07.04.2015 13.10.2015
In the era of nanotechnology and innovation in all spheres of human life, you need to know a lot for self-confidence and communication with people. Technologies of the twenty-first century have come very far, for example, in the field of medicine and genetics. In this article we will try to describe in detail the most important step of humanity in DNA research.
Description of the DNA code
What is this code? The code is degenerate by genetic properties and geneticists are studying it. All living beings on our planet are endowed with this code. Scientifically defined as a method of protein sequencing of amino acids using a chain of nucleotides.
The so-called alphabet consists of four bases, designated A, G, T, C:
A - adenine,
G – guanine,
T – thymine,
C – cytosine.
The code chain is a spiral of the above-described basics sequentially composed; it turns out that each step of the spiral corresponds to a specific letter.
The DNA code is degenerated by proteins that participate in the composition and are made up of chains. In which twenty types of amino acids are involved. The amino acids of the revealing code are called canonical, they are arranged in a certain way in each creature and form protein units.
History of detection
Humanity has been studying proteins and acids for a long time, but the first hypotheses and the establishment of the theory of heredity arose only in the middle of the twentieth century. At this point, scientists have collected a sufficient amount of knowledge on this issue.
In 1953, research showed that the protein of an individual organism has a unique chain of amino acids. It was further concluded that this chain has no restriction in the polypeptide.
The records of various world scientists, which were different, were compared. Therefore, a certain concept was formed: each gene corresponds to a specific polypeptide. At the same time, the name DNA appeared, which was definitely proven not to be a protein.
Researchers Crick and Watson first talked about the matrix explanatory cipher scheme in 1953. In the most recent work of great scientists, the fact was proven that the cipher is a carrier of information.
Subsequently, it remained to understand only the issue of determining and forming protein amino acid chains, bases and properties.
The first scientist to construct the genetic coding hypothesis was the physicist Gamow, who also proposed a certain way to test the matrix.
Genetics have suggested establishing a correspondence between the two side crossbars of the amino acid chain and the resulting diamond-shaped steps. The diamond-shaped steps of the chain are formed using four nucleotides of the genetic code. This match was called the match of diamonds.
In his further research, Gamow proposes the theory of the triplet code. This assumption becomes paramount in the question of the nature of the genetic code. Although physicist Gamow's theory has shortcomings, one of which is the coding of protein structure through the genetic code.
Accordingly, George Gamow became the first scientist who considered the question of genes as the coding of a four-digit system in its translation into a twenty-digit fundamental fact.
Operating principle
One protein is made up of several strings of amino acids. The logic of connecting chains determines the structure and characteristics of the body’s protein, which accordingly helps to identify information about the biological parameters of a living being.
Information from living cells is obtained by two matrix processes:
Transcription, that is, the synthesized process of fusion of RNA and DNA templates.
Translation, that is, the synthesis of a chain of polypeptides on an RNA matrix.
During the translation process, the genetic code is redirected into a logical chain of amino acids. 
To identify and implement gene information, at least three chain nucleotides are required, when considering twenty strictly consecutive amino acids. This set of three nucleotides is referred to as a triplet.
Genetic codes are distributed between two categories:
Overlapping – code minor, triangular and sequential.
Non-overlapping – combination code and “no commas”.
Studies have proven that the order of amino acids is chaotic and accordingly individual, based on this, scientists give preference to non-overlapping codes. Subsequently, the “no comma” theory was refuted.
Why do you need to know the DNA code?
Knowledge of the genetic code of a living organism makes it possible to determine the information of molecules in a hereditary and evolutionary sense. A record of heredity is necessary, reveals research on the formation of systemic knowledge in the world of genetics.
The universality of the genetic code is considered the most unique property of a living organism. Based on the data, answers to most medical and genetic questions can be obtained.
Use of knowledge in medicine and genetics
Advances in molecular biology of the twentieth century allowed for great strides in the study of diseases and viruses with various causes. Information about the genetic code is widely used in medicine and genetics.
Identifying the nature of a particular disease or virus overlaps with the study of genetic development. Knowledge and the formation of theories and practices can cure difficult-to-treat or incurable diseases of the modern world and the future.
Development prospects
Since it has been scientifically proven that the genetic code contains information not only about heredity, but also about the life expectancy of the organism, the development of genetics asks the question of immortality and longevity. This prospect is supported by a number of hypotheses of terrestrial immortality, cancer cells, and human stem cells.
In 1985, a researcher at a technical institute, P. Garyaev, discovered, by accident of spectral analysis, an empty space, which was later called a phantom. Phantoms detect dead genetic molecules.
Which further outlined the theory of changes in a living organism over time, which suggests that a person is able to live for more than four hundred years.
The phenomenon is that DNA cells are capable of producing sound vibrations of one hundred hertz. That is, DNA can speak.
PRACTICAL LESSON No.6
SUBJECT: MOLECULAR BASES OF HERITAGE (I)
Lesson objectives:
1) Get acquainted with the modern theory of gene structure.
2) Study the structure and properties of hereditary material (DNA, RNA).
3) Understand the mechanism of encoding and transmission of hereditary information.
Basic knowledge:
1) From a high school biology course, you should have a general understanding of the structure and functions of nucleic acids and the principles of encoding hereditary information.
Study map of the lesson:
A) Questions to prepare for the lesson:
- Evolution of ideas about the gene (Joganson, Koltsov, Benzer, Watson, Crick, Dubinin, Serebrovsky).
- Structural and functional levels of organization of hereditary material. General properties of genetic material.
- Evidence of the hereditary role of nucleic acids (transformation, transduction).
- Chemical organization of hereditary material:
a) structure, properties and functions of DNA.
b) structure and functions of various types of RNA.
- The meaning of the following nucleotide sequences:
a) unique;
b) with an average number of repetitions;
c) with a large number of repetitions;
d) moving genetic elements.
- DNA code system (works by Nirenberg, Ochoa, etc.). Properties of the genetic code.
B) A list of basic and additional literature for preparing for the lesson is provided on the website in the “Information for Students” section
D) Tasks for educational and research work of students:
Exercise 1. Studying the rules for solving genetic problems on the topic of the lesson.
Get acquainted with examples of solving typical problems using Chargaff's rule.
Task 1.
Studies have shown that 34% of the total number of mRNA nucleotides are guanine, 18% are cytosine. Determine the percentage composition of nitrogenous bases corresponding to double-stranded DNA.
Solution:
1) Single-stranded mRNA corresponds to the antisense strand of DNA in the composition of cytosine and guanine bases. Consequently, in the antisense DNA strand (5`-3`) the ratio of guanine and cytosine nucleotides is similar to mRNA: G = 18% and C = 34%
2) Guanine and cytosine of the antisense DNA chain form complementary bonds with cytosine and guanine, respectively, in the sense codogenic chain, therefore, G antisense chain (18%) = C codogenic chain (18%); C of the antisense chain (34%) = G of the codogenic chain (34%). Thus, the amount of G + C in double-stranded DNA = 18% + 34% = 52%
3) Since (A+T)+(G+C)=100%, then A+T=100%-52%=48%
4) Because according to Chargaff’s rule G=C and A=T, then in 52% of guanine-cytosine pairs ½=26% is guanine and ½=26% is cytosine. Accordingly, in 48% of adenine-thymine pairs, ½=24% is adenine and ½=24% is thymine.
