Who discovered protein biosynthesis. Main site of protein biosynthesis

Information about the primary structure of a protein molecule is contained in DNA, which is located in the nucleus of a eukaryotic cell. One strand of DNA can contain information about many proteins. A gene is a section (fragment) of DNA that carries information about the structure of a single protein. A DNA molecule contains a code for the sequence of amino acids in a protein in the form of a specific sequence of nucleotides. In this case, each amino acid in the future protein molecule corresponds to a section of three nucleotides (triplet) in the DNA molecule.

Process protein biosynthesis includes a series of consecutive events:

DNA replication (in the cell nucleus) transcription messenger RNA (in the cytoplasm with the help of ribosomes) translation protein

Synthesis of messenger RNA (i-RNA) occurs in the nucleus. It is carried out along one of the DNA strands with the help of enzymes and taking into account the principle of complementarity of nitrogenous bases. The process of rewriting the information contained in the DNA genes to the synthesized mRNA molecule is called transcription. Obviously, the information is rewritten in the form of a sequence of RNA nucleotides. The DNA strand in this case acts as a template. In the RNA molecule, in the process of its formation, instead of the nitrogenous base - thymine, uration is included.

G - C - A - A - C - T - a fragment of one of the chains of the DNA molecule
- C - G - U - U - G - A - a fragment of the messenger RNA molecule.

RNA molecules are individual, each of them carries information about one gene. Next, the mRNA molecules leave the cell nucleus through the pores of the nuclear envelope and are directed to the cytoplasm to the ribosomes. Amino acids are also delivered here with the help of transport RNA (t-RNA). The tRNA molecule consists of 70–80 nucleotides. General form molecules resembles a clover leaf.

At the "top" is atikodon (coding triplet of nucleotides), which corresponds to a specific amino acid. Therefore, each amino acid has its own specific t-RNA. The process of assembling a protein molecule takes place in ribosomes and is called broadcast. Several ribosomes are sequentially located on one mRNA molecule. Two mRNA triplets can fit in the functional center of each ribosome. The code triplet of nucleotides - a t-RNA molecule that has approached the site of protein synthesis, corresponds to a triplet of nucleotides of an i-RNA located in this moment at the functional center of the ribosome. Then the ribosome along the mRNA chain makes a step equal to three nucleotides. separates from t-RNA and becomes a chain of protein monomers. The released t-RNA goes aside and after a while can reconnect with a certain acid, which will be transported to the site. protein synthesis. Thus, the sequence of nucleotides in the DNA triplet corresponds to the sequence of nucleotides in the mRNA triplet.

In the most complex process of protein biosynthesis, the functions of many substances and organelles of the cell are realized.

Protein biosynthesis occurs in all organs, tissues and cells. The largest number protein is synthesized in the liver. Ribosomes carry out protein synthesis. By chemical nature, ribosomes are nucleoproteins consisting of RNA (50-65%) and proteins (35-50%). are constituent parts granular where biosynthesis and movement of synthesized protein molecules take place.

Ribosomes in a cell are in the form of clusters from 3 to 100 units - polysomes (polyribosomes). Ribosomes are usually interconnected by a kind of thread, visible under an electron microscope - i-RNA.

Each ribosome is able to independently synthesize one polypeptide chain, a group - several such chains and protein molecules.

Stages of protein biosynthesis

Activation of amino acids. Amino acids enter the hyaloplasm from the intercellular fluid as a result of diffusion, osmosis or active transfer. Each type of amino and imino acids interacts with an individual enzyme - aminoacyl synthetase. The reaction is activated by magnesium, manganese, cobalt cations. An activated amino acid is produced.

Protein biosynthesis (second stage) - interaction and connection of an activated amino acid with t-RNA. Activated amino acids (aminoacyladenylate) are transferred by enzymes to t-RNA in the cytoplasm. The process is catalyzed by aminoacyl-RNA synthetases. The amino acid residue is connected by a carboxyl group to the hydroxyl of the second carbon atom of the ribose of the t-RNA nucleotide.

