Genetic information（genetic information）It refers to the process by which an organism replicates the same thing as itself and transfers it from its parents toProgeny, or the information transmitted by cells to cells each time they divide, that isBase pairThe sequence of nucleotide in DNADeoxynucleotide, RNARibonucleotideThe order in which they are listed.[1]
In 1866, GJ. Mendel (1866) formed the concept of factors corresponding to various biological traits (calledgene）Contains corresponding information (later created by G. Beadle et al. (1941)Genetic biochemistryThe research of, depicts such a contour: genes and determine the biological structure and function of the protein has a one-to-one correspondence.[1]
Regarding the chemical nature of genes, according to OT. Avery et al. (1944), and AHershey and MFor Chase (1952)Escherichia coli bacteriophageThe experiment of character expression carried out with DNA has clarified that DNA is the carrier of genetic information.AttachDNA structureThe research progress has established such a concept in 1960, that isgeneThe information contained in the DNABaseThe arrangement is symbolic.When information is expressed, the base arrangement of DNA is firstTranscriptionThe bases of RNA are arranged, and then the protein is synthesized according to this arrangement.The carrier of genetic information of some viruses is not DNA, but RNA.Genetic information is not only related to proteinGenetic informationIt also includes information necessary for the interpretation of information, information necessary for controlling the expression of information, and all information necessary for organisms to replicate the same structure as themselves.[1]
type
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In geneDeoxynucleotideThe diversity of genetic information is determined by the difference of species, number and order.
Genetic transmission classification
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The flow of genetic information follows the following rules
Several types of transmission of biological genetic information;
Central ruleAnd its supplementary contents tell us the flow direction of genetic information.The decomposition process includes the following six points:dna replication The flow direction of genetic information is from DNA to DNA;DNATranscriptionThe flow direction of genetic information is from DNA to RNA;Translation, genetic information flows from RNA to protein;For RNA replication, genetic information flows from RNA to RNA;RNAReverse transcription, genetic information flows from RNA to DNA;For protein replication, genetic information flows from protein to protein.But how many of the six points should be included in the transmission of genetic information in organisms?The transmission process of genetic information is different for different types of organisms.The transmission of biological genetic information can be roughly divided into the following types:
DNA replication type
In DNAReplicatedThe flow of genetic information of organisms includes three points:Self replicationThe flow direction of genetic information is from DNA to DNA;DNATranscriptionAnd translation, the flow direction of genetic information is from DNA to RNA to protein.This type of creature is mainly aimed at the vast majority of animals, plants andbacteriophage viruses Etc.[1]
RNA replication type
stayRNA replicationIn type B organisms, the flow of genetic information of organisms includes two points: RNASelf replication, the flow direction of genetic information is RNA → RNA;Translation, genetic information flows from RNA to protein.This type of creature is mainly aimed atPlant virusasTobacco mosaic virusandAnimal virusasPoliovirusEtc.There is also only one kind of flow of some genetic information: self replication of RNA, and the flow direction of genetic information is from RNA to RNA;This type of organism mainly targets the SARS virus,influenza virusEtc.
RNA reverse transcript
In RNAReverse transcriptionIn type A organisms, the flow of genetic information of organisms includes three points: reverse transcription of RNA, and the flow direction of genetic information is from RNA to DNA;TranscriptionThe flow direction of genetic information is from DNA to RNA, translation, and the flow direction of genetic information is from RNA to protein.This type of organism is mainly aimed at cancer causing viruses andAIDSOfHuman immunodeficiency virus（HIV）。
Protein replicator
In protein replication type organisms, the flow of genetic information of organisms includes one point: protein replication, and the flow direction of genetic information is from protein to protein;Only one kind of this type of creature was found 2000 years ago, which is popular in Europe and AmericaMad cow disease virus（Prion）。
origin
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Genetic information is generated byTriplet codonTherefore, the origin of genetic information in the final analysis isCodonThe origin of.So far, several hypotheses have been put forward.These theories discussed the possible ways of the origin of genetic codons from different perspectives, such as contingency, chemical interaction, coevolution, origin of biochemical system, and comprehensive effect. In particular, the evolution mechanism from energy transformation to informatization for the purpose of building biochemical system deserves attention.[2]
Coagulation event hypothesis
Francis Crick put forward the coagulation event hypothesis, believing that the relationship between codon and amino acid is fixed at a certain time, and it is difficult to change it later.Almost all creatures use the same set of codes, which seems to support this hypothesis, which also shows that all creatures originate from a single common ancestor (Crick 1968).This speculates the important time nodes of the evolution events.[3]
Stereochemistry hypothesis
Carl Richard Woese put forward the stereochemical hypothesis, believing that amino acids have selective chemical binding power with their corresponding codons, that is, the origin and distribution of genetic codes are closely related to the direct chemical interaction between RNA and amino acids, or,The stereochemical nature of codons depends on the complementarity of physical and chemical properties between amino acids and corresponding codons (Woese et al. 1966).This may be an important chemical mechanism of codon origin.[4]
Polyansky et al. (2013) found through experiments and calculations that the density distribution of different nucleic acid bases in mRNAs is very similar to the distribution of amino acid electrophilic density of these same nucleic acid bases in the protein they encode. The genetic code is highly optimized to maximize this match.
