Sigam o Carbono -2

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Sigam o Carbono -2
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Four types of organic macromoleculesin living
systems.

• Most of the molecules in the living systems are
  water (H2O) and large organic macromolecules
• Carbohydrates
• Lipids
• Proteins
• Nucleic Acids

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Carbohydrates (sugars, starches)

• Representatives
• Glucose, Fructose
• Many hydroxyl
• groups (-OH)
• Soluble in water
• Form Polysaccharides
• Good energy source
• Structural support for
• organisms (cellulose
• - the main constituent of wood)

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Glucose
Fructose
Table sugar
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Glucose polymerization
H2O
Linked by dehydration reaction
Polysaccharides
In starch molecule (potato) there can be 100s
thousands of glucose units
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Carbohydrates are important as a source of
energy for life

• Respiration
• CH2O O2 ? CO2 H2O Energy
• In reality
• C6H12O6 6O2 ? 6CO2 6H2O Energy
• Fermentation
• C6H12O6 ? 2CO2 2C2H6O Energy

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But there are ways to get energy without
carbohydrates.

• Methanogenesis
• CO2 4 H2 ? CH4 2H2O Energy
• Sulfate reduction
• 4H2 SO42- ? S2- 4H2O Energy

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Lipids (fats and oils)

• Representatives fatty acids and cholesterol
• Poorly soluble
• Good (concentrated)
• energy source
• Flexible
• (cell membrane material)

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Lipids are important for the formation of the
cell membrane

• Some lipids have hydrophilic (love water) head
  and hydrophobic tail
• In solution these lipids can form monolayers,
  bilayers and bilayer vesicles spontaneously
  pre-cells.

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Monolayer
Micells
Bilayer
Bilayer vesicle
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Membrane Lipids are very complex
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Cell Membrane Lipids
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ORIGINS OF LIFE?
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Two Approaches to the origin of life

• Top-down strategy is to
• look at the present day biology
• and extrapolate (project) back towards
• the simplest living entities.
• Bottom-up strategy is to make
• the complex building blocks of life
• (organic macromolecules) and put
• them together.

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Top-down strategy How would the most ancient
cell look like?

• Cells are very diverse in size, shape and
  complexity but there are 2 basic cell types
• Prokaryotes are much simpler and smaller than
  eukaryotes
• Eukaryotes have a cell nucleus (to protect DNA)
  while prokaryotes do not
• Prokaryotes are single-celled only
• Eukaryotes may be either single-celled or
  multicellular

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Prokaryotes
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Eukaryotic cell
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Eukaryotes vs. Prokaryotes

• Who outnumbers and outweighs the other?
• Who is more dependent on the other?

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Eukaryotes look much more complex then
prokaryotes. Do we see the difference in the DNA
structure? Yes
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• Is the genome (order of nucleotides) of
  Eukaryotes and Prokaryotes completely different?
  No
• Some parts of the genome change more easily than
  others in the course of evolution
• A segment of the DNA responsible for coding of
  ribosomal parts (16S RNA, 1500 nucleotides) is
  very well conserved.

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• A part of the gene for 16S RNA (1500
  nucleotides) for different organisms.
• Corresponding segments of nucleotide sequence
  from an archaean (Methanococcus jannaschii), a
  eubacterium (Escherichia coli) and a eucaryote
  (Homo sapiens) are aligned in parallel.
• Sites where the nucleotides are identical between
  species are indicated by a vertical line.
• Genetic information conserved since the
  beginnings of life.

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Top-down strategyThe Tree of Life

• By looking at the changes in 16S RNA we can
  identify three domains of life Bacteria, Archaea,
  and Eucaryotes

Prokaryotes
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Bottom-up strategy

• Bottom-up strategy to the origin of life is to
  make complex building blocks of life and try to
  put them together.
• But first we need to answer how was it possible
  to make any organic molecules at all without
  biology?

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EARTH TODAY
Organics from space
Abiotic synthetic reactions on the early Earth
Prebiotic soup
Prebiotic polymers
Protein/DNA world (modern biochemistry)
RNA world
The origin of life
Bada Lazcano (Science, 2002)
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Problems with abiotic organic synthesis.

• Almost all organic carbon which we observe today
  is produced biologically (photosynthesis)
• CO2 H2O ? CH2O O2
• Carbon which comes out of volcanoes is in a form
  of CO2
• CO2 gas mixture does not produce
• organic molecules on its own

organic
inorganic
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Terrestrial vs. Extraterrestrial

• Terrestrial origin organic synthesis occurred
  somewhere in the Earth environment
• Extraterrestrial origin organic material was
  synthesized in space and was brought to Earth
  somehow

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Urey-Miller Experiment
1) At some point scientists believed that the
ancient atmosphere was rich in CH4 and NH3 2)
But! Just mixing CH4, NH3, H2O, H2 would not
produce any organic material 3) Miller showed
that a spark discharge (lightning) would produce
organic molecules up to 10-15 of the initial CH4
by mass
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The Miller-Urey-Experiment
FIRST EXPERIMENTAL FORMATION OF
BIOLOGICALLY RELEVANT MOLECULES UNDER PREBIOTIC
CONDIDTIONS
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Formation of organic molecules in the gas phase

• UV can be used for organic synthesis as well
• The key is to produce carbon radicals
• CH4 h? ? CH3 H
• CH3 CH3 ? C2H6 M
• C2H6 h? ... ? C2H
• C2nH2 C2H ? C2n2H2 H
• Polymerization is extremely sensitive to O
  abundance

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Titans Organic Haze Layer
Haze is thought to form from photolysis (and
charged particle irradiation) of CH4
(Picture from Voyager 2)
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Advantages of Organic synthesis in the ancient
atmosphere

• UM-like experiments produced many types of
  organic molecules which are used in proteins
• We would expect lightning and UV radiation in the
  prebiotic atmosphere
• No need to deliver organic material to Earth it
  would be already here

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Difficulties for the organic synthesis via UM
experiment

• It is hard to justify large amounts of NH3 and
  CH4 in the prebiotic atmosphere
• In the CO2-rich atmosphere organic production by
  spark discharge is not very efficient
• If CH4/CO2 lt 0.1 essentially no organic
  production

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Trainer et al., 2005 2006)
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Hydrothermal vents

• Fischer-Tropsch synthesis. Under high
  temperatures and pressures CO and H2 can form
  hydrocarbons
• (2n1)H2 nCO ? CnH(2n2) nH2O
• where 'n' is a positive integer

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Advantages of Organic synthesis in the
Hydrothermal Vents

• Hydrothermal vents were likely to be present in
  the prebiotic environment
• Organic synthesis requires only CO2, H2O and
  silicate rocks.
• Serpentinization
• Spinel polymerization

Olivine
Serpentine
Magnetite (spinel group)
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Difficulties of the organic synthesis via
Hydrothermal Vents

• No clean catalysts in nature. Original
  Fischer-Tropsch reaction goes fast in the
  presence of iron and cobalt
• Only very simple organics can be generated. No
  amino-acids, no PAHs etc.

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• Since both atmosphere and hydrothermal vents have
  problems producing organics we need to look
  somewhere else. Space!

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Key hole Nebula
Gaseous Pillars Eagle Nebula
Hale-Bopp
Murchinson
Titan