Protein biosynthesis (third stage) - transportation of the activated amino acid complex with t-RNA into the ribosomes of the cell. The amino acid is bound to tRNA and transferred from the hyaloplasm to the ribosome. The process is catalyzed by specific enzymes, of which there are at least 20 in the body. Some amino acids are transported by several t-RNAs (for example, valine and leucine are transported by three t-RNAs). This process uses the energy of GTP and ATP. The fourth stage of biosynthesis is characterized by the binding of aminoacyl-t-RNA to the mRNA-ribosome complex. Aminoacyl-t-RNA, approaching the ribosome, interacts with mRNA. Each tRNA has a three-nucleotide region called an anticodon. In mRNA, it corresponds to a section with three nucleotides - a codon. Each codon corresponds to a tRNA anticodon and one amino acid. During biosynthesis, amino acids are attached to ribosomes in the form of aminoacyl-tRNA, which are subsequently formed into a polypeptide chain in the order determined by the placement of codons in mRNA.

The next step in protein biosynthesis is the initiation of the polypeptide chain. After two adjacent aminoacyl-t-RNAs have joined the codons of the mRNA with their anticodons, conditions are created for the synthesis of the polypeptide chain. A peptide bond is formed. These processes are catalyzed by peptide synthetases, activated by Mg cations and protein initiation factors F1, F2, F3. source chemical energy is guanosine triphosphate.

Termination of the polypeptide chain. The ribosome, on the surface of which the polypeptide chain was synthesized, reaches the end of the mRNA chain, and then “jumps off” from it. A new ribosome joins the opposite end of the mRNA in its place, which synthesizes the next polypeptide molecule. The polypeptide chain is detached from the ribosome and released into the hyaloplasm. This reaction is carried out with the help of a specific release factor (factor R), which is connected to the ribosome and facilitates the hydrolysis of the ester bond between the polypeptide and t-RNA.

In the hyaloplasm, simple and secondary, tertiary, and in many cases, molecules are formed from polypeptide chains. Thus, protein synthesis occurs in the cell.

protein biosynthesis.

Plastic metabolism (assimilation or anabolism) is a set of reactions of biological synthesis. The name of this type of exchange reflects its essence: from the substances entering the cell from the outside, substances similar to the substances of the cell are formed.

Consider one of the most important forms of plastic metabolism - protein biosynthesis. Biosynthesis of proteins carried out in all pro- and eukaryotic cells. Information about the primary structure (order of amino acids) of a protein molecule is encoded by the sequence of nucleotides in the corresponding section of the DNA molecule - the gene.

A gene is a section of a DNA molecule that determines the order of amino acids in a protein molecule. Therefore, the order of amino acids in the polypeptide depends on the order of nucleotides in the gene, i.e. its primary structure, on which all other structures, properties and functions of the protein molecule depend in turn.

The system of recording genetic information in DNA (and - RNA) in the form of a specific sequence of nucleotides is called genetic code. Those. a unit of the genetic code (codon) is a triplet of nucleotides in DNA or RNA that codes for one amino acid.

In total, the genetic code includes 64 codons, of which 61 are coding and 3 are non-coding (terminator codons indicating the end of the translation process).

Terminator codons in and - RNA: UAA, UAG, UGA, in DNA: ATT, ATC, ACT.

The beginning of the translation process is determined by the initiator codon (AUG, in DNA - TAC), encoding the amino acid methionine. This codon is the first to enter the ribosome. Subsequently, methionine, if it is not provided as the first amino acid of this protein, is cleaved off.

The genetic code has characteristic properties.

1. Universality - the code is the same for all organisms. The same triplet (codon) in any organism codes for the same amino acid.

2. Specificity - each codon codes for only one amino acid.

3. Degeneracy - most amino acids can be encoded by several codons. The exception is 2 amino acids - methionine and tryptophan, which have only one codon variant each.

4. Between the genes there are "punctuation marks" - three special triplets (UAA, UAG, UGA), each of which indicates the termination of the synthesis of the polypeptide chain.

5. There are no “punctuation marks” inside the gene.

In order for a protein to be synthesized, information about the sequence of nucleotides in its primary structure must be delivered to the ribosomes. This process includes two stages - transcription and translation.

