Biosynthesis of the protein molecule occurs on. How does protein synthesis occur?

Metabolism- the most important property of living organisms. The set of metabolic reactions occurring in the body is called metabolism. Metabolism consists of reactions assimilation(plastic metabolism, anabolism) and reactions dissimilation(energy metabolism, catabolism). Assimilation is a set of biosynthesis reactions occurring in a cell, dissimilation is a set of reactions of decay and oxidation of high-molecular substances that release energy. These groups of reactions are interconnected: biosynthesis reactions are impossible without energy, which is released in energy exchange reactions, dissimilation reactions do not occur without enzymes formed in plastic exchange reactions.

Based on the type of metabolism, organisms are divided into two groups: autotrophs and heterotrophs. Autotrophs- organisms capable of synthesizing organic substances from inorganic ones and using for this synthesis either solar energy or energy released during the oxidation of inorganic substances. Heterotrophs- organisms that use organic substances synthesized by other organisms for their vital functions. Autotrophs use inorganic substances (CO 2) as a carbon source, and heterotrophs use exogenous organic substances. Sources of energy: in autotrophs - energy from sunlight ( photoautotrophs) or energy released during the oxidation of inorganic compounds ( chemoautotrophs), in heterotrophs - the energy of oxidation of organic substances ( chemoheterotrophs).

Most living organisms are either photoautotrophs (plants) or chemoheterotrophs (fungi, animals). If organisms, depending on conditions, behave as autotrophs or as heterotrophs, then they are called mixotrophs(green euglena).

Protein biosynthesis

Protein biosynthesis is the most important process of anabolism. All characteristics, properties and functions of cells and organisms are ultimately determined by proteins. Proteins are short-lived, their existence is limited. Every cell constantly synthesizes thousands of different protein molecules. In the early 50s. XX century F. Crick formulated the central dogma of molecular biology: DNA → RNA → protein. According to this dogma, the ability of a cell to synthesize certain proteins is inherited; information about the sequence of amino acids in a protein molecule is encoded in the form of a sequence of DNA nucleotides. A section of DNA that carries information about the primary structure of a particular protein is called genome. Genes not only store information about the sequence of amino acids in a polypeptide chain, but also encode certain types of RNA: rRNA, which are part of ribosomes, and tRNA, which are responsible for the transport of amino acids. There are two main stages in the process of protein biosynthesis: transcription- RNA synthesis on a DNA (gene) matrix - and broadcast- synthesis of the polypeptide chain.

Genetic code and its properties

Genetic code- a system for recording information about the sequence of amino acids in a polypeptide by the sequence of nucleotides of DNA or RNA. This recording system is now considered deciphered.

Properties of the genetic code:

1. triplet: each amino acid is encoded by a combination of three nucleotides (triplet, codon);
2. uniqueness (specificity): a triplet corresponds to only one amino acid;
3. degeneracy (redundancy): amino acids can be encoded by several (up to six) codons;
4. universality: the amino acid coding system is the same in all organisms on Earth;
5. non-overlapping: the nucleotide sequence has a reading frame of 3 nucleotides, the same nucleotide cannot be part of two triplets;
6. of the 64 code triplets, 61 are coding, encoding amino acids, and 3 are nonsense (in RNA - UAA, UGA, UAG), do not encode amino acids. They're called Terminator codons, because they block polypeptide synthesis during translation. In addition, there is initiator codon(in RNA - AUG), from which translation begins.

Genetic code table

* The first nucleotide in the triplet is one of the four left vertical rows, the second is one of the top horizontal rows, and the third is one of the right vertical rows.

Template synthesis reactions

This is a special category of chemical reactions that occur in the cells of living organisms. During these reactions, polymer molecules are synthesized according to the plan laid down in the structure of other polymer matrix molecules. An unlimited number of copy molecules can be synthesized on one matrix. This category of reactions includes replication, transcription, translation, and reverse transcription.

Gene- a section of a DNA molecule that encodes the primary sequence of amino acids in a polypeptide or the sequence of nucleotides in transport and ribosomal RNA molecules. The DNA of one chromosome can contain several thousand genes, which are arranged in a linear order. The location of a gene in a specific region of a chromosome is called locus. The structural features of the eukaryotic gene are: 1) the presence of a sufficiently large number of regulatory blocks, 2) mosaicism (alternation of coding regions with non-coding ones). Exons(E) - gene regions that carry information about the structure of the polypeptide. Introns(I) - gene regions that do not carry information about the structure of the polypeptide. The number of exons and introns of different genes varies; exons alternate with introns, the total length of the latter can exceed the length of exons by two or more times. Before the first exon and after the last exon there are nucleotide sequences called leader sequence (LS) and trailer sequence (TP), respectively. Leader and trailer sequences, exons and introns form the transcription unit. Promoter(P) - the region of the gene to which the RNA polymerase enzyme attaches is a special combination of nucleotides. Before and after the transcription unit, sometimes in introns there are regulatory elements (RE), which include enhancers And silencers. Enhancers speed up transcription, silencers slow it down.

