The ability of cells to maintain a high orderliness of their organization depends on genetic information, which is realized, preserved, reproduced or improved in four genetic processes: RNA and protein synthesis, DNA repair, DNA replication and genetic recombination. Proteins usually account for more than half of the dry mass of a cell, and their synthesis plays a major role in processes such as growth and differentiation of cells, maintenance of their structure and function.

Depends on the combined action of several classes of RNA molecules. First, as a result of DNA copying, which carries information about the synthesized protein, a messenger RNA (mRNA) molecule is formed. A molecule of specific transport RNA (tRNA) is attached to each of the 20 amino acids from which the protein is built, and some auxiliary protein factors are attached to the subunits of the ribosome, on which the synthesis takes place.

The beginning of protein synthesis in a cell is the moment when these components combine in the cytoplasm to form a functional ribosome. As the mRNA moves step by step through the ribosome, its nucleotide sequence is translated (transported) into the corresponding amino acid sequence, resulting in a specific protein chain.

The synthesis of RNA on a DNA template is called transcription. As a result of transcription, mRNA molecules are formed that carry information for protein synthesis in the cell, as well as transport, ribosomal and other types of RNA molecules that perform structural and catalytic functions. The synthesis of these RNA molecules - copies of the nucleotide sequences of sections of the DNA molecule - is catalyzed by enzymes called RNA polymerases.

The connection of RNA polymerase turns out to be very strong if the RNA polymerase is attached to a specific DNA sequence, to the so-called promoter containing the start signal for RNA synthesis, that is, to the site from which this synthesis should begin. The reactions that follow from this are characterized by the following: having attached to the promoter, RNA polymerase unwinds its section of the double helix, thus exposing nucleotides on a short segment of each of the two DNA strands. One of these two separated strands should become a matrix for complementary pairing of the basic DNA with the bases of incoming monomers - ribonucleoside triphosphates. Polymerase connects the first two incoming monomers and thus initiates the synthesized RNA strand. Then RNA polymerase, moving step by step along the DNA, unwinds the DNA helix in front of itself, exposing each time a new region of the matrix for complementary base pairing. Adding one nucleotide to the growing chain of RNA, it gradually builds up the chain.

The process of lengthening the RNA chain continues until the enzyme encounters on its way another specific nucleotide sequence in the DNA chain, namely the transcription termination signal (stop signal). Upon reaching this point, the polymerase is separated from both the template DNA and the newly synthesized RNA strand. During the advancement of the enzyme along the template strand, an RNA-DNA double helix is ​​formed in its active center. Behind the polymerase molecule, which has completed its work of synthesizing DNA-RNA, the DNA-RNA helix is ​​immediately restored, and RNA is displaced. Each completed RNA strand is separated from the DNA template in the form of a free single-stranded molecule, in which the number of nucleotides ranges from 70 to 10,000.

As a rule, one of the DNA strands is transcribed. Which of the two strands will be transcribed is determined by the promoter, the nucleotide sequence of which is oriented in such a way as to direct the RNA polymerase to one path or another.

It is also known that in determining which DNA regions will be transcribed by RNA polymerase, special proteins that regulate gene activity play an important role. It is from them that, first of all, it depends which proteins the cell will produce. Further, in eukaryotic cells, most of the RNA DNA transcripts will leave the cell nucleus and enter the cytoplasm in the form of mRNA, undergoing significant changes - undergoing splicing.

All cells have a set of transport RNAs (tRNAs) - small molecules that range in size from 70 to 90 nucleotides. These RNAs, attaching at one end to a specific mRNA codon, and at the other by attaching the amino acid encoded by this triplet, allow amino acids to align in the order dictated by the mRNA nucleotide sequence.

Each tRNA can only carry one of the 20 amino acids used in protein synthesis. The glycine-carrying transport RNA is referred to as tRNA Gly, etc. There is one type of tRNA for each of the 20 amino acids. It is important that each amino acid is covalently attached to a tRNA containing the correct anticodon - a three-nucleotide sequence complementary to the three-nucleotide codon that defines this amino acid in the mRNA molecule. Codon-anticodon mating allows each amino acid to be incorporated into the growing protein chain in the order dictated by the mRNA nucleotide sequence. So the genetic code is used to translate (translate) the nucleotide sequences of nucleic acids into amino acid sequences of proteins.



the mRNA strand is colored red, the ribosomes are blue, and the growing polypeptide chains are green. (Photo by Dr Elena Kiseleva).

