Self-reproduction of hereditary material. DNA replication

Replication- duplication of DNA molecules, resulting in the formation of two double helix DNA. Based on principles:

1) Complementarity– each of the two chains is a template for the synthesis of a complementary chain. This property is provided by the features chemical organization a DNA molecule consisting of two complementary strands. During the replication process, a complementary chain is synthesized on each polynucleotide chain of the parent DNA molecule. As a result, two identical double helices are formed from one DNA double helix.

2) Semi-conservative– each of the two double helices carries one strand

maternal DNA.

3) Anti-parallelism– each DNA strand has a specific orientation: the 5" end of one strand connects to the 3" end of the other, and vice versa.

4) Intermittency– replication is carried out in fragments.

Initiation of replication occurs in special regions of DNA called ori(from the English origin - beginning). They include a sequence of 300 nucleotide pairs that is recognized by specific proteins. The DNA double helix in these loci is divided into two chains, and, as a rule, areas of divergence of polynucleotide chains are formed on both sides of the origin of replication - replication forks, which move in directions opposite to the ori locus. Between replication forks a structure called replication eye, where new polynucleotide chains are formed on two strands of maternal DNA.

With the help of the helicase enzyme, which breaks hydrogen bonds, the DNA double helix unwinds at the origins of replication. The resulting single DNA strands are bound by special destabilizing proteins, which stretch the backbones of the chains, making their nitrogenous bases available for binding to complementary nucleotides located in the nucleoplasm. On each of the chains formed in the region of the replication fork, with the participation of the enzyme DNA polymerase, the synthesis of complementary chains is carried out.

During synthesis, replication forks move along the mother helix in opposite directions, capturing more and more new zones.

The separation of the helical strands of parental DNA by the enzyme helicase causes the appearance of supercoils in front of the replication fork. This is explained by the fact that for every 10 pairs of nucleotides that form one turn of the helix, the parent DNA must make one full turn around its axis. Therefore, for the replication fork to advance, the entire DNA molecule in front of it would have to rotate rapidly, which would require high costs energy. In reality this is not observed due to special class proteins called DNA topoisomerases. Topoisomerase breaks one of the DNA strands, which allows it to rotate around the second strand. This releases the accumulated tension in the DNA double helix.

Free nucleotides from the nucleoplasm, where they are present in the form of deoxyribonucleoside gryphosphates: dATP, dGTP, dCTP, dTTP, are attached to the released hydrogen bonds of the nucleotide sequences of the separated parent chains. The complementary nucleoside triphosphate forms hydrogen bonds with a specific base of the parent DNA strand. Then, with the participation of the enzyme DNA polymerase, it binds with a phosphodiester bond to the preceding nucleotide of the newly synthesized chain, releasing inorganic pyrophosphate.

As DNA polymerase adds the next nucleotide to the OH group at the 3" position of the previous nucleotide, the chain gradually lengthens at its 3" end.

A feature of DNA polymerase is its inability to begin the synthesis of a new polynucleotide chain by simply binding two nucleoside triphosphates: the 3"-OH end of any polynucleotide chain paired with the template DNA chain is required, to which DNA polymerase can only add new nucleotides. Such a polynucleotide the chain is called seed or primer.

The role of the primer for the synthesis of polynucleotide chains of DNA during replication is performed by short sequences RNA formed with the participation of an enzyme RNA primases. This feature of DNA polymerase means that only a DNA strand carrying a paired primer, which has a free 3'-OH end, can serve as a template for replication.

The ability of DNA polymerase to assemble a polynucleotide in the direction from the 5" to the 3" end with an antiparallel connection of two DNA strands means that the replication process must proceed differently on them. Indeed, if on one of the matrices (3" → 5") the assembly of a new chain occurs continuously from the 5" to the 3" end and it gradually lengthens at the 3" end, then the other chain synthesized on the matrix (5" → 3 "), would have to grow from the 3" to the 5" end. This contradicts the direction of action of the DNA polymerase enzyme.

It has now been established that the synthesis of the second strand of DNA is carried out in short fragments ( fragments of Okazaki) also in the direction from the 5" to the 3" end (by the type of sewing “back with a needle”). In prokaryotes, Okazaki fragments contain from 1000 to 2000 nucleotides; in eukaryotes they are much shorter (from 100 to 200 nucleotides). The synthesis of each such fragment is preceded by the formation of an RNA primer about 10 nucleotides long. The newly formed fragment is combined with the previous fragment using the DNA ligase enzyme after removal of its RNA primer.