Coevolutionary hypothesis
Wang Zihui (J. Tze Fei Wong) proposed the co evolution hypothesis, and believed that the codon system has imprints of the pre biological metabolic pathway of the formation of original amino acids, so it can be derived fromAmino acid metabolismThe pathway finds that the evolution process of codon, that is, the evolution of codon is parallel to the evolution of amino acid biosynthesis.This hypothesis believes that the fidelity of amino acids and corresponding codes reflects the similarity of amino acid biosynthesis paths, not the similarity of physical and chemical properties (Wong 1975).This speculated a possible route of codon origin, but the synthesis of various amino acids from simple raw materials may have occurred at the end of pre life evolution.[5]
ATP center hypothesis
Schematic Diagram of ATP Center Hypothesis
Xie Ping (2016) proposedATP center hypothesis(ATP central hypothesis)Genetic codeAs a part of the biochemical system, it must be related to the evolution of the biochemical system, and the core of the biochemical system is the energy carrier ATP (various biochemical cycles, such asCalvin cycle、GlycolysisandTricarboxylic acid cycleIt is the only end product of light energy conversion into chemical energy, and it can be derived from othernucleotideThese nucleotides can be condensed and synthesized by themselvesnucleic acid。ATP can activate amino acids, which are manyPeptide chainThe condensation of provides an energy base.Therefore, only ATP can establish nucleic acid andproteinLinks between.[6]
Synthetic evolution hypothesis
Knight et al. (1999) put forward a comprehensive hypothesis that genetic code is affected at different stages by three factors: selection, history and chemistry.This hypothesis suggests that the direct interaction between amino acids and codons may determine the coding of amino acids at the initial stage of genetic code origin;During the introduction of new amino acids and codon expansion, coevolution may play a dominant role;With the evolution of tRNA and the increase of protein functions, the direct interaction between amino acids and codons is gradually eliminated, and the exchange of codons at different scales allows optimization through the redistribution of codons to some extent.[7]
Other hypotheses
Egen put forward the hypothesis of in vitro selection in 1981, the British chemist Leslie Eleazer Orgel put forward the hypothesis of the origin of decoding mechanism in 1989, and the Belgian cell biology and biochemist Christian de Duve, who won the Nobel Prize in physiology or medicine in 1974, put forward the second genetic code in 1988Hypothesis.
University of Bath Wu et al. (2005) speculated that,Triad passwordIt evolved from two types of duplex codes, which are divided according to the fixed base position in the triplet code, including prefix codons and suffix codons.However, some people speculate that the triplet codon evolved from the longer codon (such as the quadruplet codons), because the longer codon has more coding redundancy and can withstand greater mutation pressure (Baranov et al. 2009).
2007Beijing Institute of Genomics, Chinese Academy of SciencesXiao Jingfa and Yu Jun (2007) proposed the stepwise evolution hypothesis of the genetic code. They believed that the genetic code formed initially should only be encoded by adenine A and uracil U, encoding a total of seven diverse amino acids. With the increase of life complexity, guanine G is released from the function of the main operating signal, followed by the introduction of C,The genetic code was gradually expanded to 12, 15 and 20 amino acids (Xiao Jingfa and Yu Jun 2009).
Zhao Yufen (1994-1996), an organic chemist at Xiamen University, also put forward the view that nucleic acids and proteins originated together, and believed that "phosphorus is the regulatory center of biochemical processes" becausePhosphorylated amino acidIt can generate nucleic acid and protein, LB membrane and liposome at the same time.She believed that the primitive earth had frequent volcanoes, pyrophosphates and pyrophosphates were easy to accumulate on the earth's surface, and the energy contained in the P-O-P bond was eventually transferred to peptide bonds and nucleotides by forming P-N bonds with amino acidsPhosphodiester bondMedium.She speculated that in the process of generating protein and DNA/RNA at the same time from phosphorylated amino acids, protein and DNA/RNA could interact through the regulation of phosphoryl groups, thus generating the rudiments of the original codon and further evolving to the modern form of genetic code.But the question is, why should phosphorylated amino acids direct the co evolution story of nucleic acids and proteins?
There are also four kinds of theories about the origin of codons: chemical principles, biological expansion, natural selection and information channels.According to rate distortion models in information theory research, the origin of genetic codons depends on the balance of three conflicting evolutionary forces: the demand for diverse amino acids, resistance to replication errors, and resource minimization (Freeland et al. 2003,Sella and Ardell 2006，Tlusty 2008，）。[6]
