1. The genetic code is triplet. 3 adjacent nucleotides carry information about one amino acid. There can be 64 such triplets (this shows the redundancy of the genetic code), but only 61 of them carry information about the protein (codons). 3 triplets are called anticodons, they are stop signals at which protein synthesis stops.
2. The genetic code is degenerate (20 amino acids and 61 codons), i.e. one amino acid can be coded for by several codons (from two to six). Methionine and tryptophan have one codon each, because protein synthesis begins with them (start signal).
3. The code is unambiguous - it carries information about only one amino acid.
4. The code is collinear, i.e. The sequence of nucleotides in a gene corresponds to the sequence of amino acids in a protein.
5. The genetic code is non-overlapping and compact - the same nucleotide cannot be part of two different codons, the reading goes on continuously, in a row, up to the stop codon. There are no "punctuation marks" in the code.
6. The genetic code is universal - the same for all living beings, i.e. the same triplet codes for the same amino acid. 66. What is reverse transcription? How is this process related to the development of viruses?
REVERSE TRANSCRIPTION is a method of obtaining a double-stranded DNA copy of RNA from a virus. The technique is often used in GENETIC ENGINEERING to obtain copies of INFORMATION RNA in the form of DNA. Achieved by using the enzyme reversetase, which is found in RETROVIRUS.
Viruses that use reverse transcription contain single-stranded RNA or double-stranded DNA. RNA-containing viruses capable of reverse transcription (retroviruses, such as HIV) use a DNA copy of the genome as an intermediate molecule in RNA replication, and those containing DNA (pararetroviruses, such as hepatitis B virus) use RNA. In both cases, reverse transcriptase, or RNA-dependent-DNA polymerase, is used.
Retroviruses insert the DNA produced by reverse transcription into the host genome, a state of the virus called a provirus. Viruses that use reverse transcription are susceptible to antiviral drugs.
67. Describe the structure of eukaryotic genes. How are eukaryotic genes different from prokaryotes?
A gene is a section of DNA from which RNA is copied.
The structure of genes in eukaryotes: the generally accepted model of the structure of the gene - exon - intron structure.
An exon is a DNA sequence that is present in mature RNA. A gene must contain at least one exon. On average, a gene contains 8 exons. Transcription initiation and termination factors are included in the first and last exons, respectively.
An intron is a DNA sequence included between exons that is not part of the mature RNA. Introns have certain nucleotide sequences that define their boundaries with exons: at the 5th end - GU, at the 3rd - AG. They can encode regulatory RNAs.
Polyadenylation signal 5 - AATAAA -3 is included in the last exon. Poly sites protect mRNA from degradation.
5 and 3 flanking sequences - gene copying occurs in the direction 5 - 3, on the flanks there are specific sites that limit the gene and contain regulatory elements of its transcription.
Regulatory elements - promoter, enhancers, silencers, insulators (contribute to the formation of chromosome loops that limit the influence of neighboring regulatory elements).
Eukaryotic genes differ significantly in structure and transcription from prokaryotic genes. Their distinguishing feature is discontinuity, i.e., the alternation of nucleotide sequences in them, which are presented (exons) or not presented (introns) in mRNA. Eukaryotic genes are not grouped into operons, so each of them has its own promoter and transcription terminator.
Related information:
- A. Animal and Vegetable Kingdom page 6. Even if elementary particles - the basis of the material world - exhibit such contradictory properties
Genetic code- a system for recording genetic information in DNA (RNA) in the form of a certain sequence of nucleotides. A certain sequence of nucleotides in DNA and RNA corresponds to a certain sequence of amino acids in the polypeptide chains of proteins. It is customary to write the code using capital letters of the Russian or Latin alphabet. Each nucleotide is designated by the letter with which the name of the nitrogenous base that is part of its molecule begins: A (A) - adenine, G (G) - guanine, C (C) - cytosine, T (T) - thymine; in RNA instead of thyminuracil - U (U). The sequence of nucleotides determines the sequence of incorporation of AA into the synthesized protein.
Properties of the genetic code:
1. Tripletity- a significant unit of the code is a combination of three nucleotides (triplet, or codon).
2. Continuity- there are no punctuation marks between the triplets, that is, the information is read continuously.
3. Non-overlapping- the same nucleotide cannot be part of two or more triplets at the same time (not observed for some overlapping genes of viruses, mitochondria and bacteria that encode several frameshift proteins).
