Transcript Quale Vita? - uniroma1.it

Characterization
of Extrasolar
Planets
What Life?
R.U. Claudi
Intrusion in the Biology
Habitability around
the Sun and the
other stars
Search for life
Operative definition for Life
A system is alive if it:
-contains informations
-exchanges energy with the environment
- can to breed
-is subject to random variation of its
information baggage
To Continue the generalization…
Physical structures based on solid physics and
the electronics of liquid crystal…
…with habitat that could be both rocky
planets with Tsup 200 250 K, or asteroids…
…but it is difficult to imagin a natural process
that can generate them …
…or System based on the electromagnetic plasma …
http://www.cv.nrao.edu/~awootten/allmols.html
…for which the habitability is given by the
interstellar medium condition
Carbon based Chemistry ….
it easy oxidizes itself: CO2
it easy reduces itself: CH4
100%
100%
100%
100%
100%
100%
100%
94%
89%
29%
81%
But expecially it can combine
itself with other atoms in order
to make coplex molecules
http://www.cv.nrao.edu/~awootten/allmols.html
… in acqueous solution
Evolution
Chemical Reactions
Solution
Solid
Liquid
Too Slow
Alcohol
Hydrocarbons
NH3
CH4
Water
Why water?: characteristics
ε=80 it allows the salts
dissociation
Capacity to build H bonds
with dissolved molecules
It is an optimum thermal
mediator
water remain in liquid phase in a large temperature
range
Common Ice has a lower density that water
Alternative Liquid Solvents
T fusion
C
-182.0
T boiling
C
-164.0
C 2H 6
-183.0
-88.6
Methanol
CH3OH
-97.0
64.7
Ethyl
CH3CH2OH
-114.0
78.3
Ammonia
NH3
-77.7
Hydrocarbons
Methan
Ethan
CH4
Alcohols
-33.3
they are characterized by a low value of the dielectric
constant, in some cases they do not make H bonds with
solutes, in other cases they attack the organic material (e.g.
ammonia)
…in other words:
Living system based on carbon chemestry
that exploits water as solvent for chemical
reaction…
DOES IT REMEMBER SOMETHING?
Physical structures based on chemestry and
organized in linear macro molecules
Acido Peptico
Nucleico (PNA)
p-RNA
Palad
PaladThy
Bibl.:Maurel M.C., 1999
Organic compounds of living beeing
Structural Elements
Proteins
Carbohyidrates
Enzymes
Transmission of signal in
to the cell
Energy provision
Lipids
Nucleic Acids
Provision and
transfer of
information
Proteins and Amino acids
• Proteins are made by molecular chains
known as amino acids
• Proteins are made by chains with 14500 amino acids, but they could reach
30000 amino acids.
• Only 20 amino acids (in nature there
are more).
• All of them have L chirality, only the
Glycine has D chirality)
Carboxyl group: COOH
O
O
H
Glycine
N
H
O
C
C
H
O
H
N
H
C
H
H
C
C
C
H
N
H
H
Amine Group: NH2
L-Alanine
H
O
C
C
O
H
H
C
D-Alanine
H
H
alanine
H
Peptide link
H
N
H
O
H
H
O
C
C
N
C
C
H
H
H
H
O
H
C
H
H
O
H
H
N
H
H
C
H
H
glycine
O
H
C
Central
carbon
atom
H
O
H
Alanine
H
H
The 20 amino acids
Alanine
Glutamic A.
Leucine
Serine
Arginine
Glutamine
Lysine
Threonine
Asparagine
Glycine
Methionine
Tryptophan
Aspartic A.
