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Cell Biology
I. Overview
II. Membranes: How Matter Get in and Out of Cells
III. Cellular Respiration
IV. Photosynthesis
V. DNA and Chromosome Structure
VI. Protein Synthesis
VII. Cellular Reproduction
VIII. Origin of Life Hypotheses
Cell Biology
VIII. Origin of Life Hypotheses
Origin of life
hypotheses
Evolutionary
Theory
4.5 bya: Earth Forms
A. The Early Earth and Earth History
Graviational sorting
of materials…heavy
to the core, gases
released under
pressure…
A. The Early Earth and Earth History
- Earliest Atmosphere - probably of volcanic origin
Gases produced were probably
similar to those released by
modern volcanoes (H2O, CO2,
SO2, CO, S2, Cl2, N2, H2) and
NH3 and CH4
4.0 bya: Oldest Rocks
4.5 bya: Earth Forms
A. The Early Earth and Earth History
4.0 bya: Oldest Rocks
3.4 bya: Oldest Fossils
4.5 bya: Earth Forms
A. The Early Earth and Earth History
Stromatolites - communities of layered 'bacteria'
4.0 bya: Oldest Rocks
3.4 bya: Oldest Fossils
4.5 bya: Earth Forms
A. The Early Earth and Earth History
Putative microfossil bacteria from Australia that date to 3.4 by
2.3-2.0 bya: Oxygen in
Atmosphere
4.0 bya: Oldest Rocks
3.4 bya: Oldest Fossils
4.5 bya: Earth Forms
A. The Early Earth and Earth History
1.8 bya: first eukaryote
2.3-2.0 bya: Oxygen
4.0 bya: Oldest Rocks
3.4 bya: Oldest Fossils
4.5 bya: Earth Forms
A. The Early Earth and Earth History
0.9 bya: first animals
1.8 bya: first eukaryote
2.3-2.0 bya: Oxygen
4.0 bya: Oldest Rocks
3.4 bya: Oldest Fossils
4.5 bya: Earth Forms
A. The Early Earth and Earth History
0.5 bya: Cambrian
0.9 bya: first animals
1.8 bya: first eukaryote
2.3-2.0 bya: Oxygen
4.0 bya: Oldest Rocks
3.4 bya: Oldest Fossils
4.5 bya: Earth Forms
A. The Early Earth and Earth History
0.5 bya: Cambrian
0.24 bya:Mesozoic
0.9 bya: first animals
1.8 bya: first eukaryote
2.3-2.0 bya: Oxygen
4.0 bya: Oldest Rocks
3.4 bya: Oldest Fossils
4.5 bya: Earth Forms
A. The Early Earth and Earth History
0.5 bya: Cambrian
0.24 bya:Mesozoic
0.065 bya:Cenozoic
0.9 bya: first animals
1.8 bya: first eukaryote
2.3-2.0 bya: Oxygen
4.0 bya: Oldest Rocks
3.4 bya: Oldest Fossils
4.5 bya: Earth Forms
A. The Early Earth and Earth History
0.5 bya: Cambrian
0.24 bya:Mesozoic
0.065 bya:Cenozoic
0.9 bya: first animals
1.8 bya: first eukaryote
2.3-2.0 bya: Oxygen
4.0 bya: Oldest Rocks
3.4 bya: Oldest Fossils
4.5 bya: Earth Forms
A. The Early Earth and Earth History
4.5 million to present
(1/1000th of earth
history)
B. The Formation of Biologically Important Molecules
- Oparin-Haldane Hypothesis (1924):
- in a reducing atmosphere, biomonomers would form spontaneously
Aleksandr Oparin
(1894-1980)
J.B.S. Haldane
(1892-1964)
B. The Formation of Biologically Important Molecules
- 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
B. The Formation of Biologically Important Molecules
- Oparin-Haldane Hypothesis (1924):
- in a reducing atmosphere, biomonomers would form spontaneously
- Miller-Urey (1953)
- Sydney Fox - 1970 - polymerized protein microspheres
B. The Formation of Biologically Important Molecules
- 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
C. Acquiring the Characteristics of Life
Three Primary Attributes:
- Barrier (phospholipid membrane)
- Metabolism (reaction pathways)
- Genetic System
C. Acquiring the Characteristics of Life
1. Evolution of a Membrane
- form spontaneously in aqueous solutions
C. Acquiring the Characteristics of Life
1. Evolution of a Membrane
2. Metabolic Pathways
- problem:
how can pathways with useless intermediates evolve?
