The ability of cells to maintain a highly ordered organization depends on genetic information, which is realized, maintained, 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 the cell, and their synthesis plays leading role in such processes as growth and differentiation of cells, maintenance of their structure and function.

Depends on the joint action of several classes of RNA molecules. First, as a result of copying DNA that carries information about the synthesized protein, a messenger RNA molecule (mRNA) is formed. A molecule of specific transfer RNA (tRNA) is attached to each of the 20 amino acids that make up a protein, and some auxiliary protein factors are attached to the subunits of the ribosome on which synthesis occurs.

The beginning of protein synthesis in a cell is considered the moment when these components combine in the cytoplasm, forming a functional ribosome. As the mRNA moves through the ribosome step by step, its nucleotide sequence is translated (transported) into the appropriate sequence of amino acids, 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 RNA polymerase bond is very strong if the RNA polymerase attaches 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 part of the double helix, thus exposing the nucleotides on a short segment of each of the two DNA strands. One of these two separated chains should become a template for complementary pairing of the main DNA with the bases of the incoming monomers - ribonucleoside triphosphates. The polymerase connects the first two incoming monomers and thereby initiates the synthesized RNA chain. Then RNA polymerase, moving step by step along the DNA, unwinds the DNA helix in front of itself, exposing each time a new section of the template for complementary base pairing. By adding one nucleotide to the growing RNA chain, it gradually builds up the chain.

The process of elongation of 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 separates from both the template DNA and the newly synthesized RNA strand. During the movement of the enzyme along the template chain, an RNA-DNA double helix is ​​formed in its active center. Behind the polymerase molecule, which has completed its work of DNA-RNA synthesis, the DNA-RNA helix is ​​immediately restored, and the RNA is forced out. Each completed RNA chain is separated from the DNA template as 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 chains 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 or another path.

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

All cells have a set of transfer RNAs (tRNAs) - small molecules whose sizes range from 70 to 90 nucleotides. These RNAs, by attaching one end to a specific mRNA codon and attaching the amino acid encoded by the given triplet to the other end, allow the amino acids to line up 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 transfer RNA carrying glycine 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 the tRNA containing the correct anticodon - a three-nucleotide sequence complementary to the three-nucleotide codon that defines this amino acid into an mRNA molecule. The pairing of a codon with an anticodon allows each amino acid to be included in the growing protein chain in the order dictated by the nucleotide sequence of the mRNA. So the genetic code is used to translate (translate) the nucleotide sequences of nucleic acids into the amino acid sequences of proteins.



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

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

Protein synthesis reactions require a complex catalytic stimulus. The growing end of the polypeptide chain must adapt in a certain way to the mRNA molecule in order for each subsequent mRNA codon to accurately connect to the tRNA anticodon without skipping a single nucleotide. Otherwise, this will lead to a shift in the reading sequence.

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

The second site serves to retain only the arrived tRNA molecule loaded with amino acid. It is called the aminoacyl-tRNA-binding site, or A-site. A tRNA molecule is firmly attached to both sites only if its anticodon pairs with its complementary mRNA codon. The A- and P-sites 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 consisting of three separate stages:

  1. The aminoacyl-tRNA molecule binds to the free site of the ribosome adjacent to the occupied P site. 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-site is separated from the tRNA molecule and a peptide bond is formed with the amino acid attached to the tRNA molecule in the A-site.
  3. The new peptidyl-tRNA is transferred to the P-site of the ribosome, while the ribosome advances exactly three nucleotides along the mRNA molecule.

The process of translocation, which is the third stage, also includes the return of a free tRNA molecule that separated from the polypeptide chain in the P-site during the second stage of the cytoplasmic tRNA 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 intensive process. The formation of each new peptide bond is accompanied by the arrangement of four high-energy phosphate bonds. Two of them are spent to load the tRNA molecule with an amino acid, and two - for the synthesis itself in the cycle of reactions occurring on the ribosome. At the end of the cycle, peptidyltransferase attaches to peptidyl-tRNA not an amino acid, but an H 2 O 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 the species continuity of hereditary material, as a result of its transfer in the process of division in equal amounts to both daughter cells. Daughter cells continue the evolutionarily fixed process of species metabolism, acquiring properties that are characteristic of a cell population of tissue belonging. Therefore, in a short period, 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 perform their task. 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 processes of metabolism 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 method of recording information is called coding. The genetic code is a system for recording information about the sequence of amino acids in proteins using the sequence of nucleotides in messenger RNA.

