information
All morphological, anatomical and functional features of any cell and organism as a whole are determined by the structure of specific proteins that make up the cells. The ability to synthesize only strictly defined proteins is a characteristic property inherent both for each species and for individual organisms.
A DNA molecule can encode the amino acid sequence for many proteins. A section of a DNA molecule that carries information about the structure of one protein is called a gene.
The specific sequence of amino acids in the peptide chain (the primary structure of the protein) determines the specificity of the protein molecule, and, consequently, the specificity of the characteristics that are determined by this protein.
The biological properties of proteins and their specificity depend on the location of amino acids in the polypeptide chain of a protein molecule. So
Thus, the primary structure of a protein molecule is determined by a certain sequence of nucleotides in a section of DNA (gene).
Genetic a code is a specific arrangement of nucleotides in a DNA molecule that code for amino acids in a protein molecule.
Four different nitrogenous bases (adenine, thymine, cytosine, guanine) are used to encode the 20 amino acids in the DNA molecule. Each amino acid is encoded by a group of three mononucleotides, which is called a triplet (see Table 1)
Properties of genetic code:
triplicity - one amino acid is encoded by one triplet, which contains three nucleotides. This triplet is called a codon. With a combination of four nucleotides of three 4 3, the probable combinations will amount to 64 variants (triplet), which is more than enough to encode 20 amino acids;
"degeneracy" or redundancy of the genetic code, i.e. one and the same amino acid can be encoded by several triplets, since 20 amino acids and 64 codons are known, for example, phenyl-alanine is encoded by two triplets (UUU, UUC), isoleucine by three (AUU, AUCAUA);
non-overlapping, those. there are no dividing marks between the triplets in the DNA molecule; they are arranged in a linear order, following one after the other; three adjacent nucleotides form one triplet;
linearity and the absence of separation marks, i.e. triplets in a DNA molecule follow one another in a linear order without stop signs; if one nucleotide is lost, a “frame shift” will occur, which will lead to a change in the sequence of nucleotides in the RNA molecule, and, consequently, a change in the sequence of amino acids in the protein molecule;
versatility, those. for all organisms, from prokaryotes to humans, 20 amino acids are encoded by the same triplets, which is one of the proofs of the unity of origin of all life on Earth
collinearity(correspondence) - the linear arrangement of nucleotides in a DNA molecule corresponds to the linear arrangement of amino acids in a protein molecule
Table 1 Genetic code
|
First base |
Second base |
Third base |
|||
Stages of implementation of genetic information And
I. Ttranscription - synthesis of all types of RNA on a DNA template. Transcription, or rewriting, does not occur on the entire DNA molecule, but on the section responsible for a specific protein (gene). Conditions required for transcription:
a) unwinding of a section of DNA using unwinding enzyme proteins
b) the presence of building material in the form of ATP. GTF. UTF. 1DTF
c) transcription enzymes - RNA polymerase I, II, III
d) energy in the form of ATP.
Transcription occurs according to the principle of complementarity. In this case, with the help of special enzyme proteins, a section of the DNA double helix unwinds and serves as a matrix for the synthesis of mRNA. Then along the DNA strand
The enzyme RNA polymerase moves, connecting nucleotides together according to the principle of complementarity into a growing RNA chain. The single-stranded RNA then separates from the DNA and leaves the cell nucleus through pores in the nuclear membrane (Fig. 5)
Rice. 5 Schematic representation of the transcription.
Differences in transcription between pro- and eukaryotes.
In terms of the chemical organization of hereditary material, eukaryotes and prokaryotes are not fundamentally different. It is known that the genetic material is represented by DNA.
The hereditary material of prokaryotes is contained in circular DNA, which is located in the cytoplasm of the cell. Prokaryotic genes consist entirely of coding nucleotide sequences.
Eukaryotic genes contain informative regions - exons, which carry information about the amino acid sequence of proteins, and non-informative regions - introns, which do not carry information.
Accordingly, transcription of messenger RNA in eukaryotes occurs in 2 stages:
S) all sections (introns and exons) are rewritten (transcribed) - this mRNA is called immature or pro-iR NK.
2). process sing- maturation of messenger RNA. Using special enzymes, intronic regions are cut out, then exons are stitched together. The phenomenon of joining exons together is called splicing. Post-transcriptional maturation of the RNA molecule occurs in the nucleus.
II. Broadcast(translation), or protein biosynthesis. The essence of translation is the translation of a four-letter code of nitrogenous bases into a 20-letter “dictionary” of amino acids.
The process of translation consists of transferring genetic information encoded in mRNA into the amino acid sequence of a protein. Protein biosynthesis occurs in the cytoplasm on ribosomes and consists of several stages:
The preparatory stage (activation of amino acids) consists of the enzymatic binding of each amino acid to its tRNA and the formation of an amino acid - tRNA complex.
