After the opening of the principle of molecular organization of such a substance as DNA in 1953, molecular biology began to develop. Further, in the process of research, scientists found out how the DNA is recombined, its composition and how our human genome is arranged.
Every day the molecular level occurs the most complex processes. How is the DNA molecule, what is it from? And what role is played in the cell of the DNA molecule? We will describe in detail about all the processes occurring inside the double chain.
What is hereditary information?
So why did it all start? Another 1868 found bacteria in nuclei. And in 1928, N. Koltsov highlighted the theory that all genetic information about living organism was encrypted into DNA. Then J. Watson and F. Creek found a model now the well-known DNA spiral in 1953, for which the recognition and award was deserved - the Nobel Prize.
What is DNA generally? This substance consists of 2 combined threads, or rather spirals. The plot of such a chain with certain information is called the genome.
The DNA stores all the information about the fact that proteins will be formed and in what order. DNA macromolecule is a material carrier of incredibly volumetric information that is recorded by a strict sequence of individual bricks - nucleotides. Total nucleotides 4, they complement each other chemically and geometrically. This principle of addition, or complementarity, will be described later in science later. This rule plays a key role in encoding and decoding genetic information.
Since the DNA thread is incredibly long, the repetitions in this sequence does not happen. Each living creature has its own unique DNA chain.
DNA functions
The functions include storing hereditary information and its transfer to the offspring. Without this function, the genome of the species could not be maintained and developed for thousands of years. Organisms that have undergone serious gene mutations, do not more often survive or lose the ability to produce offspring. So there is natural protection against the degeneration of the species.
Another essential function is the implementation of stored information. The cell cannot create any vital protein without those instructions that are stored in a double chain.
Composition of nucleic acids
Now it is already reliably known, from which the nucleotides themselves are - DNA bricks. Their composition includes 3 substances:
- Orthophosphoric acid.
- Nitrogen base. Pyrimidine bases - which have only one ring. These include Timin and Cytosin. Purine bases, which contain 2 rings. This is Guanine and Adenin.
- Sucrose. As part of DNA - deoxyribosis, in RNA - robose.
The number of nucleotides is always equal to the number of nitrogenous bases. In special laboratories, nucleotides are cleaved and a nitrogenous base is distinguished from it. This is how the individual properties of these nucleotides and possible mutations in them are studied.
Levels of the organization of hereditary information
Separate 3 levels of organization: gene, chromosomal and genomic. All information needed for the synthesis of a new protein is contained on a small segment of the chain - gene. That is, the gene is considered the lowest and the easiest level of encoding information.
Genes, in turn, are collected in chromosomes. Thanks to such an organization of the hereditary material of a group of signs according to certain laws, alternate and transmitted from one generation to another. It should be noted, the genes in the body are incredibly much, but the information is not lost, even when it is recombaling many times.
Several types of genes are separated:
- according to the functional purpose, 2 types are isolated: structural and regulatory sequences;
- by influence on the processes occurring in the cell, they distinguish: supervital, lethal, conditionally lethal genes, as well as genes Mutators and antimutators.
There are genes along the chromosome in linear order. In chromosomes, the information is focused not by the rules, there is a certain order. There is even a map in which the positions or locuses of gene are displayed. For example, it is known that in chromosome No. 18, data about the color of the child's eye is encrypted.
What is the genome? This is so called the entire set of nucleotide sequences in the body's cell. The genome characterizes a whole species, not a separate individual.
What is the human genetic code?
The fact is that the whole of the most huge potential of human development has already been laid during the conception. All hereditary information, which is necessary for the development of the zygota and the growth of the child after birth, is encrypted in genes. DNA sections are the most basic carriers of hereditary information.
Human 46 chromosomes, or 22 somatic couples plus one-defining chromosome floor from each parent. This diploid chromosome set encodes the entire physical appearance of a person, his mental and physical abilities and predisposition to diseases. Somatic chromosomes externally indistinguishable, but they carry different information, as one of them from the Father, the other is from the mother.
Male code differs from the female latter couple chromosomes - Hu. The female diploid set is the last couple, XX. Men get one x-chromosome from a biological mother, and then it is transmitted to daughters. The sexual y-chromosome is transmitted to sons.
The human chromosomes differ significantly in size. For example, the smallest pair of chromosomes - №17. And the largest steam is 1 and 3.
The diameter of the double helix in a person is only 2 nm. DNA is so tightly twisted that it contains in the small core of the cell, although its length will reach 2 meters, if you promote it. The length of the spiral is hundreds of millions of nucleotides.
How is the genetic code transmitted?
So, what role do DNA molecule play in the cell? Genes are carriers of hereditary information - are located inside each cell cell. To transfer your code a child organism, many creatures share their DNA on 2 identical spirals. This is called replication. In the DNA replication process, special "machines" complement each chain. After the genetic spiral is repaid, it begins to divide the core and all organelles, and then the whole cell.
But a person has another process of gene transfer - sexual. Signs of father and mothers are mixed, in the new genetic code contains information from both parents.
