Origin of Life on Earth

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Origin of Life on Earth

• Biology CP

Source Biology, The Dynamics of Life.
Glencoe/McGraw-Hill, 2002.
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Early Ideas about Origins of Life

• Spontaneous generation - life arising from
  nonliving matter
• Examples
• mud producing fish
• grain producing mice
• decaying meat producing maggots

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Redis Experiment

• Effort to disprove spontaneous generation
• Decaying meat in uncovered control jars vs.
  covered experimental jars.
• Results?

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Redis Experiment

• Effort to disprove spontaneous generation
• Decaying meat in uncovered control jars vs.
  covered experimental jars.
• Results maggots and flies filled the open jars
  but not covered jars. Showed only flies produce
  flies.

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People still didnt believe it

• Although Redi disproved spontaneous generation of
  large organisms, many scientists thought
  microorganisms must arise spontaneously, probably
  from a vital force in the air.

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Pasteurs Experiment (mid-1800s)
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Ideas about Origins of Life

• Biogenesis-life arising from other organisms
• Where did the first life come from?

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First Things First

• Before we talk about the origin of life we must
  talk about the origin of
• Universe
• Earths Oceans
• Earths Atmosphere
• Earths Crust

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Big Bang Theory

• Explains how the universe formed-13.7 bya
• Universe began as an infinitely small, hot dense
  speck that inflated, expanded and cooled to the
  size and temperature of our current universe.
• Earth formed 4.5-4.6 bya

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Formation of the Oceans

• Tremendous amounts of hydrogen and oxygen were
  trapped below the crust
• combined to form water vapor, which was released
  to the atmosphere
• The water vapor condensed in the atmosphere and
  rained down to form vast oceans

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Earths Early Atmosphere
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Sequence of conditions on primitive earth

• Heavy particles such as iron, copper and nickel
  were pulled to the center of the earth.
• Lighter particles such as helium and hydrogen
  remained at the surface.

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Sequence of conditions on primitive earth

• Radioactive material and great pressure kept the
  center of the earth in a molten state.
• Over a period of years, the outer surface or
  crust of the earth formed over the molten center
  (4 billion years ago
• As the outside of the earth cooled, hot gasses
  from the interior escaped to form the primitive
  atmosphere

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• What major gas, necessary for life, is missing
  from the atmosphere of primitive Earth?
• O2

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Primitive Earths Atmosphere

• Primitive Earth set the stage for the formation
  of organic molecules
• This could not have happened on Modern Earth!

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Why are organic molecules important to the origin
of life?

• Organization of simple organic molecules lead to
  more complex organic molecules such as proteins,
  carbohydrates, and nucleic acids.
• More complex organic molecules lead to cells
  LIFE.

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Earths Early Atmosphere

• Oxygen (O2) - a highly reactive compound. Will
  break bonds that form between simple organic
  compounds and destroy them.
• Primitive atmosphere lacked free Oxygen (O2)
  simple organic compounds could form and remain
  stable even when exposed to air

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Energy used to join atoms that form hydrocarbons !

• Forms of Energy on primitive Earth
• UV Radiation (no Ozone layer to block it)
• lightning in the atmosphere
• heat from volcanoes above and below ocean level

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Primtive Earth
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Theory of Chemical Evolution

• In 1924, Alexander Oparin and J. B. Haldane
  developed a theory for the origin of organic
  compounds
• Conditions on primitive earth gave rise to simple
  organic compounds, the precursors to life

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Theory of Chemical Evolution

• Inorganic Matter- (like CO2 NH3) plus organic
  molecules (CH4) in the atmosphere combined using
  energy
• Simple Organic Molecules like HCN (hydrogen
  cyanide) and formaldehyde formed primitive clumps
  of organic matter.

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Miller and Urey (1953)

• In 1953, Stanley Miller and Harold Urey developed
  a model to test the Oparin/Haldane Hypothesis
• Set up a simulation of conditions on early
  earthguess what they found

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Miller and Urey (1953)

• Gasses in the apparatusCH4, CH3, H2O, H2
• Source of energy electricity
• And after 1 week.
• Analysis of substances (organic soup) collected
  in the trap HCN (hydrogen cyanide), lactic acid,
  acetic acid, simple amino acids, formaldehyde

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• What would happen if you add O2 to the above
  mixture?
• reduces the amounts of organic molecules formed
  or eliminates them because oxygen gas is highly
  reactive!