Attaching one end to an amino acid, and the other by pairing with a codon, tRNA translates the sequence of nucleotides into a sequence of amino acids. The function of tRNA depends on the three-dimensional structure of its molecule. Where a given amino acid will be attached to the growing polypeptide chain depends not on the amino acid itself, but on the tRNA molecule that has attached it. The tRNA molecule covalently attaches itself to that amino acid of all twenty amino acids, which is its real partner. This mechanism is associated with the participation of enzymes called aminoacyl-tRNA synthases, which attach an amino acid to the corresponding set of tRNA molecules. Each of the amino acids has its own special synthetase (there are 20 such synthetases in total): one attaches, for example, glycine to tRNA Gly, the other alanine to tRNA Ala, etc. Thus, tRNA molecules play the role of final adapters that translate the information contained in the nucleotide sequence of a nucleic acid into the language of the protein.

A complex catalytic stimulus is required to carry out the reactions of protein synthesis. The growing end of the polypeptide chain must adjust in a certain way to the mRNA molecule in order for each subsequent mRNA codon to accurately bind to the tRNA anticodon without missing a single nucleotide. Otherwise, it will shift the read sequence.

More than half of the mass of the ribosome is RNA (rRNA), which plays a key role in the catalytic activity of the ribosome. There are three different regions in the ribosome that RNA binds to — one for mRNA and two for tRNA. Of the latter two, one site holds the tRNA molecule attached to the growing end of the polypeptide chain, therefore it is called the peptidyl-tRNA-binding site, or P-site.

The second site serves to retain only the arrived tRNA molecule loaded with an amino acid. It is called the aminoacyl tRNA binding site, or the A site. The tRNA molecule is firmly attached to both regions only if its anticodon is paired with its complementary mRNA codon. The A and P regions are located very close to each other - so that the two tRNA molecules associated with them pair with two adjacent codons in the mRNA molecule.

The process of building up a polypeptide chain on ribosomes can be considered as a cycle that consists of three separate stages:

  1. The aminoacyl-tRNA molecule binds to the free region of the ribosome adjacent to the occupied P-region. Binding is carried out by pairing the anticodon nucleotides with three mRNA nucleotides located in the A-site.
  2. At the second stage, the carboxyl end of the polypeptide chain in the P-region is separated from the tRNA molecule and a peptide bond is formed with the amino acid attached by the tRNA molecule in the A-region.
  3. The new peptidyl-tRNA is transferred to the P-region of the ribosome, while the ribosome moves along the mRNA molecule by exactly three nucleotides.

The translocation process, which constitutes the third stage, also includes the return of a free tRNA molecule that has been detached from the polypeptide chain in the P-region during the second stage of the tRNA cytoplasmic pool. Therefore, after the completion of the third stage, the unoccupied A-site can accept a new tRNA molecule loaded with the next amino acid, that is, the cycle can begin again.

A very energy consuming process. The formation of each new peptide bond is accompanied by the arrangement of four high-energy phosphate bonds. Two of them are consumed to load the tRNA molecule with the amino acid, and two to the synthesis itself in the cycle of reactions occurring on the ribosome. At the end of the cycle, peptidyltransferase does not attach an amino acid to the peptidyl-tRNA, but the H2O molecule, due to which the carboxyl end of the growing polypeptide chain is separated from the tRNA molecule - the protein chain is free and enters the cytoplasm.

Thus, a cell newly formed after mitotic division is endowed with a species continuity of hereditary material, as a result of its transfer in the process of division in an equal amount to both daughter cells. Daughter cells continue the evolutionarily fixed process of species metabolism, acquiring properties characteristic of the cell population of tissue belonging. Therefore, in a short space of time, newly formed cells undergo specialization (differentiation) according to their main genetically fixed affiliation. A number of properties become extremely common for all cells, regardless of the tissue system in which they have to carry out their life cycle. To perform their functions, cells are endowed with a number of highly specialized properties.

Sources:
Cytophysiology / Lutsenko M.T. // Novosibirsk-Blagoveshchensk, 2011.

Protein synthesis- one of the main metabolic processes in the cell. This is matrix synthesis. Protein synthesis requires DNA, mRNA, tRNA, rRNA (ribosomes), amino acids, enzymes, magnesium ions, ATP energy. The main role in determining the structure of a protein belongs to DNA.