Answer: In a double-stranded DNA molecule, 26% is guanine, 26% is cytosine, 24% is adenine, 24% is thymine.
Task 2: Independent solution of genetic problems.
Solve the following problems yourself:
Task 2.1.
As a result of experiments, it was established that in the mRNA molecule the share of adenines is 30%, and the share of uracils is 12%. Determine the percentage composition of nitrogenous bases corresponding to double-stranded DNA.
Problem 2.3.
On a fragment of one of the DNA chains, the nucleotides are arranged in the sequence:
5` TTTCTCTATCGTAT 3`
Draw a diagram of a double-stranded DNA molecule. Explain what signs of DNA construction were you guided by? What is the length of this DNA segment in nm if each nucleotide is 0.34 nm in length? How many nucleotides are there in this DNA sequence?
Problem 2.5.
What is the length of a section of a DNA molecule encoding a section of a polypeptide containing 20 amino acids if the distance occupied by one nucleotide is 0.34 nm?
Problem 2.7.
The insulin molecule consists of 51 amino acid residues. How many nucleotides does the DNA region encoding this protein have?
Problem 2.9.
On a fragment of one DNA strand, the nucleotides are located in the sequence:
A-A-G-T-C-T-A-C-G-T-A-T
Determine the percentage of all nucleotides in this DNA fragment and the length of the gene.
D) Questions on the topic for independent study:
- Genetic Engineering. Possibilities of using the achievements of genetic engineering in medicine.
E) Practical skills that the student must master on the topic of the lesson:
1) Solving typical problems in molecular biology using Chargaff’s rule and the properties of the genetic code.
Teacher's signature: ______________________________________________________________
Each living organism has a special set of proteins. Certain nucleotide compounds and their sequence in the DNA molecule form the genetic code. It conveys information about the structure of the protein. A certain concept has been accepted in genetics. According to it, one gene corresponded to one enzyme (polypeptide). It should be said that research on nucleic acids and proteins has been carried out over a fairly long period. Later in the article we will take a closer look at the genetic code and its properties. A brief chronology of the research will also be provided.
Terminology
The genetic code is a way of encoding the sequence of amino acid proteins involving the nucleotide sequence. This method of generating information is characteristic of all living organisms. Proteins are natural organic substances with high molecularity. These compounds are also present in living organisms. They consist of 20 types of amino acids, which are called canonical. Amino acids are arranged in a chain and connected in a strictly established sequence. It determines the structure of the protein and its biological properties. There are also several chains of amino acids in a protein.
DNA and RNA
Deoxyribonucleic acid is a macromolecule. She is responsible for the transmission, storage and implementation of hereditary information. DNA uses four nitrogenous bases. These include adenine, guanine, cytosine, thymine. RNA consists of the same nucleotides, except that it contains thymine. Instead, there is a nucleotide containing uracil (U). RNA and DNA molecules are nucleotide chains. Thanks to this structure, sequences are formed - the “genetic alphabet”.
Implementation of information
Protein synthesis, which is encoded by the gene, is realized by combining mRNA on a DNA template (transcription). The genetic code is also transferred into the amino acid sequence. That is, the synthesis of the polypeptide chain on mRNA takes place. To encrypt all amino acids and the signal for the end of the protein sequence, 3 nucleotides are enough. This chain is called a triplet.
History of the study
The study of proteins and nucleic acids has been carried out for a long time. In the middle of the 20th century, the first ideas about the nature of the genetic code finally appeared. In 1953, it was discovered that some proteins consist of sequences of amino acids. True, at that time they could not yet determine their exact number, and there were numerous disputes about this. In 1953, two works were published by the authors Watson and Crick. The first stated about the secondary structure of DNA, the second spoke about its permissible copying using template synthesis. In addition, emphasis was placed on the fact that a specific sequence of bases is a code that carries hereditary information. American and Soviet physicist Georgiy Gamow assumed the coding hypothesis and found a method for testing it. In 1954, his work was published, during which he proposed to establish correspondences between amino acid side chains and diamond-shaped “holes” and use this as a coding mechanism. Then it was called rhombic. Explaining his work, Gamow admitted that the genetic code could be a triplet. The physicist's work was one of the first among those that were considered close to the truth.
Classification
Over the years, various models of genetic codes have been proposed, of two types: overlapping and non-overlapping. The first was based on the inclusion of one nucleotide in several codons. It includes a triangular, sequential and major-minor genetic code. The second model assumes two types. Non-overlapping codes include combination code and comma-free code. The first option is based on the encoding of an amino acid by triplets of nucleotides, and the main thing is its composition. According to the "code without commas", certain triplets correspond to amino acids, but others do not. In this case, it was believed that if any significant triplets were arranged sequentially, others located in a different reading frame would be unnecessary. Scientists believed that it was possible to select a nucleotide sequence that would satisfy these requirements, and that there were exactly 20 triplets.
Although Gamow and his co-authors questioned this model, it was considered the most correct over the next five years. At the beginning of the second half of the 20th century, new data appeared that made it possible to discover some shortcomings in the “code without commas”. It was found that codons are capable of inducing protein synthesis in vitro. Closer to 1965, the principle of all 64 triplets was comprehended. As a result, redundancy of some codons was discovered. In other words, the amino acid sequence is encoded by several triplets.
Distinctive features
The properties of the genetic code include:
Variations
The first deviation of the genetic code from the standard was discovered in 1979 during the study of mitochondrial genes in the human body. Further similar variants were further identified, including many alternative mitochondrial codes. These include the decoding of the UGA stop codon, which is used to determine tryptophan in mycoplasmas. GUG and UUG in archaea and bacteria are often used as starting options. Sometimes genes encode a protein with a start codon that differs from that normally used by the species. Additionally, in some proteins, selenocysteine and pyrrolysine, which are nonstandard amino acids, are inserted by the ribosome. She reads the stop codon. This depends on the sequences found in the mRNA. Currently, selenocysteine is considered the 21st and pyrrolysane the 22nd amino acid present in proteins.
General features of the genetic code
However, all exceptions are rare. In living organisms, the genetic code generally has a number of common characteristics. These include the composition of a codon, which includes three nucleotides (the first two belong to the defining ones), the transfer of codons by tRNA and ribosomes into the amino acid sequence.
FSBEI HPE "Penza State University"
Pedagogical Institute named after. V.G. Belinsky
Department of "General Biology and Biochemistry"
Course work
in the discipline "Biology"
on the topic "Coding and implementation of biological information in a cell, the genetic code and its properties"
Penza 2014
Introduction
General properties of genetic material and levels of organization of the genetic apparatus
3. Gene properties
4.2 Ribonucleic acid
6. A method of recording genetic information in a DNA molecule. Biological code and its properties
6.2 Replication of a DNA molecule
6.4 Protein biosynthesis in the cell
Conclusion
genetic deoxyribonucleic acid biosynthesis protein
Introduction
Primarily, the entire diversity of life is determined by the diversity of protein molecules that perform various biological functions in cells. The uniqueness of each cell lies in the uniqueness of its proteins. Cells that perform various functions and are capable of synthesizing their own proteins using information that is written in the DNA molecule.
One of the proofs of the role of DNA in the transmission of hereditary information were experiments on the transformation of bacteria. F. Griffith (1928).