Transcription is the synthesis of RNA on a DNA template. Carried out by the enzyme RNA polymerase.

RNA polymerase can only attach to the promoter, which is located at the 3" end of the DNA template strand, and move only from the 3" to the 5" end of this DNA template strand. RNA synthesis occurs on one of the two DNA strands in accordance with the principles complementarity and antiparallelism. The building material and energy source for transcription are ribonucleoside triphosphates (ATP, UTP, GTP, CTP).

As a result of transcription, “immature” mRNA (pro-mRNA) is formed, which goes through the stage of maturation or processing. Processing includes: 1) capping of the 5" end, 2) polyadenylation of the 3" end (attachment of several dozen adenyl nucleotides), 3) splicing (excision of introns and stitching of exons). Mature mRNA is divided into a CEP, a translated region (exons stitched together), untranslated regions (UTRs), and a polyadenylate tail.

The translated region begins with an initiator codon and ends with terminator codons. UTRs contain information that determines the behavior of RNA in a cell: life span, activity, localization.

Transcription and processing occur in the cell nucleus. Mature mRNA acquires a certain spatial conformation, is surrounded by proteins, and in this form is transported through nuclear pores to ribosomes; Eukaryotic mRNAs are usually monocistronic (encode only one polypeptide chain).

Broadcast

Translation is the synthesis of a polypeptide chain on an mRNA matrix.

The organelles that ensure translation are ribosomes. In eukaryotes, ribosomes are found in some organelles - mitochondria and plastids (70S ribosomes), free in the cytoplasm (80S ribosomes) and on the membranes of the endoplasmic reticulum (80S ribosomes). Thus, the synthesis of protein molecules can occur in the cytoplasm, on the rough endoplasmic reticulum, in mitochondria and plastids. Proteins for the cell's own needs are synthesized in the cytoplasm; proteins synthesized on the ER are transported through its channels to the Golgi complex and removed from the cell. The ribosome has small and large subunits. The small subunit of the ribosome is responsible for genetic, decoding functions; large - for biochemical, enzymatic.

Located in the small subunit of the ribosome function center(FCR) with two sections - peptidyl(P-plot) and aminoacyl(A-section). The FCR may contain six nucleotides of mRNA, three in the peptidyl and three in the aminoacyl regions.

To transport amino acids to ribosomes, transfer RNAs and tRNAs are used (lecture No. 4). The length of tRNA is from 75 to 95 nucleotide residues. They have a tertiary structure, shaped like a clover leaf. In tRNA there is an anticodon loop and an acceptor region. In the anticodon loop of RNA there is an anticodon complementary to the code triplet of a certain amino acid, and the acceptor site at the 3" end is capable of attaching exactly this amino acid (with the consumption of ATP) using the enzyme aminoacyl-tRNA synthetase. Thus, each amino acid has its own tRNA and their enzymes that attach the amino acid to the tRNA.

Twenty types of amino acids are encoded by 61 codons, and theoretically there could be 61 types of tRNA with corresponding anticodons. But there are only 20 types of encoded amino acids, which means that one amino acid can have several tRNAs. The existence of several tRNAs that can bind to the same codon has been established (the last nucleotide in the anticodon of a tRNA is not always important), so only about 40 different tRNAs have been found in the cell.

Protein synthesis begins from the moment when a small ribosomal subunit is attached to the 5" end of the mRNA, into the P-site of which methionine tRNA (transporting the amino acid methionine) enters. It should be noted that any polypeptide chain at the N-terminus first has methionine, which subsequently, it is most often cleaved off. The synthesis of the polypeptide proceeds from the N-terminus to the C-terminus, that is, a peptide bond is formed between the carboxyl group of the first and the amino group of the second amino acid.

Then the large subunit of the ribosome attaches, and a second tRNA enters the A-site, whose anticodon complementarily pairs with the mRNA codon located in the A-site.

The peptidyltransferase center of the large subunit catalyzes the formation of a peptide bond between methionine and a second amino acid. There is no separate enzyme that catalyzes the formation of peptide bonds. The energy for the formation of a peptide bond is supplied by the hydrolysis of GTP.

As soon as a peptide bond is formed, the methionine tRNA is detached from the methionine, and the ribosome moves to the next mRNA code triplet, which ends up in the A site of the ribosome, and the methionine tRNA is pushed into the cytoplasm. 2 GTP molecules are consumed per cycle. The third tRNA enters the A site, and a peptide bond is formed between the second and third amino acids.