Information about the amino acid sequence in a protein molecule is encoded in the DNA molecule. The way information is recorded is called coding. The genetic code is a system for recording information about the sequence of amino acids in proteins using the sequence of the location of nucleotides in messenger RNA.

RNA contains 4 types of nucleotides: A, G, C, U. The composition of protein molecules includes 20 amino acids. Each of the 20 amino acids is encoded with a sequence of 3 nucleotides called a triplet or codon. From 4 nucleotides, 64 different combinations of 3 nucleotides each can be created (4 3 = 64).

Properties of the genetic code

1. Genetic code triplet:

2. Code degenerate. This means that each amino acid is encoded by more than one codon (2 to 6):

3. Code not overlapping. This means that sequentially located codons are sequentially located triplets of nucleotides:

4. Is universal for all cells (humans, animals, plants).

5. Specific. One and the same triplet cannot correspond to several amino acids.

6. Protein synthesis begins with a start (start) codon OUT, which codes for the amino acid methionine.

7. Protein synthesis ends with one of three stop codons, non-coding amino acids: UAT, UAA, UTA.

Genetic code table

A piece of DNA that contains information about the structure of a particular protein is called a gene. The gene is not directly involved in protein synthesis. Messenger RNA (mRNA) is the mediator between the gene and the protein. DNA plays the role of a template for mRNA synthesis in the cell nucleus. The DNA molecule at the gene site unwinds. Information on mRNA is rewritten from one of its strands in accordance with the principle of complementarity between the nitrogenous bases of nucleic acids. This process is called transcription. Transcription occurs in the cell nucleus with the participation of the enzyme RNA polymerase and using the energy of ATP (Fig. 37).

Rice. 37. Transcription.

Protein synthesis is carried out in the cytoplasm on the ribosomes, where mRNA serves as a matrix (Fig. 38). The translation of the sequence of triplets of nucleotides in the mRNA molecule into a specific sequence of amino acids is called broadcast. The synthesized mRNA comes out through the pores in the nuclear envelope into the cytoplasm of the cell, combines with ribosomes, forming polyribosomes (polysomes). Each ribosome consists of two subunits - large and small. mRNA is attached to the small subunit in the presence of magnesium ions (Fig. 39).

Rice. 38. Protein synthesis.

Rice. 39.The main structures involved in protein synthesis.

The cytoplasm contains transport RNA (tRNA). Each amino acid has its own tRNA. The tRNA molecule has a nucleotide triplet (anticodon) on one of the loops, which is complementary to the nucleotide triplet on the mRNA (codon).

Amino acids in the cytoplasm are activated (interact with ATP) and, with the help of the enzyme aminoacyl-tRNA synthetase, are attached to tRNA. The first (start) mRNA codon - AUG - carries information about the amino acid methionine (Fig. 40). This codon is matched by a tRNA molecule containing a complementary anticodon and carrying the first amino acid methionine. This allows the large and small ribosome subunits to join. The second mRNA codon attaches a tRNA containing an anticodon complementary to this codon. tRNA contains a second amino acid. A peptide bond is formed between the first and second amino acids. The ribosome intermittently, triplet by triplet, moves along the mRNA. The first tRNA is released and enters the cytoplasm, where it can combine with its amino acid.

As the ribosome moves along the mRNA, amino acids corresponding to the mRNA triplets and imported tRNA are attached to the polypeptide chain (Fig. 41).

The ribosome "reads" the information contained in the mRNA until it reaches one of the three stop codons (UAA, UGA, UAG). Polypeptide chain

Rice. 40. Protein synthesis.

A- binding of aminoacyl - tRNA;

B- the formation of a peptide bond between methionine and the 2nd amino acid;

V- displacement of the ribosome by one codon.

leaves the ribosome and acquires the structure characteristic of this protein.

The direct function of an individual gene is to encode the structure of a specific protein-enzyme, which catalyzes one biochemical reaction that occurs under certain environmental conditions.

Gene (DNA segment) → mRNA → protein-enzyme → biochemical reaction → hereditary trait.

Rice. 41. Broadcast.

Questions for self-control

1. Where does protein synthesis take place in the cell?

2. Where is the protein synthesis information recorded?

3. What properties does the genetic code have?

4. What codon does protein synthesis begin with?

5. What codons end in protein synthesis?

6. What is a gene?

7. How and where does the transcription take place?

8. What are the triplets of nucleotides in the mRNA molecule called?

9. What is broadcasting?

10. How is an amino acid attached to tRNA?

11. What is the name of the triplet of nucleotides in the tRNA molecule? 12. What amino acid provides the connection large and

small subunits of the ribosome?

