1. Explain the sequence of transmission of genetic information: gene - protein - trait.

2. Remember which protein structure determines its structure and properties. How is this structure encoded in the DNA molecule?

3. What is the genetic code?

4. Describe the properties of the genetic code.

7. Reactions of matrix synthesis. Transcription

Information about a protein is recorded as a nucleotide sequence in DNA and is located in the nucleus. Actually protein synthesis occurs in the cytoplasm on ribosomes. Therefore, protein synthesis requires a structure that would carry information from DNA to the site of protein synthesis. Such an intermediary is information, or matrix, RNA, which transmits information from a specific gene of the DNA molecule to the site of protein synthesis on ribosomes.

In addition to the information carrier, substances are needed that would ensure the delivery of amino acids to the site of synthesis and the determination of their place in the polypeptide chain. Such substances are transfer RNAs, which provide coding and delivery of amino acids to the site of synthesis. Protein synthesis proceeds on ribosomes, the body of which is built from ribosomal RNA. This means that another type of RNA is needed - ribosomal.

Genetic information is realized in three types of reactions: RNA synthesis, protein synthesis, DNA replication. In each of them, the information contained in the linear sequence of nucleotides is used to create another linear sequence: either nucleotides (in RNA or DNA molecules) or amino acids (in protein molecules). It has been experimentally proved that it is DNA that serves as a template for the synthesis of all nucleic acids. These biosynthetic reactions are called matrix synthesis. The sufficient simplicity of matrix reactions and their one-dimensionality made it possible to study and understand their mechanism in detail, in contrast to other processes occurring in the cell.

Transcription

The process of RNA biosynthesis from DNA is called transcription. This process takes place in the nucleus. On the DNA matrix, all types of RNA are synthesized - informational, transport and ribosomal, which subsequently participate in protein synthesis. The genetic code on DNA is transcribed into messenger RNA during transcription. The reaction is based on the principle of complementarity.

RNA synthesis has a number of features. The RNA molecule is much shorter and is a copy of only a small section of DNA. Therefore, only a certain section of DNA, where information about a given nucleic acid is located, serves as a matrix. The newly synthesized RNA never remains bound to the original DNA template, but is released after the end of the reaction. The transcription process proceeds in three stages.

First stage - initiation- the beginning of the process. Synthesis of RNA copies begins with a specific area on the DNA, which is called promoter. This zone contains a specific set of nucleotides that are start signals. The process is catalyzed by enzymes RNA polymerases. The RNA polymerase enzyme binds to the promoter, unwinds the double helix, and breaks the hydrogen bonds between the two strands of DNA. But only one of them serves as a template for RNA synthesis.

Second phase - elongation. In this stage, the main process takes place. On one DNA strand, as on a matrix, nucleotides line up according to the principle of complementarity (Fig. 19). The RNA polymerase enzyme, moving step by step along the DNA chain, connects the nucleotides to each other, while constantly unwinding the DNA double helix further. As a result of this movement, an RNA copy is synthesized.

Third stage - termination. This is the final stage. RNA synthesis continues until stop signal- a certain sequence of nucleotides that stops the movement of the enzyme and RNA synthesis. The polymerase is separated from the DNA and the synthesized RNA copy. Simultaneously, the RNA molecule is also removed from the matrix. DNA rebuilds the double helix. Synthesis completed. Depending on the DNA region, ribosomal, transport, and messenger RNAs are synthesized in this way.

The template for transcription of the RNA molecule is only one of the DNA strands. However, different strands of DNA can serve as templates for two adjacent genes. Which of the two strands will be used for synthesis is determined by the promoter, which directs the RNA polymerase enzyme in one direction or another.

After transcription, the messenger RNA molecule of eukaryotic cells undergoes rearrangement. Nucleotide sequences that do not carry information about this protein are cut out in it. This process is called splicing. Depending on the cell type and stage of development, different parts of the RNA molecule can be removed. Consequently, different RNAs are synthesized in one section of DNA, which carry information about different proteins. This ensures the transfer of significant genetic information from a single gene, and also facilitates genetic recombination.

Rice. 19. Synthesis of messenger RNA. 1 - DNA chain; 2 - synthesized RNA

Questions and tasks for self-control

1. What reactions are related to matrix synthesis reactions?

2. What is the initial matrix for all reactions of matrix synthesis?

3. What is the name of the process of mRNA biosynthesis?

4. What types of RNA are synthesized on DNA?

5. Set the sequence of the mRNA fragment if the corresponding DNA fragment has the sequence: AAGCTCTGATTCTGATCGGACCTAATGA.