The second proof of the role of DNA in the transmission of hereditary information was obtained by N. Zinder and J. Lederberg. In 1952 they described the phenomenon of transduction.
Proof that nucleic acids, and not proteins, are carriers of genetic information were the experiments of X. Frenkel-Konrath (1950). Thus, with the discovery of the phenomena of transformation, transduction and the experiments of Frenkel-Konrath, the role of nucleic acids in the transmission of hereditary information was proven.
In 1941, G. Beadle and E. Tatum established that genes are responsible for the formation of enzymes that, through cellular metabolism, influence the development of morphological and physiological characteristics.
In 1951, E. Chargaff discovered the phenomenon of complementarity of nitrogenous bases in the DNA molecule (Chargaff's rule), showing that the amount of adenine is always equal to the amount of thymine, and the amount of guanine is equal to the amount of cytosine.
In 1953, J. Watson, F. Crick and M. Wilkins proposed a model of the structure of the DNA molecule, which is a double helix.
Thus, in the early 50s it was proven that the material unit of heredity and variability is a gene, which has a certain structural and functional organization. The primary functions of genes are the storage and transmission of genetic information. The transfer of genetic information occurs from DNA to DNA during DNA replication. F. Crick (1958) called this path of information transfer from DNA to mRNA and protein the central dogma of molecular biology.
In the 60s The works of M. Nirenberg, S. Ochoa, X. Korana and others completely deciphered the genetic code and established the correspondence of nucleotide triplets in a nucleic acid molecule to certain amino acids.
In the 70s Genetic engineering methods began to be actively developed, making it possible to purposefully change the hereditary properties of living organisms.
By the end of the 20th century, thanks to new molecular genetic technologies, it became possible to determine the nucleotide sequences in the DNA molecules of the genomes of various organisms (reading DNA texts). The DNA texts of the human genome, represented by a total of 3 billion nucleotide pairs, were mostly read by 2001. The scientific and practical direction of molecular biology, aimed at determining the nucleotide sequences of DNA molecules, is called genomics.
1. General properties of genetic material and levels of organization of the genetic apparatus
The elementary functional unit of the genetic apparatus, which determines the possibility of developing a separate characteristic of a cell or organism of a given species, is the -gene (hereditary inclination, according to G. Mendel). The transmission of genes in a series of generations of cells or organisms achieves material continuity - inheritance by descendants of the characteristics of their parents. A trait is understood as a unit of morphological, physiological, biochemical, immunological, clinical and any other discreteness of organisms (cells), i.e. a separate quality or property by which they differ from each other.
Most of the above features of organisms or cells belong to the category of complex features, the formation of which requires the synthesis of many substances, primarily proteins with the specific properties of enzymes, immunoproteins, structural, contractile, transport and other proteins. The properties of a protein molecule are determined by the amino acid sequence of its polypeptide chain, which is directly determined by the sequence of nucleotides in the DNA of the corresponding gene and is an elementary, or simple, feature.
The basic properties of a gene as a functional unit of the genetic apparatus are determined by its chemical organization.
2. Chemical organization of the gene
Research aimed at elucidating the chemical nature of the hereditary material has irrefutably proven that the material substrate of heredity and variability are nucleic acids, which were discovered by F. Miescher (1868) in the nuclei of pus cells. Nucleic acids are macromolecules, i.e. have a high molecular weight. These are polymers consisting of nucleotide monomers, including three components: sugar (pentose), phosphate and nitrogenous base (purine or pyrimidine). A nitrogen base (adenine, guanine, cytosine, thymine or uracil) is attached to the first carbon atom in the C-1 pentose molecule, and a phosphate is attached to the fifth carbon atom C-5 using an ester bond; the third carbon atom C-3 always has a hydroxyl group-OH. The joining of nucleotides into a nucleic acid macromolecule occurs through the interaction of the phosphate of one nucleotide with the hydroxyl of another so that a phosphodiester bond is established between them. As a result, a polynucleotide chain is formed. The backbone of the chain consists of alternating phosphate and sugar molecules. One of the nitrogenous bases listed above is attached to the pentose molecules at position C-1). The assembly of the polynucleotide chain is carried out with the participation of the enzyme polymerase, which ensures the attachment of the phosphate group of the next nucleotide to the hydroxyl group located at position 3", of the previous nucleotide. Due to the noted specificity of the action of the said enzyme, the growth of the polynucleotide chain occurs only at one end: where the free hydroxyl is located at position 3". The beginning of the chain always carries a phosphate group at position 5". This allows us to distinguish 5" and 3" ends in it.
Among nucleic acids, there are two types of compounds: deoxyribonucleic acid (DNA) and ribonucleic acid (RNA). A study of the composition of the main carriers of hereditary material—chromosomes—found that their most chemically stable component is DNA, which represents the substrate of heredity and variability.
3. Gene properties
Genes are characterized by certain properties: specificity, integrity and discreteness, stability and lability, pleiotropy, expressivity and penetrance. The specificity of a gene lies in the fact that each structural gene has only its own order of nucleotides and determines the synthesis of a specific polypeptide, rRNA or tRNA. The integrity of the gene consists in the fact that when programming the synthesis of a polypeptide, it acts as an indivisible unit, a change in which leads to a change in the polypeptide molecule. The gene as a functional unit is indivisible. The discreteness of the gene is determined by the presence of subunits in it. Currently, the minimum structural subunit of a gene is considered to be a pair of complementary nucleotides, and the minimum functional unit is a codon. Genes are relatively stable and change (mutate) rarely. The frequency of spontaneous mutation of one gene is approximately 1-10-5 per generation.
The ability of a gene to change (mutate) is called lability. Genes, as a rule, have a pleiotropic (multiple) effect, when one gene is responsible for the manifestation of several traits. This phenomenon, in particular, is observed in some enzymopathies and multiple congenital malformations, for example, in Marfan syndrome.
4. Structure and functions of DNA and RNA
The term nucleic acids was proposed by the German chemist R. Altmann in 1889 after these compounds were discovered in 1868. Swiss doctor F. Miescher. He extracted the cells of purulent pneumococcus with dilute hydrochloric acid for several weeks and obtained almost pure nuclear material in the remainder, calling it nuclein (from the Latin nucleus - core). Nucleic acids - DNA (deoxyribonucleic acid) and RNA (ribonucleic acid).
1 Deoxyribonucleic acid
DNA (deoxyribonucleic acid) molecules are the largest biopolymers; their monomer is a nucleotide. It consists of residues of three substances: a nitrogenous base, the carbohydrate deoxyribose and phosphoric acid. There are four known nucleotides involved in the formation of the DNA molecule. They differ from each other in their nitrogenous bases. The two nitrogenous bases cytosine and thymine are pyrimidine derivatives. Adenine and guanine are classified as purine derivatives. The name of each nucleotide reflects the name of the nitrogenous base. Nucleotides are distinguished: cytidyl (C), thymidyl (T), adenyl (A), guanyl (G). The connection of nucleotides in a DNA strand occurs through the carbohydrate of one nucleotide and the phosphoric acid residue of the neighboring one. According to the DNA model, both strands twist together around a common axis. The two strands of the molecule are held together by hydrogen bonds that occur between their complementary nitrogen bases. Adenine is complementary to thymine, and guanine is complementary to cytosine. Two hydrogen bonds arise between adenine and thymine, and three between guanine and cytosine.