13. How is the formation of the protein polypeptide chain?

Key words of the theme "Protein synthesis"

nitrogenous bases alanine

amino acids

anticodon

protein

biochemical reaction

valine

gene

genetic code action

DNA

write information magnesium ions

mRNA

coding

codon

leucine

matrix

metabolism

methionine

hereditary trait nucleic acids peptide bond loop

pore polyribosome

sequence mediator

ribosome complementarity principle

rRNA

serine

synthesis

combination

way

structure

subunit

transcription

broadcast

triplet

tRNA

plot

phenylalanine

enzymes

chain

cytoplasm

ATP energy

Lesson outline : "Synthesis of proteins in the cell"

(For the profile 10th grade, the lesson time is 2 hours)

Teacher: Mastyukhina Anna Alexandrovna

MOU "Secondary School named after General Zakharkin I.G."

Lesson Objective:

Educational: to examinefeatures of protein biosynthesis in the cell, explore concepts:gene, genetic code, triplet, codon, anticodon, transcription, translation, polysome; NSto continue the formation of knowledge about the mechanisms of protein biosynthesis on the example of translation; elucidate the role of transport RNAs in the process of protein biosynthesis; to reveal the mechanisms of matrix synthesis of the polypeptide chain on ribosomes.

Developing: in order to develop the cognitive interest of studentsprepare messages in advance ("Interesting facts about the gene", "Genetic code", "Transcription and translation"). To develop practical skillswill make up syncwine. In order to develop logical thinkinglearn to solve problems.

Educational: In order to form a scientific worldview, prove the importance and significance of protein synthesis in cells, as well as their vital necessity.

F.O.U.R .: lesson.

Lesson type : combined

Lesson type : with presentation "Synthesis of proteins in the cell" and demonstration of magnetic models.

Equipment: presentation "Synthesis of proteins in the cell"; table "Genetic code"; Scheme "Formation of m-RNA from a DNA template (transcription)"; Scheme "Structure of t-RNA"; Scheme "Protein synthesis in ribosomes (translation)"; Scheme "Protein synthesis on a polysome"; Task cards and a crossword puzzle; magnetic models.

During the classes:

Methods and methodological techniques:

I . Organization of the class.

In previous lessons, we studied substances called nucleic acids. Because of

which examined their two types: DNA and RNA, got acquainted with their structure and functions. They found out that the composition of each of the nucleic acids includes four different nitrogenous bases, which combine with each other according to the principle of complementarity. We will need all this knowledge when studying today's new topic. So write down its name in your workbooks "Protein synthesis in the cell".

II .Learning new material:

1) Updating knowledge:

Before starting to study a new topic, let's remember: what is metabolism (metabolism):

METABOLISM - a set of all enzymatic reactions of a cell, connected with each other and with the external environment, consisting of plastic
and energy exchanges.

Let's make a syncwine, the first word of which is metabolism. (1-metabolism

2-plastic, energetic

3-leaks, absorbs, excretes

4-set of enzymatic reactions of the cell

5-metabolism)

Protein biosynthesisrefers to the reactions of plastic exchange.

Protein biosynthesis – the most important process in living nature. This is the creation of protein molecules based on information about the amino acid sequence in its primary structure, contained in the DNA structure

Assignment: Complete the sentences by filling in the missing terms.

1. Photosynthesis is ...(synthesis of organic substances in the light).

2. The process of photosynthesis is carried out in cell organelles - ...(chloroplasts).

3. Free oxygen during photosynthesis is released during splitting ...(water).

4. At what stage of photosynthesis free oxygen is formed? On …(light).

5. During the light stage ... ATP.(Synthesized.)

6. In the dark stage, chloroplast forms ...(the primary carbohydrate is glucose).

7. When the solar account hits chlorophyll ...(excitation of electrons).

8. Photosynthesis takes place in cells ...(green plants).

9. The light phase of photosynthesis occurs in ...(thylakoids).

10. The dark phase occurs in ...(any) Times of Day.

The most important process of assimilation in the cell is proteins inherent in it.

Each cell contains thousands of proteins, including those inherent only to this type of cell. Since in the process of vital activity all proteins are destroyed sooner or later, the cell must continuously synthesize proteins to restore its , organelles, etc. In addition, many cells "produce" proteins for the needs of the whole organism, for example, cells of the endocrine glands, which secrete protein hormones into the blood. In such cells, protein synthesis is especially intense.