Protein synthesis itself, which includes three stages:
a) initiation - mRNA binds to the small subunit of the ribosome, the first initiation codons are OUT or GUG. These codons correspond to the methionyl-tRNA complex. In addition, three protein factors are involved in initiation: factors that facilitate the binding of mRNA to the large subunit of the ribosome; an initiation complex is formed
b) elongation - lengthening of the polypeptide chain. The process is carried out in 3 steps and consists of binding an mRNA codon to a tRNA anticodon according to the principle of complementarity in the active center of the ribosome, then forming a peptide bond between two amino acid residues and moving the dipeptide one step forward and, accordingly, moving the ribosome along the mRNA one codon forward
c) termination - the end of translation, depends on the presence in the mRNA of termination codons or “stop signals” (UAA, UGA, UAG) and protein enzymes - termination factors (Fig. 6).
Rice. 6. Broadcast scheme
a) elongation stage;
b) entry of synthesized protein into the endoplasmic reticulum
In a cell, not one, but several ribosomes are used for protein synthesis. Such a working complex of mRNA with several ribosomes is called polyribosome. In this case, protein synthesis occurs faster than when using only one ribosome.
Already during translation, the protein begins to fold into a three-dimensional structure, and, if necessary, takes on a quaternary organization in the cytoplasm.
Fig 7 The role of nucleic acids in the transmission of genetic information
Lexico-grammatical tasks:
be
be determined
be encoded how
be characterized
be called
Task No. 1. Write the words and phrases given in brackets in the correct form.
All morphological, anatomical and functional features of any cell and organism as a whole are determined (the structure of specific proteins).
The sequence of amino acids in a polypeptide chain is determined by the (sequence) of nucleotides in a section of DNA called (gene), and the sequence of nucleotides in DNA is called (genetic code).
Each amino acid is coded for (a group of three nucleotides), which is called a (triplet).
The genetic code is characterized (the following features: tripletity, degeneracy, non-coverability, linearity and absence of commas, universality).
20 amino acids are encoded (the same triplets).
Task No. 2. Instead of periods, use short and full forms of participles formed from the verbs to be encoded - to be encoded.
The sequence of nucleotides in DNA, ... certain amino acids in a protein molecule, is called the genetic code.
The same acid can be... several triplets.
20 amino acids... in the same triplets.
There are structural genes, ... structural and enzymatic proteins, as well as genes with information for the synthesis of tRNA and rRNA, etc.
The next stage of implementation of genetic information ... in a gene is transcription.
fundamentally (not) differ significantly on what attribute
much
Task No. 3. Read part of the text “Differences in transcription in pro- and eukaryotes.” Tell us about the stages of implementation of hereditary information.
Task No. 4. Complete the sentences based on information from the text.
The hereditary material of prokaryotes is contained in...
Prokaryotic genes consist entirely of...
Eukaryotic genes contain...
Transcription in eukaryotes occurs in...
Translation consists of transferring genetic information encoded in mRNA into...
Translation occurs in the cytoplasm on...
Exercise No. 5. Make a diagram of the stages of translation and tell us according to the diagram about the stage-by-stage implementation of the translation.
Solution typical tasks
Regions of structural genes in pro- and eukaryotes have similar nucleotide sequences:
TsAT-GTC-ATSA-"PTD-TGA-AAA-CAA-CCG-ATA-CCCC-CTG-CHG-CTT-GGA-ACA-ATA. Moreover, in eukaryotes the nucleotide sequence is ACA-TTC-TGA-AAA and GGA-ACA -ATAs encode intronic regions of pro-RNA.Using a genetic code dictionary, determine:
a) what nucleotide sequence will the mRNA transcribed from this DNA section in prokaryotes have?
b) what nucleotide sequence will the mRNA transcribed from this DNA section in eukaryotes have;
c) what amino acid sequence will the protein encoded by this gene region have in pro- and eukaryotes.
Stages of implementation of genetic information
I. T transcription - synthesis of all types of RNA on a DNA template. Transcription, or rewriting, does not occur on the entire DNA molecule, but on the section responsible for a specific protein (gene). Conditions required for transcription:
a) unwinding of a section of DNA using unwinding enzyme proteins
b) the presence of building material in the form of ATP. GTF. UTF. 1DTF
c) transcription enzymes - RNA polymerase I, II, III
d) energy in the form of ATP.
Transcription occurs according to the principle of complementarity. In this case, with the help of special enzyme proteins, a section of the DNA double helix unwinds and serves as a matrix for the synthesis of mRNA. Further along the DNA strand
The enzyme RNA polymerase moves, connecting nucleotides together according to the principle of complementarity into a growing RNA chain. Next, single-stranded RNA is separated from DNA and leaves the cell nucleus through pores in the nuclear membrane (Fig. 5)
Rice. 5 Schematic representation of the transcription.
Differences in transcription between pro- and eukaryotes.
In terms of the chemical organization of hereditary material, eukaryotes and prokaryotes are not fundamentally different. It is known that the genetic material is represented by DNA.
The hereditary material of prokaryotes is contained in circular DNA, which is located in the cytoplasm of the cell. Prokaryotic genes consist entirely of coding nucleotide sequences.
Eukaryotic genes contain informative regions - exons, which carry information about the amino acid sequence of proteins, and non-informative regions - introns, which do not carry information.