Storage and transfer of hereditary information are possible thanks to the complex organization of the DNA spiral. After all, as we said, the structure of proteins is encrypted in genes. When creating during conception, this code throughout his life will copy itself. Kariotype (personal set of chromosomes) does not change during the update of organ cells. The transmission of information is carried out with the help of genital heams - male and female.
Only viruses containing one RNA chain are not capable of transmitting its information. Therefore, to reproduce, they need human or animal cells.
Implementation of hereditary information
In the kernel, the cells are constantly important processes. All information recorded in chromosomes is used to build proteins from amino acids. But the DNA chain never leaves the kernel, so here you need the help of another important compound \u003d RNA. RNA is able to penetrate the kernel membrane and interact with the DNA chain.
Through the interaction of DNA and 3 types of RNA, all encoded information is implemented. At what level is the implementation of hereditary information? All interactions occur at the level of nucleotides. Information RNA copies the DNA chain portion and brings this copy to Ribosoma. Here begins the synthesis of the nucleotide of the new molecule.
In order for the IRNK to copy the necessary part of the chain, the spiral unfolds, and then, upon completion of the transcoding process, is restored again. Moreover, this process can occur simultaneously on 2 sides of 1 chromosome.
Principle of complementarity
Consist of 4 nucleotides are adenine (a), guanine (G), cytosine (C), Timin (T). They are connected by hydrogen bonds according to the rule of complementarity. E. Chargaff's work helped to establish this rule, since the scientist noticed some patterns in the behavior of these substances. E. Chargaff discovered that adenine molar ratio to thimin is equal to one. And just as the ratio of guanin to the cytosine is always equal to one.
Based on its works, genetics have formed a rule of interaction between nucleotides. The complementarity rule states that adenine is connected only with thimine, and a guanine with a cytosine. During decoding the spiral and synthesis of the new protein in the ribosome, such an alternation rule helps to quickly find the necessary amino acid, which is attached to the transport RNA.
RNA and its types
What is hereditary information? Nucleotides in DNA double chain. What is RNA? What is her job? RNA, or ribonucleic acid helps to extract information from DNA, decode it and based on the principle of complementarity to create the necessary protein cells.
Total distinguished 3 types of RNA. Each of them performs strictly its function.
- Information (IRNA), or it is also called a matrix. She comes right in the center of the cage, in the core. Finds in one of the chromosomes the necessary genetic material for the protein construction and copies one of the sides of the double chain. Copy occurs again on the principle of complementarity.
- Transport - This is a small molecule, which on one side of the nucleotide decoders, and on the other side the corresponding amino acid codes. The task of TRNA is to deliver to the "shop", that is, in Ribosoma, where the necessary amino acid synthesizes.
- rRNA - Ribosomal. It controls the amount of protein that is produced. Consists of 2 parts - an amino acid and peptide plot.
The only difference during decoding is no thymine on RNA. Instead of Timine there is a Uracil. But then, in the process of protein synthesis, all the amino acids are still correctly installed when TRNA. If some faults occur in decoding information, mutation arises.
Reparation of the damaged DNA molecule
The recovery process of the damaged double chain is called repair. In the process of repairing damaged genes are removed.
Then the required sequence of elements is exactly played and cut back to the same place on the chain, from where it was extracted. All this is due to special chemicals - enzymes.
Why do mutations occur?
Why do some genes begin to mutate and cease to perform their function - storing the vital hereditary information? This is due to an error during decoding. For example, if adenine is accidentally replaced by Timin.
There are also chromosomal and genomic mutations. Chromosomal mutations happen if the sections of hereditary information fall out, doubles either generally transferred and embedded in another chromosome.
Genomic mutations are most serious. Their cause is a change in the number of chromosomes. That is, when instead of a pair - the diploid set is present in the karyotype triploid set.
The most famous example of triploid mutation is a Down syndrome, in which a personal set of chromosomes 47. These children formed 3 chromosomes on the site of the 21st pair.
Also known is such a mutation as polymploy. But polymploy is found only in plants.
anticodone, biosynthesis, gene, genetic information, genetic code, codon, matrix synthesis, polysoma, transcription, broadcast.
Genes, genetic code and its properties. There are already more than 6 billion people on Earth. If you do not count 25-30 million pairs of single-line twins, then genetically all people are different. This means that each of them is unique, has unique hereditary features, properties of character, abilities, temperament and many other qualities. What do such differences are determined between people? Of course, differences in their genotypes, i.e. Sets of genes of this body. Every person is unique for each person, as well as the genotype of an individual or plant is unique. But genetic signs of this person are embodied in proteins synthesized in its body. Consequently, the structure of a protein of one person is different, although quite a bit, from the protein of another person. That is why the problem of bodies transplantation arises, which is why allergic reactions to products, insect bites, plants pollen, etc. arise. This does not mean that people do not meet completely identical proteins. Proteins performing the same functions may be the same or very slightly different from one or two amino acids from each other. But there is no people on earth (with the exception of single-board twins), whose proteins would be the same.
Information on the primary structure of the protein is encoded as a sequence of nucleotides in the DNA gene - gene molecule. Gene - This is the unit of hereditary information of the body. Each DNA molecule contains many genes. The combination of all gene genes is its genotype.