These represent 'maladaptive valleys', don't they?
A
B
C
D
How do you get from A to E, if B, C, and D are non-functional?
E
C. Acquiring the Characteristics of Life
1. Evolution of a Membrane
2. Metabolic Pathways
- Solution - reverse evolution
A
B
C
D
E
C. Acquiring the Characteristics of Life
1. Evolution of a Membrane
2. Metabolic Pathways
- Solution - reverse evolution
suppose E is a useful molecule, initially available in the env.
E
C. Acquiring the Characteristics of Life
1. Evolution of a Membrane
2. Metabolic Pathways
- Solution - reverse evolution
suppose E is a useful molecule, initially available in the env.
As protocells gobble it up, the concentration drops.
E
C. Acquiring the Characteristics of Life
1. Evolution of a Membrane
2. Metabolic Pathways
- Solution - reverse evolution
D
Anything that can absorb something else (D) and MAKE E is
at a selective advantage...
E
C. Acquiring the Characteristics of Life
1. Evolution of a Membrane
2. Metabolic Pathways
- Solution - reverse evolution
D
Anything that can absorb something else (D) and MAKE E is
at a selective advantage...
but over time, D may drop in concentration...
E
C. Acquiring the Characteristics of Life
1. Evolution of a Membrane
2. Metabolic Pathways
- Solution - reverse evolution
C
D
So, anything that can absorb C and then make D and E will
be selected for...
E
C. Acquiring the Characteristics of Life
1. Evolution of a Membrane
2. Metabolic Pathways
- Solution - reverse evolution
A
B
C
D
and so on until a complete pathway
evolves.
E
C. Acquiring the Characteristics of Life
1. Evolution of a Membrane
2. Metabolic Pathways
- Solution - reverse evolution
- Problem with “Miller-Urey Experiments”
Requires source of continuous
environmental energy AND carbon,
and continual production of activated
nucleotides to drive the reactions to
form RNA.
Lightening and other sources of energy do not provide the
carbon, and they are unstable and destructively high energy
C. Acquiring the Characteristics of Life
1. Evolution of a Membrane
2. Metabolic Pathways
- Solution - reverse evolution
- Problem with “Miller-Urey Experiments”
- What’s Needed:
Continuous flow of energy
Continuous flow of carbon as source of new molecules
Rudimentary catalysts (could be inorganic FeS minerals that are
often at the heart of organic catalysts)
“Focusing” products to raise their concentrations to reactive levels
C. Acquiring the Characteristics of Life
1. Evolution of a Membrane
2. Metabolic Pathways
- Solution - reverse evolution
- Problem with “Miller-Urey Experiments”
- What’s Needed:
Continuous flow of energy
Continuous flow of carbon
Rudimentary catalysts
“Focusing” products
“Black Smokers”
Very hot – 250-400oC, driven by magma in contact
with water.
Most stable carbon compound is CO2.
Very unstable, collapsing in decades
Do have lots of FeS compounds but precipitated
organics would be blown from chimney.
Hydrothermal Vents
Hydrothermal Vents
“White Smokers” of Today
Mantle rock near spreading centers is exposed to sea
water; the olivine (rich in ferrous iron) is oxidized by
water in an exothermic reaction, giving off heat and H2.
The warm (60-90oC), H-rich water percolates up and
the carbonate minerals precipitate into microporous
chimneys.
