Origin of Life Hypotheses

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Origin of Life Hypotheses
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I. Earth History
4.5 bya Earth Forms
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I. Earth History - Earliest Atmosphere - probably
of volcanic origin
Gases produced were probably similar to those
created by modern volcanoes (H2O, CO2, SO2, CO,
S2, Cl2, N2, H2) and NH3 and CH4
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I. Earth History
4.5 bya Earth Forms
4.0 bya Oldest Rocks
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I. Earth History
4.5 bya Earth Forms
4.0 bya Oldest Rocks
3.5 bya Oldest Fossils
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I. Earth History
4.5 bya Earth Forms
4.0 bya Oldest Rocks
3.5 bya Oldest Fossils
Stromatolites - communities of layered 'bacteria'
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I. Earth History
2.3-2.0 bya Oxygen in Atmosphere
4.5 bya Earth Forms
4.0 bya Oldest Rocks
3.4 bya Oldest Fossils
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I. Earth History
2.3-2.0 bya Oxygen
1.8 bya first eukaryote
4.5 bya Earth Forms
4.0 bya Oldest Rocks
3.4 bya Oldest Fossils
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I. Earth History
2.3-2.0 bya Oxygen
1.8 bya first eukaryote
0.9 bya first animals
4.5 bya Earth Forms
4.0 bya Oldest Rocks
3.4 bya Oldest Fossils
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I. Earth History
2.3-2.0 bya Oxygen
1.8 bya first eukaryote
0.9 bya first animals
0.5 bya Cambrian
4.5 bya Earth Forms
4.0 bya Oldest Rocks
3.4 bya Oldest Fossils
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I. Earth History
2.3-2.0 bya Oxygen
1.8 bya first eukaryote
0.9 bya first animals
0.5 bya Cambrian
0.24 byaMesozoic
4.5 bya Earth Forms
4.0 bya Oldest Rocks
3.4 bya Oldest Fossils
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I. Earth History
2.3-2.0 bya Oxygen
1.8 bya first eukaryote
0.9 bya first animals
0.5 bya Cambrian
0.24 byaMesozoic
0.065 byaCenozoic
4.5 bya Earth Forms
4.0 bya Oldest Rocks
3.4 bya Oldest Fossils
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I. Earth History
4.5 million to present
(1/1000th of earth history)
2.3-2.0 bya Oxygen
1.8 bya first eukaryote
0.9 bya first animals
0.5 bya Cambrian
0.24 byaMesozoic
0.065 byaCenozoic
4.5 bya Earth Forms
4.0 bya Oldest Rocks
3.4 bya Oldest Fossils
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II. Origin of Life Hypotheses - Oparin-Haldane
Hypothesis (1924) - in a reducing atmosphere,
biomonomers would form spontaneously
Aleksandr Oparin (1894-1980)
J.B.S. Haldane (1892-1964)
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II. Origin of Life Hypotheses - Oparin-Haldane
Hypothesis (1924) - in a reducing atmosphere,
biomonomers would form spontaneously -
Miller-Urey (1953)
all biologically important monomers have been
produced by these experiments, even while
changing gas composition and energy sources
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II. Origin of Life Hypotheses - Oparin-Haldane
Hypothesis (1924) - in a reducing atmosphere,
biomonomers would form spontaneously -
Miller-Urey (1953) - Sydney Fox - 1970 -
polymerized protein microspheres
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II. Origin of Life Hypotheses - Oparin-Haldane
Hypothesis (1924) - in a reducing atmosphere,
biomonomers would form spontaneously -
Miller-Urey (1953) - Sydney Fox - 1970 -
polymerized protein microspheres - Cairns-Smith
(1960-70) - clays as templates for non-random
polymerization - 1969 - Murcheson meteorite -
amino acids present some not found on Earth. To
date, 74 meteoric AA's. - 2004 - Szostak - clays
could catalyze formation of RNA's
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III. Acquiring the Characteristics of Life A.
Three Primary Attributes - Barrier
(phospholipid membrane) - Metabolism (reaction
pathways) - Genetic System
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III. Acquiring the Characteristics of Life B.
Barrier (phospholipid membrane) - form
spontaneously in aqueous solutions
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III. Acquiring the Characteristics of Life C.
Metabolic Pathways - problem how can pathways
with useless intermediates evolve? These
represent 'maladaptive valleys', don't they?
A
B
C
D
E
How do you get from A to E, if B, C, and D are
non-functional?
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III. Acquiring the Characteristics of Life C.
Metabolic Pathways - Solution - reverse evolution
A
B
C
D
E
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III. Acquiring the Characteristics of Life C.
Metabolic Pathways - Solution - reverse evolution
E
suppose E is a useful molecule, initially
available in the env.
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III. Acquiring the Characteristics of Life C.
Metabolic Pathways - Solution - reverse evolution
E
suppose E is a useful molecule, initially
available in the env. As protocells gobble it
up, the concentration drops.
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III. Acquiring the Characteristics of Life C.
Metabolic Pathways - Solution - reverse evolution
E
Anything that can absorb something else (D) and
MAKE E is at a selective advantage...
D
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III. Acquiring the Characteristics of Life C.
