How to explain, briefly and clearly, what is protein biosynthesis, and what is its significance?

If you are interested in this topic, and would like to improve school knowledge or repeat gaps, then this article was created for you.

What is protein biosynthesis

First, it is worth familiarizing yourself with the definition of biosynthesis. Biosynthesis is the synthesis of natural organic compounds by living organisms.

To put it simply, it is the production of various substances with the help of microorganisms. This process takes important role in all living cells. Do not forget about the complex biochemical composition.

Transcription and broadcast

These are the two most important steps in biosynthesis.

Transcription from Latin means "rewriting" - DNA is used as a matrix, so synthesis occurs three types RNA (matrix / informational, transport, ribosomal ribonucleic acids). The reaction is carried out using a polymerase (RNA) and using a large number adenosine triphosphate.

There are two main actions:

Marking the end and start of translation by adding mRNA.
An event carried out due to splicing, which in turn removes non-informative RNA sequences, thereby reducing the mass of matrix ribonucleic acid by 10 times.

Broadcast from Latin means "translation" - mRNA is used as a template, polypeptide chains are synthesized.

The translation includes three stages, which could be presented in the form of a table:

First stage. Initiation is the formation of a complex that is involved in the synthesis of a polypeptide chain.
Second phase. Elongation is an increase in the size of this chain.
Third stage. Termination is the conclusion of the above mentioned process.

Diagram of protein biosynthesis

The diagram shows how the process proceeds.

The docking point of this circuit is the ribosomes, in which the protein is synthesized. In a simple form, the synthesis is carried out according to the scheme

DNA > RNA > protein.

The first stage of transcription begins, in which the molecule is changed into a single-stranded messenger ribonucleic acid (mRNA). It contains information about the amino acid sequence of the protein.

The next stop of the mRNA will be the ribosome, where the synthesis itself takes place. This happens by translation, the formation of a polypeptide chain. After this mediocre scheme, the resulting protein is transported to different places by performing certain tasks.

Sequence of protein biosynthesis processors

Protein biosynthesis is a complex mechanism that includes the two steps mentioned above, namely transcription and translation. The transcribed stage occurs first (it is divided into two events).

After comes translation, in which all types of RNA participate, each has its own function:

Informational - the role of the matrix.
Transport - addition of amino acids, determination of codons.
Ribosomal - the formation of ribosomes that support mRNA.
Transport - synthesis of a polypeptide chain.

What components of the cell are involved in protein synthesis

As we have already said, biosynthesis is divided into two stages. Each stage has its own components. At the first stage, these are deoxyribonucleic acid, messenger and transfer RNA, and nucleotides.

In the second stage, the following components are involved: mRNA, tRNA, ribosomes, nucleotides and peptides.

What are the features of protein biosynthesis reactions in a cell

The list of features of biosynthesis reactions should include:

Use of ATP energy for chemical reactions.
There are enzymes that speed up reactions.
The reaction has a matrix character, since the protein is synthesized on mRNA.

Signs of protein biosynthesis in a cell

Such a complex process, of course, is characterized by various signs:

The first of these is that there are enzymes, without which the process itself would not be possible.
All three types of RNA are involved, from this we can conclude that the central role belongs to RNA.
The formation of molecules is carried out by monomers, namely amino acids.
It should also be noted that the specificity of a protein is oriented by the arrangement of amino acids.

Conclusion

A multicellular organism is an apparatus consisting of different cell types that are differentiated - differ in structure and function. In addition to proteins, there are cells of these types, which also synthesize their own kind, this is the difference.

Protein synthesis in a cell

The main question of genetics is the question of protein synthesis. Summarizing data on the structure and synthesis of DNA and RNA, Crick in 1960. proposed a matrix theory of protein synthesis based on 3 provisions:

1. Complementarity of nitrogenous bases of DNA and RNA.

2. The linear sequence of the location of genes in a DNA molecule.

3. The transfer of hereditary information can only occur from nucleic acid to nucleic acid or to protein.

From protein to protein, the transfer of hereditary information is impossible. Thus, only nucleic acids can be a template for protein synthesis.

Protein synthesis requires:

1. DNA (genes) on which molecules are synthesized.

2. RNA - (i-RNA) or (m-RNA), r-RNA, t-RNA

In the process of protein synthesis, the stages are distinguished: transcription and translation.

