Tina Šantl-Temkiv
Rise of Complexity
Department of Bioscience
Department of Physics and
Astronomy
Aarhus University
Building blocks of life
Polymers=
Macromolecules
Elements &
monomers
Structures &
organisms
Building blocks of life
Polymers=
Macromolecules
Elements &
monomers
Structures &
organisms
The synthesis of organic compounds on
early Earth
Early atmosphere of Earth:
1. First thin atmosphere composed of
helium and hydrogen was lost
2. Volcanic out-gassing created a thicker
atmosphere composed of a variety of
gases – reducing
• Sulfur dioxide (SO2)
• Hydrogen sulfide (H2S)
• Carbon Dioxide (CO2) and
monoxide (CO)
• Nitrogen (N2)
• Hydrogen (H2)
• Methane (CH4)
• Ammonia (NH3)
The synthesis of organic compounds on
early Earth
The Oparin-Haldane Hypothesis:
• In a reducing atmosphere a
range of organic compounds
synthesized under supply of
energy (lightning or UV).
• These compounds get
concentrated in the primordial
soup => more complex
polymers.
Urey-Miller experiment (1953)
• Water vapor enters artificial early
Earth atmosphere and electrical
discharge
• Formation of diversity of
molecules:
• Amides
• Carboxylic acids
• Amino acids
Urey-Miller experiment (1953)
• The gas mixture they chose was
too reducing (<H2, CH4)
• Alternative energy by UV
radiation, geothermal heating,
impact shock, cosmic rays
• Shock pressures (asteroid &
comet impacts) produce HCN,
aldehydes and AA million times
more efficient than UV
• Variants of the Urey-Miller
experiment produce most of
amino acids, purines,
pyrimidines, and sugars
Reaction pathways of prebiotic chemistry
• HCN ubiquitous in prebiotic
reactions – production of:
• Nucleaobases
• Amino acids
• Formaldehyde at high
concentrations and acidic
conditions – formation of sugars
• Lightning can split N2 into NO or
ammonia (volatiles present on
early Earth) – formation of
nitrogenous compounds
Strecker synthesis – amino
acids from aldehyde, HCN
and NH4+
H2 O
Formose reaction
Glycolaldehyde
Glyceraldehyde
Delivery of organic compounds from
space
•
•
•
•
Carbon compounds identified in
carbonaceous chrondrites
Glycine-glycine peptides found
but no proteins
The extent significant: 1016–1018
kg of material total estimated
extraterrestrial delivery by 3.9
Ga ago
6×1014 kg total organic carbon
in life on Earth today
Life selected available compounds
Essential amino acids
70 amino acids
Building blocks of life
Polymers=
Macromolecules
Elements &
monomers
Structures &
organisms
Spontaneous generation vs.
germ theory
• Notion of spontaneous generation: abiotic
material transformed into living matter
• 16th–19th ct experiments proving
spontaneous generation or germ theory
• Louis Pasteur’s experiment with swan-neck
flasks:
• contamination by airborne organisms
• no spontaneous generation
Life timeline
Life timeline
Origin of life
Central dogma of molecular
biology:
=> One dimensional information is
transformed into a 3D structure of a
chemically active molecule.
How did early molecules come together
into a self-replicating organism?
a. How could nucleic acids appear
without the enzymes to synthesize
them?
b. How could enzymes exist without
nucleic acids to direct their synthesis?
RNA world
• Double-stranded RNA forms
bulges, loops & hairpins – 3D
folding
• Altman and Cech (1980s):
ribozymes = small fragments of
RNA can catalyze reactions
(including their replication)
• Prebiological world dominated by
RNA, proteins added later,
resulting in a more complex
replicating entities.
tRNA
rRNA
RNA world
• RNA is generally more reactive than
DNA
• Speed evolution: mutation rates very
high
• DNA is more stable – better suited to
store information
Alternative usage of nucleobases
in multiple locations in biochemistry
Adenosine triphosphate:
molecular energy currency of
the cells
Cyclic adenosine
monophosphate: secondary
messenger used for
intracellular signal transduction
Energy production and information storage emerged from the
same suite of molecules => pervasive presence of
nucleobases/nucleotides in biochemistry
NAD: coenzyme existing in an
oxidized (NAD+) and reduced
(NADH) form. involved in redox
reactions, carrying e-.
Concentration problem
How did RNA molecules became
sufficiently concentrated for
complex chemistry to occur?