Accordingly, transcription of messenger RNA in eukaryotes occurs in 2 stages:
S) all sections (introns and exons) are rewritten (transcribed) - this mRNA is usually called immature or pro-iR NK.
2). process sing- maturation of messenger RNA. Using special enzymes, intronic regions are cut out, then exons are stitched together. The phenomenon of exon joining is commonly called splicing. Post-transcriptional maturation of the RNA molecule occurs in the nucleus.
II. Broadcast (translation), or protein biosynthesis. The essence of translation is the translation of a four-letter code of nitrogenous bases into a 20-letter “dictionary” of amino acids.
The process of translation consists of transferring genetic information encoded in mRNA into the amino acid sequence of a protein. Protein biosynthesis occurs in the cytoplasm on ribosomes and consists of several stages:
1. The preparatory stage (activation of amino acids) consists of the enzymatic binding of each amino acid to its tRNA and the formation of an amino acid - tRNA complex.
2. Protein synthesis itself, which includes three stages:
a) initiation - mRNA binds to the small subunit of the ribosome, the first initiation codons are OUT or GUG. These codons correspond to the methionyl-tRNA complex. At the same time, three protein factors are involved in initiation: factors that facilitate the binding of mRNA to the large subunit of the ribosome; an initiation complex is formed
b) elongation - lengthening of the polypeptide chain. The process is carried out in 3 steps and consists of binding an mRNA codon to a tRNA anticodon according to the principle of complementarity in the active center of the ribosome, then forming a peptide bond between two amino acid residues and moving the dipeptide one step forward and, accordingly, moving the ribosome along the mRNA one codon forward
c) termination - the end of translation, depends on the presence in the mRNA of termination codons or “stop signals” (UAA, UGA, UAG) and protein enzymes - termination factors (Fig. 6).
Rice. 6. Broadcast scheme
a) elongation stage;
b) entry of the synthesized protein into the endoplasmic reticulum
In a cell, not one, but several ribosomes are used for protein synthesis. Such a working complex of mRNA with several ribosomes is usually called polyribosome. In this case, protein synthesis occurs faster than when using only one ribosome.
Already during translation, the protein begins to fold into a three-dimensional structure, and, if extremely important, in the cytoplasm it takes on a quaternary organization.
Fig 7 The role of nucleic acids in the transmission of genetic information
Lexico-grammatical tasks:
be
be determined
be encoded how
be characterized
be called
Task No. 1. Write the words and phrases given in brackets in the correct form.
1. All morphological, anatomical and functional features of any cell and organism as a whole are determined (the structure of specific proteins).
2. The sequence of amino acids in a polypeptide chain is determined by the (sequence) of nucleotides in a section of DNA, which is usually called (gene), and the sequence of nucleotides in DNA is usually called (genetic code).
3. Each amino acid is encoded (a group of three nucleotides), which is usually called (triplet).
4. The genetic code is characterized (the following features: tripletity, degeneracy, non-overlapability, linearity and absence of commas, universality).
5. 20 amino acids are encoded (the same triplets).
Task No. 2. Instead of periods, use short and full forms of participles formed from the verbs to be encoded - to be encoded.
1. The sequence of nucleotides in DNA, ... certain amino acids in a protein molecule, is usually called the genetic code.
2. The same acid must be... several triplets.
3. 20 amino acids... in the same triplets.
4. There are structural genes, ... structural and enzymatic proteins, as well as genes with information for the synthesis of tRNA and rRNA, etc.
5. The next stage of implementation of genetic information ... in a gene is transcription.
fundamentally (not) differ significantly on what attribute
much
 |
In terms of the chemical organization of the material of heredity, eukaryotes and prokaryotes are not fundamentally different. Their genetic material is DNA.
Task No. 3. Read part of the text “Differences in transcription in pro- and eukaryotes”. Tell us about the stages of implementation of hereditary information.
Task No. 4. Complete the sentences based on information from the text.
1. The hereditary material of prokaryotes is contained in....
2. Prokaryotic genes consist entirely of....
3. Eukaryotic genes contain....
4. Transcription in eukaryotes occurs in....
5. Translation consists of transferring genetic information encoded in mRNA into....
6. Translation takes place in the cytoplasm on....
Exercise No. 5. Make a diagram of the stages of translation and tell us according to the diagram about the stage-by-stage implementation of the translation.
Solution typical tasks
Regions of structural genes in pro- and eukaryotes have similar nucleotide sequences:
TsAT-GTC-ATSA-"PTD-TGA-AAA-CAA-CCG-ATA-CCCC-CTG-CHG-CTT-GGA-ACA-ATA. Moreover, in eukaryotes the nucleotide sequence is ACA-TTC-TGA-AAA and GGA-ACA -ATAs encode intronic regions of pro-RNA.Using a genetic code dictionary, determine:
a) what nucleotide sequence will the mRNA transcribed from this DNA section in prokaryotes have?
b) what nucleotide sequence will the mRNA transcribed from this DNA section in eukaryotes have;
c) what amino acid sequence will the protein encoded by this gene region have in pro- and eukaryotes.
Subject 9. Gene, his structure and functions.