The encoding of hereditary information occurs with the help of a genetic code. The code is similar to the famous Morse alphabet, which points and dash encodes information. Azbuka Morse is universal for all radists, and differences consist only in translating signals into different languages. Genetic code It is also universal for all organisms and differs only by alternating nucleotides forming genes, and coding proteins of specific organisms. So, what is the genetic code? Initially, it consists of triple (triplets) of DNA nucleotides that are combined in different sequences. For example, AAT, HCA, ACG, THC, etc. Each nucleotide triplet encodes a certain amino acid that will be built into the polypeptide chain. So, for example, the TSGT triplet encodes the amino acid alanine, and the AAG triplet is an amino acid phenylalanine. Amino acids 20, and opportunities for combinations of four nucleotides in groups of three - 64. Consequently, four nucleotides are enough to encode 20 amino acids. That is why one amino acid can be encoded by several triplets. Part of the triplets does not at all encode amino acids, but launches or stops protein biosynthesis. The actual code is considered sequence of nucleotides in the molecule and-RNAFor it removes information from DNA (transcription process) and translates it into the sequence of amino acids in the molecules of synthesized proteins (the transmission process). The composition and RNA consists of Nucleotides AqSU. Nucleotide and RNA triplets are called codons . Already given examples of DNA triplets on and-RNA will look as follows - the TsGT triplet on and-RNA will become a triplet of the HCA, and the DNA triplet - AAG will become a UUC triplet. It is codons and RNA that a genetic code is reflected in the record. So, the genetic code is triplet, universal for all organisms on Earth, degenerate (each amino acid is encrypted with more than one codon). Between the genes there are punctuation marks - these are triplets called stop codons. They signal the end of the synthesis of one polypeptide chain. There are tables of the genetic code that you need to be able to use, to decipher the codons and RNA and the construction of chains of protein molecules.
Biosynthesis protein - This is one of the types of plastic exchange, during which hereditary information encoded in DNA genes is implemented in a certain sequence of amino acids in protein molecules. Genetic information taken from DNA and translated into a molecule code and-RNA should be implemented, i.e. manifest itself in the signs of a particular body. These signs are determined by proteins. Biosynthesis proteins occurs on ribosomes in the cytoplasm. It is there that receives an information RNA from the coder of the cell. If synthesis and-RNA on the DNA molecule is called transcription, then protein synthesis on ribosomes is called broadcast - Translation of the genetic code language into the series of amino acid sequences in the protein molecule. Amino acids are delivered to ribosomes transport RNA. These RNAs have the form of a clutch sheet. At the end of the molecule, there is a platform for attaching an amino acid, and on top - a triplet of nucleotides, complementary to a certain triplet - codon on and-RNA. This triplet is called Anti-Kodon. After all, it decrypts the code and RNA. In the T-RNA cell, there are always as much as codons encrypting amino acids.
The ribosome moves along and-RNA, shifting at the approach of a new amino acid into three nucleotides, freeing them for a new anti-cycle. Amino acids delivered to ribosomes are oriented towards each other in such a way that a carboxyl group of one amino acid turns out to be next to the amino group of another amino acid. As a result, a peptide connection is formed between them. The polypeptide molecule is gradually formed.
The protein synthesis continues until one of the three stop codons will be on the ribosome - UAA, UAG, or UIG.
After that, the polypeptide leaves ribosomes and is sent to the cytoplasm. On one molecule and RNA are several ribosomes that form policy. It is on polysomes that the simultaneous synthesis of several same polypeptide chains.
Each stage of biosynthesis is catalyzed by the appropriate enzyme and is ensured by the ATP energy.
Biosynthesis occurs in cells at a huge speed. In one minute, up to 60 thousand peptide ties are formed in one minute.
Reactions of matrix synthesis. Reactions of matrix synthesis are attributed replication DNA, synthesis and RNA on DNA ( transcription), and protein synthesis on and RNA ( broadcast), as well as synthesis of RNA or DNA on RNA viruses.
DNA replication. The structure of the DNA molecule, installed by J. Watson and F. Cryk in 1953, responded to the requirements that were presented to the custodian molecule and transmitter of hereditary information. The DNA molecule consists of two complementary chains. These chains are held by weak hydrogen bonds that can be broken down by enzymes.
The molecule is capable of self-esteem (replication), and on each old half of the molecule, the new half is synthesized. In addition, the Molecule and RNA can be synthesized on the DNA molecule, which then transfers information from DNA to the site of protein synthesis. The transfer of information and protein synthesis go through the matrix principle comparable to the work of the printing machine in the printing house. Information from DNA is repeatedly copied. If errors occur when copying, they will be repeated in all subsequent copies. True, some errors when copying information from DNA molecule can be corrected. This error elimination is called reparation. The first of the reactions in the process of transmission of information is the replication of the DNA molecule and the synthesis of new DNA chains.
Replication - This is the heat dissipation process of the DNA molecule, carried out under the control of enzymes. On each of the DNA chains formed after the gap of hydrogen bonds, the subsidiary of DNA was synthesized with the participation of the DNA polymerase enzyme. The synthesis material is free nucleotides available in cytoplasm cells.
The biological meaning of replication is to accurately transmit the hereditary information from the mother molecule to the subsidiary, which is normal and occurs during the division of somatic cells.