Transcription(rewriting) of information occurs by synthesis on one of the DNA molecule chains of a single-stranded RNA molecule, the nucleotide sequence of which exactly corresponds to the nucleotide sequence of the matrix - the DNA polynucleotide chain.

She (and - RNA) is an intermediary that transmits information from DNA to the assembly site of protein molecules in the ribosome. Synthesis and - RNA (transcription) occurs as follows. An enzyme (RNA polymerase) cleaves a double strand of DNA, and on one of its strands (coding) RNA nucleotides line up according to the principle of complementarity. The i-RNA molecule synthesized in this way (matrix synthesis) enters the cytoplasm, and small subunits of ribosomes are strung on one end of it.

The second step in protein synthesis is broadcast- this is the translation of the nucleotide sequence in the molecule and - RNA into the amino acid sequence in the polypeptide. In prokaryotes that do not have a well-formed nucleus, ribosomes can bind to a newly synthesized i-RNA molecule immediately after its separation from DNA or even before its synthesis is completed. In eukaryotes, the u-RNA must first be delivered through the nuclear envelope into the cytoplasm. The transfer is carried out by special proteins that form a complex with the i-RNA molecule. In addition to their transport functions, these proteins protect i-RNA from the damaging effects of cytoplasmic enzymes.

In the cytoplasm, a ribosome enters one of the ends of the i-RNA (namely, the one from which the synthesis of the molecule in the nucleus begins) and the synthesis of the polypeptide begins. As it moves along the RNA molecule, the ribosome translates triplet after triplet, sequentially adding amino acids to the growing end of the polypeptide chain. The exact correspondence of the amino acid to the triplet code and - RNA is provided by t - RNA.

Transfer RNAs (t - RNA) "bring" amino acids to the large subunit of the ribosome. The t-RNA molecule has complex configuration. In some parts of it, hydrogen bonds are formed between complementary nucleotides, and the molecule is shaped like a clover leaf. At its apex there is a triplet of free nucleotides (anticodon), which corresponds to a certain amino acid, and the base serves as the site of attachment of this amino acid (Fig. 1).

Rice. one. Scheme of the structure of transfer RNA: 1 - hydrogen bonds; 2 - anticodon; 3 - the place of attachment of the amino acid.

Each t-RNA can only carry its own amino acid. T-RNA is activated by special enzymes, attaches its amino acid and transports it to the ribosome. Inside the ribosome at any given moment there are only two codons of mRNA. If the tRNA anticodon is complementary to the mRNA codon, then the tRNA with the amino acid is temporarily attached to the mRNA. A second t-RNA is attached to the second codon, carrying its own amino acid. Amino acids are located side by side in the large subunit of the ribosome, and with the help of enzymes, a peptide bond is established between them. At the same time, the bond between the first amino acid and its t-RNA is broken, and the t-RNA leaves the ribosome after the next amino acid. The ribosome moves one triplet and the process repeats. This is how a polypeptide molecule gradually grows, in which amino acids are arranged in strict accordance with the order of their coding triplets (matrix synthesis) (Fig. 2).

Rice. 2. Protein bisynthetic scheme: 1 - mRNA; 2 - ribosome subunits; 3 - t-RNA with amino acids; 4 - t-RNA without amino acids; 5 - polypeptide; 6 - codon i-RNA; 7- tRNA anticodon.

One ribosome is capable of synthesizing a complete polypeptide chain. However, often several ribosomes move along one mRNA molecule. Such complexes are called polyribosomes. After completion of the synthesis, the polypeptide chain is separated from the matrix - the mRNA molecule, coiled into a spiral and acquires its characteristic (secondary, tertiary or quaternary) structure. Ribosomes work very efficiently: within 1s, a bacterial ribosome forms a polypeptide chain of 20 amino acids.

Genetic information in all organisms is stored in the form of a specific sequence of DNA nucleotides (or RNA for RNA-containing viruses). Prokaryotes contain genetic information in the form of a single DNA molecule. In eukaryotic cells, the genetic material is distributed in several DNA molecules organized into chromosomes.

DNA consists of coding and non-coding regions. Coding regions code for RNA. Non-coding regions of DNA perform structural function, allowing regions of genetic material to be packaged in a particular way, or regulatory function, participating in the inclusion of genes that direct protein synthesis.