DNA is located in the nucleus, where it, together with proteins, forms linear structures - chromosomes. Chromosomes are clearly visible under microscopy during nuclear division; in interphase they are despiralized.
DNA is found in mitochondria and plastids (chloroplasts and leucoplasts), where their molecules form ring structures. Circular DNA is also present in the cells of prenuclear organisms.
DNA is capable of self-duplication (reduplication). This takes place in a certain period of the cell's life cycle, called synthetic. Reduplication allows the DNA structure to remain constant. If, under the influence of various factors during the replication process, changes in the number and order of nucleotides occur in the DNA molecule, then mutations occur.
The main function of DNA is the storage of hereditary information contained in the sequence of nucleotides that form its molecule, and the transmission of this information to daughter cells. The possibility of transmitting hereditary information from cell to cell is ensured by the ability of chromosomes to divide into chromatids with subsequent reduplication of the DNA molecule. DNA contains all the information about the structure and activity of cells, the characteristics of each cell and the organism as a whole. This information is called genetic. The DNA molecule encodes genetic information about the sequence of amino acids in a protein molecule. The transmission and implementation of information is carried out in the cell with the participation of ribonucleic acids.
2 Ribonucleic acid
Ribonucleic acids come in several types. There are ribosomal, transport and messenger RNA. The RNA nucleotide consists of one nitrogenous base (adenine, guanine, cytosine and uracil), a carbohydrate - ribose and a phosphoric acid residue. RNA molecules are single-stranded.
Ribosomal RNA (r-RNA) in combination with protein is part of the ribosomes. R-RNA makes up 80% of all RNA in the cell. Protein synthesis occurs on ribosomes. Messenger RNA (i-RNA) makes up from 1 to 10% of all RNA in the cell. In structure, i-RNA is complementary to the section of the DNA molecule that carries information about the synthesis of a specific protein. The length of the mRNA depends on the length of the DNA section from which the information was read. I-RNA carries information about nuclear protein synthesis to the cytoplasm.
Transfer RNA (tRNA) makes up about 10% of all RNA. It has a short chain of nucleotides and is located in the cytoplasm. T-RNA attaches certain amino acids and transports them to the site of protein synthesis to the ribosomes. T-RNA is shaped like a trefoil. At one end is a triplet of nucleotides (anticodon) that codes for a specific amino acid. At the other end there is a triplet of nucleotides to which an amino acid is attached. With the complementarity of the t-RNA triplet (anticodon) and the mRNA triplet (codon), the amino acid occupies a specific place in the protein molecule.
RNA is found in the nucleolus, in the cytoplasm, in ribosomes, in mitochondria and plastids.
There is another type of RNA in nature. This is viral RNA. In some viruses it performs the function of storing and transmitting hereditary information. In other viruses, this function is performed by viral DNA.
5. Evidence for the genetic role of nucleic acids
Frederick Griffith's experiments 1928 The bacterium Pneutnococcus pneumoniae is known to have several forms. The virulence of a bacterium is determined by the presence of a mucopolysaccharide capsule located on the surface of the cell. This capsule protects the bacterium from influences from the host organism. As a result, the multiplied bacteria kill the infected animal. Bacteria of this strain (S-strain) form smooth colonies. Avirulent forms of bacteria do not have a protective capsule and form rough colonies (R-strain). Microbiologist Frederick Griffiths injected mice with live R-strain pneumococcus along with an S-strain killed by high temperature (65°C) in 1928. After some time, he managed to isolate living pneumococci with a capsule from infected mice. Thus, it turned out that the property of the killed pneumococcus - the ability to form a capsule - was transferred to the living bacterium, i.e. a transformation has occurred. Since the sign of the presence of a capsule is hereditary, it should be assumed that some part of the hereditary substance from bacteria of strain S was transferred to cells of strain R.
In 1944 O.T. Avery, K.M. McLeod and M. McCarthy showed that the same transformation of pneumococcal types can occur in vitro, i.e. invitro. These researchers established the existence of a special substance - the “transforming principle” - an extract from cells of the S strain, enriched with DNA. As it turned out later, DNA isolated from cells of the S-strain and added to the culture of the R-strain transformed some of the cells into the S-form. The cells persistently passed on this property during further reproduction. Treatment of the “transforming factor” with DNAse, an enzyme that destroys DNA, blocks transformation. These data showed for the first time that it was DNA, and not protein, as previously believed, that was the hereditary material.
d. Experiment of Alfred Hershey and Martha Chase. As is known, phage T2 is a virus that infects the bacterium E. coli. phage particles are absorbed on the outer surface of the cell, their material penetrates inside and after about 20 minutes the bacterium is lysed, releasing a large number of phage particles - descendants. In 1952, Alfred Hershey and Martha Chase infected bacteria with T2 phages, which were labeled with radioactive compounds: DNA - with 32P. The protein part of the phage is 35S. After infection of bacteria with phages, using centrifugation it was possible to isolate two fractions: empty protein shells of the phage and bacteria infected with phage DNA. It turned out that 80% of the 35S tag remained in empty phage shells, and 70% of the 32P tag remained in infected bacteria. The descendant phages received only about 1% of the original protein labeled with 35S, but they also detected about 30% of the 32P tag. The results of this experiment directly showed that the DNA of the parent phages penetrates the bacteria and then becomes a component of the developing new phage particles.
Frenkel-Konrath experimentsFrenkel-Konrath worked with the tobacco mosaic virus (TMV). This virus contains RNA, not DNA. It was known that different strains of the virus cause different patterns of damage to tobacco leaves. After changing the protein shell, the “disguised” viruses caused a lesion pattern characteristic of the strain whose RNA was covered with a foreign protein.
Consequently, not only DNA, but also RNA can serve as a carrier of genetic information. Today, there are hundreds of thousands of evidence of the genetic role of nucleic acids. The above three are classics.
6. Method of recording genetic information in a DNA molecule. Biological code and its properties
1 Levels of packaging of genetic material
The double helix of the DNA molecule combines with histone and non-histone proteins, forming nucleoprotein fibrils. The length of these fibrils in the diploid set of human chromosomes is approximately 2 m, and the total length of all chromosomes in metaphase is about 150 μm. It is generally accepted that each chromatid of a chromosome contains one continuous DNA molecule. Packaging of genetic material is achieved by spiralization (condensation) of fibrils.
The first level of DNA packaging is nucleosomal. The nucleosome is a cylinder (octamer) with a diameter of 11 nm and a height of 6 nm, containing two molecules of each of the four histones (H2A, H2B, H3, H4), around which the DNA double helix forms about two turns and passes to the next cylinder. The length of the twisted DNA fragment is approximately 60 nm (about 200 nucleotide pairs). The nucleosome filament thus formed has a diameter of about 13 nm. The length of the DNA molecule decreases by 5-7 times. The nucleosomal level of packaging is detected in the electron microscope during interphase and mitosis.
The second level of packaging is solenoid (supernucleosomal). The nucleosomal thread condenses, its nucleosomes are cross-linked. histone HI and is formed with a helix diameter of about 25 nm. One turn of the helix contains 6-10 nucleosomes. This shortens the thread by another 6 times. The supernucleosomal level of packaging is detected in the electron microscope in both interphase and mitotic chromosomes.
