this chapter prompts you to wonder where did life as we know it came from. this is a presentation from Dr.Tithi Parija (asst professor) from KIIT school of biotechnology including different theories from different thinkers and scientists

1. BIOLOGY

2. What is Biology?
• Scientific study of life
• An ongoing inquiry about the nature of life
• A set of themes connect the concepts of biology
• Biologists
• Modern biology
Plant biology, animal biology, microbiology, genetics ,
cell biology, molecular biology, biochemistry,
bioinformatics, immunology, physiology,
developmental biology, environmental biology,
bioinformatics, evolutionary biology, biostatistics
etc.

3. Where did life came from?Where did Life come from?

4. The Big Bang Theory
• Describes the early development
of the Universe
• The Big Bang occurred
approximately 13.798 ±
0.037 billion years ago ( age of
universe)
• Universe was in an extremely hot
and dense state
• Expansion of the universe
• formation of hydrogen, helium,
lithium (primordial elements)
• formation of stars, galaxies
The Big Bang

5. • There was a huge explosion
• The matter is scattered in all
directions and begins to cool.
• First, quarks clump together into
protons and neutrons and then
protons capture electrons to form
Hydrogen atom. The explosion of
the Big Bang only
formed H and He
• Later, Gravity pulls the Hydrogen
and Helium together to form stars
and galaxies Heavier elements
(Carbon, Oxygen, etc) are formed
inside stars
• Stars burned out and exploded
and expelled the heavier
elements (carbon and oxygen
(and other elements)) that
formed planets

6. Earth
• The age of Earth is approximately one-third of the age of the
universe.
• Earth formed around 4.54 billion (4.54×109) years ago
by accretion from the solar nebula
• All evidence suggests that the Earth was inhospitable to life for the
first 700 million years, largely because it was so hot.
• One very large collision is thought to have been responsible for
tilting the Earth at an angle and forming the Moon
• Volcanic outgassing probably created the primordial atmosphere
• However, the Earth gradually cooled, and 4 billion years ago it
became more hospitable ( formation of solid crust, liquid water)
• The first single-cell life forms appeared (3.8 to 3.5 billion years ago)
• Photosynthetic life appeared around 2 billion years ago, enriching
the atmosphere with oxygen

7. Origin of Life
There is no scientific proof that life did (or ever
could) evolved into existence from non-living
matter. Further, there is substantial evidence
that spontaneous generation is impossible.

8. What is Life?
Fundamental properties of Life
• Cellular organization - Consist of one or more cells
• Sensitivity - Respond to stimuli—though not always to the same stimuli in the same
ways.
• Growth - Assimilate energy and use it to grow, a process called metabolism
• Development - Multicellular organisms undergo systematic gene-directed changes
as they grow and mature.
• Reproduction - Reproduce, passing on traits from one generation to the next and all
organisms die.
• Regulation - Have regulatory mechanisms that coordinate internal processes.
• Homeostasis - Maintain relatively constant internal conditions, different from their
environment
• Heredity – Possess a genetic system (DNA) that allows adaptation and evolution
over time.

9. All living things on earth are characterized by cellular
organization, heredity, and a handful of other
characteristics that serve to define the term Life

10. CONDITIONS ON EARTH
• NO OXYGEN
• VARIETY OF GASES: CH4, CO2, N2, NH3,
CO, H2, H2S etc
• MUCH HOTTER THAN TODAY: MORE
THAN 100OC
• NO ATMOSPHERE
• UV ABUNDANT
• METEORITE SHOWERS OFTEN
• FREE WATER COULD NOT EXSIST
• EARLY LIFE FORMS WERE HEAT
TOLERANT AND RESEMBLE PRESENT
DAY HYPERTHERMOPHILES

11. The Origin of Life
The fortuitious mix of physical
events and chemical elements
at the right place
and time created the first living
cells on earth

12. Life could have produced from simple cells that
is formed from four stages:
1. The abiotic (nonliving) synthesis of small organic
molecules, such as amino acids and nitrogenous bases
2. The joining of these small molecules into
macromolecules, such as proteins and nucleic acids
3. The packaging of these molecules into protocells,
droplets with membranes that maintained an internal
chemistry different from that of their surroundings
4. The origin of self-replicating molecules that
eventually made inheritance possible

13. Theories about origin of life
• Theory of Special Creation
• Theory of Spontaneous generation
• Theory of Biogenesis
• Theory of Biochemical Evolution
• Theory of Panspermia
• Deep Sea Hydrothermal Vents

14. GOD CREATED HEAVENS
AND THE EARTH

15. Theory of Spontaneous generation
• Also called abiogenesis
• Supporters:
Aristotle, Epicurous, Von Helmont
• They believed
Insects arise from dew
Fish & frog from mud
Fly maggots from meat
Opposers: Francisco Redi, Louis Pasteur,
Spallanzani

16. Theory of Biochemical evolution
• The experiment tested
Alexander Oparin's and J.
B. S. Haldane's hypothesis
that conditions on the
primitive Earth favored
chemical reactions that
synthesized organic
compounds from inorganic
precursors.

