Bio 100
Study Guide 14
http://www.swarthmore.edu/NatSci/cpurrin1/evolk12/slm/origindayimages/06soup.jpg
The Origin of Life - Issues
i.
ii.
Conditions on early earth
Abiogenic synthesis organic
molecules
iii. Hot rocks and clay help to form
polymers
iv. RNA world and aggregates
v. Why prokaryotes are critical to life on
earth
The analogy of a clock can be used to
place major events in the Earth’s history in
the context of the geological record
Cenozoic
Humans
Land plants
Origin of solar
system and
Earth
Animals
4
1
Proterozoic
Eon
Archaean
Eon
Billions of years ago
2
3
Multicellular
eukaryotes
Prokaryotes
Single-celled
eukaryotes
Atmospheric
oxygen
Working Backwards the Age of the Earth
Radioactive decay is consistent with an
age of 4.5 Billion Years
http://www.cbu.edu/~jholmes/N111/Part24/sld018.htm
STRATIGRAPHY
http://www.gobiernodecanarias.org/educacion/penelope/Strat3.gif http://earthsci.org/fossils/palaeo/images/scale.gif
The earliest stromatolite of
confirmed microbial origin
dates to 2,724 million years
ago.
Modern stromatolites in
Shark Bay, Western
Australia.
http://www.resa.net/nasa/images/mars/stromatolite.jpg
Most biologists now think that it is at least a credible hypothesis
that chemical and physical processes on early Earth
produced very simple cells through a sequence of stages
Aleksandr Oparin, in full Aleksandr
Ivanovich Oparin (born Feb. 18 [March 2,
New Style], 1894, Uglich, near Moscow,
Russia—died April 21, 1980), Russian
biochemist noted for his studies on the
origin of life from chemical matter.
Questions that are relevant to the nature and
origin of life on Earth.
http://rst.gsfc.nasa.gov/Sect20/A12.html
One Scenario - Four Stages of
Prebiotic Chemical Evolution
• Abiotic synthesis of small organic
molecules
• Joining of monomers into polymers
• Origin of heredity ―RNA‖ world
• Aggregation of o.m. into protobiont
droplets
There are a variety of potential sources of
the organic monomers that started life!
i.
ii.
iii.
iv.
Outer space
The
atmosphere
Meteorites
Oceans deep
sea
hydrothermal
vents
Synthesis of Organic Compounds on
Early Earth
• Earth formed about 4.6 billion years ago
– Along with the rest of the solar
system
• Earth’s early atmosphere
– Contained water vapor and many
chemicals released by volcanic
eruptions
Laboratory experiments simulating an
early Earth atmosphere
– Show that organic molecules, a
first step in the origin of life, can
form in a strongly reducing
atmosphere.
– Have produced organic molecules
from inorganic precursors, but the
existence of such an atmosphere
on early Earth is unlikely
Apparatus for the Miller-Urey Experiment
http://www.physics.hku.hk/~tboyce/sfseti/15origin.html
http://upload.wikimedia.org/wikipedia/commons/4/40/UreyMillerExperiment.jpeg
• Instead of forming in the atmosphere
– The first organic compounds on Earth may
have been synthesized near submerged
volcanoes and deep-sea vents
Figure 26.3
http://www.tutorvista.com/content/biology/biology-iii/origin-life/origin-life-steps.php
Extraterrestrial Sources of
Organic Compounds
• Some of the organic compounds from which
the first life on Earth arose
– May have come from space
• Carbon compounds
– Have been found in some of the meteorites
that have landed on Earth
Looking Outside Earth for Clues About
the Origin of Life
The possibility that life is not restricted to Earth Is
becoming more accessible to scientific testing
Abiotic Synthesis of Polymers
Small organic molecules
Polymerize when they are concentrated on hot
sand, clay, or rock
Abiotic Synthesis of Polymers. Small organic
molecules polymerize when they are
concentrated on hot sand, clay, or rock
Pyrite - FeS
Pyrite and the origin of life
K. R. POPPER
Nature 344, 387 (29 March 1990);
doi:10.1038/344387a0
ORIGIN OF LIFE: Life as We Don't Know It
Wächtershäuser
Science 25 August 2000: 1307
PYRITE World
http://www.wellesley.edu/Chemistry/chem227/origins/1307-1-med.gif
One reason why it is suggested that the initial
formation of ―biological-like‖ polymers must have
taken place on the surfaces of minerals was:
Minerals provide a dry surface for the
dehydration reactions needed to produce
biological polymers.
Optical Activity is an Issue
http://www.btools.com/images/fig1.gif
• Protobionts
– Are aggregates of abiotically produced
molecules surrounded by a membrane or
membrane-like structure
• Laboratory experiments demonstrate that
protobionts
– Could have formed spontaneously from
abiotically produced organic compounds
• For example, small membrane-bounded
droplets called liposomes
– Can form when lipids or other organic
molecules are added to water
Glucose-phosphate
20 m
Glucose-phosphate
Phosphorylase
Starch
Amylase
Phosphate
Maltose
Maltose
Figure 26.4a, b
(a) Simple reproduction. This liposome is ―giving birth‖ to smaller
liposomes (LM).
(b) Simple metabolism. If enzymes—in this case,
phosphorylase and amylase—are included in the
solution from which the droplets self-assemble,
some liposomes can carry out simple metabolic
reactions and export the products.
http://journalofcosmology.com/SearchForLife108.html
Natural section could refine
protobionts containing hereditary
information
• Once primitive RNA genes and
their polypeptide products were
packaged within a membrane,
the protobionts could have
evolved as units.
• Molecular cooperation could be
refined because favorable
components
were concentrated
together, rather than
spread throughout the
surroundings.
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
Fig. 26.13
Misconception: ―Evolution is a theory about the origin of life.‖
http://evolution.berkeley.edu/evosite/misconceps/IAorigintheory.shtml
The ―RNA World‖ and the Dawn
of Natural Selection
• The first genetic material
– Was probably RNA, not
DNA
• RNA molecules called ribozymes have been
found to catalyze many different reactions,
including
– Self-splicing
– Making complementary copies of short
stretches of their own sequence or other short
pieces of RNA
Ribozyme
(RNA molecule)
3
Template
Nucleotides
Figure 26.5
Complementary RNA copy
5
5
The first
ribozymes found
in bacteria were
self-splicing
introns.
http://138.192.68.68/bio/Courses/biochem2/RNA/SelfSplicingRNA.html
A Ribozyme from a Protist
The folded three-dimensional structure of this catalytic RNA, or
ribozyme, enables it to catalyze chemical reactions during protein
synthesis. RNA catalysis may have preceded enzyme catalysis in the
evolution of life.
http://www.mie.utoronto.ca/labs/lcdlab/biopic/fig/25.04.jpg
http://exobiology.nasa.gov/ssx/biomod/origin_of_life_slideshow/RNAWorldCritique.big.jpg
A Globin Gene Tree
The globin family gene tree suggests that myoglobin diverged from modern
hemoglobin precursors about 500 mya, at about the time of the origin of
vertebrates.
http://www.mie.utoronto.ca/labs/lcdlab/biopic/fig/24.07.jpg
Cytochrome c Molecules Evolved at a Constant Rate
Rates of substitution in cytochrome c are constant enough that this
molecule can be used as a molecular clock.
http://www.mie.utoronto.ca/labs/lcdlab/biopic/fig/24.06.jpg
The End