4. Uniqueness(specificity) - a certain codon corresponds to only one amino acid (however, the UGA codon in Euplotescrassus codes for two amino acids - cysteine and selenocysteine)
5. Degeneracy(redundancy) - several codons can correspond to the same amino acid.
6. Versatility- the genetic code works in the same way in organisms of different levels of complexity - from viruses to humans (genetic engineering methods are based on this; there are a number of exceptions, shown in the table in the section "Variations of the standard genetic code" below).
Conditions for biosynthesis
Protein biosynthesis requires the genetic information of a DNA molecule; informational RNA - the carrier of this information from the nucleus to the site of synthesis; ribosomes - organelles where the actual protein synthesis occurs; a set of amino acids in the cytoplasm; transport RNAs encoding amino acids and carrying them to the site of synthesis on ribosomes; ATP is a substance that provides energy for the process of coding and biosynthesis.
Stages
Transcription- the process of biosynthesis of all types of RNA on the DNA matrix, which takes place in the nucleus.
A certain section of the DNA molecule is despiralized, the hydrogen bonds between the two chains are destroyed under the action of enzymes. On one DNA strand, as on a matrix, an RNA copy is synthesized from nucleotides according to the complementary principle. Depending on the DNA region, ribosomal, transport, and informational RNAs are synthesized in this way.
After mRNA synthesis, it leaves the nucleus and goes to the cytoplasm to the site of protein synthesis on ribosomes.
Broadcast- the process of synthesis of polypeptide chains, carried out on ribosomes, where mRNA is an intermediary in the transfer of information about the primary structure of the protein.
Protein biosynthesis consists of a series of reactions.
1. Activation and coding of amino acids. tRNA has the form of a cloverleaf, in the central loop of which there is a triplet anticodon corresponding to the code of a certain amino acid and the codon on mRNA. Each amino acid is connected to the corresponding tRNA using the energy of ATP. A tRNA-amino acid complex is formed, which enters the ribosomes.
2. Formation of the mRNA-ribosome complex. mRNA in the cytoplasm is connected by ribosomes on granular ER.
3. Assembly of the polypeptide chain. tRNA with amino acids, according to the principle of complementarity of the anticodon with the codon, combine with mRNA and enter the ribosome. In the peptide center of the ribosome, a peptide bond is formed between two amino acids, and the released tRNA leaves the ribosome. At the same time, the mRNA advances one triplet each time, introducing a new tRNA - an amino acid and removing the released tRNA from the ribosome. The entire process is powered by ATP. One mRNA can combine with several ribosomes, forming a polysome, where many molecules of one protein are simultaneously synthesized. Synthesis ends when meaningless codons (stop codes) begin on the mRNA. Ribosomes are separated from mRNA, polypeptide chains are removed from them. Since the entire synthesis process takes place on the granular endoplasmic reticulum, the resulting polypeptide chains enter the EPS tubules, where they acquire the final structure and turn into protein molecules.
All synthesis reactions are catalyzed by special enzymes using ATP energy. The rate of synthesis is very high and depends on the length of the polypeptide. For example, in the ribosome of Escherichia coli, a protein of 300 amino acids is synthesized in approximately 15-20 seconds.
They line up in chains and, thus, sequences of genetic letters are obtained.
Genetic code
The proteins of almost all living organisms are built from only 20 types of amino acids. These amino acids are called canonical. Each protein is a chain or several chains of amino acids connected in a strictly defined sequence. This sequence determines the structure of the protein, and therefore all its biological properties.
CUU (Leu/L)Leucine
CUC (Leu/L)Leucine
CUA (Leu/L)Leucine
CUG (Leu/L) Leucine
In some proteins, non-standard amino acids such as selenocysteine and pyrrolysine are inserted by the stop codon-reading ribosome, which depends on the sequences in the mRNA. Selenocysteine is now considered as the 21st, and pyrrolysine as the 22nd amino acid that makes up proteins.