It is known that genes are the material carriers of genetic information. A gene is an elementary unit of heredity that determines the development of any characteristic of an organism. Genes are located on chromosomes and
occupy a specific place - locus. From the point of view of molecular biology, a gene is a section of a DNA molecule in which information about the synthesis of a specific protein is encoded. The stages of implementation of genetic information encoded in a gene can be represented in the form of a diagram:
Molecular mechanisms for the implementation of genetic Not Sky inf formalities
Basic provisions of the gene theory:
1. The gene occupies a certain place (locus) in the chromosome.
2. Gene (cistron) - part of a DNA molecule, which is distinguished by a certain sequence of nucleotides and represents a functional unit of hereditary information. The number of nucleotides that make up different genes is different.
3. Recombinations (exchange of sections) can be observed within one gene. Such sections of the cistron are called recons.
4. Regions in which the sequence of nucleotides can change are called mutons.
5. There are functional and structural genes. Structural genes encode the synthesis of protein molecules. There are structural genes that encode both structural proteins and enzyme proteins, as well as genes with information about the synthesis of tRNA, rRNA, etc.
6. Functional genes do not code for protein, but control and direct the activity of structural genes.
7. The arrangement of nucleotide triplets in structural genes collinearly corresponds to the arrangement of amino acids in the protein molecule.
8. Sections of the DNA molecule that make up the gene are capable of restoration, ᴛ.ᴇ. to repair; therefore, not all changes in the nucleotide sequence in a section of DNA lead to mutations.
9. The genotype consists of individual genes (discrete), but functions as a single whole, because genes are able to interact and influence each other. Gene function is influenced by both internal and external environmental factors.
The gene has a number of properties:
Discretion of action;
Stability (constancy);
Transmission of hereditary information in an unchanged form, in the absence of mutation;
The lability (change) of genes is associated with their ability to mutate;
Specificity - each gene determines the development of a certain trait;
Pleiotropy - one gene can be responsible for several traits;
Expressiveness is the degree of expression of a trait;
Penetration is the frequency of manifestation of a gene among its carriers.
The human genome contains about 30 thousand different genes. Some of them are active, others are blocked. The entire volume of genetic information is under strict control of regulatory mechanisms. All genes are interconnected, forming a single system. Their activity is regulated by complex mechanisms.
This includes the processes of regulation of gene activity at the stages of transcription (before, during, after it), translation (before, during, after it), as well as coordinated cascade group regulation of gene work (their expression), the participation of hormones (signaling) in this process substances), chemical modification of DNA (Fig. 8).
Rice. 8. Scheme of regulation of transcription of structural genes in a prokaryotic cell according to the type of induction.
The expression (manifestation of gene activity) of an individual gene depends on the state in which the gene is located. For this reason, there are different foam nt age(percentage quantitative phenotypic manifestation
gene) and expressivity (the degree of expression of the gene). These concepts were first introduced into genetics by M.V. Timofeev-Ressovsky. A person’s specific genotype is determined by the phenotypic degree of severity of a pathological trait, determined by a specific gene (expressiveness), even up to the absence of a clinical picture of pathology in the presence of mutant alleles in the genotype.
Lexico-grammatical tasks:
Task No. 1. Replace the attributive clauses with a participial phrase.
1. Gene is a unit of heredity that determines the development of any one trait.
2. Genes that are located on chromosomes occupy a specific place - a locus.
3. The implementation of the information that is encoded in the gene is presented in the form of a diagram.
4. A gene is a part of a DNA molecule that differs in a certain sequence of nucleotides.
5. The number of nucleotides that make up different genes is different.
Task No. 2. Replace passive structures with active ones.
1. The synthesis of a protein molecule is encoded by structural genes.
2. The activity of structural genes is controlled and directed by functional genes.
What affects What Genes can influence each other. per function what influenced by internal and external environmental factors
Task No. 3. Write sentences using parentheses.
1. Exonic regions of genes encode (primary protein structure).
2. Intronic regions of the gene play (structural, supporting role).
3. A gene is a part of a DNA molecule that is (functional unit of hereditary information).
Task No. 4. read part of the text about the basic principles of gene theory and write definitions of: a) locus, b) recons, c) mutons.
Exercise No. 5. Using the information given, complete the phrases.
1. Stability is usually called 1.... transmitting the hereditary property of genes... information in an unchanging
2. Gene lability is... 2.... degree of expression
sign.
3. Gene penentrality is 3.... frequency of gene manifestation
among its bearers.
4. Expressiveness of genes - ... 4.... is associated with their ability to
mutations
Typical solution tasks
1. The structural gene region has the following nucleotide sequence:
ATA-CIA-A1^-CTA-GGA-CGA-GTA-CAA
AGA-TCA-CGA-AAA-ATG. Using a genetic code dictionary, determine:
a) what nucleotide sequence will the pro-mRNA transcribed from this region have;
b) it is known that codons 3,4,5,9,10,11,12 in pro-mRNA are part of introns. What sequence will the mRNA have?
c) what amino acid sequence will the protein fragment encoded by the specified region of the gene have;
d) write what anticodons tRNAs must have that ensure the synthesis of this protein fragment.