Translation continues until a terminator codon (UAA, UAG or UGA) enters the A-site, to which a special protein release factor binds. The polypeptide chain is separated from the tRNA and leaves the ribosome. Dissociation occurs, the separation of ribosomal subunits.

The speed of ribosome movement along mRNA is 5-6 triplets per second; it takes a cell several minutes to synthesize a protein molecule consisting of hundreds of amino acid residues. The first protein synthesized artificially was insulin, consisting of 51 amino acid residues. It took 5,000 operations, and 10 people took part in the work over three years.

Three stages can be distinguished in translation: a) initiation (formation of the initiator complex), b) elongation (directly the “conveyor”, connecting amino acids with each other), c) termination (formation of the termination complex).

The “mechanisms” for assembling polynucleotide and polypeptide chains do not differ in prokaryotes and eukaryotes. But due to the fact that prokaryotic genes do not have exons and introns (with the exception of archaebacterial genes), they are located in groups, and this group of genes has one promoter, the following features of transcription and translation in prokaryotes appear.

1. As a result of transcription, a polycistronic mRNA is formed, encoding several proteins that jointly provide a certain group of reactions.
2. mRNA has several translation initiation, translation termination, and UTR centers.
3. CEP, polyadenylation and mRNA splicing do not occur.
4. Translation begins even before transcription is completed; these processes are not separated in time and space, as is the case in eukaryotes.

1 - DNA; 2 - RNA polymerase; 3 - Nucleoside triphosphates GTP, CTP, ATP, UTP.

It can be added that the “life” of prokaryotic mRNAs is several minutes (in eukaryotes it is hours and even days).

Go to lectures No. 9“Structure of a prokaryotic cell. Viruses"

Go to lectures No. 11“The concept of metabolism. Biosynthesis of proteins"

Protein biosynthesis is one of the types of plastic metabolism, during which hereditary information encoded in DNA genes is implemented into a specific sequence of amino acids in protein molecules.

Stages of biosynthesis of one type of protein in a cell

■ First, mRNA is synthesized in a certain section of one of the chains of the DNA molecule.

■ The mRNA exits through pores in the nuclear membrane into the cytoplasm and attaches to the small subunit of the ribosome.

■ The initiator tRNA is attached to the same ribosomal subunit. Its anticodon interacts with the start codon of mRNA - AUG. After this, a working ribosome is formed from small and large particles.

■ When a new amino acid is incorporated, the ribosome moves forward three nucleotides. The ribosome moves along the mRNA until it reaches one of its three stop codons - UAA, UAG or UGA.

■ Each step of biosynthesis is catalyzed by a corresponding enzyme and provided with energy by ATP.

■ Biosynthesis occurs in cells at tremendous speed. In the body of higher animals, up to 60 thousand peptide bonds are formed in one minute.

The accuracy of protein synthesis is ensured by the following mechanisms:

and A specific enzyme ensures the binding of a strictly defined amino acid to the corresponding transfer RNA molecules.

■ Transfer RNA, which has attached an amino acid, binds with its anticodon to the codon on the messenger RNA at the site of ribosome attachment. Only after the tRNA molecule recognizes its “own” codon is the amino acid included in the growing polypeptide chain.

EXAMPLES OF TASKS No. 9

List all the stages of protein biosynthesis. How is the beginning and end of mRNA synthesis determined?

2. One triplet of DNA contains information

a) about the sequence of amino acids in a protein;

b) about one characteristic of an organism;

c) about one amino acid included in the protein chain;

d) about the beginning of RNA synthesis.

3. Where does the transcription process take place?

4. What principle ensures the accuracy of protein biosynthesis?

ENERGY METABOLISM IN THE CELL (DISSIMILATION)

Energy metabolism is a set of chemical reactions of the gradual breakdown of organic compounds, accompanied by the release of energy, part of which is spent on the synthesis of ATP.

The processes of breakdown of organic compounds in aerobic organisms occur in three stages, each of which is accompanied by several enzymatic reactions. The participation of enzymes reduces the activation energy of chemical reactions, due to which energy is not released immediately (as when lighting a match), but gradually.

The first stage is preparatory. In the gastrointestinal tract of multicellular organisms, it is carried out by digestive enzymes. In unicellular organisms - by lysosome enzymes. At the first stage, proteins are broken down into amino acids, fats into glycerol and fatty acids, polysaccharides into monosaccharides, nucleic acids into nucleotides.

This process is called digestion.