8. Protein biosynthesis

Proteins are essential components of all cells, so the most important process of plastic metabolism is protein biosynthesis. It occurs in all cells of organisms. These are the only components of the cell (other than nucleic acids), the synthesis of which is carried out under the direct control of the genetic material of the cell. The entire genetic apparatus of the cell - DNA and different types of RNA - is tuned for protein synthesis.

Gene- This is the section of the DNA molecule responsible for the synthesis of one protein molecule. For protein synthesis, it is necessary that a certain gene with DNA be copied in the form of a messenger RNA molecule. This process has been discussed previously. Protein synthesis is a complex multi-stage process and depends on the activity of various types of RNA. The following components are required for direct protein biosynthesis:

1. Messenger RNA - a carrier of information from DNA to the site of synthesis. mRNA molecules are synthesized during transcription.

2. Ribosomes - organelles where protein synthesis occurs.

3. A set of essential amino acids in the cytoplasm.

4. Transfer RNAs encoding amino acids and carrying them to the site of synthesis on ribosomes.

5. ATP - a substance that provides energy for the processes of coding amino acids and the synthesis of a polypeptide chain.

Transfer RNA structure and amino acid coding

Transfer RNAs (tRNAs) are small molecules with 70 to 90 nucleotides. tRNAs account for approximately 15% of all cell RNA. The function of tRNA depends on its structure. The study of the structure of tRNA molecules showed that they are folded in a certain way and look like clover leaf(Fig. 20). Loops and double sections are distinguished in the molecule, connected due to the interaction of complementary bases. The most important is the central loop, which contains anticodon - nucleotide triplet corresponding to the code for a specific amino acid. With its anticodon, tRNA is able to combine with the corresponding codon on mRNA according to the principle of complementarity.

Rice. 20. The structure of the tRNA molecule: 1 - anticodon; 2 - the place of attachment of the amino acid

Each tRNA can only carry one of the 20 amino acids. This means that there is at least one tRNA for each amino acid. Since an amino acid can have several triplets, the number of tRNA species is equal to the number of amino acid triplets. Thus, the total number of tRNA species corresponds to the number of codons and is equal to 61. No tRNA corresponds to three stop codes.

At one end of the tRNA molecule there is always a guanine nucleotide (5'-end), and at the other (3'-end) there are always three CCA nucleotides. It is to this end that the amino acid is attached (Fig. 21). Each amino acid attaches to its specific tRNA with the corresponding anticodon. The mechanism of this attachment is associated with the work of specific enzymes - aminoacyl-tRNA synthetases, which attach each amino acid to the corresponding tRNA. Each amino acid has its own synthetase. The connection of an amino acid with tRNA is carried out due to the energy of ATP, while the macroergic bond passes into a bond between tRNA and amino acid. This is how amino acids are activated and encoded.

Stages of protein biosynthesis. The process of synthesis of a polypeptide chain, carried out on a ribosome, is called broadcast. Messenger RNA (mRNA) is an intermediary in the transfer of information about the primary structure of the protein, tRNA transfers encoded amino acids to the site of synthesis and ensures the sequence of their compounds. Ribosomes assemble the polypeptide chain.

The transmission and implementation of hereditary information is based on the reactions of matrix synthesis. There are only three of them: DNA replication, transcription and translation. All these reactions are related to plastic exchange reactions and require energy expenditure and the participation of enzymes.

Replication.

replication- self-doubling of DNA molecules - underlies the transmission of hereditary information from generation to generation. As a result of the replication of one parent DNA molecule, two daughter ones are formed, each of which is a double helix, in which one strand of DNA is the parent, and the other is newly synthesized. Replication requires various enzymes, nucleotides, and energy.

With the help of special enzymes, the hydrogen bonds connecting the complementary bases of the two strands of maternal DNA are broken. The strands of DNA diverge. Molecules of the DNA polymerase enzyme move along the parent DNA strands and sequentially connect nucleotides to form daughter DNA strands. The process of adding nucleotides follows the principle of complementarity. As a result, two DNA molecules are formed identical to the parent and to each other.

protein biosynthesis.

Protein biosynthesis, i.e. The process of realization of hereditary information proceeds in two stages. At the first stage, information about the primary structure of the protein is copied from DNA to mRNA. This process is called transcription. The second stage - translation - occurs on ribosomes. During translation, protein is synthesized from amino acids in accordance with the sequence recorded in mRNA, i.e. the nucleotide sequence is translated into an amino acid sequence. Thus, the process of realization of hereditary information can be expressed by the scheme:

DNA → mRNA → protein → property, sign

Transcription– synthesis of messenger RNA on a DNA template. This process takes place where there is DNA. In eukaryotes, transcription occurs in the nucleus, mitochondria, and chloroplasts (in plants), while in prokaryotes, directly in the cytoplasm. During transcription, the DNA molecule is the template, and the mRNA is the product of the reaction.