Transcription is the process of removing information from the DNA molecule synthesized on it and-RNA. Information RNA consists of one chain and is synthesized on DNA in accordance with the complementarity rule. As in any other biochemical reaction, the enzyme is involved in this synthesis. It activates the beginning and end of the synthesis of the molecule and RNA. The finished molecule and RNA goes to the cytoplasm on ribosomes, where the synthesis of polypeptide chains occurs. The process of transferring information contained in the nucleotide sequence and RNA into the sequence of amino acids in the polypeptide is called broadcast .
Examples of tasks
Part A.
A1. Which of the statements is incorrect?
1) Genetic code universal
2) genetic code degenerate
3) genetic code individual
4) Triplet Genetic Code
A2. One DNA triplet encodes:
1) Sequence of amino acids in protein
2) one sign of the body
3) one amino acid
4) several amino acids
A3. "Punctuation marks" of genetic code
1) launch protein synthesis
2) stop protein synthesis
3) coding certain proteins
4) encoded amino acids group
A4. If the amino acid frogs are coded by the GUU triplet, then the dog has this amino acid to be encoded by triplets (see table):
1) GUA and GUG 3) CHC and CSU
2) UUC and UCA 4) UAG and UIG
A5. Protein synthesis ends at the time
1) Code of Code Anti-Kodon
2) receipts and RNA on ribosomes
3) appearance on the ribosome "punctuation sign"
4) Attachment of amino acids to T-RNA
A6. Indicate a couple of cells in which one person contains different genetic information?
1) liver and stomach cells
2) neuron and leukocyte
3) muscle and bone
4) Cell of language and egg
A7. Function and RNA in the process of biosynthesis
1) storage of hereditary information
2) Amino acid transport on ribosomes
3) Transfer of information on ribosomes
4) Acceleration of the biosynthesis process
A8. Anticodone T-RNA consists of UJG nucleotides. What DNA triplet is complementary?
1) TCG 2) UUG 3) TTC 4) TsSG
Part B.
IN 1. Install the correspondence between the process characteristic and its name
Part S.
C1. Specify the sequence of amino acids in the protein molecule encoded by the following sequence of codons: UUA - AUU - GGU - GGA
C2. List all the stages of protein biosynthesis.
The cell is a genetic unit of living. Chromosome, their structure (shape and size) and functions. The number of chromosomes and their species constant. Features of somatic and sex cells. Life cycle of cells: interfac and mitosis. Mitoz - division of somatic cells. Meiosis. Phases mitosis and meiosis. The development of genital cells in plants and animals. The similarity and difference between mitosis and meiosis, their meaning. Cell division - the basis of growth, development and reproduction of organisms. The role of meiosis in ensuring the constancy of the number chromosomes in generations
Terms and concepts checked in the examination work: anafase, Gameta, Gametogenesis, cell division, cell life cycle, zygota, interfacation, conjugation, crosslinker, meyosis, metaphase, ovogenesis, semennik, spermatozoa, dispute, bondaz, ovary, structure and function chromosomes.
Chromosomes - Cell structures stored and transmitting hereditary information. Chromosome consists of DNA and protein. A complex of proteins associated with DNA forms chromatin. Proteins play an important role in the packaging of DNA molecules in the kernel. The structure of the chromosome is best visible in mitosis metaphase. It is a row-shaped structure and consists of two nursing chromatidheld by centromer in the area primary drying. The diploid set of chromosoma of the body is called karyotype . The microscope shows that the chromosomes have transverse strips, which alternate in various chromosomes in different ways. Recognize pairs of chromosomes, given the distribution, light and dark bands (alternation of AT and Hz - par). The cross-term is the chromosome of representatives of different species. Related species, for example, in humans and chimpanzees, a similar character of alternation of strips in chromosomes.
Each type of organisms has a constant number, shape and composition of chromosomes. In the karyotype of man 46 chromosomes - 44 outosomes and 2 sex chromosomes. Men heterogamy (sex chromosomes Hu), and women are homogamed (sex chromosomes XX). U-chromosome differs from the X-chromosome, the absence of some alleles. For example, in the U-chromosome there is no allele blood coagulation. As a result, hemophilia is sick, as a rule, only boys. Chromosome of one pair are called homologous. Homologous chromosomes in the same loci (locations) are allele genes.
Life cycle cells. Interfhaza. Mitosis. Life cycle cells - This is the period of her life from dividing before division. Cells multiply by doubling their contents with subsequent division in half. Cellular division underlies the growth, development and regeneration of tissues of a multicellular organism. Cell cycle divided by interfaseaccompanied by accurate copying and distribution of genetic material and mitosis - Actually cell division after doubling other cellular components. The duration of cell cycles in different species, in different tissues and at different stages varies widely from one hour (at the embryo) to the year (in the cells of the adult liver).
Interfhaza - The period between two divisions. During this period, the cell is prepared for division. Dwells the number of DNA in chromosomes. The number of other organoids is doubled, proteins are synthesized, and the most actively those that form spindle divisions, cell growth occurs.
By the end of the interfese, each chromosome consists of two chromatids, which in the mitosis process will become independent chromosomes.
