scholarly journals Role of Water for Life

2019 ◽  
Vol 03 (01) ◽  
pp. 3-19
Author(s):  
Bengt Nordén
Keyword(s):  
Chemical Potential ◽  
Genetic Recombination ◽  
Solar Systems ◽  
Gene Recognition ◽  
Low Dielectric ◽  
Sexual Recombination ◽  
Dna Strand Exchange ◽  
Living Organisms ◽  
Dna Strand ◽  
Life On Earth

The behavior of benzoic acid in polyethylene inspired me to reflect on why water is a unique molecule that all living organisms depend upon. From properties of DNA in aqueous solution a seemingly counter-intuitive conjecture emerges: water is needed for the creation of certain dry low-dielectric nm-size environments where hydrogen bonding exerts strong recognition power. Such environments seem to be functionally crucial, and their interactions with other hydrophobic environments, or with hydrophobic agents that modulate the chemical potential of water, can cause structural transformations via ‘hydrophobic catalysis’. Possibly combined with an excluded volume osmosis effect (EVO), hydrophobic catalysis may have important biological roles, e.g., in genetic recombination. Hydrophobic agents are found to strongly accelerate spontaneous DNA strand exchange as well as certain other DNA rearrangement reactions. It is hypothesized that hydrophobic catalysis be involved in gene recognition and gene recombination mediated by bacterial RecA (one of the oldest proteins we know of) as well as in sexual recombination in higher organisms, by Rad51. Hydrophobically catalyzed unstacking fluctuations of DNA bases can favor elongated conformations, such as the recently proposed [Formula: see text]-DNA, with potential regulatory roles. That living cells can survive as dormant spores, with very low water content and in principle as such travel far in space is reflected upon: a random walk model with solar photon pressure as driving force indicates our life on earth could not have originated outside our galaxy but possibly from many solar systems within it — at some place, though, where there was plenty of liquid water.

scholarly journals Homologous Recombination, but Not DNA Repair, Is Reduced in Vertebrate Cells Deficient in RAD52

1998 ◽  
Vol 18 (11) ◽  
pp. 6430-6435 ◽  
Author(s):  
Yuko Yamaguchi-Iwai ◽  
Eiichiro Sonoda ◽  
Jean-Marie Buerstedde ◽  
Olga Bezzubova ◽  
Ciaran Morrison ◽  
...  
Keyword(s):  
Genetic Recombination ◽  
Strand Break ◽  
Intermediate Step ◽  
Immunoglobulin Gene ◽  
Γ Irradiation ◽  
Focus Formation ◽  
Dna Damages ◽  
Dna Strand Exchange ◽  
Dna Strand

ABSTRACT Rad52 plays a pivotal role in double-strand break (DSB) repair and genetic recombination in Saccharomyces cerevisiae, where mutation of this gene leads to extreme X-ray sensitivity and defective recombination. Yeast Rad51 and Rad52 interact, as do their human homologues, which stimulates Rad51-mediated DNA strand exchange in vitro, suggesting that Rad51 and Rad52 act cooperatively. To define the role of Rad52 in vertebrates, we generatedRAD52 −/− mutants of the chicken B-cell line DT40. Surprisingly, RAD52 −/− cells were not hypersensitive to DNA damages induced by γ-irradiation, methyl methanesulfonate, or cis-platinum(II)diammine dichloride (cisplatin). Intrachromosomal recombination, measured by immunoglobulin gene conversion, and radiation-induced Rad51 nuclear focus formation, which is a putative intermediate step during recombinational repair, occurred as frequently inRAD52 −/− cells as in wild-type cells. Targeted integration frequencies, however, were consistently reduced inRAD52 −/− cells, showing a clear role for Rad52 in genetic recombination. These findings reveal striking differences between S. cerevisiae and vertebrates in the functions of RAD51 and RAD52.

scholarly journals Microsatellite and Chromosome Evolution of Parthenogenetic Sitobion Aphids in Australia

Genetics ◽  
1996 ◽  
Vol 144 (2) ◽  
pp. 747-756 ◽  
Author(s):  
Paul Sunnucks ◽  
Phillip R England ◽  
Andrea C Taylor ◽  
Dinah F Hales
Keyword(s):  
Sexual Reproduction ◽  
Chromosome Evolution ◽  
Genetic Recombination ◽  
Allelic Variation ◽  
Repeat Unit ◽  
Chromosomal Evolution ◽  
Microsatellite Variation ◽  
Wide Range ◽  
Sexual Recombination ◽  
Minimum Numbers

Abstract Single-locus microsatellite variation correlated perfectly with chromosome number in Sitobion miscanthi aphids. The microsatellites were highly heterozygous, with up to 10 alleles per locus in this species. Despite this considerable allelic variation, only seven different S. miscanthi genotypes were discovered in 555 individuals collected from a wide range of locations, hosts and sampling periods. Relatedness between genotypes suggests only two successful colonizations of Australia. There was no evidence for genetic recombination in 555 S. miscanthi so the occurrence of recent sexual reproduction must be near zero. Thus diversification is by mutation and chromosomal rearrangement alone. Since the aphids showed no sexual recombination, microsatellites can mutate without meiosis. Five of seven microsatellite differences were a single repeat unit, and one larger jump is likely. The minimum numbers of changes between karyotypes corresponded roughly one-to-one with microsatellite allele changes, which suggests very rapid chromosomal evolution. A chromosomal fission occurred in a cultured line, and a previously unknown chromosomal race was detected. All 121 diverse S. near fragariae were heterozygous but revealed only one genotype. This species too must have a low rate of sexual reproduction and few colonizations of Australia.

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