Transcription begins with the separation of DNA strands, which occurs in the same way as during replication (hydrogen bonds are broken with the help of enzymes). Then the RNA polymerase enzyme sequentially combines the nucleotides into a chain according to the principle of complementarity, synthesizing an mRNA molecule. The resulting mRNA molecule is separated and sent to the cytoplasm "in search of" the ribosome.

Protein synthesis on ribosomes is called broadcast. Translation in eukaryotes occurs on ribosomes located in the cytoplasm, on the surface of the EPS, in mitochondria and in chloroplasts (in plants), and in prokaryotes on ribosomes in the cytoplasm. Translation involves mRNA, tRNA, ribosomes, amino acids, ATP molecules, and enzymes.

· Amino acids serve as a material for the synthesis of a protein molecule.

· ATP is a source of energy for connecting amino acids with each other.

· Enzymes participate in the attachment of amino acids to tRNA and in the connection of amino acids with each other.

· Ribosomes They consist of rRNA and protein molecules that form an active center in which the main events of translation take place.

· Messenger RNA in this case, it is a template for the synthesis of a protein molecule. mRNA triplets, each of which codes for an amino acid, are called codons.

· Transfer RNAs bring amino acids to ribosomes and participate in the translation of the nucleotide sequence into the amino acid sequence. Transfer RNAs, like other types of RNA, are synthesized on a DNA template. They look like a clover leaf (Fig. 28.3). Three nucleotides located at the top of the central loop of the tRNA molecule form anticodon.

Translation progress.

Translation begins with the binding of mRNA to the ribosome. The ribosome moves along the mRNA, moving one triplet each time. Two triplets (codons) of mRNA can simultaneously be in the active center of the ribosome. Each of these codons is matched by a tRNA that has a complementary anticodon and carries a specific amino acid. Hydrogen bonds form between codons and anticodons, holding the tRNA in the active site. At this time, a peptide bond is formed between amino acids. The growing polypeptide chain is "suspended" on the tRNA, which entered the active center of the latter. The ribosome advances one triplet, resulting in a new codon and corresponding tRNA in the active site. The released tRNA is separated from the mRNA and sent for a new amino acid.

Biology Olympiad. school stage. 2016-2017 academic year.

10-11 grade

1. Wrong correlation of cell and tissue is

A) root hair - integumentary tissue

B) cell of the polysade parenchyma - the main tissue

C) trailing cell - integumentary tissue

D) companion cell - excretory tissue

2. For the event, which will take place in three days, ripe pears are needed. However, those pears that were bought for this purpose were not yet ripe. The ripening process can be accelerated by putting them

A) in a dark place

B) in the refrigerator

B) on the windowsill

D) in a bag of thick paper along with ripe apples

3. Bryophytes managed to survive on land because

A) they were the first plants to develop stomata

B) they do not require a moist environment for the reproductive cycle

C) they grow low above the soil in relatively humid regions

D) the sporophyte became independent of the gametophyte

4 Mammal Cheeks Are Formed Like

A) a device for collecting large amounts of food

B) the result of structural features of the skull, and in particular, the jaws

B) a sucking device

D) breathing aid

5. The heart of a crocodile in its structure

A) three-chamber with an incomplete septum in the ventricle

B) three-chamber

B) four-chamber

D) four-chamber with a hole in the septum between the ventricles

6. Fibrinogen, which is a protein, is involved in blood clotting

A) blood plasma

B) cytoplasm of leukocytes

B) part of platelets

D) formed during the destruction of red blood cells

7. Abiotic factors include such an ecological unit as

A) biocenosis

B) ecosystem

B) population

8. Reduction division (meiosis) occurs during the formation

A) bacterial spores

B) zoospores of ulotrix

B) marchantia spores

D) zoospores phytophthora

9. Of the listed biopolymers, a branched structure has

D) polysaccharides

10. Phenylketonuria is a genetic disease caused by a recessive mutation. The probability of having a sick child, if both parents are heterozygous for this trait, is

11. The similarity in the structure of the organs of vision in cephalopods and vertebrates is explained

A) convergence

B) parallelism

B) adaptation

D) a coincidence

12. A free-swimming ascidian larva has a chord and a neural tube. In an adult ascidia leading a sedentary lifestyle, they disappear. This is an example

A) adaptations

B) degeneration

B) cenogenesis

13. The water-carrying elements of pine are

A) annular and spiral vessels

B) only annular vessels

B) tracheids

D) spiral and porous vessels

14. Fertility is typical for

B) pineapple

B) a banana

15. In the chloroplasts of plant cells, light-harvesting complexes are located

A) on the outer membrane

B) on the inner membrane

B) on the thylakoid membrane

D) in the stroma

Part 2.