Due to these features, the replication fork is asymmetrical. Of the two synthesized daughter chains, one is built continuously, its synthesis proceeds faster and this chain is called leading. The synthesis of the other strand is slower, since it is assembled from individual fragments that require the formation and then removal of an RNA primer. Therefore, such a chain is called lagging (lagging). Although individual fragments are formed in the 5" → 3" direction, overall this chain grows in the 3" → 5" direction.

Due to the fact that two replication forks usually begin from the ori locus, going in opposite directions, the synthesis of the leading strands in them occurs at different circuits maternal DNA .

The end result The process of replication is the formation of two DNA molecules, the nucleotide sequence of which is identical to that in the parent DNA double helix.

The considered sequence of events occurring during replicative synthesis suggests the participation the whole system enzymes: helicases, topoisomerases, destabilizing proteins, DNA polymerase and others, acting together in the region of the replication fork.

DNA replication in prokaryotes and eukaryotes is basically similar; however, the rate of synthesis in eukaryotes (about 100 nucleotides/s) is an order of magnitude lower than in prokaryotes (1000 nucleotides/s). The reason for this may be the formation of eukaryotic DNA in fairly strong compounds with proteins, which complicates its despiralization necessary for replicative synthesis.

The DNA fragment from the point of origin of replication to the point of its termination forms a replication unit - replicon. Once started in starting point, replication continues until the entire replicon has been duplicated. Eukaryotic chromosomes contain big number replicons. In this regard, the duplication of the DNA molecule located along the eukaryotic chromosome begins at several points. In different replicons, duplication can occur in different time or at the same time.

In a reaction catalyzed by reverse transcriptase.

cDNA is often used to clone eukaryotic genes into prokaryotes. Complementary DNA is also produced by retroviruses (HIV-1, HIV-2, Simian immunodeficiency virus) and is then integrated into the host DNA, forming a provirus.

Eukaryotic genes can often be expressed in prokaryotic cells. In the most simple case, the method involves inserting eukaryotic DNA into the prokaryotic genome, then transcribing the DNA into mRNA and then translating the mRNA into proteins. Prokaryotic cells do not have enzymes to excise introns, and therefore introns from eukaryotic DNA must be excised before being inserted into the prokaryotic genome. DNA complementary to mature mRNA is thus called complementary DNA - cDNA(cDNA). Successful expression of proteins encoded in eukaryotic cDNA in prokaryotes also requires prokaryotic gene regulatory elements (eg, promoters).

One of the methods for obtaining the necessary gene (DNA molecule), which will be subject to replication (cloning) with the release of a significant number of replicas, is the construction of complementary DNA (cDNA) on mRNA. This method requires the use of reverse transcriptase, an enzyme that is present in some RNA viruses and enables the synthesis of DNA on an RNA template.

The method is widely used to obtain cDNA and involves isolating from total tissue mRNA the mRNA that encodes translation certain protein(for example, interferon, insulin) with further synthesis on this mRNA as a template for the required cDNA using reverse transcriptase.

The gene that was obtained using the above procedure (cDNA) must be introduced into the bacterial cell in such a way that it is integrated into its genome. To do this, recombinant DNA is formed, which consists of cDNA and a special DNA molecule that acts as a conductor, or vector, capable of penetrating the recipient into the cell. Viruses or plasmids are used as vectors for cDNA. Plasmids are small circular DNA molecules that are located separately from the nucleoid of the bacterial cell, contain several genes important for the function of the entire cell (for example, antibiotic resistance genes and can replicate independently of the main genome (DNA) of the cell. Biologically important and practically useful for genetic engineering The properties of plasmids are their ability to transfer from one cell to another through the mechanism of transformation or conjugation, as well as the ability to be included in the bacterial chromosome and replicate with it.

After the discovery of the principle molecular organization such a substance as DNA began to develop in 1953 molecular biology. Further in the process of research, scientists found out how DNA is recombined, its composition and how our human genome is structured.

Every day on molecular level are happening very complex processes. How is the DNA molecule structured, what does it consist of? And what role do DNA molecules play in a cell? Let's talk in detail about all the processes occurring inside the double chain.

What is hereditary information?

So where did it all begin? Back in 1868 they found it in the nuclei of bacteria. And in 1928, N. Koltsov put forward the theory that it is in DNA that all genetic information about a living organism. Then J. Watson and F. Crick found a model for the now well-known DNA helix in 1953, for which they deservedly received recognition and an award - the Nobel Prize.