The second stage is oxygen-free (glycolysis). Occurs in the cytoplasm of cells. Consists of nine sequential reactions of converting a glucose molecule into two molecules of pyruvic acid (PVA), 2ATP, H 2 0 and NADP * H:

C 6 H 12 0 6 +2ADP+2P+2NAD + -> 2C 3 H 4 0 3 +2ATP+

2H 2 0+2NADP*H (PVK)

ATP and NADP*H are compounds that store some of the energy released during glycolysis.

The rest of the energy is dissipated as heat.

In yeast and plant cells (with a lack of oxygen), pyruvic acid breaks down into ethyl alcohol and oxygen. This process is called alcoholic fermentation.

In the muscles of animals, under heavy loads and lack of oxygen, lactic acid is formed, which accumulates in the form of lactate.

The third stage is oxygen. It ends with the complete oxidation of glucose and intermediate products to carbon dioxide and water. In this case, the breakdown of one glucose molecule produces 38 ATP molecules. This process is called biological oxidation. It became possible after the accumulation of a sufficient amount of molecular oxygen in the atmosphere.

Cellular respiration occurs on the inner membranes of mitochondria, into which molecules that carry electrons are embedded. During this stage, most of the metabolic energy is released. Carrier molecules transport electrons to molecular oxygen. Some of the energy is dissipated as heat, and some is spent on the formation of ATP.

The total reaction of energy metabolism: C 6 H 12 0 6 + 60 2 -> 6C0 2 + 6H 2 0 + 38ATP.

EXAMPLES OF TASKS M10

1. The essence of heterotrophic nutrition is

a) in the synthesis of own organic compounds from inorganic ones;

b) in the consumption of inorganic compounds;

c) using organic compounds obtained from food to build one’s own body;

d) in the synthesis of ATP.

2. The end products of the oxidation of organic substances are

a) ATP and water;

b) oxygen and carbon dioxide;

c) water, carbon dioxide, ammonia;

d) ATP and oxygen.

3. Glucose molecule at the first stage of breakdown

a) oxidizes to carbon dioxide and water;

b) does not change;

c) turns into an ATP molecule;

d) splits into two three-carbon molecules (TCM).

4. What is the universal source of energy in the cell?

5. What makes up the total amount of ATP obtained during energy metabolism?

6. Tell us about the processes of glycolysis.

7. How is the energy accumulated in ATP used?

RELATIONSHIP OF ENERGY AND PLASTIC

METABOLISM IN ANIMAL AND PLANT CELLS

Metabolism (metabolism) is a set of interconnected processes of synthesis and breakdown, accompanied by the absorption and release of energy and the transformation of cell chemicals. It is sometimes divided into plastic and energy metabolism, which are interconnected. All synthetic processes require substances and energy supplied by fission processes. Decomposition processes are catalyzed by enzymes synthesized during plastic metabolism, using the products and energy of energy metabolism.

For individual processes occurring in organisms, the following terms are used:

Assimilation is the synthesis of polymers from monomers.

Dissimilation is the breakdown of polymers into monomers.

Anabolism is the synthesis of more complex monomers from simpler ones.

Catabolism is the breakdown of more complex monomers into simpler ones.

Living things use light and chemical energy. Autotrophs use carbon dioxide as a carbon source. Heterotrophs use organic carbon sources. The exception is some protists, for example green euglena, capable of autotrophic and heterotrophic types of nutrition.

Autotrophs synthesize organic compounds through photosynthesis or chemosynthesis. Heterotrophs obtain organic substances with food.

In autotrophs, the processes of plastic metabolism (assimilation) dominate - photosynthesis or chemosynthesis, in heterotrophs - the processes of energy metabolism (dissimilation) - digestion + biological decay occurring in cells.

EXAMPLES OF TASKS No. 11

1. What do photosynthesis and the process of glucose oxidation have in common?

a) both processes occur in mitochondria;

b) both processes occur in chloroplasts;

c) as a result of these processes, oxygen is formed;

d) as a result of these processes, ATP is formed.

2. What photosynthesis products are involved in the energy metabolism of mammals?

3. What is the role of carbohydrates in the formation of amino acids and fatty acids?

LIFE CYCLE OF A CELL. CHROMOSOMES

The life cycle of a cell is the period of its life from division to division.

Cells reproduce by doubling their contents and then dividing in half.

Cell division underlies the growth, development and regeneration of tissues of a multicellular organism.

The cell cycle is divided into chromosomal and cytoplasmic. Chromosomal is accompanied by the exact copying and distribution of genetic material. Cytoplasmic consists of cell growth and subsequent cytokinesis - cell division after duplication of other cellular components.

The duration of cell cycles varies widely among species, tissues, and stages, from one hour (in an embryo) to a year (in adult liver cells).