The third level of packaging is chromatid (loop). The supernucleosomal strand spirals to form loops and bends. It forms the basis of the chromatid and ensures the chromatid level of packaging. It is found in prophase. The diameter of the loops is about 50 nm. The DNP (DNA + protein) thread is shortened by 10-20 times.
The fourth level of packaging is the level of metaphase chromosome. Chromatids in metaphase are still capable of spiralization with the formation of euchromatic (weakly spiralized) and heterochromatic (strongly spiralized) regions; shortening occurs by a factor of 20. Metaphase chromosomes have a length from 0.2 to 150 µm and a diameter from 0.2 to 5.0 µm. The overall result of condensation is a shortening of the DNA strand by 10,000 times.
Chromosomes of prokaryotic cells are circular DNA molecules containing about 5-106 nucleotide pairs and forming complexes with non-histone proteins. Using special methods of destroying prokaryotes, one can find that their DNA is assembled into beads approaching the size of eukaryotic nucleosomes. These beads are very labile, indicating weak interactions between DNA and proteins.
The nature of the condensation of the prokaryotic chromosome is not entirely clear, but in general it can be distinguished in the form of a compact structure called a nucleoid. Prokaryotic cells (bacteria) also contain circular double-stranded DNA molecules consisting of several thousand nucleotide pairs, which they can exchange with other bacteria. These autonomous genetic plasmid elements are capable of replicating regardless of the replication of the nucleoid. Most plasmids contain genes for resistance to antibacterial factors. Ring-shaped DNA molecules are also found in eukaryotic cells in self-replicating organelles (mitochondria, plastids). These molecules are small and encode a small number of proteins necessary for the autonomous functions of organelles. Organelle DNA is not associated with histones.
6.2 Replication of a DNA molecule
Replication of DNA molecules occurs during the synthetic period of interphase. Each of the two chains of the parent molecule serves as a template for the synthesis of a new chain according to the principle of complementarity. After replication, the DNA molecule contains one mother strand and one newly synthesized daughter strand (DNA synthesis is semi-conservative). Since two complementary chains in a DNA molecule are directed in opposite directions, and DNA polymerase can move along the template chains only from the 5" end to the 3" end, the synthesis of new chains proceeds antiparallel (antiparallel principle). For the template synthesis of a new DNA molecule, it is necessary so that the old molecule is despiraled and elongated. But the simultaneous unwinding of helices consisting of a huge number of nucleotide pairs (several millions) is impossible. Therefore, replication begins at several places in the DNA molecule. The section of a DNA molecule from the start of one replication to the start of another is called a replicon. The bacterial chromosome contains one replicon. The eukaryotic chromosome contains many replicons in which the duplication of the DNA molecule occurs simultaneously. A replicon necessarily has control elements: a start point at which replication is initiated and an end point at which replication stops. The place where replication occurs is called the replication fork. The replication fork moves along the DNA molecule from its starting point (start point) to its end point. Since DNA polymerase can only move in one direction (5"-3"), it can gradually and continuously build only one new strand of the DNA molecule at each replication fork. Another daughter DNA molecule is synthesized in separate short sections of 150-200 nucleotides (Okazaki fragments) under the action of DNA polymerase moving in the opposite direction. These short sections of the newly synthesized polynucleotide chain of one replicon are linked together by the enzyme ligase. This principle of synthesis of new DNA chains is called discontinuous. Sites.of.subsidiaries. DNA molecules synthesized in neighboring replicons are also cross-linked by the enzyme ligase. The entire genome of a cell is replicated only once during a period of time corresponding to one mitotic cycle.
6.3 Genetic code and its properties
The structure of proteins is determined by the set and order of amino acids in their peptide chains. It is this sequence of amino acids in peptides that is encrypted in DNA molecules using a biological (genetic) code. The relative primitiveness of the DNA structure, representing the alternation of only four different nucleotides, has long prevented researchers from considering this compound as a material substrate of heredity and variability, in which extremely diverse information should be encrypted.
The complete deciphering of the genetic code was carried out in the 60s. of our century. Of the 64 possible DNA triplets, 61 code for different amino acids; the remaining 3 were called meaningless, or nonsense triplets. They do not encrypt amino acids and act as punctuation marks when reading hereditary information. These include ATT, ACT, ATC. Noteworthy is the obvious redundancy of the code, manifested in the fact that many amino acids are encrypted by several triplets. This property of the triplet code, called degeneracy, is very important, since the occurrence of changes in the structure of the DNA molecule such as substitution of one nucleotide in the polynucleotide chain may not change the meaning of the triplet. The new combination of three nucleotides thus formed encodes the same amino acid.
In the process of studying the properties of the genetic code, its specificity was discovered. Each triplet is capable of encoding only one specific amino acid. An interesting fact is the complete correspondence of the code in different types of living organisms. Such universality of the genetic code indicates the unity of origin of the entire diversity of living forms on Earth in the process of biological evolution. Minor differences in the genetic code have been found in the mitochondrial DNA of some species. This does not generally contradict the position about the universality of the code, but testifies in favor of a certain divergence of its evolution in the early stages of the existence of life.
Deciphering the code in the DNA of mitochondria of various species showed that in all cases, mitochondrial DNA has a common feature: the triplet ACC is read as ACC, and therefore turns from a nonsense triplet into a code for the amino acid tryptophan. Along with tripletity, degeneracy, specificity and universality, the most important characteristics of the genetic code are its continuity and non-overlapping codons during reading. This means that the nucleotide sequence is read triplet by triplet without gaps, and neighboring triplets do not overlap each other, i.e. Each individual nucleotide is part of only one triplet for a given reading frame. Proof of the non-overlapping genetic code is the replacement of only one amino acid in the peptide when replacing one nucleotide in the DNA. If a nucleotide is included in several overlapping triplets, its replacement would entail the replacement of 2 - 3 amino acids in the peptide chain.
Thus, the genetic code is not a random conglomeration of correspondences between codons and amino acids, but a highly organized system of correspondences supported by complex molecular mechanisms.
4 Protein biosynthesis in the cell
The mediator in the transfer of genetic information (nucleotide order) from DNA to protein is mRNA (messenger RNA). It is synthesized in the nucleus on one of the DNA strands according to the principle of complementarity after the rupture of hydrogen bonds between the two strands (RNA polymerase enzyme). The process of copying information from DNA to mRNA is called transcription. The mRNA synthesized in this way (template synthesis) exits through the pores of the nucleus into the cytoplasm and interacts with the small subunit of one or more ribosomes. Ribosomes united by one mRNA molecule are called polysomes. Each ribosome of a polysome synthesizes identical protein molecules.