Histidine
Phenylalaline Tyrosine
Cysteine
Isoleucine
Proline
Valine
desossiribonucleic Acid (DNA)
1 sugar (deoxyribose)
nucleotide
1 phosphate group
1 Nitrogenous base
Pyrimidine
Purine
Dimension
of the DNA
Super Helix
…and protein synthesis
no information
formation
Transcription
Decoding
Correspondance
between amino
acids
and
triples
Start: AUG (in
m-RNA)
Stop: UAA;
UAG,UGA (in
m-RNA)
Energy retrieval
Chemical Energy available
for the cell upon the
break of phosphoric
bonds due to enzymatic
hydrolysis
ATP: Adenosine triphosphate
N H2
High energy bonds:
30 kJ/mol
N
N
Adenosine
O
O
O
O
P~ O
P ~O
P
O
O
O
N
N
O
Ribose
O
CH2
OH
+
OH
Energetic Process
Three main process:
Photosynthesys: Energetic process that save energy
Glucose
Oxidation:
Fermentation:
Ethanol
Bio chemical
Process that
release energy
SOMETIMES LIFE IS A HARD JOB
Aerobic Batterium that obtain
the necessary energy by the iron
and sulfur oxidation
Ph
1.3-4.5
T
30-35 C
Dimension
Thiobacillus Ferrooxidans
1.0 m
Evidence of a common ancestor
•All the living beeings exploit DNA, RNA, proteins,
sugars and lipids
•Could be created only one hierarchy of species of
continuos complexity
•Similar Organisms from a biological point of view
share the most part of DNA
•Common ancestor means transitional fossils
•Primordial limb and organs like, e.g., the wings of
penguins
Phylogenetic Tree and
common ancestor
procaryote
Eucariote
Metanococcus
CO2, H2, T 50°-86°
Alobacterium
5M/Litro di NaCl
• ESTREMOPHILES
Archaea
Sulfolobus
Ph 1-5, T 65°-90°
Strain-121
T 121° (14/8/2003)
Pre-Cambrian Life
Procaryotes
Iron formation
Free oxigen accumulation
Eucaryotes
multicelluar life
CO2  O2 
CO2  O2 
Animals molluscs
Humans
Crust Formation
Plants and flowers
4 Gya
3 Gya
2 Gya
1 Gya
Dinosaurs and Birds
Trilobites
Cambrian Explosion
Three lines of evidence…
…that life existed 3.85 Gya and that it was constituted by unicellular
beeing
1. Stromatolites Finding
2. micro fossils Finding
3. 12C enrichment in the
fossil organisms
Origin of life: Ancient fossils
•Most Acient fossils have 3.5 Gy and they
have been found at Apex Chert in West
Australia and South Africa
•Evidence of organic material formation up
to 3.5 Gya in the ISUA formation in
Greenland
•Stromatolites with 3.5 Gy of age in
Australia
Cambrian Explosion
•Small fossil shells (1-5 mm)
•Shells, skeletons and teeth lead towards an
evolutive explosion of specie
•In 35 My all the modern species pop up
•Osseous and hard parts of bodies let grow
uo the fossil number (Cambrian Explosion)
Orgin of life: Urey-Miller Experiment
After a week 15% of carbon
transform itself in organic
compounds. 2% in amino acids
(Glycine, α-alanine and βalanine)
•Critiques:
–Primeval Atmosphere was
not strongly reducer, not so
much!
–UV Radiation role?
–Both chiralities are present
with the same abbunndance
Origin of Life: Thermal Vents
The necessary energy to the life
chemistry could be taken by the
geothermal heat.
Water protects by the UV
radiation
Water emitted at 450 C
Estremophiles, e.g.:
Strain 121
Water warmed up to 1000C
Origin of life: panspermia
•Amino acids have been found in space (amino acid
precursors found in molecular clouds, glycine in
Sagitarius B2).
•Excess of diversity of L chirality amino acids found
in the Murchison meteorite (Boatta, 2002)
• Amino acids production in laboratory from spatial
ice once it is UV irradiated (“Nature 416”, 28 Mar
2002).
Murchison’s Meteorite
Conclusions
•A living system is the result of a slow evolution process
due to the sum of several events with plausible probability
•As soon as the environment becom “Habitable” life start
to generate
•The living system based on the carbon chemistry and on
water is the most probable
•On Earth the information encoding and decoding system
is based on DNA and RNA, but we saw that could exists
other system for information supply…