What is DNA anyway? This substance consists of 2 united threads, or rather spirals. A section of such a chain with certain information is called a gene.

DNA stores all the information about what kind of proteins will be formed and in what order. The DNA macromolecule is a material carrier of incredibly voluminous information, which is recorded in a strict sequence of individual bricks - nucleotides. There are 4 nucleotides in total; they complement each other chemically and geometrically. This principle of complementation, or complementarity, in science will be described later. This rule plays key role in encoding and decoding genetic information.

Since the DNA strand is incredibly long, there are no repetitions in this sequence. Every living creature has its own unique strand of DNA.

Functions of DNA

Functions include storage of hereditary information and its transmission to offspring. Without this function, the genome of a species could not be preserved and developed over thousands of years. Organisms that have undergone severe gene mutations are more likely to not survive or lose the ability to produce offspring. This is what happens natural protection from degeneration of the species.

Another significant important function— implementation of stored information. A cell cannot create a single vital protein without those instructions that are stored in a double chain.

Nucleic acid composition

It is now known for certain what the nucleotides themselves—the building blocks of DNA—are made of. They contain 3 substances:

• Orthophosphoric acid.
• Nitrogenous base. Pyrimidine bases - which have only one ring. These include thymine and cytosine. Purine bases, which contain 2 rings. These are guanine and adenine.
• Sucrose. DNA contains deoxyribose, RNA contains ribose.

The number of nucleotides is always equal to the number of nitrogenous bases. In special laboratories, the nucleotide is broken down and the nitrogenous base is isolated from it. This is how they study individual properties these nucleotides and possible mutations in them.

Levels of organization of hereditary information

There are 3 levels of organization: genetic, chromosomal and genomic. All the information needed for the synthesis of a new protein is contained in a small section of the chain - the gene. That is, the gene is considered the lowest and simplest level of information encoding.

Genes, in turn, are assembled into chromosomes. Thanks to this organization of the carrier of hereditary material, groups of characteristics alternate according to certain laws and are transmitted from one generation to another. It should be noted that there are an incredible number of genes in the body, but the information is not lost even when it is recombined many times.

There are several types of genes:

• According to their functional purpose, there are 2 types: structural and regulatory sequences;
• Based on their influence on the processes occurring in the cell, they distinguish: supervital, lethal, conditionally lethal genes, as well as mutator and antimutator genes.

Genes are located along the chromosome in linear order. In chromosomes, information is not focused randomly; it exists certain order. There is even a map that shows the positions, or loci, of genes. For example, it is known that chromosome No. 18 encrypts data about the color of a child’s eyes.

What is a genome? This is the name given to the entire set of nucleotide sequences in an organism’s cell. The genome characterizes whole view, and not an individual.

What is the human genetic code?

The fact is that all the enormous potential human development laid down already during the period of conception. All hereditary information, which is necessary for the development of the zygote and the growth of the child after birth, is encoded in genes. DNA sections are the most basic carriers of hereditary information.

Humans have 46 chromosomes, or 22 somatic pairs plus one sex-determining chromosome from each parent. This diploid set of chromosomes encodes the entire physical appearance of a person, his mental and physical abilities and susceptibility to diseases. Somatic chromosomes outwardly indistinguishable, but they carry various information, since one of them is from the father, the other from the mother.

The male code differs from the female code in the last pair of chromosomes - XY. The female diploid set is the last pair, XX. Males receive one X chromosome from their biological mother, which is then passed on to their daughters. Sex Y chromosome passed on to sons.

Human chromosomes vary greatly in size. For example, the smallest pair of chromosomes is No. 17. And the biggest pair is 1 and 3.

The diameter of the double helix in humans is only 2 nm. The DNA is coiled so tightly that it fits inside the small nucleus of a cell, although it would be up to 2 meters long if untwisted. The length of the helix is ​​hundreds of millions of nucleotides.

How is the genetic code transmitted?

So, what role do DNA molecules play in cell division? Genes - carriers of hereditary information - are located inside every cell of the body. To pass on their code to a daughter organism, many creatures divide their DNA into 2 identical helices. This is called replication. During the replication process, DNA unwinds and special “machines” complete each strand. After the genetic helix bifurcates, the nucleus and all organelles begin to divide, and then the entire cell.

But humans have a different process of gene transmission - sexual. The signs of the father and mother are mixed, in the new genetic code contains information from both parents.