Match (6 points).

2.1. Establish a correspondence between the sign of the gray rat and the criterion of the species for which it is characteristic.

2.2. Establish a correspondence between the characteristics of the regulation of functions and its method.

Set the correct sequence (6 points).

2.3. Establish the correct sequence of stages of geographic speciation.

1) the emergence of territorial isolation between populations of the same species

2) expansion or division of the range of the species

3) the appearance of mutations in isolated populations

4) preservation by natural selection of individuals with traits that are useful in specific environmental conditions

5) loss by individuals of different populations of the ability to interbreed

2.4. Establish the sequence in which these processes occur during mitotic cell division.

1) chromosomes are located along the equator of the cell

2) chromatids diverge towards the poles of the cell

3) two daughter cells are formed

4) chromosomes are spiralized, each consists of two chromatids

5) chromosomes are despiralized

2.5. You are offered test tasks in the form of judgments, with each of which you should either agree or reject. In the response matrix, indicate the answer option “yes” or “no”: (10 points).

1. Nightshade flowers are collected in an umbrella inflorescence.

2. Ciliary worms do not have an anus.

3. Peroxisome is an obligatory organelle of a eukaryotic cell.

4. The peptide bond is not macroergic.

5. In liver cells, the addition of glucagon causes the breakdown of glycogen.

6. Abiotic factors do not affect the competitive relations of two related species.

7. The functions of gas exchange at the leaf are possible due to lenticels and hydathodes.

8. The section of the stomach of ruminants, corresponding to the single-chamber stomach of mammals, is the scar.

9. The length of food chains is limited by the loss of energy.

10. The smaller the diameter of the blood vessels in the body, the greater the linear velocity of blood flow in them.

Part 3

3.1. Find three errors in the given text. Indicate the numbers of the proposals in which they are made, correct them (6 points).

1. Matrix synthesis reactions include starch formation, mRNA synthesis, protein assembly in ribosomes. 2. Matrix synthesis resembles the casting of coins on a matrix: new molecules are synthesized in exact accordance with the “plan” laid down in the structure of existing molecules. 3. The role of the matrix in the cell is played by chlorophyll molecules, nucleic acids (DNA and RNA). 4. Monomers are fixed on the matrices, then they are combined into polymer chains. 5. Finished polymers exit the matrices. 6. Old matrices are immediately destroyed, after which new ones are formed.

A person has four phenotypes according to blood groups: I (0), II (A), III (B), IV (AB). The gene that determines the blood group has three alleles: IA, IB, i0; moreover, the i0 allele is recessive with respect to the IA and IB alleles. Parents have II (heterozygous) and III (homozygous) blood groups. Determine the genotypes of the blood groups of the parents. Specify the possible genotypes and phenotypes (number) of the blood group of children. Make a scheme for solving the problem. Determine the probability of inheritance in children of the II blood group.

Answers grade 10-11

Part 1. Choose one correct answer. (15 points)

2.2. maximum - 3 points, one mistake - 2 points, two mistakes - 1b, three or more mistakes - 0 points

2.4. maximum - 3 points, one mistake - 2 points, two mistakes - 1b, three or more mistakes - 0 points

Part 3

3.1. Find three errors in the given text. Indicate the numbers of sentences in which they were made, correct them (3b for correct detection of sentences with errors and 3b for correcting errors).

1. - reactions of matrix synthesis do NOT include the formation of starch, a matrix is ​​not needed for it;

3. - chlorophyll molecules are not capable of acting as a matrix, they do not have the property of complementarity;

6. - matrices are used repeatedly.

3.2. Solve the problem (3 points).

The scheme for solving the problem includes:

1) parents have blood groups: group II - IAi0 (gametes IA, i0), group III - IB IB (gametes IB);

2) possible phenotypes and genotypes of children's blood groups: group IV (IAIB) and group III (IBi0);

3) the probability of inheritance of the II blood group is 0%.

Answer form

School stage of the All-Russian Olympiad in Biology

Participant code _____________

Part 1. Choose one correct answer. (15 points)

Part 2.

Part 3

3.1._______________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

3.2. The solution of the problem

In 1869, Swiss biochemist Johann Friedrich Miescher first discovered, isolated from cell nuclei and described DNA. But only in 1944 O. Avery, S. McLeod and M. McCarthy proved the genetic role of DNA, that is, it was reliably established that the transmission of hereditary information is associated with deoxyribonucleic acid. This discovery was a powerful factor stimulating the study of heredity at the molecular level. Since then, the rapid development of molecular biology and genetics has begun.

