The tree of life:
Darwinian chemistry as the
evolutionary force from cyanic acid
to living molecules and cells
Nils G. Walter
Chemistry
Nils Walter - Origins: The Universe, Earth, and Life
Chemistry
So far we are here…
™
Chemical Evolution
™
Self-organization
™
Biological Evolution
How do we get here?
Voet & Voet, Biochemistry
Nils Walter - Origins: The Universe, Earth, and Life
Cyanic acid and friends: The molecules at the root
1953, U. Chicago:
Stanley L. Miller
& Harold C. Urey
Nils Walter - Origins: The Universe, Earth, and Life
How “complex” organic molecules formed
1961: U. Houston
Juan Oro
L.E. Orgel, Scientific American 10/1994
Nils Walter - Origins: The Universe, Earth, and Life
The basic building blocks
Amino acids
Nucleo bases
Lipids
Sugars
Voet & Voet, Biochemistry
Nils Walter - Origins: The Universe, Earth, and Life
Building larger, “biological” molecules:
Condensation and (hydrolytic) decay
Nucleotide
Clay pocket helps
exclude water!
Nils Walter - Origins: The Universe, Earth, and Life
But wait – if there is decay, doesn’t the second Law
of Thermodynamics (“entropy tends to increase”)
drive everything back to square one?
No, not if the system is far
from equilibrium and an
external energy source drives
it to increasing complexity!!!
Günter
Wächtershäuser
Pyrite
Nils Walter - Origins: The Universe, Earth, and Life
Pumping fuel into the system: Thioester formation
High temperature
acidic conditions
(e.g., thermal vents)
Christian
de Duve
Energy:
ATP, PPi
Catalysts: RNA
Pyrite,
H2S
Reduction:
Organic acids,
aldehydes
Pyrite
Nils Walter - Origins: The Universe, Earth, and Life
The resultant increase in entropy of the Universe
leads to assembly of (bio)polymers: Example RNA
RiboNucleic Acid
Leslie
Orgel
¾
Other (bio)polymers may
have preceded RNA
Nils Walter - Origins: The Universe, Earth, and Life
The RNA World: Living molecules
L.E. Orgel, Scientific American 10/1994
Nils Walter - Origins: The Universe, Earth, and Life
Driving force of evolution: Darwinian chemistry –
Replication, Mutation, Selection
Genotype: Sequence
Mutation:
Quasispecies
Replication
Energy
Phenotype:
Structure, Function
Selection
Nils Walter - Origins: The Universe, Earth, and Life
Rebuilding the RNA World, one function at a time
Peptide bond formation
by the ribosome is
catalyzed by the RNA
component:
2000, Moore & Steitz
RNA Replicase:
2001, Bartel et al.
RNA Nucleotide Synthase:
1998, Unrau & Bartel
Johnston et al., Science 292 (2001) 1319; Chapple, Bartel, Unrau, RNA 9 (2003) 1208
Nissen, Hansen, Ban, Moore, Steitz, Science 289 (2000) 905
Nils Walter - Origins: The Universe, Earth, and Life
Towards ever higher complexity – why,
and what are fractals?
Fractals are
complex, selfsimilar geometric
structures from
simple
mathematical
rules
¾ feedback loops
generate fractal
geometries in
nature
¾
Nils Walter - Origins: The Universe, Earth, and Life
Hypercycles and Metabolism
Manfred
Eigen
M. Eigen, W. Gardner, P. Schuster, R. Winkler-Oswatitsch, Scientific American 4/1981
Nils Walter - Origins: The Universe, Earth, and Life
Primitive cells in the primordial world:
Distinction between self and non-self
dies
out
Nils Walter - Origins: The Universe, Earth, and Life
Transitions to an RNA-protein,
then the modern DNA-RNA-protein world
DNA
RNA
RNA
RNA
protein
protein
Pictures from: Ramakrishnan, Cell 108 (2002) 557; Nissen, Hansen, Ban, Moore, Steitz,
Science 289 (2000) 905; Sawaya, Guo, Tabor, Richardson, Ellenberger, Cell 99 (1999)
167; Torres_Larios, Swinger, Krasilnikov, Pan, Mondragon, Nature 437 (2005) 584
Nils Walter - Origins: The Universe, Earth, and Life
Chemical Evolution took billions of years,
but left few traces
Chemical Evolution
J.P. Gogarten, J.P. Townsend, Nat. Reviews Microbiol. 3 (2005) 679
Nils Walter - Origins: The Universe, Earth, and Life
“Junk” DNA and HIV:
Modern evidence for the RNA World
¾
98% of the human genome
are “junk” DNA
¾ Such “junk” DNA plays
important, still ill-understood
roles in the regulation and
maintenance of our genome
¾
While RNA viruses
like HIV are modern,
they may be analogs of
ancient, minimal RNA
organisms
F.F. Costa, Gene 357 (2005) 83
Nils Walter - Origins: The Universe, Earth, and Life
Summary: From Astrophysics to Biology –
The force is with Chemistry
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Chemistry
Nils Walter - Origins: The Universe, Earth, and Life