The next stage of protein biosynthesis is translation, the translation of the nucleotide sequence in the mRNA molecule into the amino acid sequence in the polypeptide chain. Transfer RNAs (tRNAs) bring amino acids into the ribosome. The tRNA molecule is similar in configuration to a clover leaf and has two active centers. At one end of the molecule there is a triplet of free nucleotides, which is called an anticodon and corresponds to a specific amino acid. Since many amino acids are encoded by several triplets, the number of different tRNAs is much more than 20 (60 have been identified). The second active site is the site opposite the anticodon to which the amino acid is attached. There is always a guanine at the 5" end of the tRNA molecule, and a CCA riplet at the 3" end. Each amino acid is attached to one of its specific tRNAs using a special form of the enzyme aminoacyl-tRNA synthetase and ATP. As a result, a stRNA-aminoacyl-tRNA amino acid complex is formed, in which the binding energy between the terminal nucleotide A (in the CCA triplet) and the amino acid is sufficient for the subsequent formation of a peptide bond. Amino acids are transported to the large subunit of the ribosome. At any given moment, there are two codons and RNA inside the ribosome: one opposite the aminoacyl center, the second opposite the peptidyl center. If the anticodon of the tRNA and the codonaminoacyl center are complementary, then the tRNA and amino acid move to the peptidyl center (the ribosome moves one triplet), the amino acid is detached from the tRNA and attached to the preceding amino acid, and the tRNA leaves the ribosome after the next amino acid. The same thing happens with the second tRNA and its amino acid. Thus, the polypeptide molecule is assembled in full accordance with the information recorded on the mRNA. There are three stages in the translation process: initiation, elongation and termination. Initiation (start of translation) consists in the binding of the siRNA ribosome, for which at the beginning of the mRNA molecule there is a special initiation codon (AUG) and a certain nucleotide sequence that is responsible for the connection with the ribosome. Elongation (the process of translation) includes reactions from the formation of the first peptide bond to the addition of the last amino acid to the polypeptide molecule. During this time, the ribosome moves from the first to the last codon on the mRNA. Termination (end of translation) is due to the presence of termination codons (UAA, UAG, U GA), which stop protein synthesis; The ribosome is separated from the mRNA. Regulation of protein synthesis in eukaryotes can be carried out at the level of transcription and translation. The regulatory function is performed by chromosomal proteins (histones). Their molecules are positively charged and easily bind to negatively charged phosphates, influencing the transcription of certain genes using DNA-dependent RNA polymerase. Histone modifications (phosphorylation, acetylation, methylation) weaken their binding to DNA and facilitate transcription. Acidic non-histone proteins, by binding to certain regions of DNA, also facilitate transcription. Transcription is also regulated by low molecular weight nuclear RNAs, which are in complex with proteins and can selectively turn on genes. Protein synthesis is enhanced by various anabolic steroids, insulin, precursors of nucleotides and nucleic acids (inosine, potassium orotate). Inhibitors of protein synthesis are antibiotics (rifamycins, olivomycin), some antitumor drugs (vinblastine, vincristine, 5-fluorouracil), modified nitrogenous bases and nucleosides.
In laboratory conditions, protein synthesis requires enormous time, effort and money. In a cell, the synthesis of protein molecules consisting of hundreds or more amino acids occurs within a few seconds. This is explained primarily by the matrix principle of synthesis of nucleic acids and proteins, which ensures the exact sequence of monomer units in the synthesized polymers. If such reactions occurred as a result of random collisions of molecules, they would proceed infinitely slowly. Enzymes have a significant influence on the speed and accuracy of all protein synthesis reactions. With the participation of special enzymes, DNA and mRNA are synthesized, amino acids are combined with tRNA, etc. The process of protein synthesis also requires a lot of energy. Thus, the energy of one ATP molecule is consumed to connect each amino acid with t-RNA. You can imagine how many ATP molecules are broken down during the synthesis of a medium-sized protein consisting of several hundred amino acids.
Conclusion
The biological properties of living matter are determined by the combined properties of its components - bioorganic matter, chemical energy and molecular information. In this regard, living matter obeys not only all known physical and chemical laws, but also informational laws. It is clear that bioorganic matter is the material basis for the construction of any living system. In addition, biological macromolecules and structures also act as a carrier of molecular information, therefore information in the structure of a living thing has a chemical form of recording. Thanks to the processing and circulation of hereditary information in the process of life, biochemical and molecular processes are controlled and regulated, and the entropy (disorganization) of the living system is reduced. Only information resources and patterns allow matter, energy and information in a living system to circulate, renew, reproduce and create new biological realities. Self-government and information exchange are the most essential characteristics of the functioning of living systems. Therefore, in any living cells, the phenomena of encoding, storage, recoding, transmission, processing and use of genetic information are key to all biological processes.
Based on the achievements of molecular biology, biochemistry and genetics, a new direction in genetics, genetic engineering, has been intensively developing in recent decades, the purpose of which is to construct genetic structures according to a predetermined plan, to create organisms with a new genetic program by transferring genetic information from one organism to another.
Genetic engineering dates back to 1973, when geneticists Stanley Cohen and Herbert Boyer introduced a new gene into the bacterium Escherichia coli.
Since 1982, companies in the USA, Japan, Great Britain and other countries have been producing genetically engineered insulin. Cloned human insulin genes were introduced into a bacterial cell, where the synthesis of a hormone began, which natural microbial strains had never synthesized.
About 200 new diagnostic drugs have already been introduced into medical practice, and more than 100 genetically engineered medicinal substances are at the stage of clinical study. Among them are drugs that cure arthrosis, cardiovascular diseases, some tumor processes and, possibly, even AIDS. Among several hundred genetic engineering firms, 60% are working on the production of drugs and diagnostics.
In 1990, the Human Genome Project was launched in the United States, the goal of which was to determine the entire genetic year of a person. The project, in which Russian geneticists also played an important role, was completed in 2003. As a result of the project, 99% of the genome was determined with an accuracy of 99.99% (1 error per 10,000 nucleotides). The completion of the project has already brought practical results, for example, easy-to-use tests that make it possible to determine genetic predisposition to many hereditary diseases.
Since the 1990s, hundreds of laboratories have been conducting research into the use of gene therapy to treat diseases. Today we know that gene therapy can treat diabetes, anemia, some types of cancer, Huntington's disease, and even clear arteries. There are currently more than 500 clinical trials of various types of gene therapy.
Unfavorable environmental conditions and a number of other similar reasons lead to more and more children being born with serious hereditary defects. There are currently 4,000 known hereditary diseases, for most of which no effective treatment has been found.
Today it is possible to diagnose many genetic diseases even at the stage of the embryo or fetus. For now, it is only possible to terminate pregnancy at a very early stage in case of serious genetic defects, but soon it will become possible to correct the genetic code, correcting and optimizing the genotype of the unborn child. This will completely avoid genetic diseases and improve the physical, mental and mental characteristics of children.
Based on the above, there are convincing reasons to believe that the general laws and principles of information coding have become not only the fundamental foundations of Life, but also, subsequently, were re-discovered by man and found widespread use in many areas of human activity.
List of information sources used
1. Ayala F., Kaiger J. Modern genetics. M.: Mir, 1988. T. 3.
2.Genetic engineering. Article.
Statement of the Ministry of Defense of the Russian Federation. Biology. Textbook. 1t. GEOTAR-Media
4. Zayats R.G., Rachkovskaya I.V. Fundamentals of general and medical genetics. Mn.: VSh, 1998.
5. Kalashnikov Yu. Ya., Information control of cellular processes
6. Petukhov V.L., Korotkevich O.S., Stambekov S.Zh. Genetics. textbook manual for higher students textbook Establishments Novosibirsk: SemGPI, 2007. 628 p.