Transcription- census (rewriting) of information about the nucleic structure from DNA to RNA (t-RNA, and RNA, r-RNA).

Reading of hereditary information begins with a certain section of DNA, which is called a promoter. The promoter is located before the gene and includes about 80 nucleotides.

On the outer chain of the DNA molecule, i-RNA (intermediate) is synthesized, which serves as a matrix for protein synthesis and is therefore called matrix. It is an exact copy of the sequence of nucleotides on the DNA chain.

There are regions in DNA that do not contain genetic information(introns). The sections of DNA that contain information are called exons.

There are special enzymes in the nucleus that cut out introns, and exon fragments are “spliced” together in a strict order into a common thread, this process is called “splicing”. During splicing, mature mRNA is formed, which contains the information necessary for protein synthesis. Mature mRNA (matrix RNA) passes through the pores of the nuclear membrane and enters the channels of the endoplasmic reticulum (cytoplasm) and here it combines with ribosomes.

Broadcast- the sequence of nucleotides in i-RNA is translated into a strictly ordered sequence of amino acids in the synthesized protein molecule.

The translation process includes 2 stages: the activation of amino acids and the direct synthesis of a protein molecule.

One mRNA molecule binds to 5-6 ribosomes to form polysomes. Protein synthesis occurs on the mRNA molecule, with ribosomes moving along it. During this period, amino acids in the cytoplasm are activated by special enzymes secreted by enzymes secreted by mitochondria, each of them with its own specific enzyme.

Almost instantly, amino acids bind to another type of RNA - a low molecular weight soluble RNA that acts as an amino acid carrier to the mRNA molecule and is called transport (t-RNA). tRNA carries amino acids to ribosomes certain place, where by this time the mRNA molecule is located. The amino acids are then joined together by peptide bonds to form a protein molecule. By the end of protein synthesis, the molecule is gradually shedding from mRNA.

On one mRNA molecule, 10-20 protein molecules are formed, and in some cases much more.

The most obscure question in protein synthesis is how tRNA finds the appropriate mRNA site to which the amino acid it brings must be attached.

The sequence of arrangement of nitrogenous bases in DNA, which determines the arrangement of amino acids in the synthesized protein, is the genetic code.

Since the same hereditary information is “recorded” in nucleic acids by four characters (nitrogenous bases), and in proteins by twenty (amino acids). The problem of the genetic code is reduced to establishing a correspondence between them. Geneticists, physicists, and chemists played an important role in deciphering the genetic code.

To decipher the genetic code, first of all, it was necessary to find out what is the minimum number of nucleotides that can determine (encode) the formation of one amino acid. If each of the 20 amino acids were encoded by one base, then DNA would have to have 20 different bases, but in fact there are only 4. Obviously, the combination of two nucleotides is also not enough to code for 20 amino acids. It can only code for 16 amino acids 4 2 = 16.

Then it was proposed that the code includes 3 nucleotides 4 3 = 64 combinations and, therefore, is able to encode more than enough amino acids to form any proteins. This combination of three nucleotides is called a triplet code.

The code has the following properties:

1. The genetic code is triplet(each amino acid is encoded by three nucleotides).

2. Degeneracy- one amino acid can be encoded by several triplets, the exception is tryptophan and methionine.

3. In codons for one amino acid, the first two nucleotides are the same, and the third one changes.

4.Non-overlapping– triplets do not overlap each other. One triplet cannot be part of another; each of them independently encodes its own amino acid. Therefore, any two amino acids can be nearby in the polypeptide chain and any combination of them is possible, i.e. in the base sequence ABCDEFGHI, the first three bases code for 1 amino acid (ABC-1), (DEF-2), etc.

5.Universal, those. in all organisms, the codons for certain amino acids are the same (from chamomile to humans). The universality of the code testifies to the unity of life on earth.

6. Kneeling- the coincidence of the arrangement of codons in mRNA with the order of amino acids in the synthesized polypeptide chain.

A codon is a triplet of nucleotides that codes for 1 amino acid.

7. Pointless It does not code for any amino acid. Protein synthesis at this site is interrupted.

IN last years it turned out that the universality of the genetic code is violated in mitochondria, four codons in mitochondria have changed their meaning, for example, the codon UGA - answers to tryptophan instead of "STOP" - the cessation of protein synthesis. AUA - corresponds to methionine - instead of "isoleucine".

The discovery of new codons in mitochondria may serve as evidence that the code evolved and that it did not immediately become so.