Genes are the coding regions of DNA. Gene- a section of a DNA molecule encoding the synthesis of one mRNA (and, accordingly, a polypeptide), rRNA or tRNA.

The region of the chromosome where the gene is located is called locus. The set of genes in the cell nucleus is genotype, the totality of genes of the haploid set of chromosomes - genome, a set of extranuclear DNA genes (mitochondria, plastids, cytoplasm) - plasmon.

The implementation of the information recorded in the genes through the synthesis of proteins is called expression(manifestation) of genes. Genetic information is stored in the form of a certain sequence of DNA nucleotides, and is realized in the form of a sequence of amino acids in a protein. Intermediaries, carriers of information, are RNA, i.e. the implementation of genetic information occurs as follows:

DNA → RNA → protein

Stages of protein biosynthesis

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

Transcription(from lat. transcription- rewriting) - the synthesis of RNA using DNA as a template. As a result, mRNA, tRNA and rRNA are formed. The transcription process requires a large expenditure of energy in the form of ATP and is carried out by the enzyme RNA polymerase.

At the same time, not the entire DNA molecule is transcribed, but only its individual segments. Such a segment ( transcripton) starts promoter(a section of DNA where RNA polymerase attaches and from where transcription begins) and ends terminator(section of DNA containing the end of transcription signal). A transcripton is a gene in terms of molecular biology.

Transcription, like replication, is based on the ability of the nitrogenous bases of nucleotides to complementary binding. At the time of transcription, the DNA double strand is broken, and RNA synthesis is carried out along one DNA strand.

During translation, the DNA nucleotide sequence is transcribed onto the synthesized mRNA molecule, which acts as a template in the process of protein biosynthesis.

The genes of prokaryotes consist only of coding nucleotide sequences. Eukaryotic genes consist of alternating coding ( exons) and not encoding ( introns) plots. After transcription, mRNA regions corresponding to introns are removed during splicing, which is an integral part of processing. Processing— the process of formation of mature mRNA from its precursor pre-mRNA.

It includes two main events:

1. attachment to the ends of the mRNA short sequences of nucleotides, indicating the start and end of translation;
2. splicing— removal of non-informative mRNA sequences corresponding to DNA introns. As a result of splicing molecular mass mRNA is reduced by 10 times.

Broadcast(from lat. translation- translation) - the synthesis of a polypeptide chain using mRNA as a template.

All three types of RNA are involved in translation:

• mRNA serves as an information matrix;
• tRNAs deliver amino acids and recognize codons;
• rRNA together with proteins form ribosomes that hold the mRNA;
• tRNA and protein and carry out the synthesis of the polypeptide chain.

mRNA is translated not by one, but simultaneously by several (up to 80) ribosomes. These groups of ribosomes are called polyribosomes (polysomes). The inclusion of one amino acid in the polypeptide chain requires the energy of four ATP.

Genetic code

Information about the structure of proteins is "recorded" in DNA in the form of a sequence of nucleotides. During transcription, it is transcribed onto the synthesized mRNA molecule, which acts as a template in the process of protein biosynthesis. A certain combination of DNA nucleotides, and hence mRNA, corresponds to a certain amino acid in the polypeptide chain of a protein. This correspondence is called genetic code. One amino acid is determined by three nucleotides combined in triplet (codon). Since there are four types of nucleotides, when combined by three into a triplet, they give 4 3 = 64 variants of triplets (while only 20 amino acids are encoded). Of these, three are "stop codons" that stop translation, the remaining 61 are coding. Various amino acids are encoded different number triplets: from 1 to 6.

Notes:

1. The first nitrogenous base in the triplet is in the left vertical row, the second in the upper horizontal, and the third in the right vertical.
2. At the intersection of the lines of three bases, the desired amino acid is revealed.
3. The nitrogenous bases outside brackets are part of mRNA, the nitrogenous bases in parentheses are part of DNA.