7. Polikarpova V.A. Genetic engineering and human problems. Academy of Humanities, TRTU publishing house, 1999. - 88 p.
8. Spirin A.S. Molecular biology. M.: Higher. school 1990. 352 p.
Chebyshev N.V., Grineva G.G., Kozar M.V., Gulenkov S.I. Biology (Textbook). - M.: VUNMTs, 2000.
Yarygin V.N., V.I. Vasilyeva, I.N. Volkov, V.V. Sinelytsikova. Biology. Book 1: Textbook formedical specialist. Universities 2003.
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In the body's metabolism leading role
belongs to proteins and nucleic acids.
Protein substances form the basis of all vital cell structures, have an unusually high reactivity, and are endowed with catalytic functions.
Nucleic acids are part of the most important organ of the cell - the nucleus, as well as the cytoplasm, ribosomes, mitochondria, etc. Nucleic acids play an important, primary role in heredity, variability of the body, and in protein synthesis.
Plan synthesis protein is stored in the cell nucleus, and direct synthesis occurs outside the nucleus, so it is necessary delivery service encoded plan from the nucleus to the place of synthesis. This delivery service is performed by RNA molecules.
The process starts at core cells: part of the DNA “ladder” unwinds and opens. Thanks to this, the RNA letters form bonds with the open DNA letters of one of the DNA strands. The enzyme transfers the RNA letters to join them into a strand. This is how the letters of DNA are “rewritten” into the letters of RNA. The newly formed RNA chain is separated, and the DNA “ladder” twists again. The process of reading information from DNA and synthesizing it using its RNA matrix is called transcription , and the synthesized RNA is called messenger or mRNA .
After further modifications, this type of encoded mRNA is ready. mRNA comes out of the nucleus and goes to the site of protein synthesis, where the letters of the mRNA are deciphered. Each set of three i-RNA letters forms a “letter” that represents one specific amino acid.
Another type of RNA finds this amino acid, captures it with the help of an enzyme, and delivers it to the site of protein synthesis. This RNA is called transfer RNA, or t-RNA. As the mRNA message is read and translated, the chain of amino acids grows. This chain twists and folds into a unique shape, creating one type of protein. Even the protein folding process is remarkable: it takes a computer to calculate everything options folding an average-sized protein consisting of 100 amino acids would take 1027 (!) years. And it takes no more than one second to form a chain of 20 amino acids in the body, and this process occurs continuously in all cells of the body.
Genes, genetic code and its properties.
About 7 billion people live on Earth. Apart from the 25-30 million pairs of identical twins, genetically all people are different : everyone is unique, has unique hereditary characteristics, character traits, abilities, and temperament.
These differences are explained differences in genotypes- sets of genes of the organism; Each one is unique. The genetic characteristics of a particular organism are embodied in proteins - therefore, the structure of the protein of one person differs, although very slightly, from the protein of another person.
It does not mean that no two people have exactly the same proteins. Proteins that perform the same functions may be the same or differ only slightly by one or two amino acids from each other. But does not exist on Earth of people (with the exception of identical twins) who would have all their proteins are the same .
Protein Primary Structure Information encoded as a sequence of nucleotides in a section of a DNA molecule, gene – a unit of hereditary information of an organism. Each DNA molecule contains many genes. The totality of all the genes of an organism constitutes it genotype . Thus,
Gene is a unit of hereditary information of an organism, which corresponds to a separate section of DNA
Coding of hereditary information occurs using genetic code , which is universal for all organisms and differs only in the alternation of nucleotides that form genes and encode proteins of specific organisms.
Genetic code consists of triplets (triplets) of DNA nucleotides, combined in different sequences (AAT, HCA, ACG, THC, etc.), each of which encodes a specific amino acid (which will be built into the polypeptide chain).
Actually code
counts sequence of nucleotides in an mRNA molecule
, because it removes information from DNA (process transcriptions
) and translates it into a sequence of amino acids in the molecules of synthesized proteins (the process broadcasts
).
The composition of mRNA includes nucleotides A-C-G-U, the triplets of which are called codons
: a triplet on DNA CGT on i-RNA will become a triplet GCA, and a triplet DNA AAG will become a triplet UUC. Exactly mRNA codons
the genetic code is reflected in the record.
Thus, genetic code - a unified system for recording hereditary information in nucleic acid molecules in the form of a sequence of nucleotides . The genetic code is based on the use of an alphabet consisting of only four letters-nucleotides, distinguished by nitrogenous bases: A, T, G, C.
Basic properties of the genetic code:
1. Genetic code triplet. A triplet (codon) is a sequence of three nucleotides encoding one amino acid. Since proteins contain 20 amino acids, it is obvious that each of them cannot be encoded by one nucleotide ( Since there are only four types of nucleotides in DNA, in this case 16 amino acids remain uncoded). Two nucleotides are also not enough to encode amino acids, since in this case only 16 amino acids can be encoded. This means that the smallest number of nucleotides encoding one amino acid must be at least three. In this case, the number of possible nucleotide triplets is 43 = 64.
2. Redundancy (degeneracy) The code is a consequence of its triplet nature and means that one amino acid can be encoded by several triplets (since there are 20 amino acids and 64 triplets), with the exception of methionine and tryptophan, which are encoded by only one triplet. In addition, some triplets perform specific functions: in an mRNA molecule, triplets UAA, UAG, UGA are stop codons, i.e. stop-signals that stop the synthesis of the polypeptide chain. The triplet corresponding to methionine (AUG), located at the beginning of the DNA chain, does not code for an amino acid, but performs the function of initiating (exciting) reading.
3. Unambiguity code - at the same time as redundancy, code has the property unambiguity : each codon matches only one a certain amino acid.
4. Collinearity code, i.e. nucleotide sequence in a gene exactly corresponds to the sequence of amino acids in a protein.
5. Genetic code non-overlapping and compact , i.e. does not contain “punctuation marks”. This means that the reading process does not allow the possibility of overlapping columns (triplets), and, starting at a certain codon, reading proceeds continuously, triplet after triplet, until stop-signals ( stop codons).
6. Genetic code universal , i.e., the nuclear genes of all organisms encode information about proteins in the same way, regardless of the level of organization and systematic position of these organisms.
Exist genetic code tables for decryption codons mRNA and construction of chains of protein molecules.
Matrix synthesis reactions.
Reactions unknown in inanimate nature occur in living systems - matrix synthesis reactions.
The term "matrix" in technology they designate a mold used for casting coins, medals, and typographic fonts: the hardened metal exactly reproduces all the details of the mold used for casting. Matrix synthesis resembles casting on a matrix: new molecules are synthesized in exact accordance with the plan laid down in the structure of existing molecules.
The matrix principle lies at the core the most important synthetic reactions of the cell, such as the synthesis of nucleic acids and proteins. These reactions ensure the exact, strictly specific sequence of monomer units in the synthesized polymers.
There is directional action going on here. pulling monomers to a specific location cells - into molecules that serve as a matrix where the reaction takes place. If such reactions occurred as a result of random collisions of molecules, they would proceed infinitely slowly. The synthesis of complex molecules based on the template principle is carried out quickly and accurately. The role of the matrix macromolecules of nucleic acids play in matrix reactions DNA or RNA .
Monomeric molecules from which the polymer is synthesized - nucleotides or amino acids - in accordance with the principle of complementarity, are located and fixed on the matrix in a strictly defined, specified order.
