mardi 13 janvier 2009

「生命を定義する」 Définir la vie (2)

4 février 2008

Marie-Christine Maurel "Life as a concept and as a material subject"

 参考:彼女の講演 "Le passage du non vivant au vivant" 「無生物から生物への道」 (ビデオ1, 2

      phusis (la nature) vs nomos (the law)

The title of the symposium is in itself antinomic, because "definition" introduces a frame, a law, a convention, but "life" is full of dynamism and cannot be trapped.

In the Webster, 20 definitions:
● vital vs dead
● vitalism
●● growth, reaction to stimuli, reproduction, metabolism

questions to be asked:

● of what is composed
● from where
● how it was formed
● how it is transmitted
● what is an ancient form
● other life forms in the planets

4.5 Ga : H, C, N, O, S, P
3.6 Ga : birth of cell

topdown approach : comparative biochem
 H, C, N, S, P,  → CH2, CO2, CO, H2O,,, → biopolymer, peptide,, → living system → → today

bottom-up approach : evolutionary biochem
 today → → →  Archaea, Bacteria, Eucarya

Molecules of life
(1) synthesis of building blocks
(2) clays, metal sulfurs from hot springs may help

peptide synthesis supplied by CO underhot aqueous condition in the presence of (Fe, Ni)S

conditions for life
1) autopoiesis (Humberto Maturana and Francisco Varela in 1973)
2) self-organization / complexity
3) dorwinian evolution

# problem of complexity; physical system can be complex
Belousov-Zhabotinsky (BZ) reaction (video)

Life is characterized by a dualism (Salvador Luria)

material nature of life : historical nature of evolution

Erwin Schrödinger
laws of physics cannot be applied; must develop a new law

Systemic approach : total is more than sum of parts
autopoiesis, self organization, emergence, complexity, holism

Albert Szent-Györgyi : The living state (1972, AP)
Life has developed its process gradually, never rejecting what it has built

RNA world hypothesis and facts

early evolution; RNA replication
current RNA is fossil of ancient RNA ?

biomolecules are historical structures>
Molecular biology: evolution を in vitro で解析

viroid = naked RNA at the boundary of life
 246-574 bp
 no envelop, capsids
 not protein-coding
 resistant to high temperature, extreme pH, high pressure
 free in nature
 living fossil ?

RNA viruses = continuum from RNA world to viroids, viruses, cells

prebiotic world : accumulation of materials
aa, peptides, nitrogenous bases, sugar ..., water, clays, minerals
strates of life : phenotypic diversity, ecological niches
RNA world
free RNAs
proto cell
naked RNA → viroids
RNA → virus : cell (pro prokaryote?)
acquisition of intercellular mode of life
DNA/RNA world
endo symbiosis → chloroplasts

prion not mentioned;
 protein can transmit morphological changes upon contact (no transfer of information)

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