18. • Sydney Fox : obtained proteinoid microspheres by
heating a mixture of dry aminoacids and cooling them in
water
• Organization of macromolecules into
bodies with definite shapes and
chemical properties.
Eg. Coacervate droplets, microspheres

19. Abiotic synthesis of Polymers
Under the influence of an energy source (such as UV light,
solar radiation and heat), the concentrated compounds would
have combined to form large macromolecules, such
as polypeptides (precursors of proteins) and
polynucleotides (precursors of DNA)

20. • Vesicles can form spontaneously
when lipids or other organic
molecules are added to water
hydrophobic molecules in the
mixture organize into a
bilayer similar to the lipid bilayer
of a plasma membrane.
• Adding substances such as
montmorillonite, a soft mineral
clay produced by the
weathering of volcanic ash,
greatly increases the rate of
vesicle self-assembly

21. • Louis Pasteur had
performed experiments
that showed
spontaneous
generation was not
possible; so Huxley
called the idea of the
origin of life
“abiogenesis” and said
the evolution of
protoplasm from
nonliving matter had
happened only in the
early earth and could
no longer be observed.

22. • Stanley Miller and Harold
Urey (1952) exposed a
mixture of gaseous hydrogen,
ammonia, methane and
water to an electrical arc for a
week.
• The experiment tested
Alexander Oparin's and J. B. S.
Haldane's hypothesis that
conditions on the primitive
Earth favored chemical
reactions that
synthesized organic
compounds from inorganic
precursors.
Primordial Soup Model

23. • Considered to be the classic experiment on the origin of life
conducted in Univ. of Chicago and then Univ. of California,
San Diego.
• As much as 10–15% of the carbon within the system was
now in the form of organic compounds. Two percent of the
carbon had formed amino acids that are used to
make proteins in living cells, with glycine as the most
abundant. Sugars, formic acid, urea were also formed.
• At the end of the experiment, amino acids ( 11 out of 20
aa) and other compounds were found which are essential
to life.
• The original experiment remains today under the care of
Miller and Urey's former student Jeffrey Bada, a professor
at UCSD. Apparatus used to conduct the experiment is on
display at the Denver Museum of Nature and Science.

26. • Volcanic clouds in the early atmosphere
might have held methane, ammonia and
hydrogen and been filled with lightning
as well.

28. 1.5km below the
surface in the
hydrothermal
vents releases Sea
of Cortez the
hydrogen sulphide
and iron sulphide,
which react and
produce pyrite and
hydrogen gas.
Prokaryotes living
near the vent use
hydrogen as energy
source.

29. • For 80 years it has been accepted
that early life began in a
'primordial soup' of organic
molecules before evolving out of
the oceans millions of years later.
• Now the 'soup' theory has been
over turned in a pioneering
paper in BioEssays which claims
it was the Earth's chemical
energy, from hydrothermal vents
on the ocean floor, which kick-
started early life.

30. “Life arose from gases (H2, CO2, N2, and H2S)
and that the energy for first life came from
harnessing geochemical gradients created by
mother Earth at a special kind of deep-sea
hydrothermal vent – one that is riddled with
tiny interconnected compartments or pores."

31. Extraterrestrial origin of life
• Svante Arrhenius (1908) proposed
the "panspermia theory"
– life originated on Earth with the arrival of spores that
had drifted through space from some other planetary
or solar system.
– Among those who favor this hypothesis, Francis Crick
argues that the overwhelming biochemical and
molecular evidence suggests that the last common
ancestor was already on earth 3.5 to 3.6 billion years
ago when the history of life began on earth.

32. • Meteorites are carbonaceous chondrites and
rocks that are 1–2% carbon compounds by
mass .
• 4.5 billion yr old carbonaceous chondrites
(Murchison meteorite)collected in Southern
Australia in 1969 contain more than 80 aa, 8
used by life on earth. All 5 bases used in
RNA/ DNA , fatty acids, simple sugars also
found

33. Outside Earth for clues of life
• Galileo indicated liquid water lies beneath the
ice covered surface of Europa (Jupitor’s moon)
• Saturn’s ring made up of iced water and
vapours that escaped the gravitational
force, Enceladus has cryovolcanoes.
• Life on Mars ; evidences are there that mars was
relatively warm for a brief period with liquid water and
carbon dioxide reach atmosphere.

35. A current bubble hypothesis. In 1986 geophysicist Louis Lerman proposed that the
chemical processes leading to the evolution of life took place within bubbles on the
ocean’s surface.

