Process of protein synthesis object. Protein synthesis in the cell - description, functions of the process

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

Proteins - what are they and what are they for?

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

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

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

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

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

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

Where does synthesis take place?

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

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

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

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

Necessary materials - amino acids, place of synthesis - ribosome

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

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

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

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

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

Such different and important ribonucleic acids

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

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

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

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

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

Summary table of the main participants of the broadcast

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

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

Initiation - the beginning of the process

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

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

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

Elongation - middle of synthesis

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

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

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

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

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

Termination

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

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

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

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

How to find out more about the broadcast

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

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

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

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

What is protein biosynthesis

First, you should familiarize 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 plays an important role in all living cells. Let’s not forget about the complex biochemical composition.

Transcription and broadcast

These are the two most important steps of biosynthesis.

Transcription from Latin means “rewriting” - DNA is used as a matrix, so three types of RNA are synthesized (matrix/messenger, transport, ribosomal ribonucleic acids). The reaction is carried out using a polymerase (RNA) and using a large amount of adenosine triphosphate.

There are two main actions:

1. Designation of the end and beginning of translation by the addition of mRNA.
2. An event carried out due to splicing, which in turn removes non-informational RNA sequences, thereby reducing the mass of the template ribonucleic acid by 10 times.

Broadcast from Latin means “translation” - mRNA is used as a matrix, polypeptide chains are synthesized.

The broadcast includes three stages, which could be presented in table form:

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

Protein biosynthesis scheme

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 > PHK > protein.

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

The next stop for mRNA is the ribosome, where the synthesis itself occurs. This happens through translation, the formation of a polypeptide chain. After this run-of-the-mill scheme, the resulting protein is transported to different places to perform specific 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 with its own function:

1. Informational – the role of the matrix.
2. Transport - adding amino acids, determining codons.
3. Ribosomal - the formation of ribosomes that support mRNA.
4. Transport – synthesis of the polypeptide chain.

What cell components are involved in protein biosynthesis?

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

The second stage involves the following components: mRNA, tRNA, ribosomes, nucleotides and peptides.

What are the features of protein biosynthesis reactions in a cell?

The list of features of biosynthesis reactions includes:

1. Use of ATP energy for chemical reactions.
2. There are enzymes whose task is to speed up reactions.
3. The reaction has a matrix character, since the protein is synthesized on mRNA.

Signs of protein biosynthesis in the cell

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

1. The first of these is that enzymes are present, without which the process itself would not be possible.
2. All three types of RNA are involved, from this we can conclude that RNA plays a central role.
3. The formation of molecules is carried out by monomers, namely amino acids.
4. It is also worth noting that the specificity of a particular protein is determined by the arrangement of amino acids.

Conclusion

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

First, establish the sequence of steps in protein biosynthesis, starting with transcription. The entire sequence of processes occurring during the synthesis of protein molecules can be combined into 2 stages:

1. Transcription.

2. Broadcast.

The structural units of hereditary information are genes - sections of the DNA molecule that encode the synthesis of a specific protein. In terms of chemical organization, the material of heredity and variability in pro- and eukaryotes is not fundamentally different. The genetic material in them is presented in the DNA molecule; the principle of recording hereditary information and the genetic code are also common. The same amino acids in pro- and eukaryotes are encrypted by the same codons.

The genome of modern prokaryotic cells is characterized by a relatively small size; the DNA of E. coli has the shape of a ring, about 1 mm long. It contains 4 x 10 6 nucleotide pairs, forming about 4000 genes. In 1961, F. Jacob and J. Monod discovered the cistronic, or continuous organization of prokaryotic genes, which consist entirely of coding nucleotide sequences, and they are entirely realized during protein synthesis. The hereditary material of the DNA molecule of prokaryotes is located directly in the cytoplasm of the cell, where the tRNA and enzymes necessary for gene expression are also located. Expression is the functional activity of genes, or the expression of genes. Therefore, mRNA synthesized from DNA can immediately perform the function of a template in the process of translation of protein synthesis.

The eukaryotic genome contains significantly more hereditary material. In humans, the total length of DNA in the diploid set of chromosomes is about 174 cm. It contains 3 x 10 9 pairs of nucleotides and includes up to 100,000 genes. In 1977, discontinuity in the structure of most eukaryotic genes was discovered, called the “mosaic” gene. It is characterized by coding nucleotide sequences exonic And intronic plots. Only information from exons is used for protein synthesis. The number of introns varies in different genes. It has been established that the chicken ovalbumin gene includes 7 introns, and the mammalian procollagen gene includes 50. The functions of silent DNA introns have not been fully elucidated. It is assumed that they provide: 1) structural organization of chromatin; 2) some of them are obviously involved in the regulation of gene expression; 3) introns can be considered a store of information for variability; 4) they can play a protective role, taking on the action of mutagens.

