BIOC17H3 Lecture Notes - Lecture 5: Ribozyme, Proteobacteria, Stromatolite
12 May 2020
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Lecture 5
Origin of microbes
How did microbes take control of earth?
Tree of life organized in three
domains:
• Bacteria (exclusively microbial)
• Archaea (exclusively microbial)
• Eukarya (mainly microbial)
Carl Woese tree of life based on a comparison
of ribosomal RNA gene sequences
Origin of life and microbes
Microfossils from the Apex Chert, Australia
1 billion years old. They resemble modern
cyanobacteria
Evidence of presence of microbes in ancient earth
Evidence for microbial life can be found in rocks ~ 3.5 billion years old (Earth formed 4.5 billion
years ago)
SEM of the South African Greenstone Belt rock showing
bacteria-like rods-
3.45 billion years old
This is thought to be a bacteria-like organism obtained from
ancient rocks
Search for Past Life on Mars: Possible Relic Biogenic Activity in Martian Meteorite ALH84001
Martian nanobacteria?
To find out if this is a real microbe or just a mineral
formation...
• Cannot cultivate a microbe
• Cannot get a DNA
Bacteria came to earth through a meteorite??? How can
bacteria survive a meteorite?
- presence of endospores
Stromatolites
• Fossilized microbial mats consisting of layers of filamentous prokaryotes trapped in
sediments.
Fossilized stromatolites Modern Stromatolites
Formed by filamentous bacteria Formed by cyanobacteria
Scientists believe that oxygen was produced first
to change the composition of the atmosphere
Stromatolites in Thunder Bay
Stromatolitic limestone from the Eagle head Lake area north
of Thunder Bay. Age>1billion years old
Theories on the origin of life
• 1920’s
o Alexander Oparin (Soviet chemist) and John BS Haldane (British biochemist and
geneticist) are the precursors of the modern hypothesis on the origin of life.
Planetary science, clues for organic
Environmental
• Strongly reducing conditions in the atmosphere CH4, NH3, H2 and water vapour
• UV radiation and electric discharges
• Inorganic carbon
Reducing conditions produced hydrocarbons from CO2, giving origin to organic compounds.
Reaction of this compounds with nitrogen formed amino acids, leading to synthesis of proteins
that accumulated in hot ponds.
The hypothesis of the primordial soup
• In a primordial soup, proteins and other organic compounds formed colloidal systems:
coacervates. The first microbial forms of life evolved from coacervates.
o They are rich in organic molecules and they have the possibility of colliding and
breaking apart
Harold Urey and Stanley Miller 1950’s
• Harold Urey:
o Primitive Earth had a reducing atmosphere.
o Planets in the solar system have this kind of atmosphere. Their atmosphere
contained methane, ammonia, hydrogen and water.
• Stanley L. Miller
o First experiments designed to replicate chemical reactions in the primitive earth.
Document Summary
Tree of life organized in three domains: bacteria (exclusively microbial, archaea (exclusively microbial, eukarya (mainly microbial) Carl woese tree of life based on a comparison of ribosomal rna gene sequences. Evidence of presence of microbes in ancient earth. Evidence for microbial life can be found in rocks ~ 3. 5 billion years old (earth formed 4. 5 billion years ago) Sem of the south african greenstone belt rock showing bacteria-like rods- This is thought to be a bacteria-like organism obtained from ancient rocks. Search for past life on mars: possible relic biogenic activity in martian meteorite alh84001. To find out if this is a real microbe or just a mineral formation How can bacteria survive a meteorite? presence of endospores. Stromatolites: fossilized microbial mats consisting of layers of filamentous prokaryotes trapped in sediments. Scientists believe that oxygen was produced first to change the composition of the atmosphere. Stromatolitic limestone from the eagle head lake area north of thunder bay.
