端午节快乐用英语怎么说Special article
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激活英文INTRODUCTION
enome evolves by acquiring new quences, by the recombination of existing ones and by mutation.Recombination occurs between corresponding quences of DNA. One of typical examples is the reciprocal recombination between two copies of a quence that is repeated in the same orientation, i.e. direct repeats (DR). Two double-strand circular DNA molecules, each retaining a single copy of the DR, are the result of this rearrangement. The requirements of the reciprocal recombination are two recombination sites and multiple copies of the enzyme from the site-specific nicka-liga family. This reaction can be divided into two stages: formation of a synaptic complex containing two intertwined DR sites and enzyme mole-cules, and the breakage and reunion of DNA.
The cond stage starts with two double-strand break resulting in four 3'-OH and four 5' -P free ends. The 3'-OH ends than attack the phosphate bonds at the corresponding position in the other str
and of the duplex. This creates a hairpin structure at the one end in which the 3' end of one strand is covalently linked to the 5'end of the other strand. Strand breakage and reunion are accom-plished by two successive ester exchanges in which bond energy is conrved. It rembles to the topoisomera-, resolva-,gyra-, transposa-, inverta-like reaction, recombination of
immunoglobulin genes with RAG1 and The ancestral organism, in this ca an Archaea, from the very begin-ning already had about 4000 genes, including tho for energy production and conversion: glycolysis, pyruvate dehydrogena complex, citric acid cycle, respiratory-chain ATP production;genes necessary for different types of recombination, for cell envelop biogenesis and others. Topological characteristics of DNA are the central aspect of all its functional activities - recom-bination, replication, and transcription. One of this is a double-helical region formed by ba pairing between adjacent (inverted)complementary quences called hairpin structure. During the performance of some of its functions, prokaryotic DNA molecule is typically attached to the plasma membrane, and hairpin struc-ture is one of the candidates for this event. It is possible that in a very ancient prokaryotic cell, the plasma membrane with its attached DNA, could have invaginated and eventually formed a two-layered envelope of membrane completely surrounding DNA.This envelope is presumed to have pinched off (or spindled on)from the plasma membrane producing a DNA compartment sur-rounded by a double membrane.SCENARIO
英语专业就业At an early stage of biogenesis there was a precursor autotrophic surface metabolist followed by micellular organisms (1).Transition from surface organisms to cellular form of life suggests a step-by-step evolution of the nucleotide synthesis and ba pairing leading to gene genesis. From this point, future steps of biogenesis are bad on genome evolution as a reflection of cell-environment and its own properties. Segregation of ancestral
archaebacterial genome (Table 1) into two compartments (Figure新东方论坛
Address correspondence to:
Milanko Stupar, Laboratory for Radiobiology and Molecular Genetics, Institute for Nuclear Science, Vinèa, Po Box 522, 11001 Belgrade, Serbia and Montenegro The manuscript was received: 12. 07. 2002Provisionally accepted: 19. 07. 2002Accepted for publication: 19. 02. 2003
LABORATORY FOR RADIOBIOLOGY AND MOLECULAR GENETICS,INSTITUTE FOR NUCLEAR SCIENCE, VINÈA, BELGRADE, SERBIA AND MONTENEGRO
Genetic recombination and the origin of mitochondrion
Division of ancestral prokaryotic genome into two circular double-stranded DNA mole-cules is a basi
s for future parate evolution of nuclear and mitochondrion compart-ments. Universal double sheet of lipid molecules by invagination, at the level of mem-brane-hairpin attachment, formed two-layered envelope completely surrounding tho two DNAs. Presumed ancestral prokaryote in this ca is an Archaebacteria, which would lead to formation of six main groups of organisms: archaebacteria (Archaea),eubacteria, Protista, Fungi, Plantae and Animalia.
KEY WORDS:Recombination, Genetic; Mitochondria; Archaea; Evolution
Milanko STUPAR
G
1) is a result of this stepwi evolution. It led to the increa of evolutionary stability of growing nuclear genome and was a basis for lective advantage, as well as for mitochondrial specializa-tion. This scenario includes veral steps: DNA-membrane attachment, DNA double-strand break, DNA ligation, and rolling over (or spindle off) of the attached membrane surrounding tho two molecules. Activation of div quences (Figure 1) is probably required for its association with cell membrane. The properties of the membrane fraction to bind DNA suggest that it includes com-ponents necessary to resolve this process. Which of the events cau the others is not obvious, b
ut attachment of archaebacter-ial DNA to the membrane at the level or in the vicinity of div quence, could provide a mechanism for both DNA gregation and invagination of the covalently clod circular (CCC) molecule (Figure 1) by two-layered lipid membrane. After step c) (Figure 1)there are veral possibilities: 1. Invagination and enveloping of the mitochondrial genome, but not the nuclear; 2. Invagination and enveloping of both genomes; 3. Invagination and enveloping of nuclear but not mitochondrial genome; 4. Releasing of both genomes; 5. Archaebacterial undivided universal genome; 6.Archaea with invagination and enveloping of whole genome lead-ing to amitochondriated eukaryotes (Protists).
In the first ca there is an open possibility for evolution of future nuclear genome by acquiring new quences and specialization of the mitochondrion. One of the organisms that aro after this (archaebacteria cyanobacteria-like precursor) is a good candi-date for cond dividing recombination event that leads to the chloroplast chromosome formation (Scheme 1). Scheme 1shows overall view of phylogeny after two cycles of reciprocal genetic recombination of the universal ancestral Archaea genome. Table 1 shows possible gene/gene class contents of the Archaea donor of the mitochondrial genome. This cell has genetic starting material to evolve to the eukaryotic lineage, which means it has genes necessary to perform all forms of energy pro-duction and genetic recombination.