The composition of RNA includes nucleotides of 4 types: A, G, C, U. The composition of protein molecules includes 20 amino acids. Each of the 20 amino acids is coded for by 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 (from 2 to 6):

3. Code non-overlapping. This means that consecutive codons are sequentially arranged triplets of nucleotides:

4. Universal for all cells (human, animal, plant).

5. Specific. The same triplet cannot correspond to several amino acids.

6. Protein synthesis starts from the start (initial) 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.

Table of the genetic code

A section of DNA containing 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 a gene and a protein. DNA plays the role of a template for mRNA synthesis in the cell nucleus. The DNA molecule in the gene section unwinds. Information is written from one of its chains to mRNA 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 RNA polymerase enzyme and using the energy of ATP (Fig. 37).

Rice. 37. Transcription.

Protein synthesis is carried out in the cytoplasm on ribosomes, where mRNA serves as a template (Fig. 38). The translation of a sequence of nucleotide triplets in an mRNA molecule into a specific amino acid sequence is called broadcast. The synthesized mRNA exits 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 attaches 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.

Transfer RNAs (tRNAs) are found in the cytoplasm. Each amino acid has its own tRNA. The tRNA molecule on one of the loops has a triplet of nucleotides (anticodon), which is complementary to the triplet of nucleotides on the mRNA (codon).

Amino acids located 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) codon of mRNA - 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 ensures the connection of the large and small subunits of the ribosome. The second mRNA codon adds 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 released into the cytoplasm, where it can combine with its amino acid.

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

“Reading” by the ribosome of the information contained in the mRNA occurs until it reaches one of the three stop codons (UAA, UGA, UAG). Polypeptide chain

Rice. 40. Protein synthesis.

A- binding aminoacyl - tRNA;

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

IN- movement 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 certain protein-enzyme that catalyzes one biochemical reaction that occurs under certain environmental conditions.

Gene (section of DNA) → 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 information about protein synthesis recorded?

3. What properties does the genetic code have?

4. What codon does protein synthesis begin with?

5. What codons end protein synthesis?

6. What is a gene?

7. How and where does transcription take place?

8. What are nucleotide triplets in an mRNA molecule called?

9. What is broadcast?

10. How is an amino acid attached to tRNA?

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

small subunit of the ribosome?

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

Key words of the topic “Protein synthesis”

nitrogenous bases alanine

amino acids

anticodon

protein

biochemical reaction

valine

gene

genetic code action

DNA

record information magnesium ions

mRNA

coding

codon

leucine

matrix

metabolism

methionine

hereditary trait nucleic acids peptide bond loop

polyribosome pore

intermediary sequence

principle of ribosome complementarity

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: Anna Mastyukhina

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

Lesson objective:

Educational: explorefeatures of protein biosynthesis in the cell, learn concepts:gene, genetic code, triplet, codon, anticodon, transcription, translation, polysome; Pto continue the formation of knowledge about the mechanisms of protein biosynthesis using the example of translation; elucidate the role of transport RNAs in the process of protein biosynthesis; 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 skills of practical workwill make a syncwine. In order to develop logical thinkinglearn to solve problems.

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

F.O.U.R .: lesson.

Lesson type : combined

Type of lesson : with the 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 i-RNA on the DNA template (transcription)"; Scheme "Structure of t-RNA"; Scheme "Protein synthesis into ribosomes (translation)"; Scheme "Protein synthesis on the polysome"; Cards with tasks and a crossword puzzle; magnetic models.

During the classes:

Methods and methodological techniques:

I .Class organization.

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

which we considered two of their types: DNA and RNA, got acquainted with their structure and functions. It was found that the composition of each of the nucleic acids includes four different nitrogenous bases, which are connected to 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 a cell."

II .Learning new material:

1) Knowledge update:

Before starting to study new topic, remember: what is metabolism (metabolism):

METABOLISM - the totality of all enzymatic reactions of the cell, related to each other and with 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-flows, absorbs, excretes

4-set of enzymatic reactions of the cell

5-metabolism)

Protein biosynthesisrefers to plastic exchange reactions.

Protein biosynthesis – the most important process in 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.