Mitosis - This is a form of dividing the cell core. Consequently, it only happens in eukaryotic cells. As a result of mitosis, each of the resulting subsidiaries receives the same set of genes that the email cell. Mitosis can enter both diploid and haploid nuclei. With mitosis, the cores of the same fairness are obtained as the initial one. Mitosis consists of several consecutive phases.
Prophase. Doubted centrioles diversify various poles of cells. From them to the center of chromosomes, microtubules, forming spindle divisions, are stretched. Chromosome thickened and each chromosome consists of two chromatids.
Metafaza. In this phase, chromosomes consisting of two chromatids are clearly visible. They line up an equator for cells, forming a metaphase plate.
Anaphase. Chromatids diverge to the poles of the cell at the same speed. Microtubules are shortened.
Bulphaz. Daughter chromatids are suitable for cell poles. Microtubule disappear. Chromosomes are despirate and again acquire a filamental form. The nuclear sheath, nucleolus, ribosomes are formed.
Cytokinez - The process of separation of the cytoplasm. The cell membrane in the central part of the cell is drawn inside. A groove of division is formed, as the deepening of which the cell is splitted.
As a result of mitosis, two new nuclei are formed with identical sets of chromosomes that exactly copying genetic information of the maternal nucleus.
In tumor cells, mitosis strokes.
Examples of tasks
Part A.
A1. Chromosome consist of out
1) DNA and protein 3) DNA and RNA
2) RNA and protein 4) DNA and ATP
A2. How many chromosomes contain a human liver cell?
1) 46 2) 23 3) 92 4) 66
A3. How many DNA threads has double chromosome
1) one 2) two 3) four 4) eight
A4. If a person's zigose contains 46 chromosomes, how many chromosomes are contained in a person's egg?
1) 46 2) 23 3) 92 4) 22
A5. What is the biological meaning of doubling chromosomes in mitosis interfare?
1) In the process of doubling, hereditary information changes
2) double chromosomes are better visible.
3) As a result of doubling chromosome, the hereditary information of new cells is preserved unchanged
4) As a result of doubling chromosomes, new cells are twice as much more information
A6. In which of the phases of mitosis occurs the chromatide to the poles of the cell? IN:
1) PROFAZ 3) AnAphase
2) metaphase 4) Bulfase
A7. Specify the processes occurring in the interfax
1) the discrepancy of chromosomes to the poles of the cell
2) protein synthesis, DNA replication, cell growth
3) the formation of new cores, cells of the cell
4) Despiracy of chromosomes, the formation of the separation of division
A8. As a result of mitosis arises
1) genetic diversity of species
2) Education Games
3) Cross-chromosome
4) germination dispute moss
A9. How much chromatid has each chromosome before its doubling?
1) 2 2) 4 3) 1 4) 3
A10. As a result of mitosis formed
1) Zygota Sfagnum
2) spermatozoa in flies
3) kidney oak
4) sunflower eggs
Part B.
IN 1. Select processes occurring in mitosis interfaction
1) protein synthesis
2) Reducing the number of DNA
3) cell growth
4) doubling chromosomes
5) the discrepancy of chromosomes
6) core division
AT 2. Specify the processes based on mitosis
1) Mutation 4) Education Sperm
2) height 5) tissue regeneration
3) crushing zigotes 6) fertilization
Vz. Set the correct sequence of the cell life cycle phases
A) anafase c) bodyfase d) metaphase
B) interphase d) protoz e) cytokines
Part S.
C1. What is common between the processes of tissue regeneration, the growth of the organism and the crushing of the zygota?
C2. What is the biological meaning of doubling chromosomes and the number of DNA in interfase?
Meiosis. Meiosis is the process of dividing cell cores, leading to a decrease in the number of chromosomes by half and the formation of Games. As a result of MEIOS from one diploid cell (2N), four haploid cells (N) are formed.
Meiosis consists of two consecutive divisions that are preceded by a single replication of DNA in the interfax.
The main events of the first division of MEIOS are as follows:
- Homologous chromosomes are combined along the entire length or, as they say conjugate. When conjugation, chromosomal pairs are formed - bivalent;
- As a result, complexes consisting of two homologous chromosomes or four chromatids are formed. (Think for what you need?);
- At the end of the proofased, crossliner occurs (cross) between homologous chromosomes: chromosomes exchange with homologous areas among themselves. It is the crossing conductor that provides a variety of genetic information received by children from parents.
In metafhase I chromosomes are built up to the equator spine division. Centrometers are addressed to poles.
Anphasis I - Nights of the spindle is reduced, homologous chromosomes consisting of two chromatids are diverted to the cell poles where the haploid sets of chromosomes (2 sets per cell) are formed. At this stage, chromosomal recombinations arise that increase the degree of variability of descendants.
Bulfase I - cells are formed with haploid set chromosomes and doubled the number of DNA. A nuclear shell is formed. 2 nursing chromatids connected by the centromer fall into each cell.
The second division of MEIOS consists of proofased II, metaphase II, anAphase II, BELFAZI II and cytokinesis.