36. • Little is known about how the first cells
originated.
• Current hypotheses involve chemical
evolution within bubbles, but there is no
general agreement about their composition,
or about how the process occurred.

37. Harvard researchers
make first protocells
from clay bubbles.
Possibly first cell form
on earth.

38. RNA World
• The phrase "RNA World"
was first used by Nobel laureate Walter
Gilbert in 1986, in a commentary on how
recent observations of the catalytic properties
of various forms of RNA fit with this
hypothesis.
• The concept of RNA as a primordial molecule:
Francis Crick, Leslie Orgel, Carl Woese and
many more scientists

39. The RNA World
• Through a generic form of natural selection, only
macromolecules that resisted degradation from
entropy would exist longer than any other
• Over time, the soup became dominated by
macromolecules that were resistant to degradation
• At some point, an RNA molecule (through random
chance and bonding) Hairpin loops forming a ribozyme
(RNA Catalyst)
– This molecule can split (through catalysis) and can form a
template with free floating nucleotides (through base
pairing)
– This allows it to rapidly replicate itself, giving it a chance
to increase its numbers against the tide of entropy
– Over time, this replicating RNA becomes dominant in the
prebiotic soup

41. RNA takes the lead
• The RNA molecule, now commoner than any other
molecule in the soup, over time will develop copying
errors
• These errors, called mutations, cause some RNAs to
differ from others
– Some strands get longer, some get shorter, and most importantly,
some begin to interact with other macromolecules
– Some RNA molecules begin to interact with amino acids, forming
bonds the eventually lead to the first tRNA (Transfer RNA)
– Some become intertwined with protiens, forming elaborate
machines called ribosomes
– Some interact with free lipids forming fat bubbles that protect them
from the degradation of entropy

42. Battle continues…
• Due to the RNA molecules success, the amount of
free nucleotides in the prebiotic soup decreased
dramatically
• As the RNA molecules became more and more
different, (and free nucleotides became more rare in
the soup)many of them began degrading other RNAs
for free nucleotides
• Similar to a predator degrading its prey for nutrition
• Now it is a game of pure natural selection…

44. RNA to DNA
– The pressure was on RNA to become resistant to
degradation
• RNA was much safer from degradation in the hairpin loop
form, but couldn’t sustain this structure because of the
nature of RNA
– One replicating RNA molecule had a writing error
that allowed for a different Thymine nucleotide to
replace the common Uracil
• This one change allowed for the RNA to hairpin loop, and
remain looped in the form of a double strand
– This new double stranded RNA with a thymine in the
place of a uracil (called DNA) was extremely resistant
to entropy (Stable) and made replication even easier

45. …..and then there was DNA
• DNA was far more stable which allowed for a
decrease in mutations
• Although this likely slowed down the rate at which differentiation
occurred, it also dramatically decreased the chance that molecule
would be degraded
• Over time, this molecule began to differentiate and
compete much the same way the early RNA molecules
did
• Some DNA molecules utilized the tRNA molecules to create strands of
amino acids that it could use to become more specialized
• Others utilized lipids to form strong outer barriers that were only
permeable to things the cell needed
• A new world, a world of cells, was beginning to emerge!

46. Time line for the universe, suggesting the early existence of an RNA world of living systems

47. RNA WORLD
NATURAL SELECTION
DNA WORLD
EXPLOSION OF LIFE
PRESENT DAY LIFE FORMS

49. • Single-celled organisms originated
much earlier, perhaps as early as
3.9 billion years ago
• Prokaryotes were Earth’s sole
inhabitants from at least 3.5 billion
years ago to about 2.1 billion years
ago
• (Photosynthesis and the Oxygen
Revolution)oldest widely accepted
fossils of eukaryotic organisms are
about 2.1 billion years old
• Common ancestor of multicellular
eukaryotes lived 1.5 billion years
ago (oldest known fossils of
multicellular eukaryotes are of
relatively small algae that lived
about 1.2 billion years ago)

50. EVOLUTION OF PROKARYOTES
Microbial mats
stromatolites
• First prokaryotes were autotrophs (could make own
food and some used light as energy )
• Glucose from Formaldehyde
• Autotrophs diversified to form heterotrophs (3.5 to
2bya)
• Evolution of electron transport system in primitive
organisms which is now found in all forms of life
(Bacteria, Archaea and Eukarya)

51. The earliest evidence of life
appears in microfossils,
fossilized forms of
microscopic life (figure 4.9).

52. They physically resemble
presentday
bacteria), although some
ancient forms
cannot be matched exactly. We
call organisms with this simple
body plan prokaryotes, from
the Greek words meaning
“before” and “kernel,” or
“nucleus.”

