Download Early Earth and the Origin of Life Part 2

Early Earth and the Origin of
Life
Part 2
Created by: Sara Khan, Saba
Mashhadialireza, and Joey Ricci
RNA was probably the first
genetic material
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Protobionts (aggregates of
abiotically produced
molecules) that are most
stable and best able to
accumulate organic
molecules from the
environment would grow
and split- making “baby”
droplets
The more this happened,
the more diluted the
molecules would become
What is missing here?
HEREIDITY is missing

Genetic information would make it possible for
molecular aggregates to pass along not just
samples of key molecules, but also instructions for
making more of those molecules
 The first genes were not DNA molecules but short
strands of RNA that began self-replicating in the
prebiotic world
 This was before the present day idea of
DNARNAprotien mechanism.
Natural Selection on the
molecular level
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Observed in the lab
RNA molecules may have undergone natural
selection as those molecules with the most stable
three dimensional conformations and greatest
autcatalytic activity within a particular
environment successfully compete for monomers
and generated families of similar sequences.
 RNA-directed protein syntheses may begun with
the weak binding of specific amino acids to bases
along RNA molecules and their linkage to form a
short polypeptide.
Abiotic replication of RNA
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Short polymers of ribonucleotides have been produced abiotically in
lab experiments
If you add RNA to a solution containing monomers for making more
RNA, the sequences of 5.-10 nucleotides long are copied from the
template according to the base-pairing rules
Proteins are not the only the only biological catalysts, so is RNA
1980, Thomas Cech found that modern cells use RNA catalysts, called
ribozymes, to do things like remove introns from RNA
This is what the world may have been in early periods in the evolution
of life when RNA molecules served as both rudimentary genes and
organic catalysts
Protobiont
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When these early RNA
and polypeptide molecules
became packaged into
protobionts, molecular
cooperation could become
more effeicent
More effeicent due to
Concentrations of
components and the
potential for the
protobiont to evolve as a
unit
The Origin of hereditary info.
Made Darwinian evolution
possible

Protobionts use enzymes to make polymers
and perform other chemical processes. They
grow and split and distribute genes to the
resulting cells, or offspring.
 The mutations which occur during this
process would contribute to variation
among the protobionts.

Through evolution, DNA became the
hereditary material because it is more stable
than RNA.
 RNA then started to function the way we
see it today.
Debate About the Origin of Life
Researchers can’t prove and therefore still
question the concept of abiotic synthesis of
organic monomers.
 Another idea about the origin of life, called
panspermia, is that organic compounds were
brought to Earth by comets and meteorites.
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Amino acids have been found in meteorites
and researchers recently found that the
organic material in meteorites form vesicles
when mixed with water.
 Panspermia, however, is only believed to be
a minor contributor to the origin of life.
 Other scientists also believe that RNA is too
complex for the very first self-replicating
molecules.
Earth’s inhospitable surface around the time
life began suggests that, contrary to a
traditional belief, the beginning of life took
place in the deep sea vents in the ocean.
 Scientists have found acetyl-coA and iron
and nickel sulfides at these locations, which
are essential to cell activity.

The discovery of ice on one of Jupiter’s
moons and possibly fossilized prokaryotes
on an asteroid suggest that life is not limited
to our planet alone.
 It is not yet evident whether life ever
evolved on Mars or any other planet.
 Regardless of when or where life evolved, it
is clear that all the lineages of life arose
from the prokaryotes that lived at least 3.5
billion years ago on Earth.
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The Major Lineages of Life
Arranging the diversity of life
into the highest taxa is a work
in progress
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common to be known that there
is only two kingdoms: animals
and plants
Why?
because we rarely see organisms
that don't fit into the plant/animal
group
examples: bacteria placed in
plant kingdom, Eukaryotic
unicellular organism with
chloroplasts considered as
plants, fungi also considered as
plants though they sedentary and
aren't photosynthetic nor are
structurally close to green plants
unicellular creatures that moved
or ingest food were considered in
the animal kingdom
Microbes such as Euglena are
photosynthetic though move
were in both kingdoms
5 kingdom system
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Whittaker designed 5
kingdoms: Monera, Protista,
Plantae, fungi and Anamalia
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2 fundamentally different
types of cells: prokaryotic
and eukaryotic and they are
separated into their own
kingdoms
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Monera is the kingdom with
all prokaryotes
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3 kingdom for multicellular
eukaryotes: Plantae, Fungi,
and Anamalia
5 kingdoms in more detail
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Plants, fungi and Animal all differ in
structure, life cycles, and mode of nutrition
a. Plants are autotrophic and make food
through photosynthesis
b. fungi are heterotrophic and are
absorptive for their food, as well as
decomposers
c. animals live by ingesting food and
digesting it within specialized cavities
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Protista - contains all eukaryotes that
didn't fit in the definition of plants, fungi or
animals and most are unicellular even
though few multicellular organisms are
descendants of unicellular protists
Point of this system is an attempt to order the
diversity of life into a scheme that is useful and
reasonable
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problem with the 5
kingdom
classification
system has arrived
through systematic
using comparisons
of nucleic acids
and proteins do
probe relationships
between groups
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super kingdom
level: domains of
Bacteria, Archaea,
and eukarya
Conclusion
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Classifying life is a work in progress
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evolving view of biodiversity reflect our increased
understanding of characteristics and evolutionary
histories of different organisms
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prokaryotes are the first form of life and only ones
for at least 2 billion years which leads us into the
next chapter of the diversity and history of
prokaryotic life