The process of protein biosynthesis in a cell. Protein biosynthesis - how does it happen? During translation, three phases can be distinguished: initiation, elongation and termination.

One of the most important and characteristic properties living cell. The primary structure of a protein, as already noted, is predetermined by the genetic code embedded in the DNA molecule, with its different sections encoding the synthesis of different proteins. Consequently, one DNA molecule stores information about the structure of many proteins.

The properties of a protein depend on the sequence of amino acids in the polypeptide chain. In turn, the alternation of amino acids is determined by the sequence of nucleotides in DNA. In mRNA, each amino acid corresponds to a specific triplet - a group of three nucleotides called a codon.

Protein biosynthesis begins in the nucleus with the transfer of information about the structure of the protein molecule from DNA to mRNA according to the principle of complementarity. This process occurs as a matrix synthesis reaction and is called transcription (Fig. 7.1).

Rice. 7.1. Transcription process

As a result of transcription, “immature” mRNA (pre-mRNA) is formed, which goes through the stage of maturation or processing.

Processing includes:

1) Capping 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 polyA tail. Available alternative splicing, in which exons are cut out along with introns. In this case, different proteins can be formed from one gene. Thus, the statement – ​​“One gene – one polypeptide” is incorrect (Fig. 7.2, 7.3, 7.4)

Rice. 7.2. Splicing

Rice. 7.3. Alternative splicing (variants)

Rice. 7.4. Formation of different protein molecules due to alternative splicing variants

The resulting mRNA enters the cytoplasm, where ribosomes are strung on it. At the same time, transport RNA tRNA is activated in the cytoplasm with the help of enzymes.

The structure of a tRNA molecule resembles a clover leaf, at the top of which there is a triplet of nucleotides corresponding in code to a specific amino acid (anticodon), and the base (“petiole”) serves as the site of attachment of this amino acid. 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 aminoacyl-tRNA synthetases attach exactly this amino acid (with the expenditure of ATP) to the site SSA (Fig. 5)

Transfer RNA delivers amino acids to ribosomes. According to the principle of complementarity, an anticodon binds to its codon, and the amino acid is located at the active center of the ribosome and, with the help of enzymes, combines with previously received amino acids. The tRNA is then released from the amino acid, the mRNA molecule moves forward one triplet, and the process repeats.

Rice. 7.5. Structure of the T-RNA molecule

There are three stages in protein biosynthesis: initiation, elongation And termination .

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

Initiation. Protein synthesis begins from the moment when a small ribosomal subunit is attached to the 5" end of the mRNA, the P site of which enters methionine tRNA.

Due to ATP, the initiation complex (small ribosomal subunit, tRNA with methionine) moves along the UTR to the methionine codon AUG. This process is called scanning.

Elongation. As soon as the AUG codon enters the P-site of the scanning complex, the attachment of the large ribosomal subunit occurs. The A-site of the FCR receives a second tRNA, whose anticodon complementarily pairs with the codon of the mRNA located in the A-site.

Peptidyltransferase center 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.

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. Polypeptide synthesis 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.

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.

Termination . When a terminator codon (UAA, UAG or UGA) enters the A-site, with 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.

Rice. 7.6. Broadcast Process (Step 1)

Rice. 7.7. Broadcast Process (Step 2)

Rice. 7.8. Broadcast Process (Step 3)

Rice. 7.9. Broadcast Process (Step 4)

Rice. 7.10. Protein biosynthesis (general scheme)

In this way, a protein chain is gradually built up, in which amino acids are arranged in strict accordance with the localization of the triplets encoding them in the mRNA molecule. The synthesis of polypeptide chains of proteins using an mRNA matrix is ​​called translation (Fig. 10).

In the cells of plant and animal organisms, proteins are continuously renewed. The intensity of the synthesis of certain specific proteins is determined by the activity of the corresponding genes from which the mRNA is “read”. It should be noted that not all genes function simultaneously: only those that encode information about the structure of proteins necessary for the life of the organism at a given moment are active.

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 EXCHANGE 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 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 to 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 it is released most of metabolic energy. 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 chemical substances cells. 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 during photosynthesis or chemosynthesis. Heterotrophs receive organic matter along 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.

Duration of cell cycles different types, in different tissues and at different stages varies widely 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 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. Cell membrane in the central part of the cell it is drawn 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 methods studies 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

Protein biosynthesis- a complex multi-stage process of synthesis of a polypeptide chain from amino acid residues, occurring on the ribosomes of the cells of living organisms with the participation of mRNA and tRNA molecules.