Properties of the genetic code:

1. triplet code- one amino acid is encoded by three nucleotides (triplet) in the nucleic acid molecule;
2. the code is universal- all living organisms from viruses to humans use a single genetic code;
3. the code is unambiguous (specific) A triplet corresponds to one single amino acid.
4. redundant code— one amino acid is encoded by more than one triplet;
5. code does not overlap- one nucleotide cannot be part of several codons at once in a nucleic acid chain;
6. code is collinear— the sequence of amino acids in the synthesized protein molecule coincides with the sequence of smRNA triplets.

Broadcast stages

Translation consists of three stages: initiation, elongation and termination.

1. Initiation- Assembly of the complex involved in the synthesis of the polypeptide chain. The small subunit of the ribosome binds to the initiator meth-tRNA, and then with mRNA, after which the whole ribosome is formed, consisting of small and large subparticles.
2. Elongation- elongation of the polypeptide chain. The ribosome moves along the mRNA, which is accompanied by repeated repetition of the cycle of adding the next amino acid to the growing polypeptide chain.
3. Termination- completion of the synthesis of the polypeptide molecule. The ribosome reaches one of the three mRNA stop codons, and since there is no tRNA with anticodons complementary to the stop codons, the synthesis of the polypeptide chain stops. It is released and separated from the ribosome. Ribosomal subunits dissociate, separate from mRNA, and can take part in the synthesis of the next polypeptide chain.

Matrix synthesis reactions

Matrix synthesis reactions include:

• self-duplication of DNA (replication);
• the formation of mRNA, tRNA and rRNA on a DNA molecule (transcription);
• protein biosynthesis to mRNA (translation).

All these reactions are united by the fact that a DNA molecule in one case or an mRNA molecule in another act as a template on which identical molecules are formed. The ability of living organisms to reproduce their own kind is based on the reactions of matrix synthesis.

Regulation of gene expression

Body multicellular organism made up of a variety of cell types. They differ in structure and function, i.e. differentiated. The differences are manifested in the fact that in addition to the proteins necessary for any cell of the body, cells of each type also synthesize specialized proteins: keratin is formed in the epidermis, hemoglobin is formed in erythrocytes, etc. Cell differentiation is caused by a change in the set of expressed genes and is not accompanied by any irreversible changes in the structure of the DNA sequences themselves.

Why do we need proteins

We all know how important proteins are for a living organism, because it is from them that the tissues of our body are built. The vast majority of biochemical reactions in it are catalyzed by proteins (enzymes). These complex substances are part of cell membranes (transport) and provide protection for the whole organism from foreign agents (immunoglobulins).

With the help of them, we digest food (digestive enzymes) and move (muscle tissue proteins), they work in circulatory system, providing blood coagulation, and are a product of the endocrine system, regulating all processes in the body.

How protein is structured and where it is created

A protein molecule is made up of organic compounds- amino acids. Each cell of the body must "be able" to produce protein both for its own needs and for the whole organism. The process of this "production" is called protein biosynthesis. Where does it pass inside a living cell? In order to create protein molecules, each smallest particle of the body has "protein-synthetic stations" - ribosomes. These are small intracellular organelles whose sole function is protein synthesis. They do this quite effectively: one ribosome in one second creates a protein chain of 20 amino acids.

Stages of protein biosynthesis

To proceed with the "assembly" of a protein molecule, as already mentioned, the ribosome must receive information on how to do this, and the amino acids from which it will "build" the protein. The whole process begins with the "rewriting" of information about the structure of the future protein molecule from DNA to messenger RNA (i-RNA). The latter in a eukaryotic cell undergoes processing - maturation. It consists in the formation of a shorter molecule by "cutting out" non-informative sections. The next stage is also typical only for the eukaryotic "unit of living matter" - the transfer of mRNA from the nucleus to the cytoplasm. In parallel, in the latter, transfer RNAs (t-RNAs) are connected with the corresponding amino acid by means of enzymes. Finally, the translation stage follows - this is, in fact, protein biosynthesis occurring on the ribosome. The final stage of the whole complex process is the "maturation" of the protein. It acquires the desired secondary and tertiary structure, non-protein components (for example, heme, metal molecules, lipids, nucleotides, vitamins) join it. The "finished" protein molecule is used by the cell or released from it.