Evolution of biological macromolecules in the process of biological evolution
Molecular evolution refers to the evolution of biological macromolecules in the process of biological evolution.It mainly includes the evolution of protein molecules, nucleic acid molecules and genetic code.
Chinese name
molecular evolution
Foreign name
molecular evolution
Introduction
Evolution of biological macromolecules in the process of biological evolution
The evolution of biological macromolecules in the process of biological evolution, including the evolution of prebiotic substances;The evolution of protein molecules and nucleic acid molecules, as well as the evolution of organelles and genetic institutions (such as genetic code).The study of molecular evolution can provide evidence for the process of biological evolution, and provide an important basis for the in-depth study of evolutionary mechanism.
The broad sense of molecular evolution has two meanings. One is the evolution before the appearance of primitive life, that is, the chemical evolution of the origin of life;The second is the changes in the structure and function of biological macromolecules and the relationship between these changes and biological evolution during the evolution and development of organisms after the birth of primitive life, which is commonly referred to as molecular evolution.
Prelife evolution
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The history of the earth is about 5 billion years.In the late 1960s, an ancient bacterial fossil was found in the Precambrian strata of southern Africa. It lived about 3.2 billion years ago. In addition, some more ancient tiny bacteria similar to protoalgae were also foundBiofossilIt lived about 3.4 billion years ago, which is the earliest record of life found on the earth.
In terms of research on the evolution of life on the Earth and other celestial bodies, the agglomeration theory was proposed by the Soviet biochemist A. И. Opalin in 1936, and the British biophysicist JD. Bernard's clay surface theory, American scholar SW. The theory of protein like microsphere proposed by Fox and K. Harada Xin, and the theory of marine particles proposed by Jiang Shangshi Erfu in 1969, all have their own unique views.In 1975, American physical chemist and biochemist M. Calvin put forward a model on the basis of summarizing various theories, and believed that the original generating elements covering the earth first formed various original generating molecules (methane, hydrogen sulfide, etc.).Under the influence of many kinds of energy (including ultraviolet ray of the sun, ionizing radiation energy and meteorite shock wave, etc.), the generating molecules further form low molecular organic compounds, and then transition from low molecular organic compounds to high molecular organic compounds.It was about 4 billion years ago that the original organism with life form was formed from macromolecular organic compounds.
On the original environmental conditions of the origin of life, Opalin has written a monograph.The first successful attempt to demonstrate the theory of Opalin by experiment was the American HC. Yuri and S50. Miller.In 1952, they first imitated the environmental conditions in the pre life period, and formed a variety of products through the discharge reaction in the mixture of methane, ammonia, hydrogen and water, including various amino acids, purines, pyrimidines and some simple sugar molecules.Later, phosphorylation of nucleosides was found under other conditions.Since 1968, it has been found that similar organic compound molecules also exist in interstellar space, and there are some indications that amino acids even exist in space meteorites and lunar dust.In 1958, Fox's experiment confirmed that the mixture of anhydrous amino acids condensed into a protein like substance at a temperature higher than 100 ℃.In water and high concentration of salt solution, proteinoids can form microspheres with a diameter of about 0.5~3 microns.Microspheres can even reproduce by budding.Nucleic acids can also be formed from nucleotides under simulated laboratory conditions.All these experimental results show that biological macromolecules can be formed in vitro on the original earth surface without enzymatic reaction.What kind of protein and nucleic acid appeared first in the pre life evolution stage and how their interdependence was on earth are all issues in research and debate.
Nucleic acid evolution
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Change in quantity
Nucleic acid is a kind of genetic material, which can clearly see that everygenomeThe amount of nucleic acid in the total trend gradually increased (Table 1).
From the general trend, the lower the biological DNA content, the less, the higher the more.However, this rule is obviously not applicable to some organisms for many reasons.Generally, the higher the level of life, the more genes are needed (see genes). However, after evolution reaches a certain stage, the number of genes will no longer increase accordingly.The fact that the respiratory metabolism and amino acid and nucleotide metabolic pathways of bacteria are not very different from those of humans is enough to show that the structural genes of related enzymes are not increased significantly.Ploidy has a great influence on the content of DNA in each cell.The high DNA content of ciliates is due to this reason.for exampleParamecium binucleatumThe macronucleus of (Parameticium aurelia) is 860 ploidy,Tetrahymena pyriformis(Tetrahymena pyriformis).The high DNA content in each cell of angiosperms is also due to this reason (see chromosome ploidy).The different amount of repeat sequences and introns of non coding proteins in various organisms is another reason for the different DNA content.
Qualitative change
The quality of DNA is also changing in the process of biological evolution.The DNA similarity of various organisms can be analyzed by molecular hybridization (Table 2).
For a certain kind of organism, for exampleprimateAnd bacteria and other organisms can use the same method to determine their genetic relationship (Figure 1).
The results of conservative molecular hybridization in evolution can only show the same or different degree of DNA of two organisms, and we can know how they are the same or different through DNA sequence analysis.aboutEscherichia coliandLambda bacteriophageAccording to the nucleotide sequence analysis of 46 promoter regions, it was found that there was a conservative region called pribuno sequence in front of the mRNA transcription position of each gene 10 base pairs apart, including the nucleotide sequence TATAATG.In this case, especially from the left, if the first, second and sixth bases change to G or C, the transcription efficiency will decline, especially for the T at the sixth position. No exception has been found in 46 cases.The similar conservative region existing in higher organisms is called Hogness sequence.
Chromosomes of five Enterobacteriaceae bacteria were analyzedDNA replication starting pointThe same sequence of 245 nucleotides can be up to 85%, which also shows that this sequence is highly conservative.
