1. The Beginning of Life
I. Conditions necessary to allow life
to begin
Earth was a very hostile environment 4 billion years ago
Fig. 20-4b, p.321
1

2. First Atmosphere
• Hydrogen gas
• Nitrogen
• Carbon monoxide
• Carbon dioxide
• No gaseous oxygen
I. Conditions necessary to allow
life to begin
electrodes
to
spark
vacuum CH4 discharge
pump NH3
gases
H2O
H2
water out
condenser
water in
water droplets
water containing
organic compounds
boiling water
liquid water in trap
Fig. 20-4c, p.321
2

3. I. Conditions necessary to allow
life to begin
four formaldehyde
molecules with
four pyrrole rings
chlorophyll a
6H
porphyrin ring
system
Stepped Art
Fig. 20-5, p.322
3

4. Origin of Organic Compounds
• Amino acids, other organic compounds
can form spontaneously under conditions
like those on early Earth
• Clay may have served as template for
complex compounds
• Compounds may have formed near
hydrothermal vents
RNA ‘Ribozyme’ produced in the laboratory
Store biological information and also act as catalyst (enzyme)
Could something like this have been the first source of genetic material?
RNA World
• DNA is genetic material now
• DNA-to-RNA-to-protein system is complicated
• RNA may have been first genetic material
• RNA can assemble spontaneously
• How switch from RNA to DNA might have
occurred is not known
4

5. II. Origin of cells – precursor to
living cells
Proto-Cells
• Microscopic spheres of proteins or lipids
can self assemble
• Tiny sacs like cell membranes can form
under laboratory conditions that simulate
conditions in evaporating tidepools
• Nanobes may resemble proto-cells
Amino acids heated, then moistened.
Formed protein membranes.
5

6. II. Origin of cells – precursor to
living cells
Membrane of fatty acids and alcohol surrounding
RNA-coated clay .
Fig. 20-7b, p.323
II. Origin of cells – precursor to
living cells
6

7. Could precursors and /or proto-cells have arrived from outer space?
BBC News
Monday, 29 January, 2001
Scientists have managed to
create quot;primitive cellsquot; in an
experiment which may indicate
that life began in space and was
delivered to Earth.
Researchers working with the American
space agency NASA say their quot;proto-cellsquot;
mimic the membranous structures found
in all living things. They were produced in
a laboratory experiment that duplicated
the harsh conditions of cold interstellar
space.
This new work suggests that the early chemical steps believed to be important
for the origin of life do not require an already-formed planet.
Instead, they seem to take place in deep space long before planet formation
occurs.
This implies that the vastness of space is filled with chemical compounds which,
if they land in a hospitable environment like our Earth, can readily jump-start life.
living
membrane-bound proto-cells
cells
self-replicating system enclosed in a
selectively permeable, protective lipid sphere
enzymes and
DNA RNA
other proteins
formation of formation of
protein-RNA systems, lipid spheres
evolution of DNA
spontaneous formation of lipids,
carbohydrates, amino acids, proteins,
nucleotides under abiotic conditions
7

8. III. The first true cells
3.5 billion y –old
prokaryote
Anaerobic or aerobic?
Fig. 20-8a, p.324
The First Cells
• Originated in Archeon Eon
• Were prokaryotic heterotrophs
• Secured energy through anaerobic
pathways
– No oxygen present
– Relied on glycolysis and fermentation
8

9. Stromatolites – fossils of cyanobacteria; 3by-old
Proterozoic Eon
• Origin of photosynthetic Eubacteria
– Cyclic pathway first
– Noncyclic pathway next (cyanobacteria)
• Oxygen accumulates in atmosphere
• Origin of aerobic respiration
Eukaryotes
2.1 bya
Fig. 20-8b, p.324
9

10. IV. Where did eukaryotic organelles come from?
The evolution of the eukaryotic cell
Where did all these organelles come from?
IV. Where did eukaryotic organelles come from?
The evolution of the eukaryotic cell
10

11. DNA
ER ?
infolding of plasma membrane
Fig. 20-10a, p.326
Possible origin of nucleus
IV. Where did eukaryotic organelles come from?
The evolution of the eukaryotic cell
Origin of mitochondria and chloroplasts
11

12. Evidence
Endosymbiosis example in modern time
Amoeboid organism with green alga within
Occurred by phagocytosis
Evidence
photosynthetic organelle that
resembles a cyanobacterium
mitochondrion
nucleus
Theory of Endosymbiosis
• Lynn Margulis
• Mitochondria and chloroplasts are the
descendents of free-living prokaryotic
organisms
• Prokaryotes were engulfed by early
eukaryotes and became permanent
internal symbionts
12

13. V. The timeline of development
hydrogen-rich anaerobic atmosphere atmospheric oxygen, 10%
archaean
lineage
d
ancestors of h
eukaryotes endomembrane
system and nucleus
noncyclic pathway
of photosynthesis
cyclic pathway f
of photosynthesis
e
b
a
origin of g aerobic respiration
prokaryotes
3.8 billion 3.2 billion 2.5 billion
years ago years ago years ago
atmospheric oxygen, 20%; the ozone layer slowly develops
k origin of animals
j
k origin of fungi
origin of eukaryotes,
the first protists
i
endosymbiotic origin
k origin of lineage
of mitochondira
j leading to plants
endosymbiotic origin
of chloroplasts
Aerobic species becomes endosymbiot of
anaerobic forerunner of eukaryotes.
1.2 billion 900 million 435 million
years ago years ago years ago
Fig. 20-12b, p.328
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