2) Learning new material:

Protein synthesis is energy intensive.

The source of this energy, as well as for all cellular processes, is ... The variety of functions of proteins is determined by their primary structure, i.e. the sequence of amino acids in their molecule. In turn, hereditary about the primary structure of a protein lies in the sequence of nucleotides in the DNA molecule. The piece of DNA that contains information about the primary structure of one protein is called a gene. One chromosome contains information about the structure of many hundreds of proteins.


Genetic code.

Each amino acid of protein in corresponds to a sequence of three located one after another nucleotides - a triplet. To date, a map of the genetic code has been drawn up, that is, it is known which triplet combinations of DNA nucleotides correspond to one or another of the 20 amino acids that make up proteins (Fig. 33). As you know, DNA can contain four nitrogenous bases: adenine (A), guanine (G), thymine (T), and cytosine (C). The number of combinations from 4 to 3 is: 43 = 64, that is, 64 different amino acids can be encoded, while only 20 amino acids are encoded. It turned out that many amino acids correspond to not one, but several different triplets - codons.

It is assumed that this property of the genetic code increases the reliability of storage and transmission of genetic information during cell division. For example, 4 codons correspond to the amino acid alanine: CHA, CHG, CHT, CHC, and it turns out that an accidental error in the third nucleotide cannot affect the structure of the protein - it will still be an alanine codon.

Since the DNA molecule contains hundreds of genes, it must include triplets, which are "punctuation marks" and denote the beginning and end of a particular gene.

A very important property of the genetic code is specificity, that is, one triplet always means only one single amino acid. The genetic code is universal for all living organisms, from bacteria to humans.
Transcription. The bearer of all genetic information is DNA located in cells. The very same protein synthesis occurs in the cytoplasm of the cell, on the ribosomes. From the nucleus to the cytoplasm, information about the structure of the protein comes in the form of messenger RNA (m-RNA). In order to synthesize i-RNA, the DNA section is “unwound”, despiralized, and then, according to the principle of complementarity, RNA molecules are synthesized on one of the DNA strands with the help of enzymes (Fig. 34). This happens as follows: against, for example, the guanine of the DNA molecule, the cytosine of the RNA molecule becomes, against the adenine of the DNA molecule - uracil RNA (remember that uracil is included in RNA in nucleotides instead of thymine), opposite to thymine DNA - adenine RNA and opposite to cytosine DNA - guanine RNA. Thus, an i-RNA chain is formed, which is an exact copy of the second DNA strand (only thymine is replaced by uracil). Thus, information about the nucleotide sequence of any DNA gene is "rewritten" into the sequence of nucleotides of m-RNA. This process is called transcription. In prokaryotes, the synthesized m-RNA molecules can immediately interact with ribosomes, and protein synthesis begins. In eukaryotes, i-RNA interacts in the nucleus with special proteins and is transferred through the nuclear envelope into the cytoplasm.
The cytoplasm must contain a set of amino acids necessary for protein synthesis. These amino acids are formed as a result of the breakdown of dietary proteins. In addition, one or another amino acid can get to the site of direct protein synthesis, i.e., to the ribosome, only by attaching to a special transport RNA (t-RNA).

Transport RNAs.

For the transfer of each type of amino acid to the ribosome, a separate type of t-RNA is needed. Since proteins contain about 20 amino acids, there are the same number of types of t-RNA. The structure of all t-RNAs is similar (Fig. 35). Their molecules form peculiar structures that resemble a clover leaf. The types of t-RNA necessarily differ in the triplet of nucleotides located "at the top". This triplet, called the anticodon, according to the genetic code, corresponds to the amino acid that this T-RNA has to transfer. A special enzyme necessarily attaches to the “leaf petiole” the amino acid encoded by a triplet complementary to the anticodon.


Broadcast.

In the cytoplasm, the last stage of protein synthesis takes place - translation. A ribosome is strung at the end of the m-RNA, from which protein synthesis should be started (Fig. 36). The ribosome moves along the m-RNA molecule intermittently, "jumps", lingering on each triplet for about 0.2 s. During this instant, one t-RNA out of many is able to "identify" with its anticodon the triplet on which the ribosome is located. And if the anticodon is complementary to this m-RNA triplet, the amino acid is detached from the “leaf petiole” and is attached by a peptide bond to the growing protein chain (Fig. 37). At this moment, the ribosome shifts in the i-RNA to the next triplet, encoding the next amino acid of the synthesized protein, and the next t-RNA "brings" the necessary amino acid, which builds up the growing protein chain. This operation is repeated as many times as the number of amino acids the "under construction" protein should contain. When in the ribosome there is one nz triplets, which is a "stop signal" between genes, then not a single t-RNA can attach to such a triplet, since t-RNA does not have anticodons to them. At this point, protein synthesis ends. All described reactions occur in very short periods of time. It is estimated that it takes only about two minutes to synthesize a fairly large protein molecule.

