
Within a gene, each nucleotide is part of a significant codon.

In 1961, Seymour Benzer and Francis Crick experimentally proved that the code is triplet and compact.

The essence of the experiment: "+" mutation - the insertion of one nucleotide. "-" mutation - loss of one nucleotide. A single "+" or "-" mutation at the beginning of a gene corrupts the entire gene. A double "+" or "-" mutation also spoils the entire gene.

A triple "+" or "-" mutation at the beginning of the gene spoils only part of it. A quadruple "+" or "-" mutation again spoils the entire gene.

The experiment proves that the code is triplet and there are no punctuation marks inside the gene. The experiment was carried out on two adjacent phage genes and showed, in addition, the presence of punctuation marks between genes.

6. Versatility.

The genetic code is the same for all creatures living on Earth.

In 1979 Burrell opened ideal human mitochondrial code.

Definition:

“Ideal” is the genetic code in which the rule of degeneracy of the quasi-doublet code is fulfilled: If the first two nucleotides in two triplets coincide, and the third nucleotides belong to the same class (both are purines or both are pyrimidines), then these triplets encode the same amino acid .

There are two exceptions to this rule in generic code. Both deviations from the ideal code in the universal relate to the fundamental points: the beginning and end of protein synthesis:

codon	Universal the code	Mitochondrial codes
		Vertebrates	Invertebrates	Yeast	Plants
	STOP				STOP
With UA
A G A		STOP
		STOP			230 substitutions do not change the class of the encoded amino acid. to tearability. In 1956, Georgy Gamov proposed a variant of the overlapped code. According to the Gamow code, each nucleotide, starting from the third in the gene, is part of 3 codons. When the genetic code was deciphered, it turned out that it was non-overlapping, i.e. each nucleotide is part of only one codon. Advantages of the overlapped genetic code: compactness, lesser dependence of the protein structure on the insertion or deletion of a nucleotide. Disadvantage: high dependence of the protein structure on nucleotide substitution and restriction on neighbors. In 1976, the DNA of the φX174 phage was sequenced. It has a single stranded circular DNA of 5375 nucleotides. The phage was known to encode 9 proteins. For 6 of them, genes located one after another were identified. It turned out that there is an overlap. The E gene is completely within the gene D . Its initiation codon appears as a result of a one nucleotide shift in the reading. Gene J starts where gene ends D . Gene initiation codon J overlaps with the termination codon of the gene D due to a shift of two nucleotides. The design is called "reading frame shift" by a number of nucleotides that is not a multiple of three. To date, overlap has only been shown for a few phages. Information capacity of DNA There are 6 billion people on Earth. Hereditary information about them enclosed in 6x10 9 spermatozoa. According to various estimates, a person has from 30 to 50 thousand genes. All humans have ~30x10 13 genes, or 30x10 16 base pairs, which make up 10 17 codons. The average book page contains 25x10 2 characters. The DNA of 6x10 9 spermatozoa contains information equal in volume to approximately 4x10 13 book pages. These pages would take up the space of 6 NSU buildings. 6x10 9 sperm take up half of a thimble. Their DNA takes up less than a quarter of a thimble.

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, a literal record of the nucleotide sequence in DNA molecules from one human cell (46 chromosomes) would require 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 structural features of DNA molecules allow them to store a huge amount of information about all the features 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 in the 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 sequence of nucleotides "encodes" information about various types of RNA: information, or template (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 simultaneously be part of two or more triplets (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 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 in the "Variations of the standard genetic code" section 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 the 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 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 stained 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 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 strands 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 have one arm missing, but they are not in the karyotype (chromosome set) of a person. In some chromosomes, there may be secondary constrictions that separate a region called the satellite from the body of the chromosome.