BB proceeds in two stages– transcription (from DNA to the synthesis of mature mRNA), translation (from the release of mature mRNA into the cytoplasm and synthesis of the polypeptide.)

Broadcast. In prokaryotic cells, the process of translation is associated with the synthesis of mRNA: they occur almost simultaneously.

The proteins in the ribosome are held together by a scaffold made of ribosomal RNA. The formation of a ribosome begins when the ribosomal RNA folds and proteins begin to adhere to it in a certain order. The figure shows ribosomal RNA. In it, self-complementary sections of the RNA strand pair to form hairpins (secondary structure), and then the RNA folds (tertiary RNA structure), forming a framework of subparticles.

Another type of RNA involved in protein synthesis is transfer RNA (tRNA). tRNA molecules are relatively small (compared to ribosomal or messenger RNA). All tRNAs have a common secondary structure. Due to the pairing of complementary sections of the tRNA molecule, three “stems” are formed with loops at the ends and one “stem” formed by the 5" and 3" ends of the tRNA molecule (sometimes an additional fifth loop is formed). The image of this structure is similar to a cross or clover leaf. The “head” on this sheet is represented by an anticodon loop; here is the anticodon - those three nucleotides that complementarily interact with the codon in the mRNA. The stem opposite the anticodon loop, formed by the ends of the molecule, is called the acceptor stem - the corresponding amino acid is added here. Special enzymes called aminoacyl-tRNA synthetases recognize matching tRNAs and amino acids. Each amino acid has its own aminoacyl-tRNA synthetase.

The ribosome contains messenger RNA (mRNA). The anticodon of the transfer RNA, on which the amino acid residue hangs, is complementarily associated with the codon (three nucleotides) of the mRNA. The figure shows this structure (tRNA together with an amino acid called aminocil-tRNA).

The process of translation, as well as the process of transcription, is associated with movement along the nucleic acid molecule; the difference is that the ribosome steps three nucleotides, while RNA polymerase moves one.

Ribosomes Pro- and eukaryotes are very similar in structure and function. They consist of two subparticles: large and small. In eukaryotes, the small subparticle is formed by one rRNA molecule and 33 molecules of different proteins. The large subunit combines three rRNA molecules and about 40 proteins. Prokaryotic ribosomes and ribosomes of mitochondria and plastids contain fewer components.

15. Stages of translation (initiation, elongation, termination)

Initiating broadcast. Protein synthesis in most cases begins with the AUG codon encoding methionine. This codon is usually called the start or initiation codon. Initiation of translation involves recognition of this codon by the ribosome and recruitment of the initiator aminoacyl-tRNA. Initiation also requires the presence of certain nucleotide sequences in the region of the start codon. Equally important. role in protecting the 5" end of mRNA belonging to the 5" cap. Noun a sequence that distinguishes the starting AUG from internal ones is absolutely necessary, since otherwise the initiation of protein synthesis would occur chaotically at all AUG codons. Process initiation of provision special proteins - initiation factors. (cats are movably associated with the small subunit of the ribosome. Upon completion of the initiation and formation phase of the ribosome - mRNA - initiating aminoacyl-tRNA complex, these factors are separated from the ribosome.) The mechanisms of translation initiation in pro- and eukaryotes are significantly different: prokaryotic ribosomes are potentially capable of starting AUG and initiate synthesis at any sites in the mRNA.

Elongation phase, or peptide elongation, includes all reactions from the formation of the first peptide bond to the addition of the last amino acid. It represents cyclically repeating events in which specific recognition of the aminoacyl-tRNA of the next codon located in the A-site occurs, and a complementary interaction between the anticodon and the codon occurs. Two protein elongation factors take part in the process of growing a polypeptide chain. The first (EF1a in eukaryotes, EF-Tu in prokaryotes) transfers charged tRNA to the A (aminoacyl) site of the ribosome. After the formation of a peptide bond, which is catalyzed by rRNA, and the transfer of the peptide associated with the tRNA from the P site to the A site, a second protein (EF2 in eukaryotes, EF-G in prokaryotes) catalyzes the movement of the ribosome one triplet. Thus, the petidyl-tRNA ends up back in the P-site, and the “empty” tRNA in the P-site ends up in the E-site. The elongation cycle is completed when a new tRNA with an anticodon matching the A-site codon is delivered by EF1a (or EF-Tu). The assembly of the peptide chain is carried out with sufficient high speed, depending on temperature. In bacteria at 37 °C it is expressed in the addition of 12 to 17 amino acids per 1 s to the subpeptide. In eukaryotic cells this rate is lower and is expressed in the addition of two AAs per 1 s.