Cell cycle phases

Interphase is the period between two divisions. It is divided into presynthetic - 01, synthetic - in, post-synthetic 02.

Phase 01 is the longest period (from 10 hours to several days). It consists of preparing cells for chromosome doubling. Accompanied by the synthesis of proteins and RNA, the number of ribosomes and mitochondria increases. In this phase, cell growth occurs.

b-phase (6-10 hours). Accompanied by chromosome doubling. Some proteins are synthesized.

C2 phase (3-6 hours). Accompanied by chromosome condensation. Microtubule proteins that form the spindle are synthesized.

Mitosis is a form of division of the cell nucleus. As a result of mitosis, each of the resulting daughter nuclei receives the same set of genes that the parent cell had. Both diploid and haploid nuclei can enter into mitosis. Mitosis produces nuclei of the same ploidy as the original. The concept of "mitosis" is applicable only to eukaryotes.

Phases of mitosis

■ Prophase - accompanied by the formation of a division spindle from microtubules of the cytoplasmic skeleton of the cell and associated proteins. Chromosomes are clearly visible and consist of two chromatids.

■ Prometaphase - accompanied by the disintegration of the nuclear membrane. Some spindle microtubules are attached to kinetochores (protein-centromere complexes).

■ Metaphase - all chromosomes line up along the equator of the cell, forming a metaphase plate.

■ Anaphase - chromatids move towards the poles of the cell at the same speed. Microtubules shorten.

■ Telophase - daughter chromatids approach the cell poles. Microtubules disappear. A nuclear envelope is formed around the condensed chromatids.

■ Cytokinesis is the process of separation of the cytoplasm. The cell membrane in the central part of the cell is pulled inward. A cleavage furrow is formed, and as it deepens, the cell bifurcates.

■ As a result of mitosis, two new nuclei are formed with identical sets of chromosomes, exactly copying the genetic information of the maternal nucleus.

■ In tumor cells, the course of mitosis is disrupted.

EXAMPLES OF TASKS No. 12

1. Describe the features of each phase of mitosis.

2. What are chromatids, centromeres, and spindles?

3. How do somatic cells differ from germ cells?

4. What is the biological meaning of mitosis?

5. The longest in the cell cycle is:

a) interphase; b) prophase; c) metaphase; d) telophase.

6. How many chromatids does a pair of homologous chromosomes contain in metaphase of mitosis?

a) four; b) two; c) eight d) one.

7. Mitosis does not provide

a) formation of human skin cells; b) maintaining a constant number of chromosomes for the species; c) genetic diversity of species; d) asexual reproduction.

Meiosis is the process of division of cell nuclei, leading to a reduction in the number of chromosomes by half. Meiosis consists of two successive divisions (reduction and equationation), which are preceded by a single DNA replication. The interphase of meiosis is similar to the interphase of mitosis.

Reduction division

First, the replicated chromosomes condense.

Then the conjugation of homologous chromosomes begins. Bivalents or tetrads are formed, consisting of 4 sister chromatids.

At the next stage, crossing over occurs between homologous chromosomes. The conjugated chromosomes are separated, the bivalent chromosomes move away from each other, but continue to be connected by the places where crossing over occurred.

The nuclear envelope and nucleoli disappear.

At the end of the first division, cells with a haploid set of chromosomes and double the amount of DNA are formed. The nuclear envelope is formed. The spindle is destroyed. Each cell contains 2 sister chromatids connected by a centromere.

Equational division

The biological significance of meiosis lies in the formation of cells involved in sexual reproduction and in maintaining the genetic constancy of species. Meiosis serves as the basis for the combinative variability of organisms. Disorders of meiosis in humans can lead to pathologies such as Down's disease, idiocy, etc.

EXAMPLES OF TASKS No. 13

1. Describe the features of each phase of meiosis.

2. What are conjugation, crossover, bivalents?

3. What is the biological meaning of meiosis?

4. Can reproduce asexually

a) amphibians; b) coelenterates; c) insects; d) crustaceans.

5. The first division of meiosis ends with the formation

a) gametes; b) cells with a haploid set of chromosomes; c) diploid cells; d) cells of different ploidy.

6. As a result of meiosis, the following are formed: a) fern spores; b) cells of the fern antheridium walls; c) cells of the fern archegonium walls; d) somatic cells of bee drones.

Structure and functions of chromosomes

Chromosomes are cell structures that store and transmit hereditary information. A chromosome consists of DNA and protein. A complex of proteins bound to DNA forms chromatin. Proteins play an important role in packaging DNA molecules in the nucleus.

The DNA in chromosomes is packaged in such a way that it fits in the nucleus, the diameter of which usually does not exceed 5 microns (5 x 10 ~ 4 cm).