Despite these exceptions, the genetic code of all living organisms has common features: a codon consists of three nucleotides, where the first two are defining, codons are translated by tRNA and ribosomes into a sequence of amino acids.
| Example | codon | Usual value | Reads like: |
|---|---|---|---|
| Some types of yeast of the genus Candida | CUG | Leucine | Serene |
| Mitochondria, in particular Saccharomyces cerevisiae | CU(U, C, A, G) | Leucine | Serene |
| Mitochondria of higher plants | CGG | Arginine | tryptophan |
| Mitochondria (in all studied organisms without exception) | UGA | Stop | tryptophan |
| Mammalian mitochondria, Drosophila, S.cerevisiae and many simple | AUA | Isoleucine | Methionine = Start |
| prokaryotes | GUG | Valine | Start |
| Eukaryotes (rare) | CUG | Leucine | Start |
| Eukaryotes (rare) | GUG | Valine | Start |
| Prokaryotes (rare) | UUG | Leucine | Start |
| Eukaryotes (rare) | ACG | Threonine | Start |
| Mammalian mitochondria | AGC, AGU | Serene | Stop |
| Drosophila mitochondria | AGA | Arginine | Stop |
| Mammalian mitochondria | AG(A,G) | Arginine | Stop |
The history of ideas about the genetic code
Nevertheless, in the early 1960s, new data revealed the failure of the "comma-free code" hypothesis. Then experiments showed that codons, considered by Crick to be meaningless, can provoke protein synthesis in a test tube, and by 1965 the meaning of all 64 triplets was established. It turned out that some codons are simply redundant, that is, a number of amino acids are encoded by two, four or even six triplets.
see also
Notes
- Genetic code supports targeted insertion of two amino acids by one codon. Turanov AA, Lobanov AV, Fomenko DE, Morrison HG, Sogin ML, Klobutcher LA, Hatfield DL, Gladyshev VN. Science. 2009 Jan 9;323(5911):259-61.
- The AUG codon encodes methionine, but also serves as a start codon - as a rule, translation begins from the first AUG codon of mRNA.
- NCBI: "The Genetic Codes", Compiled by Andrzej (Anjay) Elzanowski and Jim Ostell
- Jukes TH, Osawa S, The genetic code in mitochondria and chloroplasts., Experientia. 1990 Dec 1;46(11-12):1117-26.
- Osawa S, Jukes TH, Watanabe K, Muto A (March 1992). "Recent evidence for evolution of the genetic code". microbiol. Rev. 56 (1): 229–64. PMID 1579111.
- SANGER F. (1952). "The arrangement of amino acids in proteins.". Adv Protein Chem. 7 : 1-67. PMID 14933251 .
- M. Ichas biological code. - World, 1971.
- WATSON JD, CRICK FH. (April 1953). «Molecular structure of nucleic acids; a structure for deoxyribose nucleic acid.". Nature 171 : 737-738. PMID 13054692 .
- WATSON JD, CRICK FH. (May 1953). "Genetical implications of the structure of deoxyribonucleic acid.". Nature 171 : 964-967. PMID 13063483 .
- Crick F.H. (April 1966). "The genetic code - yesterday, today, and tomorrow." Cold Spring Harb Symp Quant Biol.: 1-9. PMID 5237190.
- G. GAMOW (February 1954). "Possible Relationship between Deoxyribonucleic Acid and Protein Structures.". Nature 173 : 318. DOI: 10.1038/173318a0 . PMID 13882203 .
- GAMOW G, RICH A, YCAS M. (1956). "The problem of information transfer from the nucleic acids to proteins.". Adv Biol Med Phys. 4 : 23-68. PMID 13354508 .
- Gamow G, Ycas M. (1955). STATISTICAL CORRELATION OF PROTEIN AND RIBONUCLEIC ACID COMPOSITION. ". Proc Natl Acad Sci U S A. 41 : 1011-1019. PMID 16589789 .
- Crick FH, Griffith JS, Orgel LE. (1957). CODES WITHOUT COMMAS. ". Proc Natl Acad Sci U S A. 43 : 416-421. PMID 16590032.
- Hayes B. (1998). "The Invention of the Genetic Code." (PDF reprint). American scientist 86 : 8-14.
Literature
- Azimov A. Genetic code. From the theory of evolution to the decoding of DNA. - M.: Tsentrpoligraf, 2006. - 208 s - ISBN 5-9524-2230-6.
- Ratner V. A. Genetic code as a system - Soros Educational Journal, 2000, 6, No. 3, pp. 17-22.