Nucleic acids (from lat. nucleus - core) are natural high-molecular organic compounds that provide storage and transmission of hereditary (genetic) information in living organisms. They include: carbon (C), hydrogen (H), oxygen (O), phosphorus (P). Nucleic acids are irregular biopolymers consisting of monomers - nucleotides. Each nucleotide contains:

· nitrogen base,

· simple carbon - 5-carbon sugar pentose (ribose or deoxyribose),

· phosphoric acid residue.

There are two types of nucleic acids: deoxyribonucleic acid - DNA containing deoxyribose, and ribonucleic acid - RNA containing ribose.

Consider each type of nucleic acids.

DNA is found almost exclusively in the cell nucleus, sometimes in organelles: mitochondria, plastids. DNA is a polymer compound with a constant (stable) content in the cell.

The structure of DNA.In its structure, the DNA molecule consists of two polymer chains interconnected and twisted in the form of a double helix (Fig. 1).

A model of the DNA structure was created in 1953 by D. Watson and F. Crick, for which both were awarded the Nobel Prize. The width of the double helix is ​​only about 0.002 microns (20 angstroms), but its length is exceptionally large - up to several tens and even hundreds of micrometers (for comparison: the length of the largest protein molecule in its unfolded form does not exceed 0.1 microns).

Nucleotides are located at a distance from each other - 0,34 nm, and there are 10 nucleotides per turn of the helix. The molecular weight of DNA is large: it is tens, and even hundreds of millions. For example, the molecular weight (M r) the largest chromosome of Drosophila is 7.9 10 10 .

The basic structural unit of one chain is a nucleotide consisting of a nitrogenous base, deoxyribose and a phosphate group. DNA contains 4 types of nitrogenous bases:

· purine - adenine (A) and guanine (G),

· pyrimidine - cytosine (C) and thymine (T).

The total number of purine bases is equal to the sum of pyrimidine bases.

DNA nucleotides will also be of 4 types, respectively: adenyl (A), guanyl (G), cytidyl (C) and thymidyl (T). All DNA nucleotides are connected into a polynucleotide chain due to phosphoric acid residues located between deoxyriboses. There can be up to 300,000 or more nucleotides in a polynucleotide chain.

Thus, each strand of DNA is a polynucleotide in which nucleotides are arranged in a strictly defined order. Nitrogenous bases approach each other so close that hydrogen bonds form between them. An important pattern is clearly manifested in their arrangement: adenine (A) of one chain is connected to thymine (T) of the other chain by two hydrogen bonds, and guanine (G) of one chain is connected by three hydrogen bonds to cytosine (C) another chain, resulting in the formation of A-T and G-C pairs. This ability to selectively connect nucleotides is called complementarity, that is, the spatial and chemical correspondence between pairs of nucleotides (see Fig. 2).

The sequence of connecting the nucleotides of one chain is opposite (complementary) to that in the other, i.e., the chains that make up one DNA molecule are multidirectional, or antiparallel. The chains twist around each other and form a double helix. A large number of hydrogen bonds provides a strong connection of DNA strands and gives the molecule stability, while maintaining its mobility - under the influence of enzymes, it easily unwinds (despiralizes).

DNA replication (DNA reduplication) - the process of self-reproduction (self-doubling) of macromolecules of nucleic acids, which ensures the exact copying of genetic information and its transmission from generation to generation.

DNA replication occurs during interphase before cell division. The parent DNA molecule (the number of DNA chains in a cell is 2n) unwinds from one end under the action of enzymes, and then daughter polynucleotide chains are completed from free nucleotides according to the principle of complementarity on both chains. As a result of matrix reactions, two daughter DNA molecules of the same nucleotide composition arise, in which one of the chains is the old parent one, and the other is a new, newly synthesized one (the amount of DNA in the cell becomes 4n = 2 X 2n).

Functions of DNA.

1. Storage of hereditary information about the structure of proteins or its individual organelles. The smallest unit of genetic information after a nucleotide is three consecutive nucleotides - a triplet. The sequence of triplets in a polynucleotide chain determines the sequence of amino acids of one protein molecule (the primary structure of a protein) and represents a gene. Together with proteins, DNA is part of chromatin, the substance that makes up the chromosomes of the cell nucleus.

2. Transfer of hereditary information as a result of replication during cell division from the mother cell to the daughter.

3. Implementation of hereditary information (stored in the form of genes) as a result of matrix reactions of biosynthesis through the production of proteins specific to the cell and organism. At the same time, on one of its chains, according to the principle of complementarity, messenger RNA molecules are synthesized from the nucleotides of the environment surrounding the molecule.