The chromosome is a rod-shaped structure and consists of two sister chromatids, which are held by the centromere in the region of the primary constriction. Chromatin does not replicate. Only DNA is replicated. When DNA replication begins, RNA synthesis stops.

The diploid set of chromosomes of an organism is called a karyotype. Modern research methods make it possible to identify each chromosome in a karyotype. To do this, take into account the distribution of light and dark bands visible under a microscope (alternating pairs of AT and GC) in chromosomes treated with special dyes. Chromosomes of representatives of different species have transverse striations. Related species, such as humans and chimpanzees, have very similar patterns of alternating bands in their chromosomes.

Each type of organism has a constant number, shape and composition of chromosomes. There are 46 chromosomes in the human karyotype - 44 autosomes and 2 sex chromosomes. Males are heterogametic (XY) and females are homogametic (XX). The Y chromosome differs from the X chromosome in the absence of some alleles (for example, the blood clotting allele). Chromosomes of the same pair are called homologous. Homologous chromosomes at identical loci carry allelic genes.

EXAMPLES OF TASKS No. 14

1. What happens to chromosomes in interphase of mitosis?

2. Which chromosomes are called homologous?

3. What is chromatin?

4. Are all chromosomes always present in a cell?

5. What can you learn about an organism by knowing its number and shape of chromosomes in its cells?

2.2. Signs of organisms. Heredity and variability are properties of organisms. Unicellular and multicellular organisms. Tissues, organs, organ systems of plants and animals, identifying the variability of organisms. Techniques for growing, propagating and caring for plants and domestic animals

Information about the primary structure of a protein molecule is contained in DNA, which is located in the nucleus of a eukaryotic cell. One chain or strand of DNA can contain information about many proteins. A gene is a section (fragment) of DNA that carries information about the structure of one protein. The DNA molecule contains a code for the sequence of amino acids in a protein in the form of a specific sequence of nucleotides. In this case, each amino acid in the future protein molecule corresponds to a section of three nucleotides (triplet) in the DNA molecule.

Process protein biosynthesis includes a series of sequential events:

DNA replication (in the cell nucleus) transcription messenger RNA (in the cytoplasm with the help of ribosomes) protein translation

Messenger RNA (mRNA) synthesis occurs in the nucleus. It is carried out along one of the DNA strands with the help of enzymes and taking into account the principle of complementarity of nitrogenous bases. The process of rewriting the information contained in DNA genes into a synthesized mRNA molecule is called transcription. Obviously, the information is transcribed as a sequence of RNA nucleotides. The DNA strand in this case acts as a matrix. In the process of its formation, the RNA molecule includes uracia instead of the nitrogenous base thymine.

G - C - A - A - C - T – a fragment of one of the chains of the DNA molecule
- C - G - U - U - G - A – a fragment of a messenger RNA molecule.

RNA molecules are individual, each of them carries information about one gene. Next, mRNA molecules leave the cell nucleus through the pores of the nuclear membrane and are directed into the cytoplasm to ribosomes. Amino acids are also delivered here using transfer RNA (tRNA). A tRNA molecule consists of 70–80 nucleotides. The general appearance of the molecule resembles a clover leaf.

At the “top” there is an aticodon (a code triplet of nucleotides), which corresponds to a specific amino acid. Therefore, each amino acid has its own specific tRNA. The process of assembling a protein molecule occurs in ribosomes and is called broadcast. Several ribosomes are located sequentially on one mRNA molecule. The functional center of each ribosome can accommodate two triplets of mRNA. The code triplet of nucleotides - a t-RNA molecule that has approached the site of protein synthesis, corresponds to a triplet of i-RNA nucleotides currently located in the functional center of the ribosome. Then the ribosome takes a step along the mRNA chain equal to three nucleotides. is separated from t-RNA and becomes a chain of protein monomers. The released t-RNA moves to the side and after some time can again connect with a certain acid, which will be transported to the site protein synthesis. Thus, the sequence of nucleotides in the DNA triplet corresponds to the sequence of nucleotides in the mRNA triplet.

In the complex process of protein biosynthesis, the functions of many substances and cell organelles are realized.

To study the processes occurring in the body, you need to know what is happening at the cellular level. And there the most important role is played by protein compounds. It is necessary to study not only their functions, but also the creation process. Therefore, it is important to explain briefly and clearly. 9th grade is best suited for this. It is at this stage that students have enough knowledge to understand the topic.

Proteins - what are they and what are they for?

These high-molecular compounds play a huge role in the life of any organism. Proteins are polymers, meaning they are made up of many similar “pieces.” Their number can vary from several hundred to thousands.