- Crick FH, Barnett L, Brenner S, Watts-Tobin RJ. General nature of the genetic code for proteins - Nature, 1961 (192), pp. 1227-32
Links
- Genetic code- article from the Great Soviet Encyclopedia
Wikimedia Foundation. 2010 .
Under the genetic code, it is customary to understand such a system of signs denoting the sequential arrangement of nucleotide compounds in DNA and RNA, which corresponds to another sign system that displays the sequence of amino acid compounds in a protein molecule.
It is important!
When scientists managed to study the properties of the genetic code, universality was recognized as one of the main ones. Yes, strange as it may sound, everything is united by one, universal, common genetic code. It was formed over a long time period, and the process ended about 3.5 billion years ago. Therefore, in the structure of the code, traces of its evolution can be traced, from the moment of its inception to the present day.
When talking about the sequence of elements in the genetic code, it means that it is far from being chaotic, but has a strictly defined order. And this also largely determines the properties of the genetic code. This is equivalent to the arrangement of letters and syllables in words. It is worth breaking the usual order, and most of what we will read on the pages of books or newspapers will turn into ridiculous gibberish.
Basic properties of the genetic code
Usually the code carries some information encrypted in a special way. In order to decipher the code, you need to know the distinguishing features.
So, the main properties of the genetic code are:
- triplet;
- degeneracy or redundancy;
- uniqueness;
- continuity;
- the versatility already mentioned above.
Let's take a closer look at each property.
1. Tripletity
This is when three nucleotide compounds form a sequential chain within a molecule (i.e. DNA or RNA). As a result, a triplet compound is created or encodes one of the amino acids, its location in the peptide chain.
Codons (they are code words!) are distinguished by their connection sequence and by the type of those nitrogenous compounds (nucleotides) that are part of them.
In genetics, it is customary to distinguish 64 codon types. They can form combinations of four types of nucleotides, 3 in each. This is equivalent to raising the number 4 to the third power. Thus, the formation of 64 nucleotide combinations is possible.
2. Redundancy of the genetic code
This property is observed when several codons are required to encrypt one amino acid, usually within 2-6. And only tryptophan can be encoded with a single triplet.
3. Uniqueness
It is included in the properties of the genetic code as an indicator of healthy gene inheritance. For example, the GAA triplet in sixth place in the chain can tell doctors about a good state of blood, about normal hemoglobin. It is he who carries information about hemoglobin, and it is also encoded by him. And if a person is anemic, one of the nucleotides is replaced by another letter of the code - U, which is a signal of the disease.
4. Continuity
When writing this property of the genetic code, it should be remembered that codons, like chain links, are located not at a distance, but in direct proximity, one after another in the nucleic acid chain, and this chain is not interrupted - it has no beginning or end.
5. Versatility
It should never be forgotten that everything on Earth is united by a common genetic code. And therefore, in a primate and a person, in an insect and a bird, a hundred-year-old baobab and a blade of grass that has barely hatched out of the ground, similar amino acids are encoded in identical triplets.
It is in the genes that the basic information about the properties of an organism is stored, a kind of program that the organism inherits from those who lived earlier and which exists as a genetic code.
They line up in chains and, thus, sequences of genetic letters are obtained.
Genetic code
The proteins of almost all living organisms are built from only 20 types of amino acids. These amino acids are called canonical. Each protein is a chain or several chains of amino acids connected in a strictly defined sequence. This sequence determines the structure of the protein, and therefore all its biological properties.
CUU (Leu/L)Leucine
CUC (Leu/L)Leucine
CUA (Leu/L)Leucine
CUG (Leu/L) Leucine
In some proteins, non-standard amino acids such as selenocysteine and pyrrolysine are inserted by the stop codon-reading ribosome, which depends on the sequences in the mRNA. Selenocysteine is now considered as the 21st, and pyrrolysine as the 22nd amino acid that makes up proteins.