RNA is a compound with a fluctuating (labile) content in the cell.

The structure of RNA.In terms of their structure, RNA molecules are smaller than DNA molecules with a molecular weight of 20-30 thousand (tRNA) to 1 million (rRNA), RNA is a single-stranded molecule built in the same way as one of the DNA chains. RNA monomers - nucleotides consist of a nitrogenous base, ribose (pentose) and a phosphate group. RNA contains 4 nitrogenous bases:

· purine - adenine (A);

· pyrimidine - guanine (G), cytosine (C), uracil (U).

In RNA, thymine is replaced by uracil, which is close in structure to it (nucleotide - uridyl. Nucleotides are connected in a polynucleotide chain in the same way as in DNA, due to phosphoric acid residues located between riboses.

Location in the cell Among RNA, there are: nuclear, cytoplasmic, mitochondrial, plastid.

By function Among RNAs, there are: transport, information and ribosomal.

Transfer RNAs (tRNAs) - single-stranded, but having a three-dimensional "cloverleaf" structure created by intramolecular hydrogen bonds (Fig. 3). tRNA molecules are the shortest. Consist of 80-100 nucleotides. They account for about 10% of the total RNA content in the cell. They transfer activated amino acids (each tRNA has its own amino acid, 61 tRNAs are known in total) to ribosomes during protein biosynthesis in the cell.”

Informational (matrix) RNA (mRNA, mRNA) - a single-stranded molecule that is formed as a result of transcription on a DNA molecule (copies genes) in the nucleus and carries information about the primary structure of one protein molecule to the site of protein synthesis in ribosomes. An mRNA molecule can consist of 300-3000 nucleotides. The share of mRNA accounts for 0.5-1% of the total RNA content in the cell.

Ribosomal RNA (rRNA) - the largest single-stranded molecules that form complex complexes with proteins that support the structure of ribosomes on which protein synthesis takes place.

rRNA accounts for about 90% of the total RNA content in the cell.

All the genetic information of an organism (the structure of its proteins) is contained in its DNA, which consists of nucleotides combined into genes. Recall that a gene is a unit of hereditary information (a section of a DNA molecule) containing information about the structure of one protein - an enzyme. The genes that determine the properties of organisms are called structural. And the genes that regulate the expression of structural genes are called regulatory. The manifestation (expression) of a gene (realization of hereditary information) occurs as follows:

For the implementation of gene expression, there is a genetic code - a strictly ordered relationship between nucleotide bases and amino acids (Table 12).

Table 12 Genetic code

Basic properties of the genetic code.

Tripletity- coding of amino acids is carried out by triplets (triplets) of bases of nucleotides. The number of coding triplets is 64 (4 types of nucleotides: A, T, C, G, 4 3 = 64).

UnambiguityEach triplet encodes only one amino acid.

degeneracy- the number of coding triplets exceeds the number of amino acids (64 > 20). There are amino acids encoded by more than one triplet (such amino acids are more common in proteins). There are three triplets that do not code for any amino acid (UAA, UAG, UGA). They are called "nonsense codons" and play the role of "stop signals", meaning the end of the gene recording (the total number of coding codons is 61).

Non-overlapping (continuity) - Reading triplets from DNA during mRNA synthesis proceeds strictly along three consecutive nucleotides, without overlapping neighboring codons. There are no "punctuation marks" within the gene.

Versatility - the same triplets code for the same amino acids in all organisms living on Earth.

Common abbreviations for amino acid names:

FEN - phenylalanine; GIS - histidine;

LEI - leucine; GLN - glutamine;

ILE - isoleucine; GLU - glutamic acid;

MET - methionine; LYS - lysine;

VAL - valine; ASN - asparagine;

SER - series; ASP - aspartic acid;

PRO - proline; CIS - cysteine;

TPE - threonine; THREE - tryptophan;

ALA - alanine; ARG - arginine;

TIR - tyrosine; GLI - glycine.

Thus, the DNA carrier of all genetic information in the cell does not take a direct part in protein synthesis (ie, the implementation of this hereditary information). In animal and plant cells, DNA molecules are separated by a nuclear membrane from the cytoplasm.plasma, where protein synthesis takes place. An intermediary is sent from the nucleus to the ribosomes - the sites of protein assembly - which carries the copied information and is able to pass through the pores of the nuclear membrane. Messenger RNA, which is involved in matrix reactions, is such an intermediary.

Matrix reactions - these are reactions for the synthesis of new compounds based on "old" macromolecules that act as a matrix, that is, a form, a model for copying new molecules. The matrix reactions for the realization of hereditary information, in which DNA and RNA take part, are:

1. DNA replication- doubling of DNA molecules, due to which the transfer of genetic information is carried out from generation to generation. The matrix is ​​the maternal DNA, and the new ones formed according to this matrix are the daughter, newly synthesized 2 DNA molecules (Fig. 4).