Proteins perform many functions in a cell. Their role is also great at higher levels of organization: tissues and organs largely depend on the proper functioning of various proteins.

For example, all hormones are of protein origin. But it is these substances that control all processes in the body.

Hemoglobin is also a protein; it consists of four chains, which are connected in the center by an iron atom. This structure allows red blood cells to carry oxygen.

Let us remember that all membranes contain proteins. They are necessary for the transport of substances through the cell membrane.

There are many more functions of protein molecules that they perform clearly and unquestioningly. These amazing compounds are very diverse not only in their roles in the cell, but also in structure.

Where does synthesis take place?

The ribosome is the organelle where most of the process called protein biosynthesis takes place. The 9th grade in different schools differs in the curriculum for studying biology, but many teachers give material on organelles in advance, before studying the translation.

Therefore, it will not be difficult for students to remember the material covered and consolidate it. You should know that only one polypeptide chain can be created on one organelle at a time. This is not enough to satisfy all the needs of the cell. Therefore, there are a lot of ribosomes, and most often they combine with the endoplasmic reticulum.

This EPS is called rough. The benefit of such “cooperation” is obvious: the protein immediately after synthesis enters the transport channel and can be sent to its destination without delay.

But if we take into account the very beginning, namely the reading of information from DNA, then we can say that protein biosynthesis in a living cell begins in the nucleus. It is there that the genetic code is synthesized.

Necessary materials - amino acids, place of synthesis - ribosome

It seems that it is difficult to explain how protein biosynthesis occurs briefly and clearly; a process diagram and numerous drawings are simply necessary. They will help convey all the information, and it will also be easier for students to remember it.

First of all, synthesis requires “building materials” - amino acids. Some of them are produced by the body. Others can only be obtained from food; they are called essential.

The total number of amino acids is twenty, but due to the huge number of options in which they can be arranged in a long chain, protein molecules are very diverse. These acids are similar in structure, but differ in radicals.

It is the properties of these parts of each amino acid that determine what structure the resulting chain will “fold” into, whether it will form a quaternary structure with other chains, and what properties the resulting macromolecule will have.

The process of protein biosynthesis cannot occur simply in the cytoplasm; it requires a ribosome. consists of two subunits - large and small. At rest they are separated, but as soon as synthesis begins, they immediately connect and begin to work.

Such different and important ribonucleic acids

In order to bring an amino acid to the ribosome, a special RNA called transport RNA is needed. For abbreviation it is called t-RNA. This single-chain, cloverleaf-shaped molecule is capable of attaching one amino acid to its free end and transporting it to the site of protein synthesis.

Another RNA involved in protein synthesis is called messenger RNA. It contains an equally important component of synthesis - a code that clearly states when to attach which amino acid to the resulting protein chain.

This molecule has a single-stranded structure and consists of nucleotides, just like DNA. There are some differences in the primary structure of these nucleic acids, which you can read about in the comparison article on RNA and DNA.

Information about the composition of the protein m-RNA receives from the main keeper of the genetic code - DNA. The process of reading and synthesizing m-RNA is called transcription.

It occurs in the nucleus, from where the resulting m-RNA is sent to the ribosome. The DNA itself does not leave the nucleus; its task is only to preserve the genetic code and transfer it to the daughter cell during division.

Summary table of the main participants of the broadcast

In order to describe protein biosynthesis briefly and clearly, a table is simply necessary. In it we will write down all the components and their role in this process, which is called translation.

The process of creating a protein chain itself is divided into three stages. Let's look at each of them in more detail. After this, you will be able to easily explain protein biosynthesis to everyone, briefly and clearly.

Initiation - the beginning of the process

This is the initial stage of translation in which the small subunit of the ribosome binds to the very first tRNA. This ribonucleic acid carries the amino acid methionine. Translation always begins with this amino acid, since the start codon is AUG, which encodes this first monomer in the protein chain.

In order for the ribosome to recognize the start codon and not start synthesis from the middle of the gene, where the AUG sequence may also appear, a special sequence of nucleotides is located around the start codon. It is through them that the ribosome recognizes the place where its small subunit should sit.

After the formation of a complex with m-RNA, the initiation stage ends. And the main stage of the broadcast begins.

Elongation - middle of synthesis

At this stage, a gradual increase in the protein chain occurs. The duration of elongation depends on the number of amino acids in the protein.

First of all, the large subunit of the ribosome is attached to the small one. And the initial t-RNA ends up in it entirely. Only methionine remains outside. Next, a second t-RNA carrying another amino acid enters the large subunit.

If the second codon on the mRNA matches the anticodon at the top of the cloverleaf, the second amino acid is attached to the first via a peptide bond.