The storage and transmission of hereditary information is possible due to the complex organization of the DNA helix. After all, as we said, the structure of proteins is encrypted in genes. Once created at the time of conception, this code will copy itself throughout life. The karyotype (personal set of chromosomes) does not change during the renewal of organ cells. The transfer of information is carried out with the help of sex gametes - male and female.

Only viruses containing one strand of RNA are not capable of transmitting their information to their offspring. Therefore, they need human or animal cells to reproduce.

Implementation of hereditary information

In the nucleus of the cell constantly occur important processes. All information recorded in chromosomes is used to build proteins from amino acids. But the DNA chain never leaves the nucleus, so the help of another is needed here important connection= RNA. It is RNA that is able to penetrate the nuclear membrane and interact with the DNA chain.

Through the interaction of DNA and 3 types of RNA, all encoded information is realized. At what level does the implementation of hereditary information occur? All interactions occur at the nucleotide level. Messenger RNA copies a section of the DNA chain and brings this copy to the ribosome. Here the synthesis of a new molecule from nucleotides begins.

In order for the mRNA to copy the necessary part of the chain, the helix unfolds and then, upon completion of the recoding process, is restored again. Moreover, this process can occur simultaneously on 2 sides of 1 chromosome.

Principle of complementarity

They consist of 4 nucleotides - adenine (A), guanine (G), cytosine (C), thymine (T). They are connected hydrogen bonds according to the rule of complementarity. The work of E. Chargaff helped establish this rule, since the scientist noticed some patterns in the behavior of these substances. E. Chargaff discovered that molar ratio adenine to thymine is equal to one. And in the same way, the ratio of guanine to cytosine is always equal to one.

Based on his work, geneticists formed a rule for the interaction of nucleotides. The complementarity rule states that adenine combines only with thymine, and guanine only combines with cytosine. During the decoding of the helix and the synthesis of a new protein in the ribosome, this alternation rule helps to quickly find the necessary amino acid that is attached to the transfer RNA.

RNA and its types

What is hereditary information? nucleotides in a double strand of DNA. What is RNA? What is her job? RNA, or ribonucleic acid, helps extract information from DNA, decode it and create it based on the principle of complementarity necessary for cells proteins.

There are 3 types of RNA in total. Each of them performs strictly its own function.

1. Informational (mRNA), or also called matrix. It goes straight into the center of the cell, into the nucleus. Finds in one of the chromosomes the necessary genetic material to build a protein and copies one of the sides of the double strand. Copying occurs again according to the principle of complementarity.
2. Transport- This small molecule, which has nucleotide decoders on one side, and amino acids corresponding to the main code on the other side. The task of tRNA is to deliver it to the “workshop,” that is, to the ribosome, where it synthesizes the necessary amino acid.
3. rRNA is ribosomal. It controls the amount of protein that is produced. It consists of 2 parts - an amino acid and a peptide section.

The only difference in decoding is that RNA does not have thymine. Instead of thymine, uracil is present here. But then, during the process of protein synthesis, tRNA still correctly installs all the amino acids. If any failures occur in decoding information, then a mutation occurs.

Repair of damaged DNA molecule

The process of restoring a damaged double strand is called repair. During the repair process, damaged genes are removed.

Then the required sequence of elements is exactly reproduced and cut back into the same place on the chain from where it was removed. All this happens thanks to special chemicals- enzymes.

Why do mutations occur?

Why do some genes begin to mutate and cease to perform their function - storing vital hereditary information? This occurs due to an error in decoding. For example, if adenine is accidentally replaced with thymine.

There are also chromosomal and genomic mutations. Chromosomal mutations occur when sections of hereditary information are lost, duplicated, or even transferred and inserted into another chromosome.

Genomic mutations are the most serious. Their cause is a change in the number of chromosomes. That is, when instead of a pair - a diploid set, a triploid set is present in the karyotype.

Most famous example triploid mutation is Down syndrome, in which the personal set of chromosomes is 47. In such children, 3 chromosomes are formed in place of the 21st pair.

There is also a known mutation called polyploidy. But polyploidy occurs only in plants.

Watson and Crick showed that the formation of hydrogen bonds and a regular double helix is ​​possible only when the larger purine base adenine (A) in one chain has as its partner in the other chain the smaller pyrimidine base thymine (T), and guanine (G) associated with cytosine (C). This pattern can be represented as follows: Correspondence A "T and G" C is called the complementarity rule, and the chains themselves - complementary. According to this rule, the adenine content in DNA is always equal to the thymine content, and the amount of guanine is always equal to the amount of cytosine. It should be noted that two DNA strands, although chemically different, carry the same information, since due to complementarity, one strand uniquely specifies the other.