Metabolic Pathways - Solution - reverse evolution
E
Anything that can absorb something else (D) and
MAKE E is at a selective advantage... but over
time, D may drop in concentration...
D
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III. Acquiring the Characteristics of Life C.
Metabolic Pathways - Solution - reverse evolution
E
So, anything that can absorb C and then make D
and E will be selected for...
D
C
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III. Acquiring the Characteristics of Life C.
Metabolic Pathways - Solution - reverse evolution
A
B
C
D
E
and so on until a complete pathway evolves.
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III. Acquiring the Characteristics of Life D.
Genetic Systems - conundrum... which came first,
DNA or the proteins they encode?
DNA
RNA (m, r, t)
protein
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III. Acquiring the Characteristics of Life D.
Genetic Systems - conundrum... which came first,
DNA or the proteins they encode?
DNA
DNA stores info, but proteins are the metabolic
catalysts...
RNA (m, r, t)
protein
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III. Acquiring the Characteristics of Life D.
Genetic Systems - conundrum... which came first,
DNA or the proteins they encode? -
Ribozymes info storage AND cataylic ability
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III. Acquiring the Characteristics of Life D.
Genetic Systems - conundrum... which came first,
DNA or the proteins they encode? - Ribozymes -
Self replicating molecules - three stage
hypothesis
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Stage 1 Self-replicating RNA evolves
RNA
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Stage 1 Self-replicating RNA evolves
RNA
m- , r- , and t- RNA
PROTEINS (REPLICATION ENZYMES)
Stage 2 RNA molecules interact to produce
proteins... if these proteins assist replication
(enzymes), then THIS RNA will have a selective
(replication/reproductive) advantage... chemical
selection.
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DNA
m- , r- , and t- RNA
PROTEINS (REPLICATION ENZYMES)
Stage 3 Mutations create new proteins that read
RNA and make DNA existing replication enzymes
replicate the DNA and transcribe RNA.
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Can this happen? Are their organisms that read
DNA and make RNA?
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Can this happen? Are their organisms that read
DNA and make RNA? yes - retroviruses....
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DNA
m- , r- , and t- RNA
Already have enzymes that can make RNA...
PROTEINS (REPLICATION ENZYMES)
Stage 3 Mutations create new proteins that read
RNA and make DNA existing replication enzymes
replicate the DNA and transcribe RNA.
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DNA
m- , r- , and t- RNA
Already have enzymes that can make RNA...
PROTEINS (REPLICATION ENZYMES)
Stage 3 Mutations create new proteins that read
RNA and make DNA existing replication enzymes
replicate the DNA and transcribe RNA.
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This is adaptive because the two-step process is
more productive, and DNA is more stable (less
prone to mutation).
DNA
m- , r- , and t- RNA
PROTEINS (REPLICATION ENZYMES)
Stage 4 Mutations create new proteins that
replicate the DNA instead of replicating the
RNA...
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This is adaptive because the two-step process is
more productive, and DNA is more stable (less
prone to mutation).
DNA
And that's the system we have today....
m- , r- , and t- RNA
PROTEINS (REPLICATION ENZYMES)
Stage 4 Mutations create new proteins that
replicate the DNA instead of replicating the
RNA...
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IV. Early Life - the first cells were probably
heterotrophs that simply absorbed nutrients and
ATP from the environment. - as these substances
became rare, there was strong selection for cells
that could manufacture their own energy storage
molecules. - the most primitive cells are
methanogens, but these are NOT the oldest
fossils.
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IV. Early Life - the second type of cells were
probably like green-sulphur bacteria, which used
H2S as an electron donor, in the presence of
sunlight, to photosynthesize.
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IV. Early Life - the evolution of oxygenic
photosynthesis was MAJOR. It allowed life to
exploit more habitats, and it produced a powerful
oxidating agent! These stromatolites, which date
to gt 3 bya are microbial communities.
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IV. Early Life - about 2.3-1.8 bya, the
concentration of oxygen began to increase in the
ocean and oxidize eroded materials minerals...
deposited as 'banded iron formations'.
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IV. Early Life - 2.0-1.7 bya - evolution of
eukaryotes.... endosymbiosis.
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IV. Early Life
Eukaryote Characteristics - membrane bound
nucleus - organelles - sexual reproduction
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infolding of membrane
IV. Early Life
Origins
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IV. Early Life
endosymbiosis - mitochondria and chloroplasts
(Margulis - 1970's)
B. Origins
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IV. Early Life
Relationships among life forms - deep ancestry
and the last "concestor"
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IV. Early Life
Woese - r-RNA analyses reveal a deep divide
within the bacteria
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IV. Early Life
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IV. Early Life
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IV. Early Life
Curiously, the very root of life may be invisible
to genetic analysis. Bacteria transfer genes by
division (to 'offspring'), but they also transfer
genes "laterally" to other living bacteria. This
makes reconstructing bacterial phylogenies
difficult.
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IV. Early Life
So, reconstructing the patterns of relatedness
among these ancient life forms is
difficult. Different genes give different
patterns of relatedness among domains
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IV. Early Life C. Domains - "Ring of Life"
hypothesis (2004)