Termination phase or completion of polypeptide synthesis, is associated with the recognition by a specific ribosomal protein of one of the stop codons (UAA, UAG or UGA) when it enters the zone of the A-site of the ribosome. In this case, water is added to the last amino acid in the peptide chain, and its carboxyl end is separated from the tRNA. As a result, the completed peptide chain loses its connection with the ribosome. breaks down into two subparticles.

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 encoding, encoding amino acids, and 3 are meaningless (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.

* The first nucleotide in the triplet is one of the four left vertical rows, the second is one of the upper horizontal rows, 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 sufficient large quantity regulatory blocks, 2) mosaic (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 (TS), 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 template DNA strand, and move only from the 3′ to the 5′ end of this template DNA strand. RNA synthesis occurs on one of the two DNA strands in accordance with the principles of complementarity and antiparallelism. Construction material and the 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), in free form 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 ribosomal subunit 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.

Transfer RNAs and tRNAs are used to transport amino acids to ribosomes. 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. The anticodon loop of RNA contains an anticodon that is complementary to the code triplet of a certain amino acid, and the acceptor site at the 3′ end is capable of attaching this particular amino acid (with the expense of ATP) using the enzyme aminoacyl-tRNA synthetase. Thus, each amino acid has its own tRNA and its own 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 first has methionine at the N-terminus, which is then most often cleaved off. Polypeptide synthesis 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).

Transcription and translation in prokaryotes

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 specific 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.

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

If the video doesn't work. Additional

Hereditary information is information about the structure of a protein (information about what amino acids in what order combine during the synthesis of the primary protein structure).

Information about the structure of proteins is encoded in DNA, which in eukaryotes is part of the chromosomes and is located in the nucleus. The section of DNA (chromosome) in which information about one protein is encoded is called gene.

Transcription- This is the rewriting of information from DNA to mRNA (information RNA). mRNA carries information from the nucleus to the cytoplasm, to the site of protein synthesis (to the ribosome).

Broadcast is the process of protein biosynthesis. Inside the ribosome, tRNA anticodons are attached to the mRNA codons according to the principle of complementarity. The ribosome connects the amino acids brought by tRNA with a peptide bond to form a protein.

The reactions of transcription, translation, as well as replication (doubling of DNA) are reactions matrix synthesis. DNA serves as a template for the synthesis of mRNA, and mRNA serves as a template for protein synthesis.

Genetic code is the way in which information about the structure of a protein is written into DNA.

Genecode properties

1) Triplety: One amino acid is encoded by three nucleotides. These 3 nucleotides in DNA are called a triplet, in mRNA - a codon, in tRNA - an anticodon (but in the Unified State Exam there may also be a “code triplet”, etc.)

2) Redundancy(degeneracy): there are only 20 amino acids, and there are 61 triplets encoding amino acids, so each amino acid is encoded by several triplets.

3) Unambiguity: Each triplet (codon) codes for only one amino acid.

4) Versatility: The genetic code is the same for all living organisms on Earth.

Tasks

Problems on the number of nucleotides/amino acids
3 nucleotides = 1 triplet = 1 amino acid = 1 tRNA

Tasks at ATGC
DNA mRNA tRNA
A U A
T A U
G C G
Ts G Ts

Choose one, the most correct option. mRNA is a copy
1) one gene or group of genes
2) protein molecule chains
3) one protein molecule
4) parts of the plasma membrane

Answer

Choose one, the most correct option. The primary structure of a protein molecule, specified by the nucleotide sequence of mRNA, is formed in the process
1) broadcasts
2) transcriptions
3) reduplication
4) denaturation

Answer

Choose one, the most correct option. Which sequence correctly reflects the path of implementation of genetic information
1) gene --> mRNA --> protein --> trait
2) trait --> protein --> mRNA --> gene --> DNA
3) mRNA --> gene --> protein --> trait
4) gene --> DNA --> trait --> protein

Answer

Choose one, the most correct option. Select the correct sequence of information transfer in the process of protein synthesis in the cell
1) DNA -> messenger RNA -> protein
2) DNA -> transfer RNA -> protein
3) ribosomal RNA -> transfer RNA -> protein
4) ribosomal RNA -> DNA -> transfer RNA -> protein

Answer

Choose one, the most correct option. The same amino acid corresponds to the CAA anticodon on transfer RNA and the triplet on DNA
1) CAA
2) TsUU
3) GTT
4) GAA