2020英语高考Figure 1. Reciprocal recombination between direct repeats excis the material between them, one product has a "nuclear genes" compartment and another has a "mitochondrial genes" compartment. Each product of recombination has one copy of the direct repeats. (a) Archaebacterial genome with two direct repeats called div (dividing) quences (green boxes), between them is a nuclear (nu -clear region) and mitochondrial (mt -blue region) gene contents. (b) Pairing of direct repeats (like figure eight) and its attachment to the membrane is initiation signal for recombina enzyme action (breakage/joining). (c) Recombination releas material between repeats as covalently clod circular (CCC) molecule attached to the membrane. (d) The view from below position (b) between inner membrane and inter-membrane space. Recombina enzyme (circles) intro-duces double-strand break at the level/vicinity of div site leaving four 3' ends and four 5' ends; subquent joining reaction by the same enzyme, covalently clod tho two molecules. Arrow indicates outer membrane carpet.
Stupar M.
Table 1.
cream pieGene/genes class contents of the Archaea before genome division
DISCUSSION
Dawning and tting of the Archeozoic eon
Mitochondrion genesis and mitochondrial genome processing (genes transfer between cp- mt- nu) is one of the crucial point in the evolution, which begins with biochemical - energetic devel-opment of the membrane (at the time of the very early beginning of biogenesis cellular matrix did not exist) (1). Fundamental sim-ilarities in the metabolic pathways in cellular organisms provide a starting evidence for evolutionary conrvatism operating over four billion years. If mitochondrial genome aris after paration from the nuclear one, then Archaebacteria is the oldest group of cellular form of life and worldwide ancestor for all living organ-isms.
After first RNA ba pair forming [A - U (2)] further acquisition of G is inevitable (G - U ba pair are found in critical and most con-rvative rRNA and tRNA quences):
A - U
单词全记牢=> A-U-G.
U - G
This leads to conclusion that AUG is the first triplet of nucleotide. By this way it is possible to construct progenome of the progenot, that means alignment of the gene class in Archaea - genes for cell envelope - for energy production and conversion - for DNA replication, repair and recombination. It might be that first DNA quence rves as both gene and promoter at the same time and RNA as a primer for replication and expression. Next 1.5 billion years of evolution of the progenome results in a universal Archaea genome with about 3000-4000 genes coding for all fundamental metabolic pathways common for all organisms.
Archaea posss veral characteristics that distinguish it from both eubacteria and eukaryotes and place it at a unique position, not as an intermediate but as a starting point. At that very Genetic recombination and the origin of mitochondrion
Shema 1. Hypothetical phylogenetic tree of the biogenesis bad on the surface metabolism and subquent recombinant division of the archaebacterial genome. (1) First division of archaebacterial genome; (2) Second division of cyanobacteria precursor-like genome; (3) After first recombination events - evolution of the cytoskeleton and endomembranes (having in mind that genes for cell envelope biogenesis already exist in Archaea).
moment, before CCC progenome division, two factors play a leading part: capacity of the ancient genome and oxygen concen-tration. It ems likely that capacity of this genome depends upon gene number rather than nucleotide number.not at all
Maximal capacity of genes number (about 4000) and oxygen concentration of about 1 percent of prent-day levels fall at the same time, some 2.5 billion years ago, and it was an expected moment in time for ancestral genome division. The major part of the genome is questered in nucleus. To prevent integrity of the individual genes against interruption, nuclear DNA is gregated into chromosomes, plasmids, transposons, nucleolus, satellite DNA quences, and episomes, becau of its specialized func-tions. This all happens in the same manner - by means of genet-ic recombination.
To give proof of the reciprocal recombination engagement in the origin of mitochondrial genome, veral things have to be done: (1) To arch for div sites in the mitochondrial and nuclear genome quences.备忘录英文
(2) To arch for the function of spacer quences, unknown open reading frames (ORFs) specificity, in order to find new enzymes (such as new recombina that catalyzes the introduc-tion of P nucleotides at coding ends). To give functional vision of the "non-coding" regions by simulated ba substitution to dis-criminate inactivated (silenced) or hidden genes of the archaean origin actively participated before 2.5 billion years.
(3) Cancer cell as a model for study reversible evolution of free living organisms. Cancerogenesis is a synonym for reversible evolution, cell descents on one's back, precily at paration of nu from mt compartment. At this very moment disordered equi-librium between membrane basal metabolism (loss of contact inhibition and aberrant expression of transmembrane genes -future oncogenes) and accelerated cell division (by trigger silenced ancient genes - future oncogenes) have great influence over energy production (enormous glycolysis increa). Expression of gene cluster, gene transfer (mt- nu), and genetic recombination study of this transient pha can prove obvious succession of events in step-by-step evolution.
Acknowledgments
I thank to Prof. Dr. V. Leskovac, Prof. Dr. V. S. Vidoviæ and Jasminka Stupar who helped me write this paper. Many thanks to tho who are patient enough to wait for more detailed expla-nations.REFERENCES
1.Wachtershaur G. Before Enzymes and Templates: Theory of Surface
Metabolism. Microbiological Reviews. 1988:452-84.
2.Wachtershaur G. An all-purine precursor of nucleic acids. Proc Natl Acad
Sci 1988;85:1134-5.
Stupar M.