2. Regions of structural genes in pro- and eukaryotes have similar nucleotide sequences:
TsAT-GTC-A1TA-TTC-TGA-AAA-CAA-C1^^ ACA-ATA. It should be noted that the nucleotide sequences ACA-TTC-TGA-AAA and GGA-ACA-ATA encode intronic regions in eukaryotes. Define:
a) the nucleotide sequence in the primary transcript in eukaryotes;
b) what is the common name for mRNA maturation? Determine the nucleotide sequence in mRNA.
c) what is the difference in the sequence of amino acids in proteins in prokaryotes and eukaryotes. Explain the reason for this difference.
Stages of implementation of genetic information - concept and types. Classification and features of the category “Stages of implementation of genetic information” 2017, 2018.
The most important functions of the body - metabolism, growth, development, transmission of heredity, movement, etc. - are carried out as a result of many chemical reactions involving proteins, nucleic acids and other biologically active substances. At the same time, various compounds are continuously synthesized in cells: building proteins, enzyme proteins, hormones. During metabolism, these substances are worn out and destroyed, and new ones are formed in their place. Since proteins create the material basis of life and accelerate all metabolic reactions, the vital activity of the cell and the organism as a whole is determined by the ability of cells to synthesize specific proteins. Their primary structure is predetermined by the genetic code in the DNA molecule.
Protein molecules consist of tens and hundreds of amino acids (more precisely, amino acid residues). For example, there are about 600 of them in a hemoglobin molecule, and they are distributed into four polypeptide chains; in the ribonuclease molecule there are 124 such amino acids, etc.
The main role in determining the primary structure of a protein belongs to molecules DNA. Its different sections encode the synthesis of different proteins; therefore, one DNA molecule is involved in the synthesis of many individual proteins. The properties of proteins depend on the sequence of amino acids in the polypeptide chain. In turn, the alternation of amino acids is determined by the sequence of nucleotides in DNA, and each amino acid corresponds to a specific triplet. It has been experimentally proven that, for example, a DNA section with an AAC triplet corresponds to the amino acid leucine, an ACC triplet to tryptophan, an ACA triplet to cysteine, etc. By dividing the DNA molecule into triplets, you can imagine which amino acids and in what sequence will be located in the protein molecule. A set of triplets constitutes the material basis of genes, and each gene contains information about the structure of a specific protein (a gene is the basic biological unit of heredity; chemically, a gene is a section of DNA that includes several hundred nucleotide pairs).
Genetic code - the historically established organization of DNA and RNA molecules, in which the sequence of nucleotides in them carries information about the sequence of amino acids in protein molecules. Code properties: triplet (codon), non-overlapping (codons follow each other), specificity (one codon can determine only one amino acid in a polypeptide chain), universality (in all living organisms the same codon determines the inclusion of the same amino acid in the polypeptide), redundancy (for most amino acids there are several codons). Triplets that do not carry information about amino acids are stop triplets, indicating the start site of synthesis i-RNA.(V.B. Zakharov. Biology. Reference materials. M., 1997)
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. RNA serves as such an intermediary, onto which the nucleotide sequence is rewritten, in exact accordance with that on DNA - according to the principle of complementarity. This process is called transcriptions and proceeds as a matrix synthesis reaction. It is characteristic only of living structures and underlies the most important property of living things - self-reproduction. Protein biosynthesis is preceded by template synthesis of mRNA on a DNA strand. The resulting mRNA leaves the cell nucleus into the cytoplasm, where ribosomes are strung on it, and amino acids are delivered here with the help of RNA.
Protein synthesis is a complex multi-step process that involves DNA, mRNA, tRNA, ribosomes, ATP and various enzymes. First, amino acids in the cytoplasm are activated by enzymes and attached to tRNA (to the site where the CCA nucleotide is located). At the next stage, amino acids are combined in the order in which the alternation of nucleotides from DNA is transferred to mRNA. This stage is called broadcast. On an mRNA strand there is not one ribosome, but a group of them - such a complex is called a polysome (N.E. Kovalev, L.D. Shevchuk, O.I. Shchurenko. Biology for preparatory departments of medical institutes).
Scheme Protein biosynthesis
Protein synthesis consists of two stages - transcription and translation.
I. Transcription (rewriting) - biosynthesis of RNA molecules, carried out in chromosomes on DNA molecules according to the principle of template synthesis. With the help of enzymes, all types of RNA (mRNA, rRNA, tRNA) are synthesized in the corresponding sections of the DNA molecule (genes). 20 varieties of tRNA are synthesized, since 20 amino acids take part in protein biosynthesis. Then mRNA and tRNA are released into the cytoplasm, rRNA is integrated into ribosomal subunits, which also exit into the cytoplasm.
II. Translation (transfer) is the synthesis of polypeptide chains of proteins, carried out in ribosomes. It is accompanied by the following events:
1. Formation of the functional center of the ribosome - FCR, consisting of mRNA and two ribosomal subunits. In the FCR there are always two triplets (six nucleotides) of mRNA, forming two active centers: A (amino acid) - the center for recognizing the amino acid and P (peptide) - the center for attaching the amino acid to the peptide chain.