2. Transcription(lat. transcription - rewriting) is the synthesis of RNA molecules according to the principle of complementarity on the template of one of the DNA chains. Occurs in the nucleus under the action of the enzyme DNA-dependent - RNA polymerase. Messenger RNA is onenon-stranded molecule, and the coding of the gene comes from one strand of a double-stranded DNA molecule. If nucleotide G is in the transcribed DNA strand, then DNA polymerase includes C in the mRNA; if it is T, then it includes A in the mRNA; if it is T, it includes Y (thymine T is not included in the RNA; Fig. 5). The language of DNA triplets is translated into the language of mRNA codons (triplets in mRNA are called codons).

As a result of transcription of different genes, all types of RNA are synthesized. Then, mRNA, tRNA, rRNA through the pores in the nuclear envelope enter the cytoplasm of the cell to perform their functions.

3. Broadcast(lat. translatio - transmission, translation) is the synthesis of polypeptide chains of proteins on a mature mRNA matrix, carried out by ribosomes. There are several stages in this process:

The first stage is initiation (the beginning of synthesis - chains). In the cytoplasm, a ribosome enters one of the ends of the mRNA (exactly the one from which the synthesis of the molecule in the nucleus began) and begins the synthesis of the polypeptide. The tRNA molecule transporting the amino acid methionine (tRNA meth) connects to the ribosome and attaches to the beginning of the mRNA chain (always with the AUG code). Next to the first tRNA (which has nothing to do with the synthesizing protein), a second tRNA with an amino acid is attached. If the anticodon is tRNA, then a peptide bond arises between the amino acids, which is formed by a certain enzyme. After that, tRNA leaves the ribosome (goes to the cytoplasm for a new amino acid), and mRNA moves one codon.

The second stage is elongation (chain elongation). The ribosome moves along the mRNA molecule not smoothly, but intermittently, triplet by triplet. The third tRNA with the amino acid binds with its anticodon to the codon of the mRNA. When the complementarity of the bond is established, the ribosome takes another step one "codon", and the specific enzyme "crosslinks" the second and third amino acids with a peptide bond - a peptide chain is formed. Amino acids in the growing polypeptide chain are connected in the sequence in which the mRNA codons encoding them are located (Fig. 6).

The third stage is the termination (end of synthesis) of the chain. Occurs when the ribosome translates one of the three "nonsense codons" (UAA, UAG, UGA). Ribosomes jump off mRNA, protein synthesis is complete.

Thus, knowing the order of arrangement of amino acids in a protein molecule, it is possible to determine the order of nucleotides (triplets) in the mRNA chain, and according to it, the order of nucleotide pairs in the DNA section and vice versa, taking into account the principle of nucleotide complementarity.

Naturally, in the process of matrix reactions, due to any reasons (natural or artificial), changes can occur - mutations. These are gene mutations at the molecular level - the result of various damages in DNA molecules. Gene mutations occurring at the molecular level usually affect one or more nucleotides. All forms of gene mutations can be divided into two large groups.

First group- frame shift - is an insertion or deletion of one or more pairs of nucleotides. Depending on the site of the violation, one or another number of codons changes. This is the most severe gene damage, since completely different amino acids will be included in the protein.

Such deletions and insertions account for 80% of all spontaneous gene mutations.

The most damaging effect is possessed by the so-called nonsense mutations, which are associated with the appearance of terminator codons that cause a stopku protein synthesis. This can lead to premature termination of protein synthesis, which is rapidly degraded. The result is cell death or a change in the nature of individual development.

Mutations associated with substitution, deletion, or insertion in the coding part of a gene phenotypically appear as a substitution of amino acids in a protein. Depending on the nature of the amino acids and the functional significance of the damaged area, there is a complete or partial loss of the functional activity of the protein. As a rule, this is expressed in a decrease in viability, a change in the characteristics of organisms, etc.

Second groupare gene mutations with the replacement of base pairs of nucleotides. There are two types of base substitutions:

1. Transition- replacement of one purine for a purine base (A for G or G for A) or one pyrimidine for a pyrimidine (C for T or T for, C).

2. Transversion- replacement of one purine base with a pyrimidine base or vice versa (A for C, or G for T, or A for Y).

A striking example of transversion is sickle cell anemia, which occurs due to a hereditary disorder in the structure of hemoglobin. In the mutant gene encoding one of the hemoglobin chains, only one nucleotide is broken, and adenine is replaced by uracil (GAA by GUA) in the mRNA.