Answer

Choose one, the most correct option. The anticodon AAU on transfer RNA corresponds to a triplet on DNA
1) TTA
2) AAT
3) AAA
4) TTT

Answer

Choose one, the most correct option. Every amino acid in a cell is coded for
1) one DNA molecule
2) several triplets
3) several genes
4) one nucleotide

Answer

Choose one, the most correct option. Functional unit of genetic code
1) nucleotide
2) triplet
3) amino acid
4) tRNA

Answer

Choose three options. As a result of matrix-type reactions, molecules are synthesized
1) polysaccharides
2) DNA
3) monosaccharides
4) mRNA
5) lipids
6) squirrel

Answer

1. Determine the sequence of processes that ensure protein biosynthesis. Write down the corresponding sequence of numbers.
1) formation of peptide bonds between amino acids
2) attachment of the tRNA anticodon to the complementary codon of the mRNA
3) synthesis of mRNA molecules on DNA
4) movement of mRNA in the cytoplasm and its location on the ribosome
5) delivery of amino acids to the ribosome using tRNA

Answer

2. Establish the sequence of protein biosynthesis processes in the cell. Write down the corresponding sequence of numbers.
1) formation of a peptide bond between amino acids
2) interaction between the mRNA codon and the tRNA anticodon
3) release of tRNA from the ribosome
4) connection of mRNA with ribosome
5) release of mRNA from the nucleus into the cytoplasm
6) mRNA synthesis

Answer

3. Establish the sequence of processes in protein biosynthesis. Write down the corresponding sequence of numbers.
1) synthesis of mRNA on DNA
2) delivery of amino acids to the ribosome
3) formation of a peptide bond between amino acids
4) addition of an amino acid to tRNA
5) connection of mRNA with two ribosomal subunits

Answer

4. Establish the sequence of stages of protein biosynthesis. Write down the corresponding sequence of numbers.
1) separation of a protein molecule from a ribosome
2) attachment of tRNA to the start codon
3) transcription
4) lengthening of the polypeptide chain
5) release of mRNA from the nucleus into the cytoplasm

Answer

5. Establish the correct sequence of protein biosynthesis processes. Write down the corresponding sequence of numbers.
1) addition of an amino acid to a peptide
2) synthesis of mRNA on DNA
3) recognition by codon of anticodon
4) combining mRNA with a ribosome
5) release of mRNA into the cytoplasm

Answer

Choose one, the most correct option. Which transfer RNA anticodon corresponds to the TGA triplet in the DNA molecule
1) ACU
2) TsUG
3) UGA
4) AHA

Answer

Choose one, the most correct option. The genetic code is universal because
1) each amino acid is encoded by a triple of nucleotides
2) the place of an amino acid in a protein molecule is determined by different triplets
3) it is the same for all creatures living on Earth
4) several triplets encode one amino acid

Answer

Choose one, the most correct option. A section of DNA containing information about one polypeptide chain is called
1) chromosome
2) triplet
3) genome
4) code

Answer

Choose one, the most correct option. Translation is the process by which
1) the number of DNA strands doubles
2) mRNA is synthesized on the DNA matrix
3) proteins are synthesized on the mRNA matrix in the ribosome
4) hydrogen bonds between DNA molecules are broken

Answer

Choose three options. Protein biosynthesis, unlike photosynthesis, occurs
1) in chloroplasts
2) in mitochondria
3) in plastic exchange reactions
4) in matrix-type reactions
5) in lysosomes
6) in leukoplasts

Answer

Choose one, the most correct option. The matrix for translation is a molecule
1) tRNA
2) DNA
3) rRNA
4) mRNA

Answer

All but two of the following features can be used to describe the functions of nucleic acids in a cell. Identify two characteristics that “drop out” from the general list and write down the numbers under which they are indicated in the table.
1) carry out homeostasis
2) transfer hereditary information from the nucleus to the ribosome
3) participate in protein biosynthesis
4) are part of the cell membrane
5) transport amino acids

Answer

AMINO ACIDS - mRNA CODONS
How many mRNA codons encode information about 20 amino acids? Write down only the corresponding number in your answer.

Answer

AMINO ACIDS - NUCLEOTIDES mRNA
1. A section of a polypeptide consists of 28 amino acid residues. Determine the number of nucleotides in the mRNA section containing information about the primary structure of the protein.

Answer

2. How many nucleotides does m-RNA contain if the protein synthesized from it consists of 180 amino acid residues? Write down only the corresponding number in your answer.