After this, the ribosome moves along the m-RNA exactly three nucleotides (one codon), the first t-RNA detaches methionine from itself and separates from the complex. In its place is a second t-RNA, at the end of which there are already two amino acids hanging.

Then a third tRNA enters the large subunit and the process repeats. It will continue until the ribosome encounters a codon in the mRNA that signals the end of translation.

Termination

This stage is the last, and some may find it quite cruel. All the molecules and organelles that worked so harmoniously to create the polypeptide chain stop as soon as the ribosome hits the terminal codon.

It does not code for any amino acid, so no matter what tRNA is included in the large subunit, they will all be rejected due to a mismatch. This is where termination factors come into play, separating the finished protein from the ribosome.

The organelle itself can either disintegrate into two subunits or continue its journey along m-RNA in search of a new start codon. One m-RNA can contain several ribosomes at once. Each of them is at its own stage of translation. The newly created protein is supplied with markers, with the help of which everyone will understand its destination. And according to EPS, it will be sent to where it is needed.

To understand the role of protein biosynthesis, it is necessary to study what functions it can perform. It depends on the sequence of amino acids in the chain. It is their properties that determine the secondary, tertiary, and sometimes quaternary (if it exists) and its role in the cell. You can read more about the functions of protein molecules in an article on this topic.

How to find out more about the broadcast

This article describes protein biosynthesis in a living cell. Of course, if you study the subject further, it will take many pages to explain the process in detail. But the above material should be enough for a general idea. Video materials in which scientists have simulated all stages of the broadcast can be very useful for understanding. Some of them have been translated into Russian and can serve as an excellent textbook for students or simply an educational video.

In order to understand the topic better, you should read other articles on similar topics. For example, about or about the functions of proteins.

And RNA processing, the second step involves translation. During transcription, the enzyme RNA polymerase synthesizes an RNA molecule that is complementary to the sequence of the corresponding gene (part of DNA). A terminator in a DNA nucleotide sequence determines at what point transcription will stop. During a series of successive processing steps, some fragments are removed from the mRNA, and nucleotide sequences are rarely edited. After RNA synthesis on the DNA template, RNA molecules are transported into the cytoplasm. During the translation process, the information recorded in the nucleotide sequence is translated into a sequence of amino acid residues.

RNA processing

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

Broadcast

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

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See what “Protein biosynthesis” is in other dictionaries: In the metabolism of the body, the leading role belongs to proteins and nucleic acids. Protein substances form the basis of all vital structures of the cell; they are part of the cytoplasm. Proteins have an unusually high reactivity... ...

A set of reactions of polymerization of amino acids into the polypeptide chain of a protein molecule, occurring in cells on specialized organelles, ribosomes; violation of B. b. underlies many diseases of humans, animals and plants... Large medical dictionary

The process of synthesis of natural organic compounds by living organisms. The biosynthetic pathway of a compound is a sequence of reactions leading to the formation of this compound, usually enzymatic (genetically determined), but occasionally... ... Wikipedia

- [te], a; m. Formation of various organic substances in living organisms. B. squirrel. Mechanism of biosynthesis. * * * biosynthesis - the formation of substances necessary for the body in living cells with the participation of enzyme biocatalysts. Usually as a result... encyclopedic Dictionary

biosynthesis- (te) a; m. Formation of various organic substances in living organisms. Protein biosi/ntesis. Biosynthesis mechanism... Dictionary of many expressions

Ribosomal biosynthesis- * fishosomal biosynthesis * ribosomal biosynthesis assembly of ribosomal particles from RNA and protein components. In eukaryotes and prokaryotes, it is coordinated in such a way that neither excess protein nor excess nucleic acids accumulate. E. coli has protein synthesis... ... Genetics. encyclopedic Dictionary

This term has other meanings, see Proteins (meanings). Proteins (proteins, polypeptides) are high-molecular organic substances consisting of alpha amino acids connected in a chain by a peptide bond. In living organisms... ... Wikipedia

Crystals of various proteins grown on the Mir space station and during NASA shuttle flights. Highly purified proteins form crystals at low temperatures, which are used to obtain a model of the protein. Proteins (proteins, ... ... Wikipedia

I Squirrels (Sciurus) is a genus of mammals of the squirrel family of the order of rodents. Distributed in the forests of Europe, Asia and America. About 50 species. Adapted to an arboreal lifestyle. Body length up to 28 cm. The fur is usually thick, some are fluffy.… … Great Soviet Encyclopedia

Books

• Lehninger's Fundamentals of Biochemistry. In 3 volumes. Volume 3. Pathways of Information Transmission, D. Nelson, M. Cox. This educational publication, written by American scientists who have received recognition as talented teachers at the university level, examines modern concepts of biochemistry in...