Transcription

The process of rewriting information in the cell nucleus from a section of a DNA molecule to an mRNA molecule (mRNA) is called transcription(Latin Transcriptio - rewriting). The primary gene product, mRNA, is synthesized. This is the first stage of protein synthesis. At the corresponding DNA site, the enzyme RNA polymerase recognizes the sign for the start of transcription - promotr. The starting point is the first DNA nucleotide that is incorporated into the RNA transcript by the enzyme. As a rule, coding regions begin with the codon AUG; sometimes in bacteria GUG is used. When RNA polymerase binds to the promoter, local unwinding of the DNA double helix occurs and one of the strands is copied according to the principle of complementarity. mRNA is synthesized, its assembly speed reaches 50 nucleotides per second. As RNA polymerase moves, the mRNA chain grows, and when the enzyme reaches the end of the copying region - terminator, the mRNA moves away from the template. The DNA double helix behind the enzyme is restored.

Transcription of prokaryotes occurs in the cytoplasm. Due to the fact that DNA consists entirely of coding nucleotide sequences, therefore the synthesized mRNA immediately acts as a template for translation (see above).

Transcription of mRNA in eukaryotes occurs in the nucleus. It begins with the synthesis of large molecules - precursors (pro-mRNA), called immature, or nuclear RNA. The primary product of the gene - pro-mRNA is an exact copy of the transcribed section of DNA, includes exons and introns. The process of forming mature RNA molecules from precursors is called processing. mRNA maturation occurs by splicing- these are cut by enzymes restriction enzyme introns and connection of regions with transcribed exon sequences by ligase enzymes. (Fig.). Mature mRNA is much shorter than the precursor molecules of pro-mRNA; the sizes of introns in them vary from 100 to 1000 nucleotides or more. Introns account for about 80% of all immature mRNA.

It has now been proven possible alternative splicing, in which nucleotide sequences can be removed from one primary transcript in different parts of it and several mature mRNAs will be formed. This type of splicing is typical in the immunoglobulin gene system in mammals, which makes it possible to form different types of antibodies based on one mRNA transcript.

Once processing is complete, the mature mRNA is selected before exiting the nucleus. It has been established that only 5% of mature mRNA enters the cytoplasm, and the rest is cleaved in the nucleus.

Broadcast

Translation (Latin Translatio - transfer, transfer) is the translation of information contained in the nucleotide sequence of an mRNA molecule into the amino acid sequence of a polypeptide chain (Fig. 10). This is the second stage of protein synthesis. The transfer of mature mRNA through the pores of the nuclear envelope is produced by special proteins that form a complex with the RNA molecule. In addition to transporting mRNA, these proteins protect mRNA from the damaging effects of cytoplasmic enzymes. In the translation process, tRNA plays a central role; they ensure the exact match of the amino acid to the code of the mRNA triplet. The translation-decoding process occurs in ribosomes and is carried out in the direction from 5 to 3. The complex of mRNA and ribosomes is called a polysome.

During translation, three phases can be distinguished: initiation, elongation and termination.

Initiation.

At this stage, the entire complex involved in the synthesis of the protein molecule is assembled. The two ribosomal subunits are united at a certain section of the mRNA, the first aminoacyl-tRNA is attached to it, and this sets the information reading frame. In any m-RNA molecule there is a region that is complementary to the r-RNA of the small ribosomal subunit and is specifically controlled by it. Next to it is the initiating start codon AUG, which encodes the amino acid methionine. The initiation phase ends with the formation of a complex: ribosome, -mRNA- initiating aminoacyl-tRNA.

Elongation

— it includes all reactions from the moment of formation of the first peptide bond to the addition of the last amino acid. The ribosome has two sites for binding two tRNA molecules. In one region, the peptidyl (P), there is the first t-RNA with the amino acid methionine, and the synthesis of any protein molecule begins with it. The second tRNA molecule enters the second section of the ribosome, the aminoacyl section (A), and attaches to its codon. A peptide bond is formed between methionine and the second amino acid. The second tRNA moves along with its mRNA codon to the peptidyl center. The movement of t-RNA with a polypeptide chain from the aminoacyl center to the peptidyl center is accompanied by the advancement of the ribosome along the m-RNA by a step corresponding to one codon. The T-RNA that delivered methionine returns to the cytoplasm, and the amnoacyl center is released. It receives a new t-RNA with an amino acid encrypted by the next codon. A peptide bond is formed between the third and second amino acids and the third t-RNA, together with the m-RNA codon, moves to the peptidyl center. The process of elongation, lengthening of the protein chain. It continues until one of the three codons that do not code for amino acids enters the ribosome. This is a terminator codon and there is no corresponding tRNA for it, so none of the tRNAs can take a place in the aminoacyl center.