Then it happens "cross-linking" of monomer units into a polymer chain, and the finished polymer is discharged from the matrix.
After that matrix is ready to the assembly of a new polymer molecule. It is clear that just as on a given mold only one coin or one letter can be cast, so on a given matrix molecule only one polymer can be “assembled”.
Matrix reaction type- a specific feature of the chemistry of living systems. They are the basis of the fundamental property of all living things - its ability to reproduce its own kind.
Template synthesis reactions
1. DNA replication - replication (from Latin replicatio - renewal) - the process of synthesis of a daughter molecule of deoxyribonucleic acid on the matrix of the parent DNA molecule. During the subsequent division of the mother cell, each daughter cell receives one copy of a DNA molecule that is identical to the DNA of the original mother cell. This process ensures that genetic information is accurately passed on from generation to generation. DNA replication is carried out by a complex enzyme complex consisting of 15-20 different proteins, called replisome . The material for synthesis is free nucleotides present in the cytoplasm of cells. The biological meaning of replication lies in the accurate transfer of hereditary information from the mother molecule to the daughter molecules, which normally occurs during the division of somatic cells.
A DNA molecule consists of two complementary strands. These chains are held together by weak hydrogen bonds that can be broken by enzymes. The DNA molecule is capable of self-duplication (replication), and on each old half of the molecule a new half is synthesized.
In addition, an mRNA molecule can be synthesized on a DNA molecule, which then transfers the information received from DNA to the site of protein synthesis.
Information transfer and protein synthesis proceed according to a matrix principle, comparable to the operation of a printing press in a printing house. Information from DNA is copied many times. If errors occur during copying, they will be repeated in all subsequent copies.
True, some errors when copying information with a DNA molecule can be corrected - the process of error elimination is called reparation. The first of the reactions in the process of information transfer is the replication of the DNA molecule and the synthesis of new DNA chains.
2. Transcription (from Latin transcriptio - rewriting) - the process of RNA synthesis using DNA as a template, occurring in all living cells. In other words, it is the transfer of genetic information from DNA to RNA.
Transcription is catalyzed by the enzyme DNA-dependent RNA polymerase. RNA polymerase moves along the DNA molecule in the direction 3" → 5". Transcription consists of stages initiation, elongation and termination . The unit of transcription is an operon, a fragment of a DNA molecule consisting of promoter, transcribed part and terminator . mRNA consists of a single chain and is synthesized on DNA in accordance with the rule of complementarity with the participation of an enzyme that activates the beginning and end of the synthesis of the mRNA molecule.
The finished mRNA molecule enters the cytoplasm onto ribosomes, where the synthesis of polypeptide chains occurs.
3. Broadcast (from lat. translation- transfer, movement) - the process of protein synthesis from amino acids on a matrix of information (messenger) RNA (mRNA, mRNA), carried out by the ribosome. In other words, this is the process of translating the information contained in the sequence of nucleotides of mRNA into the sequence of amino acids in the polypeptide.
4. Reverse transcription is the process of forming double-stranded DNA based on information from single-stranded RNA. This process is called reverse transcription, since the transfer of genetic information occurs in the “reverse” direction relative to transcription. The idea of reverse transcription was initially very unpopular because it contradicted the central dogma of molecular biology, which assumed that DNA is transcribed into RNA and then translated into proteins.
However, in 1970, Temin and Baltimore independently discovered an enzyme called reverse transcriptase (revertase)
, and the possibility of reverse transcription was finally confirmed. In 1975, Temin and Baltimore were awarded the Nobel Prize in Physiology or Medicine. Some viruses (such as the human immunodeficiency virus, which causes HIV infection) have the ability to transcribe RNA into DNA. HIV has an RNA genome that is integrated into DNA. As a result, the DNA of the virus can be combined with the genome of the host cell. The main enzyme responsible for the synthesis of DNA from RNA is called reversease. One of the functions of reversease is to create complementary DNA
(cDNA) from the viral genome. The associated enzyme ribonuclease cleaves RNA, and reversease synthesizes cDNA from the DNA double helix. The cDNA is integrated into the host cell genome by integrase. The result is synthesis of viral proteins by the host cell, which form new viruses. In the case of HIV, apoptosis (cell death) of T-lymphocytes is also programmed. In other cases, the cell may remain a distributor of viruses.
The sequence of matrix reactions during protein biosynthesis can be represented in the form of a diagram.
Thus, protein biosynthesis- this is one of the types of plastic exchange, during which hereditary information encoded in DNA genes is implemented into a specific sequence of amino acids in protein molecules.
Protein molecules are essentially polypeptide chains made up of individual amino acids. But amino acids are not active enough to combine with each other on their own. Therefore, before they combine with each other and form a protein molecule, amino acids must activate . This activation occurs under the action of special enzymes.
As a result of activation, the amino acid becomes more labile and, under the action of the same enzyme, binds to t- RNA. Each amino acid corresponds to a strictly specific t- RNA, which finds “its” amino acid and transfers it into the ribosome.
Consequently, various activated amino acids combined with their own T- RNA. The ribosome is like conveyor to assemble a protein chain from various amino acids supplied to it.
Simultaneously with t-RNA, on which its own amino acid “sits,” “ signal"from the DNA that is contained in the nucleus. In accordance with this signal, one or another protein is synthesized in the ribosome.
The directing influence of DNA on protein synthesis is not carried out directly, but with the help of a special intermediary - matrix or messenger RNA (m-RNA or mRNA), which synthesized into the nucleus e under the influence of DNA, so its composition reflects the composition of DNA. The RNA molecule is like a cast of the DNA form. The synthesized mRNA enters the ribosome and, as it were, transfers it to this structure plan- in what order must the activated amino acids entering the ribosome be combined with each other in order for a specific protein to be synthesized? Otherwise, genetic information encoded in DNA is transferred to mRNA and then to protein.
The mRNA molecule enters the ribosome and stitches her. That segment of it that is currently located in the ribosome is determined codon (triplet), interacts in a completely specific manner with those that are structurally similar to it triplet (anticodon) in transfer RNA, which brought the amino acid into the ribosome.
Transfer RNA with its amino acid matches a specific codon of the mRNA and connects with him; to the next, neighboring section of mRNA another tRNA with a different amino acid is added and so on until the entire chain of i-RNA is read, until all the amino acids are reduced in the appropriate order, forming a protein molecule. And tRNA, which delivered the amino acid to a specific part of the polypeptide chain, freed from its amino acid and exits the ribosome.
Then, again in the cytoplasm, the desired amino acid can join it and again transfer it to the ribosome. In the process of protein synthesis, not one, but several ribosomes - polyribosomes - are involved simultaneously.
The main stages of the transfer of genetic information:
1. Synthesis on DNA as a template for mRNA (transcription)
2. Synthesis of a polypeptide chain in ribosomes according to the program contained in mRNA (translation)
.
The stages are universal for all living beings, but the temporal and spatial relationships of these processes differ in pro- and eukaryotes.
U prokaryote transcription and translation can occur simultaneously because DNA is located in the cytoplasm. U eukaryotes transcription and translation are strictly separated in space and time: the synthesis of various RNAs occurs in the nucleus, after which the RNA molecules must leave the nucleus by passing through the nuclear membrane. The RNAs are then transported in the cytoplasm to the site of protein synthesis.