Biological meaning of meiosis It is to form cells involved in sexual reproduction, in maintaining the genetic constancy of species, as well as in sporing formation from higher plants. Maoyotic means disputes of moss, ferns and some other plants groups are formed. Meiosis serves as the basis for combinative variability of organisms. Maizo violations in humans can lead to such pathologies as Down Dauna, Idioth, etc.
- DNA - protein synthesis matrix
- DVN DNA. The course of education and RNA.
- Genetic code and its properties.
1. DNA- matrix for protein synthesis. How much in the erythrocytes of a healthy person are formed millions of identical hemoglobin molecules, as a rule, without a single error in the arino acid location? Why in red blood cells of patients with sickle-cell anemia all hemoglobin molecules have the same error in the same place?
To answer these questions, we turn to the example with a typography. The textbook that you hold in your hands is issued by circulation pinstances. Everything pbooks are printed from one template - typographic matrix, so they are exactly the same. If an error was embryed in the matrix, it would be played in all copies. The role of the matrix in the cells of living organisms is performed by DNA molecules. DNA of each cell carries information not only about structural proteins that determine the shape of the cell (remember the erythrocyte), but also about all proteins-enzymes, proteins-hormones and other proteins.
Carbohydrates and lipids are formed in a cell as a result of complex chemical reactions, each of which is catalyzed by its protein-enzyme. Owning information about enzymes, DNA programms the structure and other organic compounds, and also manages the processes of their synthesis and splitting.
Since the DNA molecules are matrices for the synthesis of all proteins, information about the structure and activity of cells is enclosed in DNA, about all signs of each cell and the body as a whole.
Each protein is represented by one or more polymer chains. DNA molecule site serving a matrix for the synthesis of one polypeptide chain, i.e. in most cases of one protein, called genome.Each DNA molecule contains many different genes. All information concluded in DNA molecules are called genetic.The idea that genetic information is recorded at the molecular level and that protein synthesis goes through the matrix principle, first was formulated back in the 20s with an outstanding domestic biologist N. K. Koltsov.
2. Doubling DNA.DNA molecules have a striking property that does not inherent in any other known molecules, - the ability to doubl. What is the process of doubling? You remember that the DNA double helix is \u200b\u200bbuilt on the principle of complementarity. The same principle underlies the doubling of DNA molecules. With the help of special enzymes, hydrogen bonds, fastening the DNA threads, are broken, the threads are diverted, and complementary nucleotides are consistently attached to each nucleotide of each of these threads. The initial (maternal) yield of the DNA molecule is matrix - they define the location of the nucleotides in the newly synthesized chain. As a result of the action of a complex recruitment of enzymes, a nucleotide compound is connected to each other. At the same time, new DNA threads are formed, complementary by each of the separated chains. Thus, as a result of doubling, two double DNA spirals (daughter molecules) are created, each of them has one thread obtained from the mother molecule, and one thread synthesized again.
DNA daughter molecules are no different from each other and from the maternal molecule. When dividing the cell, the daughter of DNA molecules diverge in two generated cells, each of which will have the same information that was contained in the maternal cell. Since the genes are sections of DNA molecules, the two subsidiaries formed during division have the same genes.
Each cell of the multicellular organism arises from one embryonic cell as a result of multiple divisions, so all organism cells have the same set of genes. Randomly arose error in the germinal cell gene will be reproduced in the genes of millions of its descendants. That is why all erythrocytes of patient with sickle-cell anemia have the same "spoiled" hemoglobin. Children, sick anemia, receive a "spoiled" gene from parents through their sex cells. The information concluded in the DNA of the cells (genetic information) is transmitted not only from the cell in the cell, but also from parents to children. The gene is a genetic unit,or hereditary information.
It is difficult, looking at the typographical matrix, judge that, a good or bad book will be printed on it. It is impossible to judge the quality of genetic information on the fact that the "good" or "bad" gene received descendants by inheritance, until proteins are built on the basis of this information and the whole body will not be built.
The course of education and RNA.To ribosomams, places of protein synthesis, the carrier information is received from the kernel, capable of passing through the pores of the nuclear shell. Such an intermediary is information RNA (and-RNA). This is a single-stranded molecule, complementary by one thread of the DNA molecule. A special enzyme - polymerase, moving along DNA, selects on the principle of nucleotide complementarity and connects them into a single chain (Fig. 21). The formation process and RNA is called transcription(from lat. "Transcripcio" - rewriting). If a Timin is standing in DNA, then the polymerase includes the adenine and-RNA chain, if the guanine is worth it - includes cytosin if adenine is uracil (Timin is not included in the RNA).
The length each of the molecules and RNA is hundreds of times shorter than DNA. Information RNA is a copy of the entire DNA molecule, but only part of it, one gene or group alongside the underlying genes carrying information on the structure of the proteins necessary to perform one function. Prokaryotes such a group of genes is called opero.At the beginning of each group of genes there is a kind of polymerase landing platform, called promoter.This is a specific DNA nucleotide sequence that the enzyme "learns" thanks to chemical affinity. Just joining the promoter, polymerase is able to start synthesis and-RNA. At the end of the gene group, the enzyme encounters a signal (as a certain sequence of nucleotides), which means the end of the rewriting. Finished and RNA departs from DNA, leaves the kernel and heads to the site of the synthesis of protein - ribosome, located in the cytoplasm of the cell.