The cell needs not one, but many molecules of each protein. Therefore, as soon as the ribosome, which first started protein synthesis on the i-RNA, moves forward, the second ribosome, synthesizing the same protein, is strung behind it on the same i-RNA. Then the third, fourth ribosomes, etc., are sequentially strung on the m-RNA. All ribosomes synthesizing the same protein encoded in this m-RNA are called a polysome.

When protein synthesis is over, the ribosome can find another i-RNA and begin to synthesize the protein whose structure is encoded in the new i-RNA.

Thus, translation is the translation of the nucleotide sequence of the m-RNA molecule into the amino acid sequence of the synthesized protein.

It is estimated that all proteins in the mammalian body can be encoded with only two percent of the DNA contained in its cells. And what is the remaining 98% of DNA for? It turns out that each gene is much more complex than previously thought, and contains not only the region in which the structure of a protein is encoded, but also special regions that can "turn on" or "turn off" the work of each gene. That is why all cells, for example in the human body, which have the same set of chromosomes, are capable of synthesizing different proteins: in some cells, proteins are synthesized with the help of some genes, while in others completely different genes are involved. So, in each cell only part of the genetic information contained in its genes is realized.

Protein synthesis requires the participation of a large number of enzymes. And each individual protein synthesis reaction requires specialized enzymes.

IV .Fixing the material:

Fill the table:

IN 1

Protein biosynthesis consists of two sequential stages: transcription and translation.

Solve problem 1:

The anticodons of tRNA are given: GAA, HCA, AAA, ACG. Using the genetic code table, determine the amino acid sequence in the protein molecule, mRNA codons and triplets in the fragment of the gene encoding this protein.

Solution:

MRNA codons: TsUU - TsGU - UUU - UGTs.

The sequence of amino acids: leu - arg - phen - cis.

DNA triplets: GAA - HCA - AAA - ACG.

Assignment 2

TGT-ACA-TTA-AAA-TsTsT. Determine the sequence of mRNA nucleotides and the sequence of amino acids in the protein, which is synthesized under the control of this gene.

Answer: DNA: TGT-ACA-TTA-AAA-CCT

iRNC: ACA-UGU-AAU-UUU-GGA

Protein: tre --- cis --- asp --- fen --- gli.

IN 2

Solve problem 1:

A fragment of a double-stranded DNA molecule is given. Using the table of the genetic code, determine the structure of the fragment of the protein molecule encoded by this section of DNA:

AAA - TTT - YYY - ЦЦЦЦ

TTT - AAA - ЦЦЦ - ГГГ.

Solution:

Since mRNA is always synthesized only on one DNA strand, which is usually represented in writing as the upper one, then

mRNA: UUU - AAA - CCC - YGG;

a protein fragment encoded by the upper chain: phen - lysis - pro - gly.

Assignment 2 : a piece of DNA has the following nucleotide sequence:

TGT-ACA-TTA-AAA-TsTsT. Determine the sequence of nucleotides of m-RNA and the sequence of amino acids in the protein, which is synthesized under the control of this gene.

Answer: DNA: AGG-CTsT-TAT-YGG-CHA

mRNA: UCTs-GGA-AUA-CTSC-HCU

Protein: sulfur --- gli --- iso --- pro --- ala

And now let's listen to the interesting messages that you have prepared.

    "Interesting facts about the gene"

    "Genetic code"

    "Transcription and Broadcast"

VI . Summing up the results of the lesson.

1) Conclusion from the lesson: One of the most important processes in the cell is protein synthesis. Each cell contains thousands of proteins, including those inherent only to this type of cell. Since in the process of life all proteins sooner or laterare destroyed, the cell must continuously synthesize proteins to restore its membranes, organelles, etc. In addition, many cells produce proteins for the needs of the whole organism, for example, endocrine gland cells that release protein hormones into the blood. In such cells, protein synthesis is especially intense. Protein synthesis is energy intensive. The source of this energy, as well as for all cellular processes, is ATP.