• Concentrate RNA within vesicles
• Mineral or clay surfaces bind RNA
acting as concentration
mechanism
Self-assembly of
phospholipids in water to
form cellular
compartments
Early cells
• Metabolism of sugars and proteins
• RNA polymerase and ADPs external to
vesicles –> RNA polymers
• Vesicles concentrate hydrophobic
substances within them
• The exterior of lipid vesicles binds
sugars – a carbohydrate ‘coat’ = proto
cell wall
Darwinian evolution operated on the
whole cell not on isolated molecules
Self-replicating entity defined by
cellular processes
0.1 um in size – small due
to lack of bulky molecules
(e.g. ribosomes)
Where did early life emerge?
PRE-REQUIREMENTS
1. An available energy source to
drive chemical syntheses.
2. A means of concentrating
molecules.
3. A physical environment
conducive to complex
molecules and their
assembly.
Where did early life emerge?
POTENTIAL ENVIRONMENTS
a. Deep Sea Hydrothermal Vents
b. Land-based Volcanic Pools
c. Impact Craters
d. Beaches
e. Bubbles
f. The Deep Sub-Surface
g. Mineral Surfaces
Origin of metabolism in the earliest organisms
• Anaerobic prokaryotes,
probably heterotrophs
• Derived nutrients from
environment
• Heterotrophs became
more frequent –> nutrient
supply depleted
• Autotrophs gained a
selective advantage
Life timeline
Life timeline
Origin of photosynthesis:
liberation of life from point energy sources
Chemotrophy
chemical energy
Chemolithotrophy
anorganic energy source
(e.g., H2, H2S, NH4+, Fe2+)
Chemolithoautotrophs
C = CO2
Mixotrophs
C = organic
Phototrophy
light as energy source
Chemoorganotrophy
organic energy source
(e.g., glucose, acetate...)
C = organic
Photoautotrophs
C = CO2
Photoheterotrophs
C = organic
Rise of oxygen and reactive oxygen species
• Free radicals oxidize membrane
lipids, proteins and nucleic acids
• There are enzymatic pathways to
cope with this stress
• These pathways must have
evolved before the rise of
atmospheric oxygen
• The large-scale rise in atmospheric
oxygen
–> a spread of oxygen
adapted organisms into
surface habitats.
Life timeline
Life timeline
Prokaryotic and eukaryotic cells
1 um
• A single DNA molecule, lacking histones, not
bound by nuclear membranes.
• No organelles: mitochondria, plastids, Golgi
apparatus and endoplasmic reticulum.
10 um
• Membrane bound nucleus.
• More DNA, eukaryotic chromatin contains
histones.
• Membrane-bound organelles in cytoplasm
Eukaryotic cells: endosymbiotic theory
• Origin of eukaryotic cells from prokaryotic
organisms
• Mitochondria & plastids (e.g. chloroplasts) are
formerly free-living prokaryotes taken inside the
other in endosymbiosis.
Evidence:
1. New mitochondria/plastids
formed by binary fission
2. Double membrane
3. Similarity between
membranes of organelles
and bacteria
4. Plastid and mitochondrial
rRNA are more closely
related to bacterial rRNA.
Life timeline
Life timeline
Rise of oxygen and aerobic respiration
Aerobic respiration yields at least ten times as much ATP than anaerobic metabolisms.
GOE
Cyanobacterial
biomarkers
The oldest
stromatolite
The great oxidation event and body size
2.4 Ga:
atmospheric
free oxygen in
appreciable
quantities
preserved remains
of small complex
organisms begin to
appear
The second rise of
oxygen coincidental
with the rise of large
animals.
Rise of multicellularity
Billion years ago
• Aerobic respiration => emergence
of complex organisms
• ~10% atmospheric O2 => animal
respiration.
• Cells remain associated following
cell division, may differentiate and
organize into tissues and organs
• Multicellularity evolved
independently >46 times
Rise of multicellularity
Billion years ago
THEORIES OF ORIGIN
• A group of cells aggregated into a
slug-like mass, a multicellular unit
with coordinated movement.
• Primitive cell underwent nucleus
division, thereby becoming a
syncytium.
• As a unicellular organism divided,
daughter cells do not separate,
and later develop specialized
tissues.
Ecosystem complexity
• The movement of energy from one
trophic level in a food chain to the
next.
• Aerobic respiration can support more
trophic levels due to the capacity:
• to generate more energy,
• and higher biomass
=> greater complexity in ecosystems,
longer food chains and successively
larger organisms at each level.