54. FOSSILIZED ROCKS: presence of photosythetic
organims
• STROMATOLITES
• Layered rocks, domed,
formed due to
incorporation of mineral
sediments into microbial
mats dominated by
cyanobacteria
• Age of stromatolites is
3.5 by
• Responsible for evolution
of oxygenic environment
FILAMENTOUS PHTOTROPHIC
BACTERIA
TRAPPED IN SEDIMENT FORMING
ROCKLIKE STRUCTURES

55. MICROBIAL MATS
Hot spring

56. EVOLUTION OF PROKARYOTES
EVOLUTION OF PHOTOSYNTHESIS AND OXYGEN
FIRST O2 EVOLVING ORGANISM:
CYANOBACTERIA
O2
Reacted with dissolved Fe and form FeO (iron ore)
Marine sediments are source of banded iron formations
All iron precipitated and O2 gassed out, leading to O2 accumulation in
atmosphere
This change can be seen as rusted iron rich terrestrial rocks (2.7
bya)

58. O2 kept on evolving from 2.7-2.2 bya leading to
OXYGEN REVOLUTION
• Enormous and dramatic impact on life
• O2 has damaging effects on H2O2, enzymes, chemical bonds
• Many types of metabolism, aerobic, anaerobic, facultative, obligate
LEAD TO EVOLUTION OF
CELLULAR RESPIRATION (uses Oxygen in ETC)

59. EVOLUTION OF EUKARYOTES
• More complex
• Oldest fossils 2.1 billion years old
• Single cell algae (2.2 bya)
ENDOSYMBIONTIC THEORY
Eukaryotes have evolved by the internalization and symbiosis of
prokaryotes
• Prokaryotes have no nucleus, internal organelles, no cytoskeleton,
unable to change shape, and cannot engulf
• Eukaryotes have internal organelles, cytoskeleton, able to change
shape (mitosis/meiosis), can engulf and were predatory in nature (as
parasites, undigested prey)

61. Those prokaryotes which were
• aerobic
• heterotrophic nutrition
• carry cellular respiration (non photosynthetic)
• carry photosynthesis (photosynthetic)
Were engulfed by (process of endocytosis) early
eukaryotes and became symbionts to later form organelles
like mitochondria and chloroplast.
Since relationship was mutually beneficial the organelles
became a part of the system and did not leave
Chloroplast containing eukaryotes were the first to use
light in an anaerobic environment and generate O2
(aerobic)

62. Endosymbiotic Theory
• First articulated by the
Russian
botanist Konstantin
Mereschkowski in 1910.
• Advanced and
substantiated with
microbiological
evidence by Lynn
Margulis in a 1967
paper, On the origin of
mitosing cells.

63. • Several key organelles of eukaryotes originated
as symbioses between separate single-celled
organisms.
• Mitochondria and plastids (e.g. chloroplasts) and
possibly other organelles, represent formerly
free-living bacteria that were taken inside
another cell as an endosymbiont.
• Molecular and biochemical evidence suggest that
the mitochondrion developed
from proteobacteria or close relatives) and the
chloroplast from cyanobacteria.

64. The Endosymbiotic Theory
Evidences
• Mitochondria and chloroplasts
have striking similarities to
bacteria cells.
• They have their own DNA, which
is separate from the DNA found in
the nucleus of the cell.
• And both organelles use their
DNA to produce many proteins
and enzymes required for their
function.
• A double membrane surrounds
both mitochondria and
chloroplasts, further evidence
that each was ingested by a
primitive host.
• The two organelles also
reproduce like bacteria,
replicating their own DNA and
directing their own division.

65. EVOLUTION OF EUKARYOTES
• Eukaryotes are Genetic chimeras (mito, chlorop, nuclear
genome (mixture of parts), other prokar. DNAs)
• Origin of nucleus from Archaea
• Process of genetic annealing by horizontal gene transfer
mechanism (engulfing of prokaryotes by eukaryotes)
• Origin of golgi and Endo. reticulum from infoldings of
Plasma memb.
• Origin of cytoskeleton (similar proteins like actin and
tubulin found in bacteria)
• Origin of eukar. Cillia and flagella from prokary.

66. The colonial connection
• First multicellular organisms
were colonies, collection of
autonomously replicating
cells.
• Multicellularity evolved
several times among early
eukaryotes.
• Division of functions led to
the evolution of tissues,
organs, organ systems etc. Pediastrum, a photosynthetic
eukaryote that forms flat colonies.

67. MORE THE COMPLEXITY MORE THE VARIATIONS
EUKARYOTES CATALYZED EVOLUTION OF
STRUCTURAL DIVERSITY
ADAPTIVE RADIATION (ecological and phenotypic
diversity within a rapidly multiplying lineage)
METABOLIC DIVERSIFICATION OF PROKARYOTES
ORIGIN OF MULTICELLULAR EUKARYOTES