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• Other scientists used UV light in this model and
  formed
• Simple organic molecules like HCN which can be
  used to form adenine, a nitrogen base
• Importance?
• Formation of Nucleic Acids- DNA, RNA

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The Heterotroph Hypothesis

• Once simple, organic compounds were formed,
  polymers of carbohydrates, proteins, lipids and
  nucleic acids are formed.HOW?

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How did simple organic molecules form complex
organic molecules?

• Studies in 1950s showed that if amino acids are
  heated without oxygen, they form proteins. A
  similar process produces ATP and nucleic acids
  from small molecules.
• Therefore, this may have occurred on early earth
  in the warm pools of water.

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Formation of Life

• Complex organic molecules can form primitive
  cells LIFE!
• Protocells, simple precursors to cells then
  evolved into primitive cells with RNA as the
  genetic material

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Origin of Life

• simple organic compounds ? polymers ? protocells
  ? primitive cells

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How did these molecules become CELLS?

• Sidney Fox Protocells could be formed by
  heating solutions of amino acids.
• Protocell is a large, ordered structure, enclosed
  by a membrane, that carries out some life
  activities, such as growth and division.

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Were the primitive cells

• Heterotrophs?-organism which requires an external
  supply of energy in the form of food as it cannot
  synthesize its own
• Autotrophs?-is an organism that produces complex
  organic compounds from simple inorganic molecules
  using energy from light (by photosynthesis) or
  inorganic chemical reactions.

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Which form of life is a simpler design?

• Heterotrophs!
• Why?
• Autotrophs have to make glucose (high energy
  organic molecules) which requires A LOT more
  enzymes and extra genes (DNA)
• Plus Autotrophs have to convert glucose just like
  heterotrophs (go through same reactions)

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Which form of cellular respiration was used?

• Aerobic (uses O2) OR anaerobic (no O2 used)
• Answer anaerobic respiration (fermentation)
• Anaerobic heterotrophs consumed organic matter
  (organic soup) and underwent anaerobic
  respiration
• The first Autotrophs 2.5 bya primitive
  cyanobacteria
• Example blue green algae

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• The first Autotrophs 2.5 bya primitive
  cyanobacteria
• Example blue green algae

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Photosynthesis provided two important things

• source of food for heterotrophs and
• 2) free O2 for the environment aerobic (uses
  O2) respiration

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The effect of photosynthesis on development of
the ozone layer

• 1)  Some of the O2 formed by producers is used to
  form the ozone layer O2 UV light ? O3
• 2)  Ozone blocks most Ultraviolet radiation from
  reaching the Earth.
• 3)  One source of energy for formation of organic
  compounds is reduced BUT,
• 4) Organisms exposed to the atmosphere are not
  harmed by the UV radiation.
• 5) O2 becomes available for aerobic cellular
  respiration

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The effect of photosynthesis on development of
the ozone layer
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LIFE BEGAN!

• We have found fossils of photosynthetic
  prokaryotic cells from 3.5 billion years ago.
  However, these were probably not the first cells.

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LIFE BEGAN!

• We have found fossils of photosynthetic
  prokaryotic cells from 3.5 billion years ago.
  However, these were probably not the first cells.
• Reminder
• prokaryotic simple cell structure, no nucleus
• example bacteria
• eukaryoticcomplex cell structure, has nucleus
• examples protists, fungi, plants, animals

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The First Cells

• First cells were probably prokaryotes that
  evolved from protocells didnt need oxygen, used
  molecules in oceans for food.
• At some point, some cells developed the ability
  to make their own food
• CHEMOSYNTHESIS - making glucose from inorganic
  molecules, probably near deep sea vents or in hot
  springs. No light needed.

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And later...

• Some cells developed the ability use light to
  perform PHOTOSYNTHESIS. This started increasing
  the amount of oxygen in the atmosphere.
• Some cells developed the ability to use oxygen
  through respiration.
• Lightning caused some oxygen (O2) to form ozone
  (O3).
• Protective layer, prevents most UV radiation from
  sun
• stopped origin of cells enabled evolution of
  more complex cells.

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Evolution of Eukaryotic Cells

• Lynn Margulis (1960s) - Endosymbiont Theory
• Ancient bacteria may have taken in other
  bacteria, which evolved to become cell structures
  such as mitochondria and chloroplasts.
• Supporting Evidence
• M C have their own DNA (similar to prokaryotes)
• M C have ribosomes (similar to prokaryotes)
• M C reproduce independently within cells

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And finally...

• Over millions of years, these early cells evolved
  to the diversity of living things we have on
  Earth today!!
• This likely involved many, many different
  mutations over time. Survival was likely
  determined through natural selection (survival
  of the fittest).