2. Transport of amino acids attached to tRNA from the cytoplasm to the FCR. In the active center A, the anticodon of the tRNA is read with the codon of the mRNA; in the case of complementarity, a bond is formed, which serves as a signal for advancement (jump) along the ribosomal mRNA by one triplet. As a result of this, the complex “rRNA codon and tRNA with amino acid” moves to the active center of P, where the amino acid is added to the peptide chain (protein molecule). The tRNA then leaves the ribosome.
3. The peptide chain lengthens until translation ends and the ribosome jumps off the mRNA. One mRNA can contain several ribosomes at the same time (polysome). The polypeptide chain is immersed in the channel of the endoplasmic reticulum and there acquires a secondary, tertiary or quaternary structure. The assembly speed of one protein molecule consisting of 200-300 amino acids is 1-2 minutes. Formula for protein biosynthesis: DNA (transcription) --> RNA (translation) --> protein.
Having completed one cycle, polysomes can take part in the synthesis of new protein molecules.
The protein molecule separated from the ribosome has the form of a thread that is biologically inactive. It becomes biologically functional after the molecule acquires a secondary, tertiary and quaternary structure, that is, a certain spatially specific configuration. The secondary and subsequent structures of the protein molecule are predetermined in the information contained in the alternation of amino acids, i.e., in the primary structure of the protein. In other words, the program for the formation of a globule, its unique configuration, are determined by the primary structure of the molecule, which in turn is built under the control of the corresponding gene.
The rate of protein synthesis is determined by many factors: the temperature of the environment, the concentration of hydrogen ions, the amount of the final product of synthesis, the presence of free amino acids, magnesium ions, the state of ribosomes, etc.
1. What processes relate to matrix synthesis reactions?
Fermentation, translation, transcription, photosynthesis, replication.
Template synthesis reactions include translation, transcription and replication.
2. What is transcription? How does this process work?
Transcription is the process of rewriting genetic information from DNA to RNA (RNA biosynthesis in the corresponding sections of one of the DNA chains); one of the matrix synthesis reactions.
Transcription is carried out as follows. At a certain section of the DNA molecule, the complementary strands are separated. RNA synthesis will take place on one of the strands (called the transcribed strand).
The enzyme RNA polymerase recognizes a promoter (a special sequence of nucleotides located at the beginning of a gene) and interacts with it. Then RNA polymerase begins to move along the transcribed chain and at the same time synthesize an RNA molecule from nucleotides. The transcribed DNA strand is used as a template, so the synthesized RNA will be complementary to the corresponding section of the transcribed DNA strand. RNA polymerase grows the RNA chain, adding new nucleotides to it, until it reaches a terminator (a special sequence of nucleotides located at the end of the gene), after which transcription stops.
3. What process is called translation? Describe the main stages of translation.
Translation is the process of protein biosynthesis from amino acids that occurs on ribosomes; one of the matrix synthesis reactions.
Main stages of broadcast:
● Binding of mRNA to the small subunit of the ribosome, followed by attachment of the large subunit.
● Penetration of methionine tRNA into the ribosome and complementary binding of its anticodon (UAC) with the start codon of mRNA (AUG).
● Penetration of the next tRNA carrying an activated amino acid into the ribosome and complementary binding of its anticodon with the corresponding mRNA codon.
● The appearance of a peptide bond between two amino acids, after which the first (methionine) tRNA is freed from the amino acid and leaves the ribosome, and the mRNA is shifted by one triplet.
● Growth of the polypeptide chain (according to the mechanism described above), which occurs until one of the three stop codons (UAA, UAG or UGA) enters the ribosome.
● Cessation of protein synthesis and breakdown of the ribosome into two separate subunits.
4. Why, during translation, not any amino acids are included in the protein in a random order, but only those encoded by mRNA triplets, and in strict accordance with the sequence of these triplets? How many types of tRNA do you think are involved in protein synthesis in a cell?
The correct and sequential incorporation of amino acids into the growing polypeptide chain is ensured by the strict complementary interaction of tRNA anticodons with the corresponding mRNA codons.
Some students may answer that 20 types of tRNA are involved in protein synthesis - one for each amino acid. But in fact, 61 types of tRNA are involved in protein synthesis - there are as many of them as there are sense codons (triplets encoding amino acids). Each type of tRNA has a unique primary structure (nucleotide sequence) and, as a result, has a special anticodon for complementary binding with the corresponding mRNA codon. For example, the amino acid leucine (Leu) can be encoded by six different triplets, so there are six types of leucine tRNAs, all of which have different anticodons.
The total number of codons is 4 3 = 64, but there are no tRNA molecules for stop codons (there are three of them), i.e. 64 – 3 = 61 types of tRNA.
5. Should matrix synthesis reactions be classified as assimilation or dissimilation processes? Why?
Reactions of matrix synthesis relate to assimilation processes because:
● accompanied by the synthesis of complex organic compounds from simpler substances, namely, biopolymers from the corresponding monomers (replication is accompanied by the synthesis of daughter DNA chains from nucleotides, transcription by the synthesis of RNA from nucleotides, translation by the synthesis of proteins from amino acids);
● require energy expenditure (ATP serves as the energy supplier for matrix synthesis reactions).
