How Did Life Begin? And What is Life?

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How Did Life Begin?And What is Life?

• Barry Selinsky
• Chemistry Department
• Villanova University

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How was life established on earth?
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• God did it.

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God School
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God School Final Written Examination

• As a community committed to the Augustinian
  ideals of truth, unity and love, God School
  prides itself on maintaining the highest
  standards of academic integrity and does not
  tolerate any forms of academic dishonesty or
  misconduct. Accordingly, each student who takes
  an examination is expected to sign the following
  statement
• I, (sign your name)
• have not had any unsanctioned prior access to
  this examination and will conduct myself in an
  honest manner in regard to all aspects of this
  examination. Unless authorized, I will not
  discuss the contents of this examination with
  other students.

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Final Thesis Project

• Create life.
• You may use any atomic materials up to and
  including the element iron.

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Periodic Table
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Final Written Examination - Continued

• You may also use small molecules consisting of no
  more than 5 total atoms and no more than 3
  different elements. That is, water and HCN are
  ok acetate (CH3COOH) is not.

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Final Written Examination - Continued

• You may also assume any environmental conditions
  needed to complete the assignment.

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Good news and bad news

• The bad news there is no partial credit.
  Either you make a living organism or you dont.
• The good news you have 800 million years to
  complete the exam!

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Assumptions in our attempts to determine how life
began

• All of todays organisms arose from a single
  ancestor organism.
• Support all organisms today share many common
  features, proteins, and metabolic pathways.

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Evolution in pictures
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Corollary to first assumption

• If multiple types of organisms developed
  simultaneously (or nearly so), one type dominated
  and eliminated the others.

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What is the simplest life as we know it?

• Bacteria single cell organisms with the ability
  to independently reproduce and generate new
  bacteria.

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Bacteria are comprised of numerous small
molecules and four classes of macromolecules

• Nucleic acids (DNA and RNA)
• Proteins
• Polysaccharides (polymers of sugars)
• Lipids

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King of Prussia Mall A Multicellular Organism
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Costco A Modern Single Celled Organism
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The General store A primitive single cell
organism
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Definitions of Life

• Any population of entities which has the
  properties of multiplication, heredity, and
  variation. John Maynard Smith
• Life is an expected, collectively self-organized
  property of catalytic polymers. Stuart Kauffman
• Life possesses the properties of replication,
  catalysis, and mutability. Norman Horowitz

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Definitions of life

• Life is a self-sustained chemical system capable
  of undergoing Darwinian evolution. Gerald Joyce
• From this definition, what minimal elements must
  life contain?

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• Life must be chemical
• As a result, computer generated artificial
  intelligence is excluded.
• Life sustains itself by gathering atoms and
  energy form its environment.
• If it doesnt eat, its not alive. Life requires
  metabolism.
• Living organisms must display variation.
• No two people, bunnies, or bacteria are
  necessarily the same. Life requires reproduction
  and genetic variability.

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Bacteria are comprised of numerous small
molecules and four classes of macromolecules

• Nucleic acids (DNA and RNA polymers of
  nucleotides)
• Proteins (polymers of amino acids)
• Polysaccharides (polymers of sugars)
• Lipids
• How can we make these?

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Millers experiments A production of amino acids
under possible primitive earth conditions.
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Millers amino acid synthesis
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Oros purine synthesis
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Amino acids, sugars, purines, and pyrimidines can
be made from simple precursors.Next, is it
possible to generate polymers of these materials
to make biomacromolecules important to life?
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Polymerization on crystalline templates
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The chirality issue
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Chiral molecules
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Order out of chaos the entropy problem

• Second law of thermodynamics
• In any spontaneous process there is always an
  increase in the entropy of the universe.

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The theory of emergence

• While systems become more disordered with time,
  local order and complexity arise due to the input
  of energy.

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The Iron-Sulfur World

• Hypothesis life began at hydrothermal vents at
  the bottom of the ocean, fed by a constant stream
  of hot volcanic gas.

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Energy from volcanic gas
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The Reverse Citric Acid Cycle
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In support of the reverse citric acid cycle

• At hydrothermal vents, there is a constant stream
  of hydrogen gas and energy generated from the
  reaction of hydrogen sulfide with iron sulfide.
• The reactions can be catalyzed by iron sulfide,
  pyrite, or other iron-sulfur complex.
• In organisms, the reactions are catalyzed by
  enzymes. Most enzymes require iron-sulfur
  clusters to work.

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Problems with the Iron-Sulfur world

• The iron sulfur world does not explain the
  generation of genetic material, and does not
  include reproduction or genetic variability.

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The RNA World

• Hypothesis Life began as a collection of a small
  number of self-reproducing catalytic RNA
  molecules localized within a small area.

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What is RNA?
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Evidence in support of the RNA World

• Some RNA molecules can catalyze chemical
  reactions (mostly done by proteins).
• Some RNA molecules can replicate themselves if
  ribonucleotides are present.
• This explains both metabolism and genetic
  variability.

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Problems with the RNA world

• Self-replicating RNA molecules have only been
  made up to 14 nucleotides long. Catalytic RNAs
  are estimated to require at least 50 nucleotides.
• There is no known physical encouragement for
  multiple self-replicating RNA molecules to
  collect in the same local area.

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Thanks for living!