Termination

– completion of polypeptide synthesis. It is associated with the recognition by a specific ribosomal protein of one of the termination codons (UAA, UAG, UGA) when it enters the aminoacyl center. A special termination factor is attached to the ribosome, which promotes the separation of ribosomal subunits and the release of the synthesized protein molecule. Water is added to the last amino acid of the peptide and its carboxyl end is separated from the tRNA.

The assembly of the peptide chain occurs at high speed. In bacteria at a temperature of 37°C, it is expressed in the addition of 12 to 17 amino acids per second to the polypeptide. In eukaryotic cells, two amino acids are added to a polypeptide every second.

The synthesized polypeptide chain then enters the Golgi complex, where the construction of the protein molecule is completed (the second, third, and fourth structures appear sequentially). This is where protein molecules combine with fats and carbohydrates.

The entire process of protein biosynthesis is presented in the form of a diagram: DNA ® pro mRNA ® mRNA ® polypeptide chain ® protein ® complexation of proteins and their transformation into functionally active molecules.

The stages of implementation of hereditary information also proceed in a similar way: first it is transcribed into the nucleotide sequence of mRNA, and then translated into the amino acid sequence of a polypeptide on ribosomes with the participation of tRNA.

Transcription in eukaryotes is carried out under the action of three nuclear RNA polymerases. RNA polymerase 1 is located in the nucleolus and is responsible for the transcription of rRNA genes. RNA polymerase 2 is found in nuclear sap and is responsible for the synthesis of precursor mRNA. RNA polymerase 3 is a small fraction in the nuclear sap that synthesizes small rRNA and tRNA. RNA polymerases specifically recognize the nucleotide sequence of a transcription promoter. Eukaryotic mRNA is first synthesized as a precursor (pro-mRNA), and information from exons and introns is transferred to it. The synthesized mRNA is larger than necessary for translation and is less stable.

During the maturation of the mRNA molecule, introns are excised using restriction enzymes, and exons are stitched together using ligase enzymes. The maturation of mRNA is called processing, and the joining of exons is called splicing. Thus, mature mRNA contains only exons and is much shorter than its predecessor, pro-mRNA. The sizes of introns vary from 100 to 10,000 nucleotides or more. Intons account for about 80% of all immature mRNA. The possibility of alternative splicing has now been proven, in which nucleotide sequences can be removed from one primary transcript in different parts of it and several mature mRNAs will be formed. This type of splicing is typical in the immunoglobulin gene system in mammals, which makes it possible to form different types of antibodies based on one mRNA transcript. Upon completion of processing, the mature mRNA is selected before being released into the cytoplasm from the nucleus. It has been established that only 5% of the mature mRNA enters, and the rest is cleaved in the nucleus. The transformation of primary transcriptons of eukaryotic genes, associated with their exon-intron organization, and in connection with the transition of mature mRNA from the nucleus to the cytoplasm, determines the features of the implementation of genetic information of eukaryotes. Therefore, the eukaryotic mosaic gene is not a cistron gene, since not the entire DNA sequence is used for protein synthesis.

The set of reactions of biological synthesis is called plastic exchange, or assimilation. The name of this type of exchange reflects its essence: from simple substances entering the cell from the outside, substances similar to the substances of the cell are formed.

Let's consider one of the most important forms of plastic metabolism - protein biosynthesis. The entire variety of properties of proteins is ultimately determined by the primary structure, i.e., the sequence of amino acids. A huge number of unique combinations of amino acids selected by evolution are reproduced by the synthesis of nucleic acids with a sequence of nitrogenous bases that corresponds to the sequence of amino acids in proteins. Each amino acid in the polypeptide chain corresponds to a combination of three nucleotides - a triplet.

The process of implementing hereditary information in biosynthesis is carried out with the participation of three types of ribonucleic acids: information (template) - mRNA (mRNA), ribosomal - rRNA and transport - tRNA. All ribonucleic acids are synthesized in the corresponding sections of the DNA molecule. They are much smaller in size than DNA and represent a single chain of nucleotides. Nucleotides contain a phosphoric acid residue (phosphate), a pentose sugar (ribose) and one of four nitrogenous bases - adenine, cytosine, guanine and uracil. The nitrogenous base, uracil, is complementary to adenine.