6. The section of the transcribed DNA chain has the following nucleotide order:
TACTGGATTATTCAAGATST
Determine the sequence of amino acid residues of the peptide encoded by this region.
Using the principle of complementarity, we will establish the nucleotide sequence of the corresponding mRNA, and then, using the genetic code table, we will determine the sequence of amino acid residues of the encoded peptide.
Answer: the sequence of amino acid residues of the peptide: Met–Tre–Cis–Ile–Met–Phen.
7. Research has shown that in an mRNA molecule, 34% of the total number of nitrogenous bases is guanine, 18% is uracil, 28% is cytosine and 20% is adenine. Determine the percentage composition of the nitrogenous bases of the double-stranded DNA section, one of the chains of which served as a template for the synthesis of this mRNA.
● Using the principle of complementarity, we will determine the percentage composition of nitrogenous bases of the corresponding transcribed DNA chain. It contains 34% cytosine (complementary to guanine mRNA), 18% adenine (complementary to uracil mRNA), 28% guanine (complementary to cytosine mRNA) and 20% thymine (complementary to adenine mRNA).
● Based on the composition of the transcribed chain, we will determine the percentage composition of the nitrogenous bases of the complementary (non-transcribed) DNA chain: 34% guanine, 18% thymine, 28% cytosine and 20% adenine.
● The percentage of each type of nitrogenous base in double-stranded DNA is calculated as the arithmetic average of the percentage of these bases in both strands:
C = G = (34% + 28%) : 2 = 31%
A = T = (18% + 20%) : 2 = 19%
Answer: the corresponding double-stranded DNA section contains 31% cytosine and guanine, 19% adenine and thymine.
8*. In mammalian red blood cells, hemoglobin synthesis can occur for several days after these cells lose their nuclei. How can you explain this?
The loss of the nucleus is preceded by intense transcription of genes encoding the polypeptide chains of hemoglobin. A large amount of corresponding mRNA accumulates in the hyaloplasm, so hemoglobin synthesis continues even after the loss of the cell nucleus.
*Tasks marked with an asterisk require students to put forward various hypotheses. Therefore, when marking, the teacher should focus not only on the answer given here, but take into account each hypothesis, assessing the biological thinking of students, the logic of their reasoning, the originality of ideas, etc. After this, it is advisable to familiarize students with the answer given.
The process of protein biosynthesis is carried out on ribosomes, and the keeper of genetic information is DNA. To transfer information from DNA located in the nucleus to the site of protein synthesis, an intermediary is required. His role is played by messenger RNA, which is synthesized on one of the chains of the DNA molecule according to the principle of complementarity.
Thus, the implementation of hereditary information in the cell is carried out in two stages: first, information about the structure of the protein is copied from DNA to mRNA (transcription), and then implemented on the ribosome in the form of the final product - protein (translation). This can be represented as a diagram:
Transcription. The rewriting of hereditary information from DNA to mRNA is called transcription(from lat. transcription- rewriting). This process works as follows.
At a certain section of the DNA molecule, the complementary strands are separated. Along one of the chains (called the transcribed chain), the enzyme RNA polymerase begins to move.
c) genetic code
RNA polymerase synthesizes an mRNA molecule from nucleotides, while the transcribed DNA strand is used as a template (Fig. 65). The resulting mRNA is complementary to the section of the transcribed DNA chain, which means that the order of nucleotides in the mRNA is strictly determined by the order of the nucleotides in DNA. For example, if a section of the transcribed DNA chain has the nucleotide sequence A C G T G A, then the corresponding section of the mRNA molecule will have the form U G CATSU (note Please note that RNA nucleotides contain uracil instead of thymine). Thus, as a result of transcription, genetic information is rewritten from DNA to mRNA
Transcription can occur simultaneously on several genes on the same chromosome and on genes located on different chromosomes.
Since one DNA molecule contains many genes, it is very important that RNA polymerase begins the synthesis of mRNA from a strictly defined section of DNA. Therefore, at the beginning of each gene there is a special specific sequence of nucleotides called a promoter. RNA polymerase recognizes the promoter, interacts with it and begins the synthesis of the mRNA chain from the right place. The enzyme synthesizes mRNA, adding new nucleotides to it, until it reaches a special sequence of nucleotides in the DNA molecule - the terminator. This nucleotide sequence indicates that mRNA synthesis should be stopped.
In prokaryotes, synthesized mRNA molecules can immediately interact with ribosomes and participate in protein synthesis. In eukaryotes, mRNA is synthesized in the nucleus. There it interacts with special nuclear proteins and is transported through pores in the nuclear membrane into the cytoplasm.
Two other types of RNA are also synthesized on special genes: tRNA and rRNA
Broadcast. The process of protein synthesis from amino acids that occurs on ribosomes is called broadcast(from lat. broadcast- translation). During translation, the nucleotide sequence of an mRNA molecule is translated into the amino acid sequence of a protein molecule. In other words, the “language” of nucleotides is translated into the “language” of amino acids.
