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1: Introduction
In the very beginning
Living world is very distinct from the rest
of the world.
If it was not “created” it must have been
introduced from outer space: the
panspermia notion.
Oparin, Aleksandr Ivanovich (18941980)
(A friend of Lysenko, a power figure in USSR
that was a plant breeder who considered
genetics to be an obstacle to agriculture
development. Put his opponents in prison.)
First attempt to give a scientific description of
how life started that is not creationist nor via
panspermia was by the Russian scientists
Alexander Oparin in 1920.
Oparin “theory”
The primitive
oceans were a
“soup” of various
biochemicals that
were created by
UV, lightings, etc
(in a nonoxidizing
enviroment).
According to Woese, this is a “vague” and “is
frankly a “Just So Story””.
Oparin “theory”
There is no •
fundamental difference
between a living
organism and lifeless
matter. Life must have
arisen from simple
molecules.
Oparin “theory”
Taking into account the recent discovery of •
methane in the atmospheres of Jupiter
and the other giant planets, Oparin
postulated that the infant Earth had
possessed a strongly reducing
atmosphere, containing methane,
ammonia, hydrogen, and water vapor.
In his opinion, these were the raw •
materials for the evolution of life.
The “soup” in details (I)
1. There had to be a supply of organic •
molecules produced by a non-biological
process
2. They had to be assembled into •
polymers like proteins and nucleic acids.
3. Those polymers had to be assembled •
into a self-replicating system.
The “soup” in details (II)
•The first organisms to develop had all the
nutrients they needed: they were extreme
heterotrophs.
•When the nutrients were exhausted, they
somehow developed the ability to use light as an
energy source, and had became autotrophs.
An empty fridge serves as a driving force for evolution
Oparin suggested that cells came first, then
enzymes, and genes later. Found that when
lipids are inserted to water, they form cell like
structures. He suggested that these
structures accumulated metabolites, and that
cell division was without replication but rather
– a random process.
The “soup” in details (III)
• In many textbooks, this was taken a step
forward, suggesting that these early
organisms were anaerobic heterotrophic
procaryotes, such as some streptococcus…
• One primitive cell (called urcaryote) gained
the ability for endocytosis, ingested other
procaryotes and the fused organism
eventually became the eucaryotic cell.
Stanley Miller (1930-
Miller’s experiments fail in an oxidizing
atmosphere containing CO2 or SO2.
His experiments work with electrical charge, UV,
or ionization radiation.
When one add
hydrogen sulphide
(SH2), there are sulphur
containing AA in the
output: methionine and
cystein.
Nucleic acids were not produced
Joan Oro (1923-2004)
Synthesized adenine in
prebiotic conditions (maybe)
from hydrogen cyanide.
He suggested that organic
molecules arrived to our early
biosphere by comets.
The problem is that the
synthesis requires very specific
conditions – not necessarily
realistic to prebiotic era.
Tom Cech (1947Discovered that RNA can also
be enzymes. These RNA
enzyme are known as
ribozymes. Received the Nobel
prize in chemistry 1989 for his
discoveries.
His discovery strongly supports
the RNA world hypothesis.
DNA world / RNA world
The RNA world hypothesis proposes that a world
filled with life based on ribonucleic acid (RNA)
predates the current world of life based on
deoxyribonucleic acid (DNA).
RNA is everywhere…
Important RNA property
The ability to self-duplicate, or duplicate •
other RNA molecules.
Relatively short RNA molecules that can duplicate •
others have been artificially produced in the lab.
The ability to catalyze simple chemical •
reactions which would enhance the
creation of molecules.
RNA can bind to form a double helical •
structure.
RNA default
RNA is less stable than DNA •
Storing large amounts of information in •
RNA is not easy
large RNA molecules are inherently fragile •
Meet LUCA:
The Last Universal Common Ancestor
Also called LUA (last universal ancestor)
What was: LUCA
It had properties shared by all •
independently living organisms on Earth
The genetic code is based on DNA.