The biosynthesis process is complex and includes a number of stages - transcription, splicing and translation.

The first stage (transcription) occurs in the cell nucleus: mRNA is synthesized in a section of a specific gene on a DNA molecule. This synthesis is carried out with the participation of a complex of enzymes, the main of which is DNA-dependent RNA polymerase, which attaches to the starting point of the DNA molecule, unwinds the double helix and, moving along one of the strands, synthesizes a complementary strand of mRNA next to it. As a result of transcription, mRNA contains genetic information in the form of a sequential alternation of nucleotides, the order of which is exactly copied from the corresponding section (gene) of the DNA molecule.

Further studies showed that during the transcription process, the so-called pro-mRNA is synthesized - the precursor of mature mRNA involved in translation. Pro-mRNA is significantly larger and contains fragments that do not code for the synthesis of the corresponding polypeptide chain. In DNA, along with regions encoding rRNA, tRNA and polypeptides, there are fragments that do not contain genetic information. They are called introns in contrast to the coding fragments, which are called exons. Introns are found in many parts of DNA molecules. For example, one gene, the DNA section encoding chicken ovalbumin, contains 7 introns, and the rat serum albumin gene contains 13 introns. The length of the intron varies - from two hundred to a thousand pairs of DNA nucleotides. Introns are read (transcribed) at the same time as exons, so pro-mRNA is much longer than mature mRNA. In the nucleus, introns are cut out in pro-mRNA by special enzymes, and exon fragments are “spliced” together in a strict order. This process is called splicing. During the splicing process, mature mRNA is formed, which contains only the information that is necessary for the synthesis of the corresponding polypeptide, that is, the informative part of the structural gene.

The meaning and functions of introns are still not entirely clear, but it has been established that if only exon sections are read in DNA, mature mRNA is not formed. The splicing process was studied using the example of the ovalbumin gene. It contains one exon and 7 introns. First, pro-mRNA containing 7700 nucleotides is synthesized on DNA. Then in pro-mRNA the number of nucleotides decreases to 6800, then to 5600, 4850, 3800, 3400, etc. until 1372 nucleotides corresponding to the exon. Containing 1372 nucleotides, mRNA leaves the nucleus into the cytoplasm, enters the ribosome and synthesizes the corresponding polypeptide.

The next stage of biosynthesis - translation - occurs in the cytoplasm on ribosomes with the participation of tRNA.

Transfer RNAs are synthesized in the nucleus, but function in a free state in the cell cytoplasm. One tRNA molecule contains 76-85 nucleotides and has a rather complex structure, reminiscent of a clover leaf. Three sections of tRNA are of particular importance: 1) an anticodon, consisting of three nucleotides, which determines the site of attachment of the tRNA to the corresponding complementary codon (mRNA) on the ribosome; 2) a region that determines the specificity of tRNA, the ability of a given molecule to attach only to a specific amino acid; 3) acceptor site to which the amino acid is attached. It is the same for all tRNAs and consists of three nucleotides - C-C-A. The addition of an amino acid to tRNA is preceded by its activation by the enzyme aminoacyl-tRNA synthetase. This enzyme is specific for each amino acid. The activated amino acid is attached to the corresponding tRNA and delivered to the ribosome.

The central place in translation belongs to ribosomes - ribonucleoprotein organelles of the cytoplasm, which are present in large numbers in it. The sizes of ribosomes in prokaryotes are on average 30x30x20 nm, in eukaryotes - 40x40x20 nm. Typically, their sizes are determined in sedimentation units (S) - the rate of sedimentation during centrifugation in an appropriate medium. In the bacterium Escherichia coli, the ribosome has a size of 70S and consists of two subunits, one of which has a constant of 30S, the second 50S, and contains 64% ribosomal RNA and 36% protein.

The mRNA molecule leaves the nucleus into the cytoplasm and attaches to the small ribosomal subunit. Translation begins with the so-called start codon (initiator of synthesis) - A-U-G-. When tRNA delivers an activated amino acid to the ribosome, its anticodon is hydrogen bonded to the nucleotides of the complementary codon of the mRNA. The acceptor end of the tRNA with the corresponding amino acid is attached to the surface of the large ribosomal subunit. After the first amino acid, another tRNA delivers the next amino acid, and thus the polypeptide chain is synthesized on the ribosome. An mRNA molecule usually works on several (5-20) ribosomes at once, connected into polysomes. The beginning of the synthesis of a polypeptide chain is called initiation, its growth is called elongation. The sequence of amino acids in a polypeptide chain is determined by the sequence of codons in the mRNA. Synthesis of the polypeptide chain stops when one of the terminator codons appears on the mRNA - UAA, UAG or UGA. The end of the synthesis of a given polypeptide chain is called termination.