Answer

3. How many nucleotides does m-RNA contain if the protein synthesized from it consists of 250 amino acid residues? Write down only the corresponding number in your answer.

Answer

AMINO ACIDS - DNA NUCLEOTIDES
1. Protein consists of 140 amino acid residues. How many nucleotides are there in the gene region that encodes the primary structure of this protein?

Answer

2. Protein consists of 180 amino acid residues. How many nucleotides are in the gene that encodes the sequence of amino acids in this protein. Write down only the corresponding number in your answer.

Answer

3. A fragment of a DNA molecule encodes 36 amino acids. How many nucleotides does this fragment of a DNA molecule contain? Write down the corresponding number in your answer.

Answer

4. The polypeptide consists of 20 amino acid units. Determine the number of nucleotides in the gene region that encode these amino acids in the polypeptide. Write your answer as a number.

Answer

5. How many nucleotides in a gene section encode a protein fragment of 25 amino acid residues? In your answer, write down only the corresponding number.

Answer

6. How many nucleotides in a fragment of the DNA template strand encode 55 amino acids in a polypeptide fragment? Write down only the corresponding number in your answer.

Answer

AMINO ACIDS - tRNA
1. What number of tRNAs took part in the synthesis of a protein that includes 130 amino acids? Write the corresponding number in your answer.

Answer

2. A fragment of a protein molecule consists of 25 amino acids. How many tRNA molecules were involved in its creation? Write down only the corresponding number in your answer.

Answer

3. How many transfer RNA molecules were involved in translation if the gene region contains 300 nucleotide residues? Write down only the corresponding number in your answer.

Answer

AMINO ACIDS - TRIPLETS
1. How many triplets does a DNA fragment encoding 36 amino acids contain? Write down the corresponding number in your answer.

Answer

2. How many triplets code for 32 amino acids? In your answer, write down only the corresponding number.

Answer

NUCLEOTIDES - AMINO ACIDS
1. What number of amino acids is encrypted in a gene section containing 129 nucleotide residues?

Answer

2. How many amino acids does 900 nucleotides code for? In your answer, write down only the corresponding number.

Answer

3. What is the number of amino acids in a protein if its coding gene consists of 600 nucleotides? In your answer, write down only the corresponding number.

Answer

4. How many amino acids does 1203 nucleotides code for? In your answer, write down only the number of amino acids.

Answer

5. How many amino acids are needed for the synthesis of a polypeptide if the coding part of the mRNA contains 108 nucleotides? Write down only the corresponding number in your answer.

Answer

mRNA NUCLEOTIDES - DNA NUCLEOTIDES
An mRNA molecule, a fragment of which contains 33 nucleotide residues, takes part in protein synthesis. Determine the number of nucleotide residues in a section of the DNA template strand.

Answer

NUCLEOTIDES - tRNA
What number of transport RNA molecules were involved in translation if the gene region contains 930 nucleotide residues?

Answer

TRIPLETS - mRNA NUCLEOTIDES
How many nucleotides are there in a fragment of an mRNA molecule if the fragment of the DNA coding strand contains 130 triplets? Write down only the corresponding number in your answer.

Answer

tRNA - AMINO ACIDS
Determine the number of amino acids in the protein if 150 tRNA molecules were involved in the translation process. Write down only the corresponding number in your answer.

Answer

JUST
How many nucleotides make up one mRNA codon?

Answer

How many nucleotides make up one stop codon of mRNA?

Answer

How many nucleotides make up the tRNA anticodon?

Answer

DIFFICULT
The protein has a relative molecular weight of 6000. Determine the number of amino acids in a protein molecule if the relative molecular mass one amino acid residue is 120. Write down only the corresponding number in your answer.

Answer

There are 3000 nucleotides in two strands of a DNA molecule. Information about the protein structure is encoded on one of the chains. Count how many amino acids are encoded on one DNA strand. In your answer, write down only the number corresponding to the number of amino acids.

