The Origin of Life
What features define living systems?
ν
I. Introduction: What is life?
II. The Primitive Earth
III. Evidence for Life’
Life’s Beginning
A. Fossil Record: a point in
time
B. Requirements for Chemical
and Cellular Evolution:
1. Abiotic synthesis
2. Polymerization
3. Protobiont formation
4. Mutable genetic blueprint
ν
ν
ν
ν
ν
ν
ν
ν
ν
15 Billion Years of History compressed into
90 seconds:
Reconstructing the history of life:
ν
ν
ν
1. Exhibit multiple levels of organization with
emergent properties.
2. Share a similar chemical composition:CHNOPS
3. Made up of cells.
4. Capable of transforming energy.
5. Maintains homeostasis.
6. Capable of responding to stimuli.
7. Exhibit coordinated/directed growth and
development.
8. Capable of reproduction.
9. Capable of adaptation.
10. Can effect changes on its environment.
The fossil record
Experimental models and simulations
Deductions based on existing organisms
The Big Bang (15 bya)
Condensation of Solar System (5 bya)
The Third Planet (4.6 bya)
Earth and Primitive Atmosphere
Crust Solidifies (4 bya)
Oceans and land masses
(solid, liquid and gas states)
Compressing Geological Time:
If 4.5 billion years = a single year
The scale of geological time and fossil evidence:
ν
ν
ν
ν
ν
Jan 1 - formation of
earth
Feb 17 - Meteor
bombardment ends
Mar 20 - Simple cells
appear
Nov 17 - Simplest
animals (750 mya)
Nov 20 - Cambrian
Explosion and the
Burgess Fauna (520
mya)
ν
ν
ν
ν
ν
ν
Nov 28 - first land plants
Dec 13 - Permian
extinction
Dec 2121-27 - Dinosaurs
present and gone
Dec 31 8:45pm - Last ice
age begins
Dec 31 9:07pm - Early
man (Homo)
Dec 31 11:45pm - Man
(Homo sapiens)
Fossil Evidence for the Origin of Life
3.5 billion years ago:
Requirements for Chemical and Cellular
Evolution:
ν
ν
ν
ν
A. Abiotic synthesis and accumulation of
monomers (e.g., simple sugars and amino
acids)
B. Condensation of monomers into
polymers (molecules macromolecules)
C. Formation of protobionts:
protobionts: chemically
isolated systems
D. Origin of genetic material: directive,
continuity and changeable (mutable)
The Miller-Urey experiment: brewing the prebiotic soup
Experimental Evidence for
Abiotic Synthesis:
ν
ν
A. Oparin and Haldane’
(1920’s):
Haldane’s Hypothesis (1920’
υ Elemental requirements:CHNOPS
υ Reducing atmosphere? (CH4 & NH3 red. vs N2
&CO2 neither)
υ Energy sources
B. Miller and Urey: Testing Ho w/ Primitive Earth
apparatus
υ H2O, H2, CH4, NH3
υ CO2, CO, N2
Evidence for the production of
organic polymers:
ν
Polymerization=dehydration synthesis
H + OH
ν
ν
ν
+ H2O
Building blocks become concentrated on hot sand
or clay forming proteinoids
The importance of clay and zinc to concentration
and catalysis
Other mineralizing events: pyrite formation
(joining of iron and sulfur releases electrons that
lead to bonding)
Protobionts: Chemical Isolation
ν
ν
ν
Microspheres from proteinoids
Liposomes from phospholipids: David Deamer
Coacervates from colloidal droplets of
polypeptides, NA and/or polysaccharides
Self-replicating liposomes
A liposome w/ trapped enzymes as a model for
chemically isolated metabolism
The Evolution of Cellular Metabolism:
The gradual emergence of a heritable
blueprint and metabolism based on
catalysis
Protobionts: The selfself-assembly of
phospholipids into liposomes,
spontaneously forming chemically
isolated systems
ν
The 3 functions of the genetic material in the cell:
υ
υ
υ
ν
ν
“1st Generation”: RNA may have been
the first genetic material: The abiotic
replication of RNA
To direct metabolism
Serve as the basis of heredity
Mutability as a basis for adaptation
The cellular rate of metabolism relies on
biological catalysts
The stepwise evolution of a complex process
υ RNARNA-based genome and catalysis
υ RNARNA-directed protein synthesis
υ DNA as the genetic material
“2nd Generation”: Hypothesis for the
beginnings of molecular cooperation
RNA
protein
“3rd Generation”: The central
dogma of molecular biology
DNA
The Panspermia Hypothesis
ν
ν
RNA
protein
ν
Could the stuff of life
have originated
extraterrestrially?
extraterrestrially?
Life evolved in situ
but…
but…
Prebiotic chemicals the raw materials of life
- transported on comets
and meteorites may
have spiced up the soup.