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

1. Photosynthesis is ...(synthesis organic matter in the world).

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

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

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

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

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

7. When the sun counts on chlorophyll, ...(excitation of electrons).

8. Photosynthesis occurs in cells...(green plants).

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

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

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

Each cell contains thousands of proteins, including those inherent only this species cells. Since all proteins are destroyed sooner or later in the course of life, the cell must continuously synthesize proteins to restore its , organelles, etc. In addition, many cells "manufacture" proteins for the needs of the whole organism, for example, cells of the endocrine glands that secrete protein hormones into the blood. In such cells, protein synthesis is especially intensive.

2) Learning new material:

Protein synthesis requires a lot of energy.

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


Genetic code.

Each amino acid in a protein corresponds to a sequence of three nucleotides located one after another - a triplet. To date, a map of the genetic code has been compiled, 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, four nitrogenous bases can be included in DNA: adenine (A), guanine (G), thymine (T) and cytosine (C). The number of combinations of 4 to 3 is: 43 = 64, i.e. 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: CGA, CHG, CHT, CHC, and it turns out that a random 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 necessarily includes triplets, which are “punctuation marks” and indicate the beginning and end of a particular gene.

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

transport RNA.

For the transfer of each type of amino acid to ribosomes, separate view tRNA. Since there are about 20 amino acids in proteins, there are just as many types of tRNA. The structure of all tRNAs is similar (Fig. 35). Their molecules form peculiar structures resembling a clover leaf in shape. Types of tRNA necessarily differ in the triplet of nucleotides located "at the top". This triplet, called the anticodon, corresponds in its genetic code to the amino acid that this tRNA is to carry. A special enzyme attaches to the "petiole of the leaf" the amino acid encoded by the triplet complementary to the anticodon.


Broadcast.

In the cytoplasm, the last stage of protein synthesis occurs - translation. At the end of the i-RNA, from which protein synthesis must begin, a ribosome is strung (Fig. 36). The ribosome moves along the i-RNA molecule intermittently, "jumps", lingering on each triplet for approximately 0.2 s. In this instant, one t-RNA out of many is able to “recognize” with its anticodon the triplet on which the ribosome is located. And if the anticodon is complementary to this mRNA 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 moves along 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 protein under construction must contain. When the ribosome contains one of the triplets, which is a “stop signal” between genes, then not a single t-RNA can join such a triplet, since t-RNA does not have anticodons for them. At this point, protein synthesis ends. All the described reactions occur in very small time intervals. It is estimated that the synthesis of a fairly large protein molecule takes only about two minutes.

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

When protein synthesis is completed, the ribosome can find another mRNA and begin to synthesize the protein whose structure is encoded in the new mRNA.

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

It is estimated that all the proteins of a mammalian body can be encoded by only two percent of the DNA contained in its cells. What is the other 98% of DNA for? It turns out that each gene is much more complicated than previously thought, and contains not only the section in which the structure of a protein is encoded, but also special sections that can “turn on” or “turn off” the work of each gene. That is why all cells, for example human body, having the same set of chromosomes, are able to synthesize different proteins: in some cells, protein synthesis occurs with the help of some genes, while in others, completely different genes are involved. So, in each cell only a part of the genetic information contained in its genes is realized.

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

IV .Fixing material:

Fill the table:

IN 1

Protein biosynthesis consists of two successive steps: transcription and translation.

Solve problem 1:

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

Solution:

mRNA codons: TSUU - CGU - UUU - UGC.

Amino acid sequence: leu - arg - phene - cis.

DNA triplets: GAA - HCA - AAA - ACH.

Task 2

TGT-ACA-TTA-AAA-TsTsT. Determine the mRNA nucleotide sequence and the amino acid sequence in the protein that is synthesized under the control of this gene.

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

mRNA: ACA-UGU-AAU-UUU-GGA

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

AT 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 DNA segment:

AAA - TTT - YYY - CCC

TTT - AAA - CCC - YYY.

Solution:

Since mRNA is always synthesized on only one strand of DNA, which is usually depicted in writing as the top one, then

mRNA: UUU - AAA - CCC - GGY;

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

Task 2 : a section of DNA has the following nucleotide sequence:

TGT-ACA-TTA-AAA-TsTsT. Determine the nucleotide sequence of i-RNA and the sequence of amino acids in a protein that is synthesized under the control of this gene.

Answer: DNA: AGG-TsT-TAT-YGG-TsGA

mRNA: UCC-GGA-AUA-CCC-GCU

Protein: ser---gli---iso---pro---ala

Now let's listen interesting posts that you have prepared.

    "Interesting Facts About the Gene"

    "Genetic code"

    "Transcription and Broadcast"

VI .Summing up the lesson.