High flux of carbon and energy is channeled over
inorganic catalysts
Thermal currents through pores can concentrate
organics 1000 – 106 fold
Vents persist for millennia
500 um
The role of a proton gradient:
Likewise, if the free H+ is placed in an alkali
environment (rich in OH-), it will bind to
form stable water. The H2 has reacted with
the CO2 irreversibly.
If these fluids are separated by a thin
inorganic membrane with FeS minerals, the
FeS will draw the electrons from the H2 and
transfer them to CO2.
Physical structure of vent drives the
synthesis of organics.
These accumulate 1000x
Pore
Wall
Seawater
percolating
through pores:
pH = 6
H+
Percolating
from mantle:
Fe
S
pH = 11
OH-
CO2-2 + 2H+  CH2OO
If the formate (CO2- ) can accept a H+ to
balance the charge, it won’t get rid of the
electron. If the CO2 is placed in an acidic
environment rich in H+, this will tend to
happen.
H2O
H2
Fe
S 2e-
e-
2
H+
STEP 2: Energy Harvest
The proton gradient can be exploited by protein synthesized organically for Energy Harvest
(ATP Synthase).
So, both E harvest AND organic production
ATP
C. Acquiring the Characteristics of Life
1. Evolution of a Membrane
2. Metabolic Pathways
3. Evolution of a Genetic System
- conundrum... which came first, DNA or the proteins they
encode?
DNA
RNA
(m, r, t)
protein
C. Acquiring the Characteristics of Life
1. Evolution of a Membrane
2. Metabolic Pathways
3. Evolution of a Genetic System
- 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
C. Acquiring the Characteristics of Life
1. Evolution of a Membrane
2. Metabolic Pathways
3. Evolution of a Genetic System
- conundrum... which came first, DNA or the proteins they
encode?
- Ribozymes
info storage AND
cataylic ability
C. Acquiring the Characteristics of Life
1. Evolution of a Membrane
2. Metabolic Pathways
3. Evolution of a Genetic System
- conundrum... which came first, DNA or the proteins they
encode?
- Ribozymes
- Self replicating molecules
- three stage hypothesis
Stage 1: Self-replicating
RNA evolves
RNA
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.
DNA
Reverse
transcriptases
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.
Can this happen? Are their organisms that read RNA
and make DNA?
Can this happen? Are their organisms that read RNA
and make DNA?
yes - retroviruses....
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.
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.
DNA
This is adaptive because
the two-step process is
more productive, and DNA
is more stable (less prone
to mutation).
m- , r- , and t- RNA
PROTEINS
(REPLICATION ENZYMES)
Stage 4: Mutations create new proteins that replicate the DNA instead of
replicating the RNA...
DNA
m- , r- , and t- RNA
This is adaptive because
the two-step process is
more productive, and DNA
is more stable (less prone
to mutation).
And that's the system we
have today....
PROTEINS
(REPLICATION ENZYMES)
Stage 4: Mutations create new proteins that replicate the DNA instead of
replicating the RNA...
D. Summary:
STEPS REQUIRED FOR THE SPONTANEOUS, NATURAL FORMATION
OF LIFE, and the evidence to date:
1. Spontaneous synthesis of biomolecules - strong evidence; MillerUrey experiments.
2. Polymerization of monomers into polymers (proteins, RNA, sugars,
fats, etc.) - strong evidence; Fox and Cairns-Smith experiments.
3. Formation of membranes - strong evidence; behavior of
phospholipids in solution.
4. Evolution of metabolic systems - reasonable hypotheses, and
genetic similarity in genes involved in particular pathways
(suggesting gene duplication and subsequent evolution of new genes
and elaboration of existing pathways)
5. Evolution of a genetic system - a reasonable hypothesis and
significant corroborating evidence that it could happen. But no
experimental evidence of the process evolving through all three steps.
6. How did these three elements (membrane, metabolism, genetic
system come together?) a few untested hypotheses.