Organization of Life:
Simple to Complex
BM101
02-01-2021
FUNDAMENTAL CHARACTERISTICS OF LIFE
1. Respond to their environment
2. Grow and change
3. Reproduce and have offspring
4. Complex chemistry
5. Maintain homeostasis
6. Built of cells
7. Pass their traits onto their offspring
Deciphering the Earliest History of the Earth: Zircon Grains
Radiometric dating estimates
the age of the earth at 4.56 BY
Orion Nebula
PANSPERMIA
EXTRATERRESTRIAL ORIGIN OF LIFE
EXTRATERRESTRIAL ORIGIN OF LIFE
Meteoroid
Asteroid
Comet
Planetoids Asteroid
Comet
Comets
Dirty snowballs
Formed in the outer part of the
solar system
Contain many organic molecules
‘Comets giveth and comets taketh
away’ Carl Sagan (1934-1997)
Jan 2006 comet dust sampled
Wild-2 comet
Organic compounds,
including glycine, found.
Stardust mission 2006
First Detection of Sugars in Murchison meteorite Gives Clues to Origin of Life
More than 70 amino acids and 14,000 other molecular
compounds have been detected in the Murchison meteorite.
SUGARS FOUND IN THE MURCHISON METEORITE
From: Cooper et al. 2001 Nature 414:897-883
EVIDENCE OF LIFE ON MARS?
Microscopic fossil
Are these biological microfossils?
From: MacKay et al. 1996 Science
SURFACE OF ENCELADUS
SURFACE OF EUROPA
Life on the moons of Jupiter or Saturn?
Atmosphere found on Enceladus. ... Enceladus has joined the small but select band of moons known to have an atmosphere.
The Cassini spacecraft, currently orbiting Saturn, has found a layer of water vapors surrounding the icy moon, which is
likely to be issuing from its surface or interior.
Biochemical evolution
According to physical and chemical
laws:-
Life appeared after a period of chemical
reactions.
© 2016 Paul Billiet ODWS
Conditions on Early Earth
• Reducing atmosphere on the primitive Earth. No free
oxygen (O2).
• Free hydrogen (H2) and saturated hydrides (CH4, NH3
and H2O).
• Energy for chemical reactions between these gases could
come from electric discharge in storms or solar energy
(no ozone layer).
• The Earth’s surface temperature was hotter than today.
Oparin-Haldane Model
[Primordial soup]
Oparin [1924] and Haldane [1929] theory
JBS Haldane AI Oparin
Life originated through ABIOGENESIS.
BIG UNANSWERED QUESTIONS OF OPARIN-HALDANE
HYPOTHESIS IN ORIGIN-OF-LIFE RESEARCH
How did the “primordial soup” acquire the simple monomeric
building blocks essential for the production of information bearing
polymers?
What conditions are necessary for the initial(pre-biotic) assembly of
such polymers?
Can a polymer be produced that is capable of self-replication as well
as information storage?
How did compartmentalization, necessary for self-recognition during
replication and for the diffusion of gene products, evolve?
Which came first---DNA, RNA, protein, or something else, or did
complex systems involving all of these emerge simultaneously?
Miller-Urey Experiment
[Conditions on early Earth]
• Reducing atmosphere on the primitive Earth. No free
oxygen.
• Free hydrogen (H2) and saturated hydrides (CH4, NH3
and H2O).
• Energy for chemical reactions between these gases could
come from electric discharge in storms or solar energy
(no ozone layer).
• The Earth’s surface temperature was probably hotter
than today.
Miller-Urey Experiment 1952
Simulating Ancient Earth Conditions
Stanley Miller
Demonstrated that many of
the compounds necessary
for life could be produced in
a “pre-biotic” atmosphere.
H2CO - Formaldehyde
HCN – Hydrogen Cyanide
Amino Acids [2%]
Urea
Organic compounds: 10-
Methane, ammonia, water, hydrogen - the
15%
atmospheric conditions believed to be on early Earth
Chemistry of Miller’s experiments
One-step reactions among the mixture components can produce hydrogen
cyanide (HCN), formaldehyde (HCHO) and other active intermediate
compounds (acetylene, cyanoacetylene, etc.):
CO2 → CO + [O] (atomic oxygen)
CH4 + 2[O] → HCHO + H2O
CO + NH3 → HCN + H2O
CH4 + NH3 → HCN + 3H2
The formaldehyde, ammonia, and HCN then react by Strecker synthesis to
form amino acids and other biomolecules:
HCHO + HCN + NH3 → NH2-CH2-CN [aminoacetonitrile] + H2O
NH2-CH2-CN + 2H2O → NH3 + NH2-CH2-COOH (glycine)
Furthermore, water and formaldehyde can react, via Butlerov's reaction to
produce various sugars like ribose.
The experiments showed that simple organic compounds of building blocks of
proteins and other macromolecules can be formed from gases with the
addition of energy.
Joan Oró
In 1961, Joan Oró found that amino acids could be made from
hydrogen cyanide (HCN) and ammonia in a water solution.
He also found that his experiment produced a large amount of the
nucleotide base adenine, which is one of the four bases in RNA and
DNA. It is also a component of ATP, which is a major energy releasing
molecule in cells.
From monomers to polymers
Amino acids polypeptides, could have
occurred when dry or highly concentrated
monomers are heated.
Condensation reactions take place forming:
peptide bonds between amino acids or
phosphodiester bonds form between
nucleotides.
© 2016 Paul Billiet ODWS
First Polynucleotides
Polynucleotides show a tendency to copy
themselves using complementary base
pairing.
This was probably catalysed by the presence
of clay particles and metal ions.
These single stranded polynucleotides would
have been the equivalent of RNA.
© 2016 Paul Billiet ODWS
First Hereditary Information
• RNA was probably the first hereditary
molecule having the ability to copy itself.
• RNA shows enzymic (catalytic) properties –
called ribozymes.
• Polynucleotides are very good molecules at
storing and transmitting information but
they lack the versatility for all the chemical
functions of a cell.
© 2016 Paul Billiet ODWS
The First Membrane, The First Cell
If a piece of RNA codes for a protein, then that
protein might have been used to make
membrane.
If the RNA is enclosed in a membrane, then it
can keep its protein to itself and it gains a
selective advantage.
So membranes probably pushed evolution by
natural selection forwards.
Membranes defined the first cell
The phospholipids form lipid bilayers when
they are surrounded by water.
All the components of a simple prokaryotic
cell were now assembled.
They diversified in their metabolism.
By 2 billion years ago, free oxygen was
appearing in the atmosphere due to the activity
of photosynthetic bacteria.
© 2016 Paul Billiet ODWS
Genomics Data and Molecular Biology indicate
that all modern organisms originated from an
ensemble of prokaryotic genes, dating back to
the first appearance of life on Earth over 4.2 Bya,
which means life was present on Earth from
almost the beginning.
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