Lecture 2 Outline
Life and Its Origins
Schematic of the Urey/Miller experiment
Panspermia - life came to Earth from somewhere else in the Universe
Chemical Origins
Cold environment
concentration of organic molecules by freezing out
upside-down icicles with organic matter concentrated at tip
then exposed to UV light to enhance chemical reactions
Warm environment
early Earth atmosphere was reducing not oxidizing
major components include N2, CH4, NH3, CO, H2O
oxygen would be inhibitory to the chemical reactions needed to form the building blocks of life from simple molecules
gases in primordial atmosphere react to form more complex molecules like amino acids
the energy to drive these reactions could come from sunlight, heat, lightening and radioactive decay
Urey/Miller experiment
take a mixture of presumed primordial gases
expose to electrical arcing to simulate lightening
pass reacted gases through a cooling unit
collect materials that are no longer gases in simulated ocean
find that simple gases can react to form the building blocks of life; amino acids, sugars, and nucleic acids
taken by most to proof that prebiotic chemistry could happen easily on early Earth
Biological origins
What is life?
The nature of life
"Life as we know it" vs. "Life on Star Trek"
Hot environment
mineral rich hot vents like those in today's ocean ridges could be a source of energy and minerals needed to support early life
Fox's experiment
hypothesis that volcanic heat may have been important in the polymerization of amino acid into proteins
take mixture of amino acids and heat above 200 C
this causes random polymerization of amino acids in proteins
cool and add water and the random proteins fold up
these random proteins form vesicles, hollow microspheres
the random proteins have slight enzymatic (catalytic) activity
the microspheres have semi-permeable membranes
the microspheres have some weak enzymes inside
the microspheres move towards zinc and with iodine crystals can bud and form new microspheres
experiment demonstrates that random proteins can have enzymatic activity and the microspheres have some features of living systems (reproduction, movement, membrane)
Cellular origins
Three advances: the cell, metabolism, information
The Cell
cells maintain an inside and outside
the semi-permeable membrane allows food to enter and toxins to leave and holds in what the cell needs
Oparin talks about oil in water emulsions or coascervates
analogy to salad dressing - oil/water mixtures
image of cell membranes in modern cells
Metabolism
anabolism is making things - from simple to complex
catabolism is breaking things down - from complex to simple
metabolism is a mixture of anabolism and catabolism
living things need energy and need to extract energy from the environment
heterotrophs - sugar burns - cellular metabolism as a controlled fire
reduction/oxidation reactions - redox reactions don't need oxygen
Information
reproduction and heredity are based on information transfer between generations
Central dogma of molecular biology
mention of RNA world, but refer to readings
DNA as a late-comer
enzymatic RNA molecules -ribozymes
RNA can hold information and perform reactions, can act like DNA and proteins, and may predate them both
Cellular: mutation (rate of mutation, deleterious mutations), sex (increased mixing)