Answer

Choose one, the most correct option. The same amino acid corresponds to the anticodon UCA on transfer RNA and a triplet in the gene on DNA
1) GTA
2) ACA
3) TGT
4) TCA

Answer

Choose one, the most correct option. The synthesis of hemoglobin in a cell is controlled by a certain segment of the DNA molecule, which is called
1) codon
2) triplet
3) genetic code
4) genome

Answer

In which of the listed cell organelles do matrix synthesis reactions occur? Identify three true statements from the general list and write down the numbers under which they are indicated.
1) centrioles
2) lysosomes
3) Golgi apparatus
4) ribosomes
5) mitochondria
6) chloroplasts

Answer

Look at the picture depicting the processes occurring in a cell and indicate A) the name of the process indicated by the letter A, B) the name of the process indicated by the letter B, C) the name of the type of chemical reactions. For each letter, select the corresponding term from the list provided.
1) replication
2) transcription
3) broadcast
4) denaturation
5) exothermic reactions
6) substitution reactions
7) matrix synthesis reactions
8) splitting reactions

Answer

Look at the picture and indicate (A) the name of process 1, (B) the name of process 2, (c) the final product of process 2. For each letter, select the corresponding term or concept from the list provided.
1) tRNA
2) polypeptide
3) ribosome
4) replication
5) broadcast
6) conjugation
7) ATP
8) transcription

Answer

1. Establish a correspondence between the processes and stages of protein synthesis: 1) transcription, 2) translation. Write numbers 1 and 2 in the correct order.
A) transfer of amino acids by tRNA
B) DNA is involved
B) synthesis of mRNA
D) formation of a polypeptide chain
D) occurs on the ribosome

Answer

2. Establish a correspondence between the characteristics and processes: 1) transcription, 2) translation. Write numbers 1 and 2 in the order corresponding to the letters.
A) three types of RNA are synthesized
B) occurs with the help of ribosomes
C) a peptide bond is formed between monomers
D) in eukaryotes occurs in the nucleus
D) DNA is used as a matrix
E) carried out by the enzyme RNA polymerase

Answer

All of the signs listed below, except two, are used to describe the process shown in the figure. Identify two characteristics that “drop out” from the general list and write down the numbers under which they are indicated.
1) according to the principle of complementarity, the nucleotide sequence of a DNA molecule is translated into the nucleotide sequence of molecules various types RNA
2) the process of converting a nucleotide sequence into an amino acid sequence
3) the process of transferring genetic information from the nucleus to the site of protein synthesis
4) the process occurs in ribosomes
5) the result of the process is RNA synthesis

Answer

The molecular weight of the polypeptide is 30,000 c.u. Determine the length of the gene encoding it if the molecular weight of one amino acid is on average 100, and the distance between nucleotides in DNA is 0.34 nm. Write down only the corresponding number in your answer.

Answer

Select two of the reactions listed below that are related to matrix synthesis reactions. Write down the numbers under which they are indicated.
1) cellulose synthesis
2) ATP synthesis
3) protein biosynthesis
4) glucose oxidation
5) DNA replication

Answer

Choose three correct answers out of six and write down the numbers under which they are indicated in the table. Matrix reactions in cells include
1) DNA replication
2) photolysis of water
3) RNA synthesis
4) chemosynthesis
5) protein biosynthesis
6) ATP synthesis

Answer

All of the following characteristics, except two, can be used to describe the process of protein biosynthesis in a cell. Identify two characteristics that “drop out” from the general list, and write down the numbers under which they are indicated in your answer.
1) The process occurs in the presence of enzymes.
2) The central role in the process belongs to RNA molecules.
3) The process is accompanied by the synthesis of ATP.
4) Amino acids serve as monomers to form molecules.
5) The assembly of protein molecules is carried out in lysosomes.

Answer

Find three errors in the given text. Indicate the numbers of the proposals in which they are made.(1) During protein biosynthesis, matrix synthesis reactions occur. (2) Template synthesis reactions include only replication and transcription reactions. (3) As a result of transcription, mRNA is synthesized, the template for which is the entire DNA molecule. (4) After passing through the pores of the nucleus, the mRNA enters the cytoplasm. (5) Messenger RNA is involved in tRNA synthesis. (6) Transfer RNA delivers amino acids for protein assembly. (7) The energy of ATP molecules is spent on the connection of each amino acid with tRNA.

Answer

All but two of the following concepts are used to describe translation. Identify two characteristics that “fall out” from the general list and write down the numbers under which they are indicated.
1) matrix synthesis
2) mitotic spindle
3) polysome
4) peptide bond
5) higher fatty acids

Answer

All of the characteristics listed below, except two, are used to describe the processes necessary for the synthesis of a polypeptide chain. Identify two characteristics that “drop out” from the general list and write down the numbers under which they are indicated.
1) transcription of messenger RNA in the nucleus
2) transport of amino acids from the cytoplasm to the ribosome
3) DNA replication
4) formation of pyruvic acid
5) connection of amino acids

Answer

© D.V. Pozdnyakov, 2009-2019