Let hereditary information from a gene to a protein molecule can be expressed schematically.

DNA - RNA - protein

Studying chemical composition cells showed that different tissues of the same organism contain a different set of protein molecules, although they have the same number of chromosomes and the same genetic hereditary information.

We note the following circumstance: despite the presence in each cell of all the genes of the whole organism, very few genes work in a single cell - from tenths to several percent of the total number. The rest of the areas are "silent", they are blocked by special proteins. This is understandable, why, for example, hemoglobin genes work in nerve cell? Just as the cell dictates which genes to be silent and which to work, it must be assumed that there is some perfect mechanism in the cell that regulates the activity of genes, which determines which genes in this moment should be active and how should be in an inactive (repressive) state. Such a mechanism, according to the French scientists F. Jacobo and J. Monod, was called induction and repression.

Induction- stimulation of protein synthesis.

Repression- inhibition of protein synthesis.

Induction ensures the work of those genes that synthesize a protein or enzyme, and which is necessary at this stage of the cell's life.

In animals, cell membrane hormones play an important role in the process of gene regulation; in plants, environmental conditions and other highly specialized inductors.

Example: when thyroid hormone is added to the medium, a rapid transformation of tadpoles into frogs takes place.

For the normal functioning of the bacteria E (Coli) is necessary milk sugar(lactose). If the environment in which the bacteria are located does not contain lactose, these genes are in a repressive state (i.e. they do not function). The lactose introduced into the medium is an inductor, including the genes responsible for the synthesis of enzymes. After the removal of lactose from the medium, the synthesis of these enzymes stops. Thus, the role of a repressor can be played by a substance that is synthesized in the cell, and if its content exceeds the norm or it is used up.

Involved in protein or enzyme synthesis Various types genes.

All genes are in the DNA molecule.

Their functions are not the same:

- structural - genes that affect the synthesis of an enzyme or protein are located in the DNA molecule sequentially one after another in the order of their influence on the course of the synthesis reaction, or you can also say structural genes - these are genes that carry information about the amino acid sequence.

- acceptor- genes do not carry hereditary information about the structure of the protein, they regulate the work of structural genes.

Before a group of structural genes is a common gene for them - operator, and in front of him promoter. In general, this functional group is called feathered.

The entire group of genes of one operon is included in the synthesis process and is switched off from it simultaneously. Turning on and off structural genes is the essence of the entire process of regulation.

The function of switching on and off is performed by a special section of the DNA molecule - gene operator. The gene operator is the starting point of protein synthesis or, as they say, "reading" of genetic information. further in the same molecule at some distance is a gene - a regulator, under the control of which a protein called a repressor is produced.

From all of the above, it can be seen that protein synthesis is very difficult. The cell genetic system, using the mechanisms of repression and induction, can receive signals about the need to start and end the synthesis of a particular enzyme and carry out this process at a given rate.

The problem of regulating the action of genes in higher organisms is of great practical importance in animal husbandry and medicine. Establishment of the factors regulating protein synthesis would open up wide possibilities for controlling ontogeny, creating highly productive animals, as well as animals resistant to hereditary diseases.

Control questions:

1. Name the properties of genes.

2. What is a gene?

3. Name what biological significance DNA, RNA.

4. Name the stages of protein synthesis

5. List the properties of the genetic code.

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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its inherent proteins.

Each cell contains thousands of proteins, including those inherent only to this type of cell. Since all proteins are destroyed sooner or later in the course of life, the cell must continuously synthesize proteins to restore its membranes, 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.

Protein synthesis requires a lot of energy.

The source of this energy, as for all cellular processes, is ATP. The diversity of protein functions is determined by their primary structure, i.e. the sequence of amino acids in their molecule. In turn, hereditary information 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 DNA 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.

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, an i-RNA chain is formed, which is an exact copy of the second DNA chain (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 the ribosome, a separate type of tRNA is needed. 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.

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, the 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.

Gene. Genetic code. Triplet. Codon. Transcription. Anticodon. Broadcast. Polysome.

1. What is transcription?
2. What is a broadcast?
3. Where does transcription and translation take place?
4. What is a polysome?
5. Why in various cells of any organism, only part of the genes “works”?
6. Can there be a cell that is not capable of independent synthesis of substances.

Kamensky A. A., Kriksunov E. V., Pasechnik V. V. Biology Grade 9
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