2022-09-20 カリフォルニア大学サンタバーバラ校(UCSB)
How life on Earth may have gotten its start between mica sheets
他の自然発生(生命が非生物の中からどのように発生したか)の概念の要素を取り入れており、生体分子や代謝プロセスの前駆体はすべて雲母の層の間に集められた可能性があると主張している。
雲母が優れている点は、カリウムイオンによって雲母シートが結合しているため、膨潤せず、より安定した環境を提供できる。
化学エネルギーが存在しなかった時代には、水が出入りするときに雲母の開閉運動によって、分子を押し付け合っていたようだ。
このように強制的に接近させることで、分子間の相互作用が促進され、現在の酵素の作用と同じような働きをした可能性がある。相互作用する異なる分子が結合して、RNA、DNA、タンパク質が形成される。その中に含まれる脂質が、やがて大きな分子群を包み込み、細胞膜となる。
<関連情報>
- https://www.news.ucsb.edu/2022/020714/life-imitates-mica
- https://www.cell.com/biophysj/fulltext/S0006-3495(22)00692-0
DNAと生命の起源を解明する雲母粘土 DNA and the origins of life in micaceous clay
Helen Greenwood Hansma
Biophysical Journal Published:September 20, 2022
DOI:https://doi.org/10.1016/j.bpj.2022.08.032
Abstract
Reproducible imaging of DNA by atomic force microscopy was a useful predecessor to Ned Seeman’s DNA nanotechnology. Many of the products of DNA nanotechnology were imaged in the atomic force microscope. The mica substrate used in this atomic force microscopy research formed the inspiration for the hypothesis that micaceous clay was a likely habitat for the origins of life. Montmorillonite clay has been a successful substrate for the polymerization of amino acids and nucleotides into peptides and DNA oligomers in research on life’s origins. Mica and montmorillonite have the same anionic lattice, with a hexagonal spacing of 0.5 nm. Micas are nonswelling clays, with potassium ions (K+) holding the crystal sheets together, providing a stable environment for the processes and molecular complexes needed for the emergence of living cells. Montmorillonite crystal sheets are held together by smaller sodium ions (Na+), which results in swelling and shrinking during wet-dry cycles, providing a less stable environment. Also, the cells in all types of living systems have high intracellular K+ concentrations, which makes mica a more likely habitat for the origins of life than montmorillonite. Finally, moving mica sheets provides mechanical energy at the split edges of the sheets in mica “books.” This mechanical energy of mica sheets, moving open and shut, in response to fluid flow, may have preceded chemical energy at life’s origins, powering early prebiotic processes, such as the formation of covalent bonds, the interactions of molecular complexes, and the budding off of protocells before the molecular mechanism of cell division had developed.