The genetic code is expressed via RNA
intermediates.
The genetic code is expressed into proteins.
synthesis of lipids or carbohydrates are the result of
protein enzymes.
ATP is used as an energy intermediate.
The cell is surrounded by a cellular membrane
composed of a lipid bilayer.
The cell multiplies by duplicating all its contents
followed by cellular division
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1: Introduction
1: Introduction
1: Introduction
In the very beginning
•Life was classified as
plants and animals
•When Bacteria were discovered
they were initially classified as plants.
•Ernst Haeckel (1866) placed all unicellular
organisms in a kingdom called Protista,
separated from Plantae and Animalia.
1: Introduction
1: Introduction
When electron microscopes were developed, it was
found that Protista in fact include both cells with and
without nucleus. Also, fungi were found to differ from
plants, since they are heterotrophs (they do not
synthesize their food).
Thus, life were classified to 5 kingdoms:
LIFE
Procaryotes
Plants
Animals
Protists
Fungi
1: Introduction
Later, plants, animals, protists and fungi were
collectively called the Eucarya domain, and the
procaryotes were shifted from a kingdom to be a
Bacteria domain.
Domains
Kingdoms
Bacteria
Plants
Eucarya
Animals
Protists
Fungi
Even later, a new Domain was discovered…
1: Introduction
rRNA was sequenced from a great
number of organisms to study phylogeny
•The translation apparatus is universal and
probably already existed in the “beginning”.
1: Introduction
Carl R. Woese and rRNA phylogeny
1: Introduction
A distance matrix was computed for each two
organisms. In a very influential paper, they showed
that methanogenic bacteria are as distant from
bacteria as they are from eucaryota (1977).
1: Introduction
One sentence about methanogenic
“bacteria”
“There exists a third kingdom which, to date, is
represented solely by the methanogenic bacteria,
a relatively unknown class of anaerobes that
possess a unique metabolism based on the
reduction of carbon dioxide to methane”.
These "bacteria" appear to be no more related to
typical bacteria than they are to eucaryotic
cytoplasms.“
1: Introduction
From sequence analysis only, it was thus
established that life is divided into 3:
Bacteria
Archaea
Eucarya
1: Introduction
The rRNA phylogenetic tree
Iron monosulphide
precipitates
Model of Martin and Russel
Phil. Trans. R. Soc. Lond. B
(2003) 358, 59–85
Eukaryote diversity
Domains
Kingdoms
Bacteria
Plants
Eucarya
Animals
Protists
This is also completely wrong !!!
Fungi
The tree of eukaryotes
Our understanding of eukaryotic •
relationships has been transformed by the
use of molecular data to reconstruct
phylogenies (Sogin et al., 1986). Prior to
that, the diversity of microbial eukaryotes
was vastly underestimated, and the
relationships between them and
multicellular eukaryotes were difficult to
resolve (Taylor, 1978).
The tree of eukaryotes
The current view of eukaryotic phylogeny •
is of a small number of large
‘supergroups’, each comprising a
spectacular diversity of structures,
nutritional modes, and behaviours. Some
of these supergroup hypotheses are well
supported, while others remain the subject
of vigorous debate. Furthermore the
relationships between supergroups are
poorly understood.
[Sciences vol. 300, no. 5626 pp.1703]
Foraminifera
Plasmodium
Apicomplexa
Dinoflagellate
Brown algae
Foraminifera
Red algae
Amoeba
Tetrahymena
Ciliate
Trypanosoma
Giardia
[Sciences
vol. 300, no. 5626 pp.1703]
Parabasalida
Main point of eukaryote tree
Multicellularity developed independently in
different lineages.
The ability to photosynthesized, also
occurred independently in different
lineages.
Algae do not have a common ancestor.
Fungi are our close cousins.
Plant and Fungi are not related.
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