Chapter 26: Early Earth and the Origin of Life

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Chapter 26Early Earth and the Origin of Life
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Phylogeny

• Traces life backward to common ancestors.
• How did life get started?

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Fossil Record

• Earliest - 3.5 billion years old.
• Earth - 4.5 billion years old.

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Prokaryotes

• Fossil Modern

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Bacterial Mats
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Point

• Life on earth started relatively soon after the
  earth was formed.

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Chemical Evolution

• The evolution of life by abiogenesis.

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Steps

• 1. Monomer Formation
• 2. Polymer Formation
• 3. Protobiont Formation
• 4. Origin of Heredity

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Primitive Earth Conditions

• Reducing atmosphere present.
• Simple molecules
• Ex H2O, CH4, H2, NH3

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Complex Molecule Formation

• Requires energy sources
• UV radiation
• Radioactivity
• Heat
• Lightning

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Oparin and Haldane 1920s

• Hypothesized steps of chemical evolution from
  primitive earth conditions.

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Miller and Urey, 1953

• Tested Oparin and Haldanes hypothesis.
• Experiment - to duplicate primitive earth
  conditions in the lab.

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Results

• Organic monomers formed including Amino Acids.

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Other Investigator's Results

• All 20 Amino Acids
• Sugars
• Lipids
• Nucleotides
• ATP

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Hypothesis

• Early earth conditions could have formed monomers
  for life's origins.

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Polymer Synthesis

• Problem
• Monomers dilute in concentration.
• No enzymes for bond formation.

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Possible Answer

• 1. Clay
• 2. Iron Pyrite

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Explanation

• Lattice to hold molecules, increasing
  concentrations.
• Metal ions present which can act as catalysts.

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Protobionts

• Aggregates of abiotically produced molecules.
• Exhibit some properties of life.
• Ex Osmosis, Electrical Charge, Fission

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Protobionts
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Protobiont Formation

• Proteinoids H2O ? microspheres
• Liposomes H2O ? lipid membranes

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Coacervates

• Colloidal droplets of proteins, nucleic acids and
  sugars surround by a water shell.
• Will form spontaneously from abiotically produced
  organic compounds.

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Summary

• Protobionts have membrane-like properties and are
  very similar to primitive cells.
• Start for selection process that lead to cells?

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Question ?

• Where did the energy come from to run these early
  cells?

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Answer

• ATP.
• Reduction of sulfur compounds.
• Fermentation.
• Rs and Ps developed much later.
• Review materials in Chapter 27.

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Genetic Information

• DNA ? RNA ? Protein
• Too complex for early life.
• Other forms of genetic information?

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RNA Hypothesis

• RNA as early genetic information.

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Rationale

• RNA polymerizes easily.
• RNA can replicate itself.
• RNA can catalyze reactions including protein
  synthesis.

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Ribozymes

• RNA catalysts found in modern cells.
• e.g. ribosomes
• Possible relic from early evolution?

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Molecular Cooperation

• Interaction between RNA and the proteins it made.
• Proteins formed may serve as RNA replication
  enzymes.

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Molecular Cooperation

• Works best inside a membrane.
• RNA benefits from the proteins it made.

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Selection favored

• RNA/protein complexes inside membranes as they
  were the most likely to survive and reproduce.

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DNA Developed later as the genetic information

• Why? More stable than RNA

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Alternate View

• Life developed in Volcanic Vents.

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Volcanic Vents

• Could easily supply the energy and chemical
  precursors for chemical evolution.
• Most primitive life forms are the prokaryotes
  found in or near these vents.

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Modern Earth

• Oxidizing atmosphere.
• Life present.
• Prevents new abiotic formation of life.

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Hypothesis

• Life as a natural outcome of chemical evolution.
• Life possible on many planets in the universe.

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Kingdom

• Highest Taxonomic category
• Old system - 2 Kingdoms
• 1. Plant
• 2. Animal

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5 Kingdom System

• R.H. Whittaker - 1969
• System most widely used today.

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Main Characteristics

• Cell Type
• Structure
• Nutrition Mode

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Monera

• Ex Bacteria, Cyanobacteria
• Prokaryotic

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Protista

• Ex Amoeba, Paramecium
• Eukaryotic
• Unicellular or Colonial
• Heterotrophic
• Review Chapter 28

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Fungi

• Ex Mushrooms, Molds
• Eukaryotic
• Unicellular or Multicellular
• Heterotrophic - external digestion
• Cell wall of chitin

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Plantae

• Ex Flowers, Trees
• Eukaryotic
• Multicellular
• Autotrophic
• Cell wall of Cellulose/Silicon

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Animalia

• Ex Animals, Humans
• Eukaryotic
• Multicellular
• Hetrotrophic - internal digestion
• No cell wall

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Other Systems

• Multiple Kingdoms split life into as many as 8
  kingdoms. (review Chapter 28)
• Domains a system of classification that is
  higher than kingdom.

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3 Domain System

• Based on molecular structure for evolutionary
  relationships.
• Prokaryotes are not all alike and should be
  recognized as two groups.
• Gaining wider acceptance.

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3 Domains

• 1. Bacteria prokaryotic.
• 2. Archaea prokaryotic, but biochemically
  similar to eukaryotic cells.
• 3. Eucarya the traditional eukaryotic cells.

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Summary

• Systematics is still evaluating the evolutionary
  relationships of life on earth.
• Be familiar with the conditions of primitive
  earth.
• Know the steps of chemical evolution.

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Summary

• Recognize the 5 Kingdoms.
• Recognize alternate systems for classification.
• Know about Domains.