In the cell, genetic information is transmitted due to the transcription from DNA to the protein:
DNA and RNA protein.
3. Genetic code -certain combinations of nucleotides carrying information on the structure of the protein, and the sequence of their location in the DNA molecule. \\
The gene is a DNA molecule section, which brings information about the structure of one protein molecule.
Properties of the genetic code:
- triplet - one amino acid is encoded by three next to the nucleotides - a triplet, or to Don;
- universality - The code is one for everything that lives on Earth (at moss, pine, amoeba, man, ostrich, etc. The same amino acids encode the same thrips);
- departure - One amino acid can correspond to a few triplets (from two to six). The exception is the amino acids of methionine and tryptophan, each of which is encoded by only one triplet (methionine is encoded by a triplet AURA);
- specificity - Each triplet encodes only one amino acid.
Gaa or Gag Triplets, which occupy the sixth place in the gene of healthy people, carry information about the chain of hemoglobin, coding glutamic acid. In patients with sulfur cell anemia, the second nucleotide is replaced with y, and the GUA and GUG trips are encoded by Valin;
- non-discrepancy - the codons of one gene cannot simultaneously enter into the neighbor;
- continuity- Within one gene, the reading of genetic information occurs in one direction.
Genetic information is encoded in DNA. The genetic code was found out by M. Nirenberg and H.G. Quran, for which they were awarded the Nobel Prize in 1968.
Genetic code - Nucleotide location system in nucleic acid molecules, which monitors the sequence of amino acids in the polypeptide molecule.
Basic postulates code:
1) The genetic code is triplet. Triplet and RNA received the name of the codon. The codon encrypts one amino acid.
2) Genetic code is degenerate. One amino acid is encrypted, more than one codon (from 2 to 6). Exceptions are methionine and tryptophan (AUG, GOG). In the codons for one amino acid, the first two nucleotides are most often the same, and the third varies.
3) Code do not overlap. The nucleotide sequence is read in one direction in a row, a triplet for a triplet.
4) The code is unambiguous. The codon encrypts a specific amino acid.
5) AUG is the starting codon.
6) Inside the gene there are no punctuation marks - Stop Codons: UAG, UAA, UAA.
7) The genetic code is universal, it is one for all organisms and viruses.
Disclosure The DNA structure, the material carrier of heredity contributed to the solution of many questions: reproduction of genes, the nature of mutations, protein biosynthesis, etc.
The genetic code transmission mechanism contributed to the development of molecular biology, as well as genetic engineering, gene therapy.
DNA is in the kernel and is part of chromatin, as well as mitochondria, centrosome, plastists, and RNA - in nucleoli, matrix cytoplasm, ribosomes.
The carrier of hereditary information in the cell is DNA, and RNA - serves to transfer and implement genetic information from pro- and eukaryotes. With the help of and-RNA, the process of translation of the DNA nucleotide sequence in the polypeptide is taken.
In some organisms, in addition to DNA, the carrier of hereditary information may be RNA, for example, viruses of tobacco mosaic, poliomyelitis, AIDS.
Nucleic acid monomers are nucleotides. It has been established that in the chromosomes of eukaryota, a gigantic double DNA molecule is formed by 4 types of nucleotides: adenyl, guanilla, thymidyl, cytosyl. Each nucleotide consists of a nitrogen base (purine g + a or pyrimidine c + T), deoxyribose and phosphoric acid residue.
Analyzing DNA of various origins, Charguff formulated the patterns of quantitative ratio of nitrogen bases - Chargaff Rules.
a) the amount of adenine is equal to the amount of thymine (A \u003d T);
b) the amount of guanin is equal to the amount of cytosine (r \u003d c);
c) the amount of purines is equal to the amount of pyrimidines (g + a \u003d c + t);
d) the amount of bases with 6-amino groups is equal to the amount of bases with 6-keto groups (A + C \u003d r + T).
At the same time, the ratio of the bases of A + T \\ G + C is a strictly visual-specific coefficient (for a person - 0.66; mice - 0.81; bacteria - 0.41).
In 1953 by a biologist J.Uoton and physician F. Krikom. A spatial molecular DNA model was proposed.
The main postulates of the model are as follows:
1. Each DNA molecule consists of two long anti-parallel polynucleotide chains that form a double spiral, twisted around the central axis (human rights - in-form, left-handed-z-form, found by A. Rich in the late 70s).
2. Each nucleoside (pensose + nitrogen base) is located in the plane perpendicular to the axis of the spiral.
3. Two polynucleotide chains are fastened with hydrogen bonds formed between nitrogen bases.
4. Pairing nitrogenous bases is strictly specific, purin bases are connected only with pyrimidine: A-T, Mr.
5. The sequence of bases of one chain can vary significantly, but nitrogenous bases of another chain must be strictly complementary to them.
Polynucleotide chains are formed due to covalent bonds between adjacent nucleotides through the residue of phosphoric acid, which connects carbon in the fifth position of sugar with the third carbon of the adjacent nucleotide. Chains have an orientation: the beginning of the chain 3 "It is in the third position of the deoxyribose carbon. It is joined by a hydroxyl group. It is the end of the chain - 5" f, to the fifth carbon of deoxyribose.