2) Assess the independent work of students and their work at the blackboard. Also evaluate the activity of the participants in the conversation and speakers.

V II ... Homework:

Repeat § 2.13.

Solve the crossword puzzle:

1. The specific sequence of nucleotides located at the beginning of each gene.

2. Transition of the sequence of nucleotides of the mRNA molecule into the sequence of the AK of the protein molecule.

3. Sign of the beginning of the broadcast.

4. The carrier of genetic information located in the cell nucleus.

5. A property of the genetic code that increases the reliability of storage and transmission of genetic information during cell division.

6. A piece of DNA containing information about the primary structure of one protein.

7. A sequence of three DNA nucleotides located one after another.

8. All ribosomes that synthesize protein on one mRNA molecule.

9. The process of translating information about the sequence of AK in a protein from the "language of DNA" to "language of RNA".

10. A codon that does not code for AK, but only indicates that the protein synthesis must be completed.

11. The structure, where the sequence of AK in the protein molecule is determined.

12. An important property of the genetic code is that one triplet always encodes only one AK.

13. "Punctuation mark" in the DNA molecule, indicating that the synthesis of mRNA must be stopped.

14. The genetic code ... for all living organisms from bacteria to humans.

- up to 2 minutes

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Each cell contains thousands of proteins. The properties of proteins are determined by their primary structure , i.e. the sequence of amino acids in their molecules.

In turn, hereditary information about the primary structure of the protein is contained in the sequence of nucleotides in the DNA molecule. This information was named genetic , and the section of DNA that contains information about the primary structure of one protein is called gene .

A gene is a piece of DNA that contains information about the primary structure of a single protein.

A gene is a unit of hereditary information in an organism.

Each DNA molecule contains many genes. The totality of all genes of an organism makes it genotype .

Protein biosynthesis

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

The process of protein biosynthesis consists of two stages: transcription and translation.

Each stage of biosynthesis is catalyzed by a corresponding enzyme and supplied with the energy of ATP.

Biosynthesis occurs in cells at a tremendous rate. In the body of higher animals, up to \ (60 \) thousand peptide bonds are formed in one minute.

Transcription

Transcription is the process of removing information from a DNA molecule by an mRNA (mRNA) molecule synthesized on it.

The carrier of genetic information is DNA located in the cell nucleus.

During transcription, a section of double-stranded DNA is "unwound", and then an mRNA molecule is synthesized on one of the strands.

Informational (messenger) RNA consists of one strand and is synthesized on DNA in accordance with the rule of complementarity.

An mRNA chain is formed, which is an exact copy of the second (non-template) DNA strand (only uracil is included instead of thymine). So information about the sequence of amino acids in a protein is translated from the "language of DNA" to "language of RNA".

As in any other biochemical reaction, an enzyme is involved in this synthesis - RNA polymerase .

Since there can be many genes in one DNA molecule, it is very important that the RNA polymerase starts the synthesis of mRNA from a strictly defined place in the DNA. Therefore, at the beginning of each gene there is a special specific nucleotide sequence called promoter... RNA polymerase "recognizes" the promoter, interacts with it and, thus, starts the synthesis of the mRNA chain from the right place.

The enzyme continues to synthesize mRNA until it reaches the next "punctuation mark" in the DNA molecule - terminator (this is a nucleotide sequence indicating that mRNA synthesis must be stopped).

In prokaryotes the synthesized mRNA molecules can immediately interact with ribosomes and participate in the synthesis of proteins.

In eukaryotes mRNA is synthesized in the nucleus, so it first interacts with special nuclear proteins and is transported across the nuclear membrane into the cytoplasm.

Broadcast

Translation is the translation of the nucleotide sequence of the mRNA molecule into the amino acid sequence of the protein molecule.

The cytoplasm of the cell must contain a complete set of amino acids necessary for the synthesis of proteins. These amino acids are formed as a result of the breakdown of proteins that the body receives from food, and some can be synthesized in the body itself.

Pay attention!

Amino acids are delivered to ribosomes transport RNA (tRNA). Any amino acid can enter the ribosome only by attaching to a special tRNA).

A ribosome is strung at the end of the mRNA, from which you need to start protein synthesis. It moves along the mRNA intermittently, "jumps", lingering on each triplet for about \ (0.2 \) seconds.