The existence of this kind of conservative region shows that these structures are very important for their respective functions, so they cannot be easily changed in the process of biological evolution.As for the location changes of individual genes or chromosome segments, they can occur and be preserved during evolution.Changes in individual nucleotides can also occur and be preserved. These changes can be clearly reflected in the comparative study of chromosomes and genetic maps of various related organisms, as well as in the comparative study of proteins.
Protein evolution
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Protein differences can be measured by immunological methods to determine the affinity of proteins of various organisms. For example, human albumin is injected into rabbits, antiserum is obtained from rabbits, and the antiserum is measured by precipitation reaction with albumin of humans, gorillas, chimpanzees, etc. It can be seen that the more closely the affinity is, the stronger the precipitation reaction of albumin is.
The electrophoretic determination of isozymes was developed in the 1970s and can be used for comparisonBiological proteinQualitative kinship method.Isozymes are enzymes with the same function but different primary structures.The substitution of any amino acid in a protein can be detected as long as it brings charge difference that can be distinguished by electrophoresis, but it cannot be detected if it does not bring charge difference.Because this method is simple and fast, it is often used in the study of molecular evolution.For example, the isozymes of 36 enzymes in 14 subspecies of 9 drosophila species, including Drosophila wil listoni, were analyzed by electrophoresis, and their pedigrees could be drawn according to the analysis results.
Amino acid difference
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The results of amino acid analysis can provide more information for the study of biological kinship.CytochromeC is a protein that exists from human to yeast, which is convenient for extensive comparison.Cytochrome CIt is composed of 140 amino acids.Comparing the amino acid composition of cytochrome C of various organisms with that of human, it can be seen that the closer the relatives are, the more similar the cytochrome C of organisms is to that of human (Table 3).stayhemoglobin、Blood FibrinThe same research has been conducted in both.According to the research results of amino acid composition of these three proteins in many animals, we can also see thatCytochrome CThe evolutionary rate of is the lowest.fibrinThe highest evolutionary rate of is hemoglobin (Fig. 2), which means that cytochrome C is the most conservative protein.For example, the common ancestor of humans and macaques lived 40 to 50 million years ago, but now only one amino acid in cytochrome C has changed (Table 3).Histones in chromosomes are more conservative proteins.
AdulthemoglobinIt is composed of two alpha chains and two beta chains, and fetal hemoglobin is composed of two alpha chains and two gamma chains.α. Both β and γ chains are composed of 146 amino acids, and many amino acids are the same and very similar to myoglobin.According to the research on hemoglobin and myoglobin of many animals, we can drawHemoglobin molecule(Figure 3).
Sources of change
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In the long evolutionary process, biological DNA has undergone various changes.It includes gene mutation, gene recombination, chromosome translocation, etc.
Base substitution mutations often result in the change of an amino acid in a protein.For example, if the glutamic acid in the 6th position of normal hemoglobin is changed to valine, it will become HbS of sickle cell anemia. If it is replaced by lysine, it will become HbC. The base of the former is from GAA (glutamic acid) to GUA (valine), and the latter is from GAA (glutamic acid) to AAA (valine).It has been found that it is caused by the change of single amino acid on the α chainAbnormal hemoglobinThere are no less than 40 kinds of abnormal hemoglobin, and more than 80 kinds of abnormal hemoglobin are caused by the change of single amino acid on the β chain.
The duplication of DNA molecules is also an important reason for the changes of protein molecules.for examplehemoglobinThis is the case for the relationship between α, β, γ and δ polypeptide chains in (Fig. 3).
Translocation is another reason for the change of amino acid sequence in protein molecules.For example, there is an anemia called Lepore. The amino end of a hemoglobin chain in the patient is the same as the amino end of the delta chain, and its carboxyl end is the same as the carboxyl end of the beta chain.
Deletions often occur in the evolution of protein molecules.For example, according to the corresponding comparison of the sequence of different types of polypeptide chains, the 22nd residue of hemoglobin can confirm that the difference between human and horse alpha chains is caused by one deletion.
Another case is chain extension, such ashemoglobinHbCS is a variant with normal alpha chain. It extends 31 additional amino acid residues from arginine at the carboxyl end of the normal alpha chain to become a peptide chain with 172 amino acids. The additional amino acid sequence has nothing to do with other parts of the alpha chain or other hemoglobin chains.
The evolution of genetic code The nuclear gene codes of existing organisms are the same (see genetic code), indicating that the genetic code system has long been fixed in the process of biological evolution.
In 1979, it was found in three laboratories that the principle of uniformity of genetic code did not apply to mitochondrial genes.For example, UGA in mitochondria of human and yeast is notTermination codonIt's the tryptophan codon. AUA is notisoleucineIt'smethionineCodon.These facts show that the genetic code has indeed changed in the process of biological evolution.
MammalianMitochondrial DNAThe full sequence of the has been analyzed clearly, and there are 23 sequences encoding the transport of RNA (tRNA).The sequence analysis and molecular hybridization of yeast mitochondrial DNA also yielded about the same number of tRNA sequences as mammalian mitochondria.There are at least 50 tRNAs encoded by chromosome genes.The type of tRNA in mitochondria is less than that encoded by chromosome genes.This fact shows that the mitochondrial code system is relatively primitive.
principle
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Three dimensional structure principle
For each protein of various biological species, the rate of molecular evolution measured by the number of amino acid substitutions per site per year is roughly constant, as long as the function and three-dimensional structure of the molecule remain unchanged;
Principle of molecular primary and secondary
The evolution rate of molecules or molecular regions with less function (calculated by the number of mutation substitutions/each point/year) is faster than that of molecules or molecular parts with important function.
Destructive principle
The mutation replacement (i.e. conservative replacement) that has less damage to the structure or function of existing molecules will evolve more frequently than the mutation replacement with greater destructive power.
Principles of gene renewal
Gene replication always occurs before a new function is acquired