1) Conclusion on the lesson: One of the most important processes occurring in the cell is the synthesis of proteins. 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, cells of the endocrine glands that secrete protein hormones into the blood. In such cells, protein synthesis is especially intensive. Protein synthesis requires a lot of energy. The source of this energy, as for all cellular processes, is ATP.

2) Rate independent work 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:

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

2. Transition of the nucleotide sequence of the mRNA molecule into the AA sequence of the protein molecule.

3. Sign of the beginning of the broadcast.

4. A 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 section of DNA containing information about the primary structure of one protein.

7. A sequence of three consecutive DNA nucleotides.

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

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

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

11. Structure, where the sequence of AK in a protein molecule is determined.

12. An important property of the genetic code, which consists in the fact that one triplet always encodes only one AK.

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

14. Genetic code... for all living organisms from bacteria to humans.

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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 is called genetic , and the section of DNA that contains information about the primary structure of one protein is called gene .

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

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

Each DNA molecule contains many genes. The totality of all the genes of an organism makes up its genotype .

Protein biosynthesis

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

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

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

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

Transcription

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

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 chains.

Messenger (matrix) RNA consists of a single 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 chain (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 the “language of RNA”.

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

Since many genes can be in one DNA molecule, it is very important that RNA polymerase start mRNA synthesis with a strictly certain place DNA. Therefore, at the beginning of each gene there is a special specific sequence of nucleotides 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 synthesized mRNA molecules can immediately interact with ribosomes and participate in protein synthesis.

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

Broadcast

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

In the cytoplasm of the cell, there must be 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 received by the body with food, and some can be synthesized in the body itself.

Pay attention!

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

At the end of the mRNA, from which protein synthesis must begin, a ribosome is strung. It moves along the mRNA intermittently, "jumps", lingering on each triplet for approximately \(0.2\) seconds.

During this time, the tRNA molecule, the anticodon of which is complementary to the codon located in the ribosome, manages to recognize it. The amino acid that has been linked to this tRNA is detached from the tRNA "stem" and is attached to form a peptide bond to the growing protein chain. At the same moment, the next tRNA (whose anticodon is complementary to the next triplet in the mRNA) approaches the ribosome, and the next amino acid is included in the growing chain.

Amino acids delivered to ribosomes are oriented with respect 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 a polypeptide (protein) molecule is gradually formed.

Protein synthesis continues until one of the three is found 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, as soon as the ribosome, which was the first to start protein synthesis on mRNA, moves forward, the second ribosome is strung behind it on the same mRNA. Then the following ribosomes are sequentially strung onto the mRNA.

All ribosomes that synthesize 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 a given protein is completed, the ribosome can find another mRNA and begin to synthesize another protein.

General scheme of protein synthesis shown in the figure.

The process of protein biosynthesis is extremely important for the cell. Because proteins are complex substances, which 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 reproduction and the possibility of existence.

The essence of the process of protein biosynthesis

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

After copying the DNA, the process of creating messenger RNA is required. Based on it, the synthesis of the protein chain will be performed. Moreover, all the steps 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 takes place.

Ribosomal protein biosynthesis

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

Amino acids are supplied to the site where protein synthesis occurs with the help of one such molecule can bring one amino acid at a time. They join in turn, depending on the codon sequence of messenger RNA. Also, the synthesis may stop for a while.

When moving along the mRNA, the ribosome can enter regions (introns) that do not code for amino acids. In these places, the ribosome simply moves along the mRNA, but no amino acids are added to the chain. As soon as the ribosome reaches the exon, that is, the site 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 fully function, a molecule must be organized into a certain structure: secondary, tertiary, or even more complex - quaternary.

Structural organization of a protein

Secondary structure - first stage structural organization. To achieve it, the primary polypeptide chain must coil (form alpha helices) or fold (create beta layers). Then, in order to take up even less space along the length, the molecule is even more contracted and coiled into a ball due to hydrogen, covalent and ionic bonds, as well as interatomic interactions. Thus, we get a globular

Quaternary protein structure

The quaternary structure is the most complex of all. It consists of several sections with a globular structure, connected by fibrillar filaments of the polypeptide. In addition, the tertiary and quaternary structure can contain a carbohydrate or lipid residue, which expands the spectrum of protein functions. In particular, glycoproteins, protein and carbohydrate, are immunoglobulins and perform 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 the possibility of attachment of lipids, metals and carbohydrates to protein domains.