Origin of Life

PROPOSED SEQUENCE OF EVENTS INVOLVED IN EVOLUTION OF ORGANISMS FROM INORGANIC MATERIALS

• 1. SYNTHESIS OF ABIOTIC SIMPLE ORGANIC MOLECULES (amino acids, sugars, fatty acids, and nitrogen & phosphorous compounds)
  • may have occurred in outer space (simple organic molecules have been detected in interstellar gases & nebulae and in meteorites)
• 2. BUILDUP OF COMPLEX ORGANIC MOLECULES FROM SIMPLE ONES (polymerization)
  • proteins from amino acids; nucleic acids (DNA, RNA) from sugars and nitrogen & phosphate compounds; lipids from fatty acids and phosphate compounds
• 3. ASSEMBLY OF THESE COMPLEX ORGANIC MOLECULES INTO PROTO-ORGANISMS
• 4. DEVELOPMENT OF THE ABILITY TO REPLICATE (inherent in DNA)

ALL OF THESE STEPS EXCEPT THE LAST HAVE BEEN DUPLICATED EXPERIMENTALLY

• 1. MILLER/UREY - SYNTHESIS OF AMINO ACIDS UNDER PRIMITIVE EARTH CONDITIONS
  • atmosphere of NH3, CH4, H2O & H2 and devoid of free oxygen (the critical element), + energy source (electric sparks [lightning], ultraviolet radiation, or heat [from Mid-Ocean Ridge])
  • others have synthesized sugars & phosphates (which are used to build DNA) in the lab as well
• 2. FOX & ASSOCIATES - AMINO ACIDS READILY POLYMERIZE INTO PROTEIN-LIKE MOLECULES (proteinoids) AT MODERATE TEMPERATURES (AS LOW AS 70 degrees C)
  • upon cooling, proteinoids form tiny spheres with characteristics common to living cell membranes
• DREAMER & ASSOCIATES - FATTY ACIDS & PHOSPHATES READILY POLYMERIZE INTO LIPID MOLECULES
  • lipids also form tiny spheres with characteristics common to living cell membranes
• 3. KHORANA & ASSOCIATES - SYNTHESIZED SHORT SEGMENTS OF NUCLEIC ACIDS
• 4. CARINS-SMITH & NISBIT HAVE SUGGESTED THAT THESE EARLY PROCESSES MAY HAVE USED CLAY MINERALS AS TEMPLATES, PARTICULARY FOR REPLICATION

Study Questions

1. Summarize the sequence of events thought to be involved in the evolution of organisms from inorganic materials.

2. Which events have been duplicated in the lab?

3. What are the natural environments on Earth where they might have occurred?

4. What is the significance of clay minerals in the origin of life on Earth?

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