As a result, there is a change in the biochemical phenotype, in the hemoglobin chain, glutamic acid is replaced by valine. This replacement changes the surface of the hemoglobin molecule: instead of a biconcave disk, erythrocyte cells become sickle-like and either clog small vessels or are quickly removed from the circulation, which quickly leads to anemia.

Thus, the significance of gene mutations for the life of an organism is not the same:

· some "silent mutations" do not affect the structure and function of the protein (for example, a nucleotide substitution that does not lead to an amino acid substitution);

· some mutations lead to complete loss of protein function and cell death (for example, nonsense mutations);

· other mutations - with a qualitative change in mRNA and amino acids, lead to a change in the characteristics of the organism;

· and, finally, some mutations that change the properties of protein molecules have a damaging effect on the vital activity of cells - such mutations cause a severe course of diseases (for example, transversions).

DNA- a linear polymer having the form of a double helix formed by a pair of antiparallel complementary chains. The monomers of DNA are nucleotides.

Each DNA nucleotide consists of a purine (A - adenine or G - guanine) or pyrimidine (T - thymine or C - cytosine) nitrogenous base, a five-carbon sugar - deoxyribose and a phosphate group.

The DNA molecule has the following parameters: the width of the helix is ​​about 2 nm, the pitch, or full turn of the helix, is 3.4 nm. One step contains 10 complementary base pairs.

Nucleotides in the DNA molecule face each other with nitrogenous bases and are combined in pairs in accordance with the rules of complementarity: thymine is located opposite adenine, and cytosine is opposite guanine. The A-T pair is connected by two hydrogen bonds, and the G-C pair by three.

The backbone of DNA chains is formed by sugar-phosphate residues.

DNA replication is the process of self-doubling of the DNA molecule, carried out under the control of enzymes.

On each of the chains formed after the rupture of hydrogen bonds, with the participation of the DNA polymerase enzyme, a daughter DNA chain is synthesized. The material for synthesis is free nucleotides present in the cytoplasm of cells.

The synthesis of daughter molecules on neighboring chains proceeds at different rates. On one chain, a new molecule is assembled continuously, on the other - with some delay and fragmentarily. After the process is completed, fragments of new DNA molecules are linked by the DNA ligase enzyme. So, from one DNA molecule, two arise, which are an exact copy of each other and the parent molecule. This type of replication is called semi-conservative.

The biological meaning of replication lies in the exact transfer of hereditary information from the parent molecule to the daughter ones, which occurs during the division of somatic cells.

DNA repair- a mechanism that provides the ability to correct the disturbed sequence of nuileotides in the DNA molecule.

If during DNA replication the sequence of nucleotides in its molecule is disturbed for any reason, then in most cases these damages are repaired by the cell itself. The change usually occurs in one of the DNA strands. The second chain remains unchanged. The damaged section of the first chain can be "cut out" with the help of enzymes - DNA repair nucleases. Another enzyme, DNA polymerase, copies information from an intact strand, inserting the necessary nucleotides into the damaged strand. The DNA ligase then "crosslinks" the DNA molecule, and the damaged molecule is repaired.

RNA - a linear polymer, consisting, as a rule, of one chain of nucleotides. In RNA, a thymine nucleotide is replaced by a uracil nucleotide (U). Each RNA nucleotide contains a five-carbon sugar - ribose, one of the four nitrogenous bases and a phosphoric acid residue.

Matrix, or informational, RNA is synthesized in the nucleus with the participation of the enzyme RNA polymerase, which is complementary to the DNA site where the synthesis occurs, and makes up 5% of the cell's RNA. Ribosomal RNA is synthesized in the nucleolus and is part of the ribosomes, making up 85% of the cell's RNA. Transfer RNA (more than 40 types) carries amino acids to the site of protein synthesis, has the shape of a cloverleaf and consists of 70-90 nucleotides.

Matrix synthesis reactions include DNA replication, RNA synthesis to DNA (transcription), protein synthesis to mRNA (translation), and RNA or DNA synthesis to viral RNA.

During transcription, the RNA polymerase enzyme attaches to a group of DNA nucleotides - the promoter. The promoter specifies the site from which mRNA synthesis should begin. It is built from free nucleotides complementary to the DNA molecule. The enzyme works until it encounters another group of DNA nucleotides - a stop signal announcing the end of mRNA synthesis.

The mRNA molecule enters the cytoplasm on the ribosomes, where the synthesis of polypeptide chains occurs. The process of translating the information contained in the mRNA nucleotide sequence into the amino acid sequence in the polypeptide is called translation.

A certain amino acid is delivered to the ribosomes by a certain type of tRNA.