Despite these exceptions, the genetic code of all living organisms has common features: a codon consists of three nucleotides, where the first two are defining, codons are translated by tRNA and ribosomes into a sequence of amino acids.
| Example | codon | Usual value | Reads like: |
|---|---|---|---|
| Some types of yeast of the genus Candida | CUG | Leucine | Serene |
| Mitochondria, in particular Saccharomyces cerevisiae | CU(U, C, A, G) | Leucine | Serene |
| Mitochondria of higher plants | CGG | Arginine | tryptophan |
| Mitochondria (in all studied organisms without exception) | UGA | Stop | tryptophan |
| Mammalian mitochondria, Drosophila, S.cerevisiae and many simple | AUA | Isoleucine | Methionine = Start |
| prokaryotes | GUG | Valine | Start |
| Eukaryotes (rare) | CUG | Leucine | Start |
| Eukaryotes (rare) | GUG | Valine | Start |
| Prokaryotes (rare) | UUG | Leucine | Start |
| Eukaryotes (rare) | ACG | Threonine | Start |
| Mammalian mitochondria | AGC, AGU | Serene | Stop |
| Drosophila mitochondria | AGA | Arginine | Stop |
| Mammalian mitochondria | AG(A,G) | Arginine | Stop |
The history of ideas about the genetic code
Nevertheless, in the early 1960s, new data revealed the failure of the "comma-free code" hypothesis. Then experiments showed that codons, considered by Crick to be meaningless, can provoke protein synthesis in a test tube, and by 1965 the meaning of all 64 triplets was established. It turned out that some codons are simply redundant, that is, a number of amino acids are encoded by two, four or even six triplets.
see also
Notes
- Genetic code supports targeted insertion of two amino acids by one codon. Turanov AA, Lobanov AV, Fomenko DE, Morrison HG, Sogin ML, Klobutcher LA, Hatfield DL, Gladyshev VN. Science. 2009 Jan 9;323(5911):259-61.
- The AUG codon encodes methionine, but also serves as a start codon - as a rule, translation begins from the first AUG codon of mRNA.
- NCBI: "The Genetic Codes", Compiled by Andrzej (Anjay) Elzanowski and Jim Ostell
- Jukes TH, Osawa S, The genetic code in mitochondria and chloroplasts., Experientia. 1990 Dec 1;46(11-12):1117-26.
- Osawa S, Jukes TH, Watanabe K, Muto A (March 1992). "Recent evidence for evolution of the genetic code". microbiol. Rev. 56 (1): 229–64. PMID 1579111.
- SANGER F. (1952). "The arrangement of amino acids in proteins.". Adv Protein Chem. 7 : 1-67. PMID 14933251 .
- M. Ichas biological code. - World, 1971.
- WATSON JD, CRICK FH. (April 1953). «Molecular structure of nucleic acids; a structure for deoxyribose nucleic acid.". Nature 171 : 737-738. PMID 13054692 .
- WATSON JD, CRICK FH. (May 1953). "Genetical implications of the structure of deoxyribonucleic acid.". Nature 171 : 964-967. PMID 13063483 .
- Crick F.H. (April 1966). "The genetic code - yesterday, today, and tomorrow." Cold Spring Harb Symp Quant Biol.: 1-9. PMID 5237190.
- G. GAMOW (February 1954). "Possible Relationship between Deoxyribonucleic Acid and Protein Structures.". Nature 173 : 318. DOI: 10.1038/173318a0 . PMID 13882203 .
- GAMOW G, RICH A, YCAS M. (1956). "The problem of information transfer from the nucleic acids to proteins.". Adv Biol Med Phys. 4 : 23-68. PMID 13354508 .
- Gamow G, Ycas M. (1955). STATISTICAL CORRELATION OF PROTEIN AND RIBONUCLEIC ACID COMPOSITION. ". Proc Natl Acad Sci U S A. 41 : 1011-1019. PMID 16589789 .
- Crick FH, Griffith JS, Orgel LE. (1957). CODES WITHOUT COMMAS. ". Proc Natl Acad Sci U S A. 43 : 416-421. PMID 16590032.
- Hayes B. (1998). "The Invention of the Genetic Code." (PDF reprint). American scientist 86 : 8-14.
Literature
- Azimov A. Genetic code. From the theory of evolution to the decoding of DNA. - M.: Tsentrpoligraf, 2006. - 208 s - ISBN 5-9524-2230-6.
- Ratner V. A. Genetic code as a system - Soros Educational Journal, 2000, 6, No. 3, pp. 17-22.
- Crick FH, Barnett L, Brenner S, Watts-Tobin RJ. General nature of the genetic code for proteins - Nature, 1961 (192), pp. 1227-32
Links
- Genetic code- article from the Great Soviet Encyclopedia
Wikimedia Foundation. 2010 .