The cytoplasm must contain a complete set of amino acids necessary for protein synthesis. These amino acids are formed as a result of the breakdown of proteins received by the body with food, or are synthesized in the body itself.
Messenger RNA binds to the small subunit of the ribosome, after which the large subunit attaches (Fig. 66).
Protein synthesis begins at the start codon OUT. Since this triplet encodes the amino acid methionine, all proteins (except in special cases) will begin with a methionine residue. The cleavage of this residue in most proteins occurs later, during the maturation of the protein molecule.
Starting from the start codon, the mRNA molecule sequentially, triplet by triplet, moves through the ribosome, which is accompanied by the growth of the polypeptide chain. The combination of amino acids into the desired sequence (in accordance with the mRNA codons) is carried out on ribosomes with the participation of transport RNAs
Due to the specific arrangement of complementary nucleotides, the tRNA molecule, as already noted, has a shape resembling a clover leaf (Fig. 67). Each tRNA has an acceptor end to which a specific amino acid, previously activated by ATP energy, is attached. To activate one amino acid, one ATP molecule must be broken down.
In the opposite part of the tRNA molecule there is a specific triplet - an ant and a codon, which is responsible for attachment according to the principle of complementarity to the corresponding mRNA triplet (codon).
Thanks to the anticodon, a tRNA molecule with an attached activated amino acid binds complementarily to the corresponding mRNA codon. In the same way, a second tRNA with an activated amino acid is attached to the next mRNA codon. A peptide bond occurs between two amino acids, after which the first tRNA is freed from the amino acid and leaves the ribosome.
After this, the mRNA is shifted by one triplet, and the next tRNA molecule with an amino acid penetrates into the ribosome. As a result, a third amino acid is added to the formed dipeptide and the mRNA is shifted by another triplet. This is how the polypeptide chain grows.
The translation process continues until one of three stop codons enters the ribosome:
UAA, UAG or UGA, after which protein synthesis stops and the ribosome breaks down into two subunits.
All the reactions described occur very quickly. It is estimated that the synthesis of a large protein molecule occurs in approximately 1-2 minutes.
Each stage of protein biosynthesis is catalyzed by appropriate enzymes and supplied with energy by the breakdown of ATP.
An mRNA molecule can bind to several ribosomes simultaneously. A complex of mRNA and ribosomes (from 5-6 to several dozen) is called sex and soma. The formation of polysomes increases the efficiency of mRNA functioning, as it allows the simultaneous synthesis of several identical protein molecules.
If protein synthesis occurred on ribosomes associated with the rough ER, then the resulting polypeptide chain first appears inside the cavity of the endoplasmic reticulum and is then transported to the Golgi complex. In these organelles, protein maturation occurs - the formation of a secondary, tertiary and quaternary structure, the attachment of non-protein components to the protein molecule, etc. If protein synthesis was carried out on free ribosomes located in the hyaloplasm, then the synthesized protein molecule is transported to the desired part of the cell, where it acquires the corresponding structure.
Thus, the genetic information contained in DNA, as a result of the processes of transcription and translation, is realized in the cell in the form of protein molecules. Protein synthesis is ensured by the interaction of all types of RNA: rRNA is the main structural component of ribosomes, mRNA is the carrier of information about the primary structure of the protein, tRNA delivers amino acids to the ribosome and also ensures their correct inclusion in the polypeptide chain.
RNA biosynthesis (transcription) and protein biosynthesis (translation) are carried out using templates - DNA and mRNA, respectively. Therefore, just like replication, the processes of transcription and translation are matrix synthesis reactions.
1. What processes relate to matrix synthesis reactions?
Fermentation, translation, transcription, photosynthesis, replication.
2. What is transcription? How does this process work?
3. What process is called translation? Describe the main stages of translation.
4. Why, during translation, not any amino acids are included in the protein in a random order, but only those encoded by mRNA triplets, and in strict accordance with the sequence of these triplets? How many types of tRNA do you think are involved in protein synthesis in a cell?
5. Should matrix synthesis reactions be classified as assimilation or dissimilation processes? Why?
6. The section of the transcribed DNA chain has the following nucleotide order: TACTGGACATATTACAAGACT. Determine the sequence of amino acid residues of the peptide encoded by this region.
7. Research has shown that in an mRNA molecule, 34% of the total number of nitrogenous bases is guanine, 18% is uracil, 28% is cytosine and 20% is adenine. Determine the percentage composition of the nitrogenous bases of the double-stranded DNA section, one of the chains of which served as a template for the synthesis of this mRNA.
8. In mammalian red blood cells, hemoglobin synthesis can occur for several days after these cells lose their nuclei. How can you explain this?
- § 1. Content of chemical elements in the body. Macro- and microelements
- § 2. Chemical compounds in living organisms. Inorganic substances
- § 10. History of the discovery of the cell. Creation of cell theory
- § 15. Endoplasmic reticulum. Golgi complex. Lysosomes
- § 24. General characteristics of metabolism and energy conversion
Chapter 1. Chemical components of living organisms
Chapter 2. Cell - structural and functional unit of living organisms
Chapter 3. Metabolism and energy conversion in the body
Chapter 4. Structural organization and regulation of functions in living organisms