It has been established that in animal cells the polypeptide chain lengthens by 7 amino acids in one second, and the mRNA advances on the ribosome by 21 nucleotides. In bacteria, this process occurs two to three times faster.

Consequently, the synthesis of the primary structure of the protein molecule - the polypeptide chain - occurs on the ribosome in accordance with the order of alternation of nucleotides in the template ribonucleic acid - mRNA. It does not depend on the structure of the ribosome.

Protein biosynthesis occurs in every living cell. It is most active in young growing cells, where proteins are synthesized to build their organelles, as well as in secretory cells, where enzyme proteins and hormone proteins are synthesized.

The main role in determining the structure of proteins belongs to DNA. A piece of DNA containing information about the structure of one protein is called a gene. A DNA molecule contains several hundred genes. The DNA molecule contains a code for the sequence of amino acids in a protein in the form of specifically combined nucleotides. The DNA code was almost completely deciphered. Its essence is as follows. Each amino acid corresponds to a section of a DNA chain consisting of three adjacent nucleotides.

For example, the T-T-T section corresponds to the amino acid lysine, the A-C-A section corresponds to cystine, C-A-A to valine, etc. There are 20 different amino acids, the number of possible combinations of 4 nucleotides of 3 is 64. Therefore , triplets are abundantly sufficient to encode all amino acids.

Protein synthesis is a complex multi-stage process, representing a chain of synthetic reactions proceeding according to the principle of matrix synthesis.

Since DNA is located in the cell nucleus, and protein synthesis occurs in the cytoplasm, there is an intermediary that transfers information from DNA to ribosomes. This messenger is mRNA. :

In protein biosynthesis, the following stages are determined, occurring in different parts of the cell:

1. The first stage, i-RNA synthesis, occurs in the nucleus, during which the information contained in the DNA gene is transcribed into i-RNA. This process is called transcription (from the Latin “transcript” - rewriting).
2. At the second stage, amino acids are combined with tRNA molecules, which sequentially consist of three nucleotides - anticodons, with the help of which their triplet codon is determined.
3. The third stage is the process of direct synthesis of polypeptide bonds, called translation. It occurs in ribosomes.
4. At the fourth stage, the formation of the secondary and tertiary structure of the protein occurs, that is, the formation of the final structure of the protein.

Thus, in the process of protein biosynthesis, new protein molecules are formed in accordance with the exact information contained in the DNA. This process ensures the renewal of proteins, metabolic processes, cell growth and development, that is, all the life processes of the cell.

Chromosomes (from the Greek “chroma” - color, “soma” - body) are very important structures of the cell nucleus. They play a major role in the process of cell division, ensuring the transmission of hereditary information from one generation to another. They are thin strands of DNA linked to proteins. The strands are called chromatids, consisting of DNA, basic proteins (histones) and acidic proteins.

In a non-dividing cell, chromosomes fill the entire volume of the nucleus and are not visible under a microscope. Before division begins, DNA spiralization occurs and each chromosome becomes visible under a microscope. During spiralization, chromosomes are shortened tens of thousands of times. In this state, the chromosomes look like two identical strands (chromatids) lying next to each other, connected by a common section - the centromere.

Each organism is characterized by a constant number and structure of chromosomes. In somatic cells, chromosomes are always paired, that is, in the nucleus there are two identical chromosomes that make up one pair. Such chromosomes are called homologous, and paired sets of chromosomes in somatic cells are called diploid.

Thus, the diploid set of chromosomes in humans consists of 46 chromosomes, forming 23 pairs. Each pair consists of two identical (homologous) chromosomes.

The structural features of chromosomes make it possible to distinguish them into 7 groups, which are designated by the Latin letters A, B, C, D, E, F, G. All pairs of chromosomes have serial numbers.

Men and women have 22 pairs of identical chromosomes. They are called autosomes. A man and a woman differ in one pair of chromosomes, which are called sex chromosomes. They are designated by letters - large X (group C) and small Y (group C). In the female body there are 22 pairs of autosomes and one pair (XX) of sex chromosomes. Men have 22 pairs of autosomes and one pair (XY) of sex chromosomes.

Unlike somatic cells, germ cells contain half the set of chromosomes, that is, they contain one chromosome from each pair! This set is called haploid. The haploid set of chromosomes arises during cell maturation.