The structure of RNA is less ordered. It is usually a single-stranded molecule, although the RNA of some viruses consists of two strands. But even this RNA is more flexible than DNA. Some regions in the RNA molecule are mutually complementary and, when the strand is bent, pair up to form double-stranded structures (hairpins). This primarily applies to transfer RNAs (tRNAs). Some bases in tRNA undergo modification after the molecule is synthesized. For example, sometimes methyl groups are added to them.

FUNCTION OF NUCLEIC ACIDS One of the main functions of nucleic acids is to determine the synthesis of proteins. Information about the structure of proteins encoded in the nucleotide sequence of DNA must be transmitted from one generation to another, and therefore its error-free copying is necessary, i.e. synthesis of exactly the same DNA molecule (replication).Replication and transcription. From a chemical point of view, synthesis nucleic acid this is polymerization, i.e. sequential connection of building blocks. Nucleoside triphosphates serve as such blocks; the reaction can be represented as follows:
The energy required for synthesis is released when pyrophosphate is removed, and the reaction is catalyzed by special enzymes called DNA polymerases.

As a result of such a synthetic process, we would obtain a polymer with random sequence grounds. However, most polymerases only work in the presence of a pre-existing template nucleic acid, which dictates which nucleotide will be added to the end of the chain. This nucleotide must be complementary to the corresponding template nucleotide, so new chain turns out to be complementary to the original one. By then using the complementary strand as a template, we obtain an exact copy of the original.

DNA consists of two mutually complementary strands. During replication, they diverge, and each of them serves as a template for the synthesis of a new chain:

This creates two new double helices with the same base sequence as the original DNA. Sometimes the replication process “fails” and mutations occur (see also HEREDITY). As a result of DNA transcription, cellular RNAs (mRNA, rRNA and tRNA) are formed:They are complementary to one of the DNA strands and are a copy of the other strand, except that uracil takes the place of thymine. In this way, you can get many RNA copies of one of the DNA chains.In a normal cell, information is transmitted only in the direction of DNA® DNA and DNA ® RNA. However, other processes are also possible in cells infected with a virus: RNA® RNA and RNA ® DNA. The genetic material of many viruses is an RNA molecule, usually single-stranded. Having penetrated the host cell, this RNA is replicated to form a complementary molecule, on which, in turn, many copies of the original viral RNA are synthesized:Viral RNA can be transcribed by the enzyme- reverse transcriptase- in DNA that is sometimes incorporated into the chromosomal DNA of the host cell. This DNA now carries viral genes, and after transcription, viral RNA can appear in the cell. So after long time, during which no virus is detected in the cell, it will reappear in it without re-infection. Viruses whose genetic material is inserted into the host cell's chromosome are often the cause of cancer.

Solution principles typical tasks in molecular biology

Problem 1

One of the chains of the DNA molecule has the following order of nucleotides: ACG TAG CTA HCG... Write the order of nucleotides in the complementary DNA chain.

Explanation of the solution to the problem. It is known that two chains in a DNA molecule are connected by hydrogen bonds between complementary nucleotides (A-T, G-C). The order of nucleotides in a known DNA chain is:

A C G T A G C T A G C G

T G C A T C G A T C G C is the order of nucleotides in the complementary DNA chain.

Answer: the order of nucleotides in the complementary strand of DNA: TGCATCGATTCGC

Problem 2

The order of nucleotides in one of the chains of the DNA molecule is as follows: AGCTACGTACA... Determine the order of amino acids in the polypeptide encoded by this genetic information.

Explanation of the solution to the problem. It is known that the matrix for the synthesis of a polypeptide is an mRNA molecule, the matrix for the synthesis of which, in turn, is one of the chains of the DNA molecule. The first stage of protein biosynthesis: transcription - rewriting the order of nucleotides from a DNA chain to mRNA. The synthesis of mRNA occurs according to the principle of complementarity (A-U, G-C). Instead of thymine in mRNA, the nitrogenous base is uracil. Known DNA strand:

A G C T A C G T A C G A...

U C G A U G C A U G C U... is the order of nucleotides in i-RNA.

One amino acid is encoded by three adjacent nucleotides of the i-RNA chain (codons) - we break the i-RNA into codons:

UCG, AUG, CAU, HCU and using the codon table we find the corresponding amino acids: UCG - corresponds to serine, AUG - methionine, CAC - hiscidine, HCU - alanine.