Autosynthetic DNA function is replication - copyrofalization. Replication is based on the principles of semi-servers, anti-parallelity, complementarity and intermittentness. DNA hereditary information is implemented as a result of replication by the type of matrix synthesis. It takes place in the stages: binding, initiation, elongation, termination. The process is timed to the s-period of the interphase. The DNA polymerase enzyme uses single-chain DNA as a matrix and in the presence of 4 nucleotides, the seed (RNA) builds the second DNA chain.
DNA synthesis is carried out according to the principle of complementarity. There is phosphodiester communication between the Nucleotides of the DNA chain due to the compounds 3 "it is the group of the most recent nucleotide with the 5" phosphate of the next nucleotide, which should join the chain.
The three main types of DNA replication are distinguished: conservative, semi-seruous, dispersed.
Conservative - The preservation of the integrity of the original two-chain molecule and the synthesis of a subsidiary. Half of the daughter molecules is completely built of new material, and half - from the old maternal.
Halfonsonvative - The synthesis of DNA begins with attachment to the point of the start of the replication of the enzyme Helichaza, which brings down the DNA sections. Each of the chains is joined by DNA binding protein (DSB), which prevents them with a compound. The replication unit is replicon - this is a plot between the two points of the beginning of the synthesis of the child chains. The interaction of enzymes with a point of the beginning of replication is called initiation. This point moves along the chain (3 "it → 5" f) and a replicative fork is formed.
The synthesis of the new chain is intermittent with the formation of fragments of a length of 700-800-2000 nucleotide residues. There is a point of the beginning and end of replication. The replicon moves along the DNA molecule and its new plots are broken. Each of the mother chains is a matrix for a subsidiary, which is synthesized according to the principle of complementarity. As a result of consecutive nucleotide compounds, the DNA chain is extended (stage of elongation) using the DNA ligase enzyme. When the desired length is reached, the synthesis molecule stops the termination. Eukarot employs thousands of replicative forks at once. Prokaryotes - initiation occurs at one point of the DNA ring, while two replicative forks move in 2 directions. At the place of their meeting, two DNA chain molecules are disconnected.
Dispersed - DNA disintegration on nucleotide fragments, new two-chain DNA consists of spontaneously gained new and parent fragments.
DNA eukaryota in structure is similar to DNA prokaryotes. The differences relate to: the amount of DNA on genes, the length of the DNA molecule, the order of alternation of nucleotide sequences, the form of laying (in eukaryota - linear, in prokaryotm - ring).
For eukaryotes, DNA redundancy is characterized: the amount of its DNA, which participates in coding is only 2%. Some of the excess DNA is represented by the same sets of nucleotides, repeating many times (repeats). There are multiple and moderately repetitive sequences. They form constitutional heterochromatin (structural). It is built into between unique sequences. Excessive genes have 10 4 copies.
Methazna chromosome (Spiralized chromatin) consists of two chromatids. The form is determined by the presence of primary drying - centromers. It shares the chromosome to 2 shoulders.
The location of the centrometers determines the main forms of chromosomes:
Metuclear,
Submetrical,
Acroccentric,
Bascentric.
The degree of spiralization chromosomes is not the same. Sections of chromosomes with weak spiralization call Eukhromatinov. This is a zone of high metabolic activity, where DNA consists of unique sequences. Zone with strong spiralization - heterochromatin Plot capable of transcription. Distinguish constitutive heterochromatin-genetic inert, does not contain genes, does not go into euchromatin, as well as optional, which can go to active eukhromatin. The end departments of distal sections chromosomes are called telomeres.
Chromosome are divided into autosomes (somatic cells) and heterochromosomes (genital cells).
At the proposal of Levitsky (1924), the diploid set of somatic chromosomes of the cell was named karyotype. It is characterized by a number, shape, chromosomes. To describe the karyotype chromosoma at the suggestion of this year. Navishashina they are posted as idiogram - Systematized karyotype. In 1960, a Denver International Classification of Chromosomes was proposed, where the chromosomes are classified by the magnitude and location of centromers. In the karyotype of the somatic cell of a person distinguish 22 pairs of autos and a pair of sex chromosomes. Set chromosomes in somatic cells called diploid, and in sex cells - haploid (It is equal to half a set of autosomes). In the human karyotype φiogram, chromosome are divided into 7 groups, depending on their size and form.
1 - 1-3 large meticenter.
2 - 4-5 large submetrical.
3 - 6-12 and X-chromosome medium meticenteric.
4 - 13-15 medium acrocentric.
5 - 16-18 relatively small meta-submet centers.
6 - 19-20 small metuclear.
7 - 21-22 and Y-chromosome are the smallest acrocentric.
According to Paris classification Chromosomes are divided into groups by their size and shape, as well as linear differentiation.
Chromosome possess the following properties (rules chromosomes):
1. Individuality - differences in non-homologous chromosomes.
2. Parity.
3. The consistency of the number is characteristic of each species.
4. Continuity - ability to reproduce.
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