During this time, the tRNA molecule, the anticodon of which is complementary to the codon in the ribosome, manages to recognize it. The amino acid that was bound to this tRNA is detached from the tRNA “petiole” and attaches to the growing protein chain to form a peptide bond. At the same moment, the next tRNA approaches the ribosome (the anticodon of which is complementary to the next triplet in the mRNA), and the next amino acid is included in the growing chain.

The amino acids delivered to the ribosomes are oriented in relation to each other so that the carboxyl group of one molecule is next to the amino group of another molecule. As a result, a peptide bond is formed between them.

The ribosome gradually shifts along the mRNA, lingering on the next triplets. This is how the polypeptide (protein) molecule is gradually formed.

Protein synthesis continues until one of the three is on the ribosome stop codons (UAA, UAG or UGA). After that, the protein chain is detached from the ribosome, enters the cytoplasm and forms the secondary, tertiary and quaternary structures inherent in this protein.

Since the cell needs many molecules of each protein, then as soon as the ribosome, which first started protein synthesis on mRNA, moves forward, after it on the same mRNA, the second ribosome is strung. Then the following ribosomes are sequentially strung on the mRNA.

All ribosomes synthesizing the same protein encoded in a given mRNA form polysome ... It is on polysomes that the simultaneous synthesis of several identical protein molecules occurs.

When the synthesis of this protein is over, the ribosome can find another mRNA and start synthesizing another protein.

General scheme of protein synthesis is shown in the figure.

The process of protein biosynthesis is extremely important for the cell. Since proteins are complex substances that play a major role in tissues, they are irreplaceable. For this reason, a whole chain of protein biosynthesis processes is realized in the cell, which takes place in several organelles. This guarantees the cell to reproduce and to exist.

The essence of the process of protein biosynthesis

The only place for the synthesis of proteins is rough. Here the bulk of the ribosomes, which are responsible for the formation of the polypeptide chain, are located. However, before the translation stage (the process of protein synthesis) begins, the activation of the gene that stores information about the protein structure is required. After that, copying of this section of DNA (or RNA, if bacterial biosynthesis is considered) is required.

After DNA copying, a process of making messenger RNA is required. On its basis, the synthesis of the protein chain will be carried out. Moreover, all the stages that occur with the involvement of nucleic acids must occur in However, this is not the place where protein synthesis occurs. where preparation for biosynthesis is carried out.

Ribosomal protein biosynthesis

The main place where protein synthesis takes place is the cell organelle, which consists of two subunits. There are a huge number of such structures in the cell, and they are mainly located on the membranes of the rough endoplasmic reticulum. The biosynthesis itself occurs as follows: the informational RNA formed in the cell nucleus leaves through the nuclear pores into the cytoplasm and meets the ribosome. Then mRNA is pushed into the gap between the ribosome subunits, after which the first amino acid is fixed.

Amino acids are supplied to the place where protein synthesis takes place. One such molecule can bring one amino acid at a time. They are attached in turn depending on the sequence of messenger RNA codons. Also, the synthesis may stop for a while.

When moving along the mRNA, the ribosome can enter regions (introns) that do not encode amino acids. In these places, the ribosome simply moves along the mRNA, but the attachment of amino acids to the chain does not occur. As soon as the ribosome reaches the exon, that is, the region that codes for the acid, then it reattaches to the polypeptide.

Postsynthetic modification of proteins

After the ribosome reaches the stop codon of messenger RNA, the process of direct synthesis is completed. However, the resulting molecule has a primary structure and cannot yet perform the functions reserved for it. In order to function fully, a molecule must organize itself into a specific structure: secondary, tertiary, or even more complex - quaternary.

Protein structural organization

Secondary structure is the first stage of structural organization. To achieve this, the primary polypeptide chain must spiral (form alpha helices) or bend (create beta layers). Then, in order to take up even less space along the length, the molecule contracts even more and coils into a ball due to hydrogen, covalent and ionic bonds, as well as interatomic interactions. Thus, a globular

Quaternary protein structure

The quaternary structure is the most complex of all. It consists of several regions with a globular structure, connected by fibrillar polypeptide filaments. In addition, tertiary and quaternary structures can contain a carbohydrate or lipid residue, which broadens the spectrum of protein functions. In particular, protein and carbohydrate glycoproteins are immunoglobulins and have a protective function. Also, glycoproteins are located on cell membranes and work as receptors. However, the molecule is modified not where protein synthesis occurs, but in the smooth endoplasmic reticulum. Here there is a possibility of lipids, metals and carbohydrates to attach to protein domains.