Answer: the order of amino acids in the encoded polypeptide: ser - met - gis - ala ...

Problem 3

One of the chains of the DNA molecule has the following nucleotide order: GGCATGGATCAT...

a) Determine the amino acid sequence in the corresponding polypeptide if it is known that RNA is also synthesized on a complementary DNA strand.

b) How will it change? primary structure polypeptide if the third nucleotide is dropped?

Explanation of the solution to the problem.

a) It is known that the mRNA molecule is synthesized according to the principle of complementarity on one of the chains of the DNA molecule. We know the order of nucleotides in one DNA strand and are told that mRNA is synthesized on a complementary strand. Therefore, it is necessary to build a complementary DNA strand, remembering that adenine corresponds to thymine, and guanine to cytosine. The double strand of DNA will look like this:

G G C A T G G A T C A T…

C C G T A C C T A G T A ...

Now you can build a molecule and - RNA. It should be remembered that instead of thymine, the RNA molecule contains uracil. Hence:

DNA: C C G T A C C T A G A T...

I-RNA: G G C A U G G A U C A U….

Three adjacent nucleotides (triplet, codon) of mRNA determine the addition of one amino acid. We find the amino acids corresponding to triplets using the codon table. Codon GHC corresponds to gly, A UG – met, GAU – asp, CAU – gis. Therefore, the sequence of amino acids of a section of the polypeptide chain will be: gly - met - asp - gis ...

b) If the third nucleotide falls out in the chain of a DNA molecule, it will look like this:

GGATGGATTSAT…

Complementary chain: CCTACCTAGTA...

Information i-RNA: GGAUGGAUCA...

All codons will change. The first codon GGA corresponds to the amino acid gly, the second UUG corresponds to three, the third AUC corresponds to ile, and the fourth is incomplete. Thus, the polypeptide section will look like:

Gly - three - ile..., i.e. there will be a significant change in the order and number of amino acids in the polypeptide.

Answer: a) sequence of amino acids in the polypeptide: gly – met – asp – gis...,

b) after the loss of the third nucleotide, the sequence of amino acids in the polypeptide is: gly - three - ile...

Problem 4

The polypeptide has the following order of amino acids: fen - tre - ala - ser - arg...

a) Determine one of the variants of the nucleotide sequence of the gene encoding this polypeptide.

b) Which tRNAs (with which anticodons) are involved in the synthesis of this protein? Write one of the possible options.

Explanation of the solution to the problem.

a) The polypeptide has the following sequence amino acids: fen - tre - ala - ser - arg... Using the codon table, we find one of the triplets that encodes the corresponding amino acids. Fen - UUU, tre - ATSU, ala - GCU, ser - AGU, arg - AGA. Therefore, the mRNA encoding this polypeptide will have the following nucleotide sequence:

UUUATSUGTSUAGUAGA...

The order of nucleotides in the coding strand of DNA is: AATGATCGATCATCT...

Complementary DNA strand: TTTACTGCTAGTAGA...

b) Using the codon table, we find one of the variants of the mRNA nucleotide sequence (as in the previous version). T-RNA anticodons are complementary to i-RNA codons:

i-RNA UUUATSUGTSUAGUAGA...

tRNA anticodons AAA, UGA, CGA, UCA, UCU

Answer: a) one of the variants of the nucleotide sequence in the gene will be:

AAATGATSGATTSATTST

TTTATCTTGCTAGTAGA,

b) t-RNAs with anticodons (one of the options): AAA, UGA, CGA, UCA, UCU will participate in the synthesis of this protein.

Self-control tasks

1. One of the chains of a DNA molecule fragment has the following nucleotide sequence: AGTGATGTTGGTGTA... What will be the structure of the second chain of the DNA molecule?

2. A section of one DNA strand has the following sequence of nucleotides: TGAACACTAGTTTAGAATACCA... What is the sequence of amino acids in the polypeptide corresponding to this genetic information?

3. A section of one DNA strand has the following structure: TATTTCTTTTTTGT... Indicate the structure of the corresponding part of the protein molecule synthesized with the participation of the complementary chain. How will the primary structure of a protein fragment change if the second nucleotide from the beginning is lost?

4. Part of a protein molecule has the following sequence of amino acids: ser - ala - tyr - lei - asp... Which tRNAs (with which anticodons) are involved in the synthesis of this protein? Write one of the possible options.

5. Write one of the variants of the nucleotide sequence in the gene if the encoded protein has the following primary structure:

Ala - tre - liz - asn - ser - gln - glu - asp ...